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Hi there, I am happy to help you out but I need some info first: just like medicine, pharmacy involves quite a broad range of subjects/disciplines, each with its own branches or sub-topics. So you need to narrow down your scope first - subjects studied in the pharmacy course include basic anatomy and physiology first with organic chemistry followed by pharmaceutics, pharmacognosy and pharmacology plus medicinal chemistry and other subjects depending on the uni. So first please select one or two of these subjects, then look up the topics involved in those [let us say] two you have shortlisted, and narrow down into one or two sub-topics.
What you choose might be related to e.g.an illness that an older relative might suffer from or something recently in the news abouyt e.g. medical research or just s-t that has fascinated you.
Once you do this, I am happy to suggest possible actual EPQ title and direct you to sources of info.
Best,
M
What you choose might be related to e.g.an illness that an older relative might suffer from or something recently in the news abouyt e.g. medical research or just s-t that has fascinated you.
Once you do this, I am happy to suggest possible actual EPQ title and direct you to sources of info.
Best,
M
Hello and thank you for replying so quickly to me this is really amazing of you to do so! Yes so out of the subjects you have listed i think i'm most interested with pharmacology or pharmaceutics so i narrowed it down to the 2 as you said but then after doing a bit more research i think Pharmocology strikes me more as its to do with how the medicine works within the body which i am more interested in - but i'm a bit unsure now how i narrow down pharmocology?
Original post by ZM20
Hello and thank you for replying so quickly to me this is really amazing of you to do so! Yes so out of the subjects you have listed i think i'm most interested with pharmacology or pharmaceutics so i narrowed it down to the 2 as you said but then after doing a bit more research i think Pharmocology strikes me more as its to do with how the medicine works within the body which i am more interested in - but i'm a bit unsure now how i narrow down pharmocology?
What i have looked at recently is on Alzheimer's disease and possibly doing it around there as it is a disease that i have been interested in
Original post by ZM20
Hello and thank you for replying so quickly to me this is really amazing of you to do so! Yes so out of the subjects you have listed i think i'm most interested with pharmacology or pharmaceutics so i narrowed it down to the 2 as you said but then after doing a bit more research i think Pharmocology strikes me more as its to do with how the medicine works within the body which i am more interested in - but i'm a bit unsure now how i narrow down pharmocology?
Hi as you will see from pic below, pharmacology is a vast subject with new drugs being discovered and appearing on the market all the time. Hence, it is very difficult for me to narrow down for you.
You could select a body system from cardiovascular [my special interest], respiratory, neorological [incl the special senses e.g. vision, hearing], gastrointestinal, genitourinary, musculoskeletal, renal, etc
OR:
You could look at the treatment of a disease from one of the following classes: inflammatory e.g. infective, degenerative; neoplastic [cancer]; traumatic;
OR;
You could look at mechanisms of drug action e.g. stimulation or blockade of receptors e.g. beta-blockers in hypertension; inhibition of an enzyme e.g. allopurinol [inhibits xanthine oxidase so used to treat gout [due to too much uric acid]]; interference with bacterial protein synthesis by certain antibiotics e,g. tetracycline [very interesting mechanism]; use of specific antibodies to target a diseased tissue; etc.
Try and narrow down somewhat, otherwise I am looking for a needle in a haystack! [I personally would not recommend Alzheimer's disease as it is very commonly selected by students - it is better to make your EPQ unique].
M
Hi there i think out of the suggestions you have given me the one that strikes to me the most would probably be cardiovascular as thorugh biology alevel it was one of my favourite topics to learn about - but i kind of figured that alzhemier's would be a popular topic
(edited 6 months ago)
2000+ page book!
Original post by ZM20
Hi there i think out of the suggestions you have given me the one that strikes to me the most would probably be cardiovascular as thorugh biology alevel it was one of my favourite topics to learn about - but i kind of figured that alzhemier's would be a popular topic
Hi you seem to be very quick with your mouse [replied in a few ms!!] -these tiny guys run very fast anyway!
[sorry!]Ok you are interested in a topic right up my street [cardiology]: I shall provide you with a couple of hopefully v interesting topics now [I can assure you no-one else will have chosen these and I will guide you to sources of info as well as explain the terminology if you visit confused.com [
], so dw:A] "Myocarditis is very rarely caused by the COVID-19 vaccine - it is much more common for myocarditis to be caused by coronavirus-2 infection itself; how do we explain to the lay public that it is still crucial to be vaccinated against this terrible virus?"
B] "Beta-blockers were dubbed "The greatest discovery of the century" in the 1970s for the treatment of hypertension and angina pectoris - should their use be abandoned with the advent of so-called better treatment options of recent times?"
C] "Technology including AI and machine-learning are increasingly being applied to perform the analysis of cardiac function such as in the computerized views of the heart obtained using echocardiography - is this a trend we should applaud or is it "tempting the devil"?" [sorry this is not directly pharmacology, but you might like it anyway]
If you like one of these and go for it, le me know - I will direct you to websites, books, research papers, etc.
Good night [
]!Thank you so much for these ideas, i think i'm going to just go over and have a look at these three that you suggested and probably pick one, you've been a huge help so far! haha i think i'm just a bit too keen on EPQ and panicking a bit so i'm always checking if any ideas or suggestions have been given - but i kind of want to have some guidance on it so sorry if i keep replying very quickly haha - but thank you again
goodnight
goodnight
Good morning! - somehow I missed your text stating that you are interested in mechanisms of drug action - this is one of the two major branches of pharmacology - it is called pharmacodynamics i.e. what the drug does to the body [the other is pharmacokinetics i.e. what the body does to the drug [absorption, distribution, metabolism & excretion]].
After noting this post of yours, here's a topic that combines therapy of cardiovascular disease and mechanism of drug action:-
D] "The intricate mechanisms by which heart rate and blood pressure are controlled by the normal human body: the treatment of hypertension through the decades has evolved using a variety of drug types - should we stick with older drugs with longer clinical experience and proven safety or are modern novel drugs preferable? A broad perspective."
I hope this combines your interests and that you like it [oc you can modify the exact wording to your taste, yeah?][I believe that in an EPQ, the examiners prefer a kind of debate rather than a pure description hence the "question" in the topics I suggest].
M
After noting this post of yours, here's a topic that combines therapy of cardiovascular disease and mechanism of drug action:-
D] "The intricate mechanisms by which heart rate and blood pressure are controlled by the normal human body: the treatment of hypertension through the decades has evolved using a variety of drug types - should we stick with older drugs with longer clinical experience and proven safety or are modern novel drugs preferable? A broad perspective."
I hope this combines your interests and that you like it [oc you can modify the exact wording to your taste, yeah?][I believe that in an EPQ, the examiners prefer a kind of debate rather than a pure description hence the "question" in the topics I suggest].
M
Hi there i won't lie after looking at the 3 suggestions you gave me yesterday i've grown more of an interest to the Myocarditis is very rarely caused by COVID - 19 Vaccine but now it is - i think i am most intrigued with this one so i would for you to send me articles based on this - all 3 were really good suggestions i didn't know which to choose from!
Ok glad to hear you liked one of them - however, b4 you jump off the springboard [do you watch Olympic diving competition? ] with your final decision, have you looked at [D] above, which I thought of later? Nor tring to sway you in either direction, but just thought you might want to look at that too before making a final choice.
Once you are sure and you let me know, hold tight to your handrail lest you are blown away by the volume of data I will send you!! Also, do you need approval from your teacher[s]?
] with your final decision, have you looked at [D] above, which I thought of later? Nor tring to sway you in either direction, but just thought you might want to look at that too before making a final choice.Once you are sure and you let me know, hold tight to your handrail lest you are blown away by the volume of data I will send you!! Also, do you need approval from your teacher[s]?
okay haha i will have a look at the other one you sent as well - and as of approval, we do have a teacher who is leading this and the only warning they have given is that whatever we do for EPQ it must not be taught on my current specification for any of my Alevels - but i think as long as i show proof of articles and give an outline of what i am planning to do with this research i am good to go!
[quote="macpatgh-Sheldon;98844460"]Ok glad to hear you liked one of them - however, b4 you jump off the springboard [do you watch Olympic diving competition?] with your final decision, have you looked at [D] above, which I thought of later? Nor tring to sway you in either direction, but just thought you might want to look at that too before making a final choice.
Once you are sure and you let me know, hold tight to your handrail lest you are blown away by the volume of data I will send you!! Also, do you need approval from your teacher
[quote="macpatgh-Sheldon;98844460"]Ok glad to hear you liked one of them - however, b4 you jump off the springboard [do you watch Olympic diving competition?
] with your final decision, have you looked at [D] above, which I thought of later? Nor tring to sway you in either direction, but just thought you might want to look at that too before making a final choice.Once you are sure and you let me know, hold tight to your handrail lest you are blown away by the volume of data I will send you!! Also, do you need approval from your teacher
Original post by ZM20
okay haha i will have a look at the other one you sent as well - and as of approval, we do have a teacher who is leading this and the only warning they have given is that whatever we do for EPQ it must not be taught on my current specification for any of my Alevels - but i think as long as i show proof of articles and give an outline of what i am planning to do with this research i am good to go!
Have u made a final decision? Being a super-nerd I am almost getting carried away in learning more about these concepts
Hi nice to hear that you have reached a well-considered decision.
Good topic for data availability; however, I don't want to push you into the deep end! [I know what that feels cos I am a v good swimmer, but for some reason when I reach the deep end, I find that I have sunk to the bottom [!] - doing s-t right or wrong??
!
Ok first look up the term "myocarditis" [you] - you youngsters adore google so read up the basics of this term on reliable authoritative sites.
Then go through the paper at-d by Fried et al, which presents 4 case reports of cardiac involvement in COVID-19 in the early days of this pandemic [don't worry about all the tests described there e.g. ECG findings, troponin levels, etc. - just get a feel, ok?]
After that, check out the 2nd paper at-d, which is much more recent and gives you a rough idea of what is involved and the relative incidence of myocarditis in non-vaccinated patients and that presumed to be due to the mRNA vaccine.
These are short papers to give you a taste of the subject matter; last thing I want to do yet is to overwhelm u with 50+ page reviews - please don't be scared by the detail in these papers - if not sure of terminology, etc., you know where to find Sheldon!! - it will all gradually fall in place - be patient & positive!
M.
Good topic for data availability; however, I don't want to push you into the deep end! [I know what that feels cos I am a v good swimmer, but for some reason when I reach the deep end, I find that I have sunk to the bottom [!] - doing s-t right or wrong??
!Ok first look up the term "myocarditis" [you] - you youngsters adore google so read up the basics of this term on reliable authoritative sites.
Then go through the paper at-d by Fried et al, which presents 4 case reports of cardiac involvement in COVID-19 in the early days of this pandemic [don't worry about all the tests described there e.g. ECG findings, troponin levels, etc. - just get a feel, ok?]
After that, check out the 2nd paper at-d, which is much more recent and gives you a rough idea of what is involved and the relative incidence of myocarditis in non-vaccinated patients and that presumed to be due to the mRNA vaccine.
These are short papers to give you a taste of the subject matter; last thing I want to do yet is to overwhelm u with 50+ page reviews - please don't be scared by the detail in these papers - if not sure of terminology, etc., you know where to find Sheldon!!
- it will all gradually fall in place - be patient & positive!M.
okay i will go slowly bit by bit before i scare you with my enthusasim and now my quick response to this message (Original post by macpatgh-Sheldon)Hi nice to hear that you have reached a well-considered decision.
Good topic for data availability; however, I don't want to push you into the deep end! [I know what that feels cos I am a v good swimmer, but for some reason when I reach the deep end, I find that I have sunk to the bottom [!] - doing s-t right or wrong??!
Ok first look up the term "myocarditis" [you] - you youngsters adore google so read up the basics of this term on reliable authoritative sites.
Then go through the paper at-d by Fried et al, which presents 4 case reports of cardiac involvement in COVID-19 in the early days of this pandemic [don't worry about all the tests described there e.g. ECG findings, troponin levels, etc. - just get a feel, ok?]
After that, check out the 2nd paper at-d, which is much more recent and gives you a rough idea of what is involved and the relative incidence of myocarditis in non-vaccinated patients and that presumed to be due to the mRNA vaccine.
These are short papers to give you a taste of the subject matter; last thing I want to do yet is to overwhelm u with 50+ page reviews - please don't be scared by the detail in these papers - if not sure of terminology, etc., you know where to find Sheldon!! - it will all gradually fall in place - be patient & positive!
M.
Good topic for data availability; however, I don't want to push you into the deep end! [I know what that feels cos I am a v good swimmer, but for some reason when I reach the deep end, I find that I have sunk to the bottom [!] - doing s-t right or wrong??
!Ok first look up the term "myocarditis" [you] - you youngsters adore google so read up the basics of this term on reliable authoritative sites.
Then go through the paper at-d by Fried et al, which presents 4 case reports of cardiac involvement in COVID-19 in the early days of this pandemic [don't worry about all the tests described there e.g. ECG findings, troponin levels, etc. - just get a feel, ok?]
After that, check out the 2nd paper at-d, which is much more recent and gives you a rough idea of what is involved and the relative incidence of myocarditis in non-vaccinated patients and that presumed to be due to the mRNA vaccine.
These are short papers to give you a taste of the subject matter; last thing I want to do yet is to overwhelm u with 50+ page reviews - please don't be scared by the detail in these papers - if not sure of terminology, etc., you know where to find Sheldon!!
- it will all gradually fall in place - be patient & positive!M.
Dw young man/lady you will not scare me at all - nothing does, so relax and load as much ammunition as you like - as a child in Kenya, I had to look out that I was not eaten by a Maumau cannibal or a lion or other hungry beast!!
I fact, any burning enthusiasm will only impress me/motivate me to help u out!
One secret of yours would be worth knowing: how do you detect that there is a post for u when not logged in? I suppose you check your email every 0.472 seconds!!
I fact, any burning enthusiasm will only impress me/motivate me to help u out!
One secret of yours would be worth knowing: how do you detect that there is a post for u when not logged in? I suppose you check your email every 0.472 seconds!!
Hi @ZM20 you have suddenly gone all quiet - has your chronometer packed up?
If you are still looking for tons of info, pls reply to this post.
In the interim period, search for info at:
https://www.ncbi.nlm.nih.gov
Select PMC from the databases dropdown top left then search to get FOC access to literally millions of full-text research papers.
To whet your appetite, I shall try to attach one slightly content-heavy paper herewith [unless it is too large a file for TSR to cope with]
Be in touch!
M
OK too large: I shall try to copy part of content here [brace yourself!]
Journal Pre-proof
COVID-19 for the Cardiologist: A Current Review of the Virology, Clinical
Epidemiology, Cardiac and Other Clinical Manifestations and Potential Therapeutic
Strategies
Deepak Atri, MD, Hasan K. Siddiqi, MD MSCR, Joshua Lang, MD, Victor Nauffal, MD,
David A. Morrow, MD MPH, Erin A. Bohula, MD DPhil
PII: S2452-302X(20)30157-1
DOI: https://doi.org/10.1016/j.jacbts.2020.04.002
Reference: JACBTS 443
To appear in: JACC: Basic to Translational Science
Received Date: 7 April 2020
Accepted Date: 7 April 2020
Please cite this article as: Atri D, Siddiqi HK, Lang J, Nauffal V, Morrow DA, Bohula EA, COVID-19 for
the Cardiologist: A Current Review of the Virology, Clinical Epidemiology, Cardiac and Other Clinical
Manifestations and Potential Therapeutic Strategies, JACC: Basic to Translational Science (2020), doi:
https://doi.org/10.1016/j.jacbts.2020.04.002.
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition
of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of
record. This version will undergo additional copyediting, typesetting and review before it is published
in its final form, but we are providing this version to give early visibility of the article. Please note that,
during the production process, errors may be discovered which could affect the content, and all legal
disclaimers that apply to the journal pertain.
© 2020 Published by Elsevier on behalf of the American College of Cardiology Foundation.
1
COVID-19 for the Cardiologist: A Current Review of the Virology, Clinical Epidemiology,
Cardiac and Other Clinical Manifestations and Potential Therapeutic Strategies
Deepak Atri MD*, Hasan K. Siddiqi MD MSCR*, Joshua Lang MD, Victor Nauffal MD, David
A. Morrow MD MPH, and Erin A. Bohula MD DPhil
Cardiovascular Division, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA
*Denotes co-first authors.
Corresponding Author:
Erin A. Bohula MD DPhil
350 Longwood Ave
First Office Floor
Boston, MA 02115
Email: [email protected]
2
Highlights
- Severe acute respiratory virus-2 (SARS-CoV2), the infection responsible for coronavirus
disease-2019 (COVID-19), has spread globally leading to a devastating loss of life. In a
few short months, the clinical and scientific communities have rallied to rapidly evolve
our understanding of the mechanism(s) of disease and potential therapeutics.
- This review discusses the current understanding of the basis virology of SARS-CoV2 and
the epidemiology, clinical manifestations, including cardiovascular, and mortality of
COVID-19. A detailed review of the viral life cycle and putative mechanism(s) of injury
frames the discussion of possible preventative and therapeutic strategies.
- The ongoing, unprecedented collective effort will, without a doubt, advance our ability to
prevent the spread and optimally care for patients suffering from COVID-19.
Summary
The coronavirus disease-2019 (COVID-19), a contagious disease caused by severe acute
respiratory syndrome coronavirus-2 (SARS-CoV2), has reached pandemic status. As it spreads
across the world, it has overwhelmed healthcare systems, strangled the global economy and led
to a devastating loss of life. Widespread efforts from regulators, clinicians and scientists are
driving a rapid expansion of knowledge of the SARS-CoV2 virus and the COVID-19 disease.
We review the most current data with a focus on our basic understanding of the mechanism(s) of
disease and translation to the clinical syndrome and potential therapeutics. We discuss the basic
virology, epidemiology, clinical manifestation, multi-organ consequences, and outcomes. With a
focus on cardiovascular complications, we propose several mechanisms of injury. The virology
and potential mechanism of injury form the basis for a discussion of potential disease-modifying
therapies.
Key words: COVID-19, SARS-CoV2, Cardiovascular, Virology, Treatments
Abbreviations
ACE2 – angiotensin-converting enzyme 2
ARDS – acute respiratory distress syndrome
CDC – Centers for Disease Control
CFR – case fatality rate
COVID-19 – coronavirus disease-2019
CoV – coronavirus
DIC – disseminated intravascular coagulation
ER - endoplasmic reticulum
hsCRP – high sensitivity c-reactive protein
ICU – intensive care unit
SARS-CoV1 or 2– severe acute respiratory syndrome coronavirus-1 or -2
SOFA – sequential organ failure assessment
TMPSS2 – trasmembrane serine protease-2
3
Introduction
The coronavirus disease-2019 (COVID-19), a contagious disease caused by severe acute
respiratory syndrome coronavirus-2 (SARS-CoV2), has reached pandemic status. As it spreads
across the world, it has overwhelmed healthcare systems, strangled the global economy and led
to a devastating loss of life. In the ongoing wake of COVID-19, the world’s medical and
scientific communities have come together to rapidly expand our knowledge of the pathogenesis,
disease manifestations and possible preventive and therapeutic strategies. Virologists have
looked to related diseases to understand the life cycle of this novel viral infection. Despite being
overwhelmed, through conventional and historically unconventional mechanisms, clinicians
managing patients with COVID-19 have made a concerted effort to rapidly educate colleagues in
expectant regions of the world on lessons learned. The world’s regulatory agencies and
pharmaceutical industry are using emergency mechanisms to expedite access to and study of
therapeutic options. These widespread efforts, drawn from many arenas, are driving a rapid
expansion of collective experience and understanding of COVID-19.
Here, we review this body of work with a focus on our basic understanding of the mechanism(s)
of disease and translation to the clinical syndrome and potential therapeutic options.
Specifically, we discuss the basic virology, epidemiology and clinical manifestations, including
presentation, progression, multi-organ consequences and outcomes. With a focus on the
cardiovascular complications, we propose several potential mechanisms of injury. We discuss a
range of possible therapeutic options in the context of the viral life cycle and possible
mechanisms of injury. Finally, in recognition of the scale of this crisis, we address the ethical
considerations around standards of care in the event of resource scarcity.
4
Basic Virology of SARS-CoV2
Genetics and Structure
Coronaviridae comprise a family of enveloped, single stranded, positive sense, RNA viruses
with comparable genomic organization and functional mechanisms. Coronaviruses (CoV) are
canonically divided into alpha- and beta-, gamma- and delta- genera predicated on genetic
clustering. The alpha- and beta-CoV are known to cause human diseases, such as common
respiratory infections. The SARS-CoV2 and SARS-CoV1 are beta-CoV (1-3). CoV are sonamed
because of the characteristic crown, or corona, of electron density that they exhibit on
transmission electron micrographs. This appearance is thought to be caused by the densely
packed protein that studs the viral membrane and is responsible for receptor binding on targetcell
membranes.
The CoV genome is organized into two parts. Highly conserved with the CoV family, the 5’
terminal end, encodes the replicase - the nonstructural proteins responsible for viral replication
within the cell (1-3). It is translated as one peptide (~790 kDa) from which the constituent
functional proteins are subsequently cleaved. CoV genomes encode 16 nonstructural proteins, as
in SARS-CoV2, and they exhibit a multitude of functions required for viral replication (2,4,5).
Critical proteins for viral replication include the main protease (nsp5), the papain-like protease
(nsp3) and the RNA-dependent RNA polymerase (nsp12, RdRp). The other replicase constituent
proteins repurpose the cellular machinery to facilitate viral replication and to blunt the intrinsic
host immune functions (1,6).
5
The remaining third of the CoV genome encodes the structural proteins and a variety of
accessory proteins (latter not discussed here). The structural proteins are the constituent proteins
of the transmissible viral particle, or virion. The key structural CoV proteins are the nucleocapsid
protein (N) and three transmembrane proteins: the spike protein (S), the membrane protein (M),
and the envelope protein (E) (1-5)(Figure 1). The S protein is responsible for virus-cell receptor
interactions (7-11)(Figure 1). The E and M proteins are responsible for membrane structure and
fusion. The N protein binds viral RNA and mediates its interaction with the S, E, and M proteins
for genome encapsulation (1,12).
Life Cycle
The life cycle of SARS-CoV2 has not been rigorously established; however, given the
considerable sequence homology, it is presumed to be similar to that of SARS-CoV1 and other
CoV (4,5). In general, the CoV life cycle consists of a series of steps that begins with viral
binding to a target cell and culminates in viral reproduction. Knowledge of this process informs
an understanding of viral physiology and also will serve as the basis for discussion of antiviral
therapeutics (8)(Figure 1). The aim of evolving therapeutics will be to break the “links in the
chain” of the viral life cycle in order to forestall the propagation of infection within the cells of
an individual patient.
SARS-CoV2 is known to bind to cells via the same receptor as SARS-CoV1, the membranebound
glycoprotein Angiotensin Converting Enzyme 2 (ACE2) (4). It has not been observed to
bind other CoV receptors, namely dipeptidyl peptidase 4 (DPP4) or aminopeptidase N (APN)
(4,13). After binding of ACE2, the virus is internalized via endocytosis without access to the
6
host intracellular compartment until a membrane fusion event occurs (4)(Figure 1). This process
is mediated, at least in part, by another membrane bound protease known as transmembrane
serine protease 2 (TMPRSS2), which cleaves the S protein as a necessary step of membrane
fusion (7). Interestingly, the protease activity of the CoV receptors, ACE2, DPP4 and APN, does
not seem necessary for membrane fusion (14).
Upon membrane fusion, the viral RNA genome enters the intracellular compartment. At this
point, the viral RNA may be translated into its encoded structural and nonstructural proteins. The
translation of the nonstructural proteins, or replicase, results in the production of a single massive
polypeptide chain, from which the sixteen constituent nonstructural proteins are cleaved. This
process is initially mediated by intracellular proteases, and then further propagated by the
function of the CoV main protease and papain-like protease (1). Another replicase protein, the
RNA-dependent RNA polymerase (RdRp) is responsible for the replication and amplification of
the viral genome (15). During this process, mutations may be acquired by errors in replication
and recombination events (1).
Upon amplification of the viral RNA, more viral structural and nonstructural proteins may be
generated. Viral structural proteins, because of their transmembrane nature (with the exception of
the N protein), are targeted to the ER membrane with appropriate signal sequences. Viral RNA,
bound by N protein, interacts with the structural proteins on the membrane of the ER and Golgi
apparatus before another membrane fusion event on these membranes results in viral budding
and exocytosis (1,8,12).
7
Importantly, the precise molecular differences that account for the important clinical differences
between SARS-CoV2 and SARS-CoV1 infections, such as prolonged latency, widely variable
symptoms, a possible predisposition for individuals with pre-existing cardiovascular conditions,
and a predilection for myocardial complications, remain unclear.
Pathogenesis: Angiotensin-Converting Enzyme 2
SARS-CoV2, SARS-CoV, and HCoV-NL63, a virus that causes a mild respiratory infection, are
all known to employ ACE2 as a receptor (3,4,16,17). Given the functions of ACE2 in the
cardiovascular system, the importance of angiotensin-directed pharmacology in cardiovascular
disease and the apparent propensity for severe illness among patients with COVID-19 with
cardiovascular comorbidity, the ACE2 molecule has been the subject of much attention (18).
Indeed, major clinical societies have issued consensus statements on the use of ACE inhibitors
(ACEi) and angiotensin-receptor blockers (ARBs) in the setting of the COVID-19 pandemic, as
discussed later (19).
Angiotensin-Converting enzyme 2 (ACE2) is a single-pass transmembrane protein with protease
activity that cleaves the vasoconstrictor angiotensin II into the vasodilator angiotensin 1-7 (20-
23). In doing so, it functions as a counter-regulatory enzyme to the functions of ACE1, which
generates angiotensin II (20). In humans, the protein has a broad pattern of expression and has
been found in the lung epithelium (in particular the type II pneumocyte), the myocardium, the
endothelium, the GI tract, bone marrow, kidneys and spleen among other tissues; potentially
explaining the multi-organ injury observed with SARS-CoV2 infection (24). Another relevant
8
feature of Ace2 gene expression is its encoding on the X chromosome, which may account for
possible sex differences observed in the epidemiology of COVID-19 (25).
In animal models of acute respiratory distress syndrome (ARDS), due to chemical pneumonitis,
overwhelming sepsis, endotoxemia, or influenza, Ace2KO mice have more severe acute lung
injury (ALI) relative to their wild-type counterparts as evaluated histologically and by measures
of elastance (26-28). The phenotype of increased elastance was rescued by administration of
recombinant human ACE2, which affirms a causal link between Ace2 deficiency and a more
profound state of ALI (26,28). Additionally, the administration of losartan, an angiotensin II
type-1 receptor (AT1R) blocker mitigated the exacerbating effects of SARS-CoV spike protein in
an animal model of ARDS (29). Losartan also abrogated the severity of ALI due to influenza in
mice (27,28).
In regard to the counter-regulatory properties of ACE1 and ACE2, the effects of Ace2-deficiency
appear to be rescued by Ace1-deficiency in mice. For example, the effects of Ace2-deficiency to
result in more severe ALI are abrogated by Ace1-deficiency. Ace2KO mice demonstrated more
severe ALI than Ace2KO;Ace1+/-, with further reduction in severity observed in Ace2KO;Ace1-/-
(26). This dose-responsiveness also implies causation. Comparable effects were seen with
myocardial dysfunction, as Ace2KO;Ace1+/- and Ace2KO;Ace1-/- had no evidence of the
contractile deficit observed in Ace2KO mice (30). Of note, in each of the above cases, however,
the animal models were constitutive knockout systems (rather than lineage-specific or inducible
knockout). Thus, the ACE2-expressing cell that mediates each phenotypic abnormality has not
been determined.
9
SARS-CoV2 is able to utilize ACE2 isoforms from swine, bats, civets and humans suggesting a
mechanism whereby the virus may have been initially transmissible from species to species and,
with mutation, evolved into a novel pathogen (4). Notably, murine ACE2 is not a functional
receptor for SARS-CoV2; thereby requiring transgenic expression of human ACE2 if mice are to
be used as a research model (4).
ACE2 undergoes cleavage by the membrane-bound protease ADAM17; resulting in the release
of soluble ACE2 into the blood stream (31). The effects of soluble ACE2 are unclear in humans,
however it appears to have favorable effects on lung function in models of ARDS, influenza, and
RSV infection (26,28,32). Soluble ACE2 has been studied in a phase II trial of ARDS, but largescale,
well-powered clinical outcomes trials are needed (33). Research is ongoing to determine
whether soluble ACE2 may act as a specific therapeutic to SARS-CoV2 in the role of a decoy
receptor, as discussed later (34).
Finally, given the necessity of ACE2 for viral infection, the role of ACE inhibitors (ACEi) or
angiotensin receptor blockers (ARBs) in COVID-19 has drawn intense attention. Importantly,
the ACE2 enzyme itself is not inhibited by ACEi/ARB use (21). ACEi or ARB exposure may
result in ACE2 protein upregulation in animal models; however not all animal models exhibit
this effect. The existing epidemiology of COVID-19 among patients taking ACEi or ARB is
confounded by cardiovascular comorbidities which may alter ACE2 and angiotensin II
expression (18). At this time, it is unclear if ACEi or ARBs use influences receptor expression
and whether variable expression impacts the propensity for or severity of SARS-CoV2 infection.
10
Transmission
Exposure to the Huanan seafood market was common among the earliest cases contributing to
the SARS-CoV2 epidemic in China suggesting that this was a zoonotic disease with an
intermediate animal host (non-aquatic animals were sold in the market) (35). Genomic analyses
have identified approximately 87% DNA sequence homology between SARS-CoV2 and two
SARS-like CoV isolated from Chinese horseshoe bats, bat-SL-CoVZC45 and bat-SLCoVZXC21,
in the Zhejiang province in China (36). Notably, no bats are sold in the market and
at the onset of the outbreak in December most bat species in Wuhan would be hibernating. Thus,
similar to SARS-CoV1 and MERS-CoV, while bats may be the natural reservoir for SARSCoV2,
there is likely an unidentified intermediate animal host responsible for animal-to-human
transmission. Despite closure of the Huanan market on January 1, 2020, the epidemic continued
to expand and case clusters with no exposure to the market were reported indicating the
occurrence of human-to-human transmission (37).
Akin to other respiratory viruses, SARS-CoV2 spreads primarily through small respiratory
droplets that are expelled from infected individuals and can travel approximately 3-6 feet. The
virus can exist in nature on surfaces and can last for up to 4 hours on copper, 24 hours on
cardboard and up to 72 hours on plastic and stainless steel surfaces leading to fomite
transmission (38). In fact, the Japanese National Institute of Infectious Disease reported detection
of SARS-CoV2 RNA on surfaces in the cabins of symptomatic and asymptomatic passengers on
the Diamond Princess up to 17 days after they were vacated (39). Live virus has also been
isolated and cultured from fecal specimens raising the possibility of oro-fecal transmission,
11
though corroborating clinical evidence for this method of transmission is lacking (40). Airborne
transmission may be facilitated in healthcare settings where aerosol-producing interventions are
being performed including endotracheal intubation, bronchoscopy, suctioning, nebulizer
treatment, non-invasive positive pressure ventilation and delivery of oxygen via a high-flow
nasal cannula. These transmission data support the clinical recommendations that airborne
precautions, including use of N-95 masks, should be implemented in these aerosol-producing
settings whereas standard droplet precautions should be used during all other encounters with
infected individuals (41).
In a fully susceptible population, reflected by early stages of the epidemic in China, studies have
estimated a basic reproductive number (Ro) of 2.38 for SARS-CoV2, meaning that every infected
individual is likely on average to spread the virus to 2 to 3 other individuals (42). An outbreak
will continue to increase in size if the Ro>1. For context, seasonal influenza has an Ro of 1.5 (43).
Substantial transmission from asymptomatic hosts has facilitated the widespread transmission of
SARS-CoV2 and contributed to its pandemic potential (42). A study from Singapore with
extensive contact tracing identified 7 clusters of cases where secondary spread of the infection
occurred 1-3 days prior to symptom development in the source patient (44). Thus, containment
measures aimed solely at isolating symptomatic individuals are inadequate. Furthermore, contact
tracing efforts should take in to account the pre-symptomatic contagious period to
comprehensively capture all potentially exposed individuals. Ro is not a static measure and
interventions including self-quarantine, contact isolation, social distancing and enhanced hygiene
measures have proven to be effective in China. Following implementation of such measures in
12
China, the Ro steadily decreased from 2.38 prior to January 23rd to 0.99 during the period of
January 24-February 8, 2020 (42).
Epidemiology and Clinical Manifestations of SARS-CoV2
Epidemiology
The burden of the SARS-CoV2 virus has evolved rapidly since it first appeared in Wuhan, China
in December 2019. What began as a few case reports of atypical pneumonia now spans the globe
as a pandemic. At present, most published data come from China and form the basis for our
understanding of the epidemiology of COVID-19. In the largest published registry to date, the
Chinese Centers for Disease Control and Prevention (CDC) reported high-level details for patient
characteristics, severity of manifestations and survival in 72,314 cases of putative (47%) and
confirmed (63%) COVID-19 (45). In this population, predominantly identified by the presence
of symptoms (~99%), <2% of cases occurred in children < 19 years of age suggesting that
children either are either resistant to infection or rarely symptomatic. Of confirmed cases, most
(87%) were mild, defined by no or mild pneumonia, 14% were severe with significant infiltrates
or signs of respiratory compromise and 5% were critical with respiratory failure (e.g. mechanical
ventilation), shock or multiorgan system failure.
The first confirmed case of COVID-19 in the US was identified on January 20, 2020 and the US
has now surpassed all other countries in the absolute number of cases. However, given the rapid
and recent onset of the burden, there are few published data reflecting the experience with
COVID-19 in the US. In an early snap shot from the US CDC in 4,226 confirmed cases with
symptoms or exposure, only 5% occurred in those under the age of 20 (46).
13
While data are rapidly accumulating, much of the epidemiology of this virus remains unknown.
Most publications are small, single center studies, and detail the clinical characteristics,
complications and outcomes in the subset of patients who were hospitalized. As a result of the
limitations on testing and the data suggesting that many infected individuals may be
asymptomatic, the true burden of infected individuals is unclear and underestimated (42,47). Not
only does the variable manifestation of symptoms hamper public health initiatives to trace and
isolate infected individuals, but also it limits our ability to accurately estimate infectivity,
symptom burden, and non-fatal and fatal complication rates in the overall population of infected
individuals. With that caveat, the published data provide insights into the more vulnerable, atrisk
populations who require hospitalization. While the individual studies are small, the
predictors of more severe manifestations and poor outcomes have been generally consistent as
detailed below.
Clinical Presentation / Syndrome
In a multi-center case series of 1,099 hospitalized patients from China, the most common
symptoms were fever in up to 90%, followed by cough, fatigue, sputum production, and
shortness of breath (48). Less common symptoms included headache, myalgias, sore throat,
nausea, vomiting, and diarrhea. The American Association of Otolaryngology has recently
highlighted anosmia and dysgeusia as possible symptoms of disease as well (49). The median
incubation period, or time from probable exposure to first symptom, was 4 days (IQR 2-7) (48).
Another report detailed that 99% of infected patients develop symptoms within 14 days (50).
Common lab derangements on admission included lymphopenia, elevations in c-reactive protein,
14
lactate dehydrogenase, liver transaminases and d-dimer (48). Notably, procalcitonin was rarely
elevated (48). These data are generally consistent across multiple smaller studies, several of
which noted elevations in other inflammatory markers, such as IL-6, ferritin and ESR (51-55).
Evidence of cardiac or kidney injury at admission was variable across studies, but tended to be
absent upon hospitalization (48,51-53,56). Chest computed tomography at the time of admission
was abnormal in 87% of patients with ground glass opacities or local or patchy “shadowing”
(48).
Disease Progression
Many of the more severe manifestations, such as ARDS, acute kidney injury (AKI) and
myocardial injury, tend to occur as many as 8-14 days after the onset of symptoms and portend
worse outcomes (53). Within a hospitalized population, rates of ICU admission range between
26-32% across most studies (35,48,51-53,57). Several studies have identified older age and
baseline burden of comorbidity, such as diabetes, hypertension, prior coronary disease and prior
lung disease, as predictors of more significant disease progression with higher rates of ARDS,
AKI, cardiac injury, ICU admission and death (51-53,58,59). Increases in markers of
inflammation, coagulation, and cardiac injury also correlate with disease severity and rise
throughout the course of the disease (53,54,56). In hospitalized populations, the timing of death
occurred at a median of 16-19 days after illness onset (53,58). The median time from symptom
onset to discharge in survivors was around 3 weeks (53).
Non-Cardiovascular Clinical Manifestations
Respiratory Failure
15
The most prominent complication of COVID-19 is respiratory failure. As previously described,
the majority of patients have no or mild symptoms (45). In hospitalized patients, respiratory
symptoms are common and range in severity from cough (60-80%) or dyspnea (19-40%) to
ARDS (17-42%) (51-53,56,57). ARDS rates were only 3.2% in the largest case series, but this
may be an underestimate due to a short average follow up time of 12 days, with the vast majority
of patients remaining hospitalized at the end of study (48). ARDS tends to occur ~1-2 weeks
into illness and is often precipitous and protracted (51,53,57). For these reasons, and to avoid
risk of provider infection with emergent intubation, professional societies recommend early
intubation in the event of respiratory decline (41). Intubation was required in 10-33% in the
various Chinese series; however, rates of high-flow nasal cannula and non-invasive mechanical
ventilation also were high (35,51-53). These therapies are believed to result in aerosolization
and are generally not recommended – consequently, more patients will be intubated when unable
to be supported by nasal cannula or a non-rebreather mask (41). Older age, baseline
hypertension, diabetes, high fever, lymphopenia, injury to other organs (e.g. AKI, ALI), and
elevated d-dimer and inflammatory markers were predictors of ARDS; advanced age,
neutropenia, elevated d-dimer and inflammation are associated with higher mortality in those
with ARDS (51). Development of ARDS, along with acute cardiac injury, was an independent
predictor of death (56). Importantly, hypoxemic respiratory failure is the leading cause of death
in COVID-19, contributing to 60% of deaths (58).
Renal injury
Estimates vary as to the incidence of acute kidney injury in COVID-19, ranging between 0.5-
15% (35,48,52,53,56,59). Among hospitalized patients the rates of proteinuria (43.9%) and
16
hematuria (26.7%) appear to be even higher (59). Acute kidney injury occurs in the first few
days after admission in patients with baseline chronic kidney disease, and after 7-10 days in
patients with normal baseline renal function (59). Mechanisms of renal injury have been
hypothesized to include both acute tubular necrosis (ATN), direct cytotoxic effects of the virus
itself, and immune-mediated damage (59).
Liver injury
Transaminitis is common with an incidence of 21-37%, and as high as 48-62% of patients who
are critically ill or who do not survive (35,48,53). Acute liver injury, defined as either alanine
aminotransferase or aspartate aminotransferase greater than three times the upper limit of
normal, occurs less frequently, and was reported to occur in 19.1% (n=4) of 21 patients who
were admitted to an ICU in Washington State (55).
Cardiovascular Manifestations
Cardiac injury
Numerous studies have reported acute cardiac injury as an important manifestation of COVID-
19. In studies published to date, acute cardiac injury was variably defined as either cardiac
troponin elevation >99th percentile alone or a composite of troponin elevation, ECG or
echocardiographic abnormalities (52-56,58). Importantly, many aspects of this endpoint remain
undefined including the frequency and severity of associated structural abnormalities. The
reported rate of cardiac injury varies between studies, from 7% to 28% of hospitalized patients, a
number which is likely partially dependent upon the definition used and the severity of cases at
the hospital from which the data was drawn (52-54,56). Notably, patients with evidence of
17
cardiac injury tend to be older with more comorbidities, including baseline hypertension,
diabetes, coronary heart disease, and heart failure (54,56). Across all studies, cardiac injury is
associated with worse outcomes, including ICU admission and death (52-54,56). Based on serial
assessment of troponin, researchers in China reported that the median time to the development of
acute cardiac injury was 15 days (IQR 10 -17) after illness onset, occurring after the
development of ARDS (53). Of note, early cardiac injury has been reported, even in the absence
of respiratory symptoms (60). In a case series by Shi et al, the mortality rate for those
hospitalized with subsequent evidence of cardiac injury was significantly higher than those
without cardiac injury (51.2% vs 4.5%, p<0.001) and, along with ARDS, was an independent
predictor of death (56). The magnitude of troponin elevation correlates modestly with the degree
of hsCRP elevation (54). Dynamic increases in troponin were associated with a higher mortality
rate (54,61). Importantly, the mechanism of cardiac injury may be multifactorial, including
demand-ischemia, toxicity from direct viral injury, stress, inflammation, microvascular
dysfunction or plaque rupture, as discussed later (Central Illustration).
Arrhythmia
Arrhythmias have been noted in several published reports. In a case series of 138 hospitalized
patients with COVID-19, 16.7% (n=23) developed an unspecified arrhythmia during their
hospitalization (52); higher rates were noted among patients admitted to the ICU (44.4%, n=16).
A case series of 187 hospitalized patients provided insight into specific arrhythmias, reporting
sustained ventricular tachycardia or ventricular fibrillation amongst 5.9% (n=11) of the patients
(54). These findings are consistent with arrhythmias documented in influenza, which has been
known to cause both AV node dysfunction and ventricular arrhythmias (62).
18
Heart failure, cardiogenic shock and myocarditis
Heart failure and myocardial dysfunction have been described in COVID-19 (53,55,58,60,63). In
a case series of 191 patients, heart failure was noted as a complication of COVID-19 in 23%
(n=44) of all patients and among 52% (n=28) of non-survivors, though the definition of heart
failure was not clearly detailed (53). A smaller series of 21 elderly, critically-ill patients in
Washington State reported incident systolic dysfunction and cardiogenic shock in 7 patients
(33%).(55) Outside of this series, the incidence of cardiogenic shock has not been reported.
Two case reports have documented cardiogenic shock in the setting of an elevated troponin, ST
elevations, a reduction in left ventricular systolic function and no obstructive coronary disease in
patients with COVID-19.(60,63) One report confirmed fulminant myocarditis by cardiac
MRI.(60) Neither patient underwent endomyocardial biopsy. Both were treated with inotropes
and steroids with recovery of LV function. The potential etiologies of the clinical myocarditis
are discussed in detail below (Central Illustration). In one case series from China, myocardial
damage or heart failure contributed to 40% of deaths overall with 7% attributed to solely to
circulatory failure without respiratory failure.(58)
Thrombosis
One of the prominent findings replicated across most early studies of COVID-19 includes
disarray of the coagulation and fibrinolytic system. Hospitalized patients with moderate and
severe COVID-19 and those with poorer outcomes are noted to have prolonged prothrombin
time (PT), elevated D-dimer, and activated partial thromboplastin time (APTT).(35,53,54,64) In
the context of a clinical picture that is consistent with disseminated intravascular thrombosis, it is
19
reasonable to speculate that COVID-19 would be associated with venous or arterial thrombi,
however the incidence has not been published. A pathology report from SARS-CoV1
demonstrated fibrin thrombi in 17 of 20 patients examined with 12 of them showing pulmonary
infarcts (65). One preliminary case report, which has not been peer-reviewed, from a COVID-19
patient described autopsy findings of microthrombi in the pulmonary vasculature (66). While
empiric anticoagulation is being used in some centers (Personal communication Lorenzo
Grazioli, Papa Giovanni XXIII hospital in Bergamo, Italy), the absence of published data
documenting thrombotic events in COVID-19, routine use of anticoagulation is not
recommended without evidence a thrombotic indication (67).
Mortality
COVID-19 has a lower estimated case fatality rate (CFR) than its predecessors, SARS-CoV1 and
MERS-CoV which were 9.4% and 34.4%, respectively (68). However, given the high global
burden of infection seen in COVID-19 compared to SARS and MERS, the absolute number of
fatalities is staggeringly high, crossing 70,000 fatalities at the time of this review (69). CFR
estimates have been challenging with SARS-CoV2, as populations have not been widely
screened for infection – leading to an underestimate of the denominator and probable
overestimate of the CFR. Crude, unadjusted estimates for the global CFR are ~5% at the time
writing with notable variation by country: Italy 11.9% (13,155 deaths), Spain 9.0% (9,387
deaths), South Korea 1.7% (169 deaths), China 4.1% (3312 deaths), Iran 6.4% (3036 deaths),
Germany 1.2% (931 deaths) and the United States 2.3% (5,137 deaths) (69). Regional and
national differences in CFR may be a result of multiple factors, including a) variable testing of
the general and asymptomatic/mildly symptomatic population, b) differing age across countries,
20
c) variable health care system resources and preparedness as well as d) widely different public
health measures for virus control. Importantly, as healthcare capacity is exceeded, a large
number of deaths may occur because of limited availability of critical care resources, such as
mechanical ventilation. When adjusted for underlying demography and under-ascertainment of
cases, the CFR rate was estimated to be 1.4% in China.(70)
The general pattern of fatalities across the age groups appears to be consistent throughout the
world. In general, greater age is associated with greater risk of severe disease as well as death.
According to the Chinese CDC report of over 70,000 cases, the age-related CFR was as follows:
<1% in age <50 years, 1.3% in age 50-59 years, 3.6% in age 60-69 years, 8% in age 70-79 years,
and 14.8% in age 80 years and greater (45). This steep increase in age-related mortality was also
observed in Italy, the US and South Korea (46,71,72). In fact, age, along with markers of
disease severity (d-dimer and sequential organ failure assessment [SOFA] score) were the only
independent predictors of mortality in one study (53).
Multiple associations have been reported between baseline characteristics and comorbid
conditions with mortality in COVID-19. In univariate analyses of predictors of death, Zhou and
colleagues reported that age, coronary heart disease, diabetes, hypertension, respiratory rate,
SOFA score, elevated WBC, lymphocyte count, creatinine, lactate dehydrogenase, high
sensitivity troponin I, D-dimer, and elevated inflammatory markers such as ferritin, IL-6 and
procalcitonin were associated with death (53). However, in multivariable modeling only age
(OR 1·10 [95% CI 1·03–1·17] per year increase), SOFA score (OR 5.7 [95% CI 2.6-12.2]) and
elevated D-dimer (18.4 [95% CI 2.6 - 128.6]) remained independent predictors of mortality as
21
described above (53). In another multivariate analysis of 416 patients from Wuhan, after
controlling for age, baseline cardiovascular, pulmonary, and renal disease, only presence of
cardiac injury and development of ARDS were significantly associated with mortality (4.3 [95%
CI, 1.9-9.5] and 7.9 [95% CI, 3.7-16.7], respectively).(56) It should be noted, however, that
both of these complications tend to occur in older individuals.(56,73)
Putative Mechanisms of Cardiovascular Manifestations in SARS-CoV2
As mentioned in prior sections, COVID-19 patients present with highly variable acuities of
disease and disease progression. Cardiac injury is a common feature of the disease process, and
40% of patients die with myocardial injury as a proximate finding (58). While multiple therapies
are currently under development and in trials for treatment of COVID-19, as discussed in a later
section, understanding the mechanism(s) of cardiac disease will be vital to effective and timely
targeted treatment of this syndrome and its devastating sequelae. Here we propose several
putative mechanisms of COVID-19-induced cardiovascular disease (Central Illustration).
Direct viral myocardial injury
The presence of ACE2 receptors on the myocardium and vascular endothelial cells provides a
theoretical mechanism for direct viral infection of the heart with resultant myocarditis. Reports
have documented clear cases of myocarditis syndromes (60,63). However, to date there no
reports of biopsy proven SARS-CoV2 viral myocarditis with viral inclusions or viral DNA
detected in myocardial tissue. The closely related SARS-CoV1 has been documented to cause a
viral myocarditis with detection of viral RNA in autopsied hearts (74,75). In light of the shared
22
host cell entry receptor between SARS-CoV2 and CoV1, a direct viral myocardial entry and
resulting injury is plausible with SARS-CoV2 as well (76).
Another hypothesized mechanism of direct viral injury to the myocardium is through an
infection-mediated vasculitis. The ACE2 receptor is highly expressed in arterial and venous
endothelial cells (24). There are pathologic data from SARS-CoV1 showing evidence of
vasculitis with monocyte and lymphocyte infiltration, vascular endothelial cell injury and stromal
edema in the heart (77). Either direct viral entry into myocardial endothelial cells could trigger a
vasculitis or presence of virus could lead to an indirect immunological response and resulting
hypersensitivity reaction (78,79). This insult would be associated with myocardial injury and
perhaps even overt myocardial dysfunction in COVID-19.
Microvascular injury
Micro- and macro-thromboses were observed in autopsy evaluations of 3 patients who died from
SARS-CoV1 (80). A prominent finding of SARS-CoV2 is disarray of the coagulation and
fibrinolytic system, with >70% of non-survivors meeting criteria for DIC (81). It may be
hypothesized that myocardial injury is a result of microthrombus formation in the myocardial
vasculature in the setting of a hypercoagulable state like DIC.
Infections and sepsis are a leading cause of DIC in general (82). The exact mechanism of DIC in
the setting of sepsis and ARDS is complex, but is generally thought to be related to an immunemediated
exhaustion of the coagulation and fibrinolytic systems promoting bleeding and
thrombosis in the same patient (83). Endothelial injury and inflammatory cytokines, such as IL23
6 and TNF-alpha, upregulate tissue factor expression, driving a pro-thombotic state (84-87).
Dysregulation of antithrombin III, plasminogen activator inhibitor type 1 (PAI-1) and protein C
in the setting of significant inflammation and sepsis promote an anti-coagulated state (88-90).
Furthermore, platelet activation also ensues in the context of sepsis and inflammation, further
tipping the fine balance of the coagulation system (91-94). In summary, the hyperinflammation
and immune activation seen in severe COVID-19 infection is likely sufficient to trigger DIC,
microvascular dysfunction and myocardial injury.
Stress cardiomyopathy
The role of stress (Takotsubo) cardiomyopathy in COVID-19 related cardiac injury is not known
at this time, with no cases in the literature currently. However, several of the proposed
mechanisms of COVID-19 related cardiac injury detailed in this review are also thought to be
implicated in the pathophysiology of stress cardiomyopathy, particularly those of microvascular
dysfunction, cytokine storm and sympathetic surge (95).
Acute coronary syndrome
Any discussion of myocardial injury would be incomplete without addressing the issue of acute
coronary syndrome (ACS) and myocardial infarction (MI). The current published experience
does not detail the incidence of ACS or epicardial plaque rupture as a mechanism for the acute
cardiac injury observed in COVID-19. However, there is historical precedent for an association
between infection and an elevated risk of ACS. Epidemiologic studies have shown that
hospitalization for pneumonia is associated with a higher risk for atherosclerotic events (96).
Influenza infection has been well studied and shown to have a temporal association with
24
cardiovascular complications and acute coronary syndrome (97,98). Annual vaccination against
seasonal influenza was associated with a 36% lower rate of major adverse cardiovascular events
in a meta-analysis of clinical trials evaluating this question (97). Therefore, viral infection is
associated with an increased risk for coronary events and prevention with a reduction in this risk.
Therefore, it is plausible that ACS will also be an important cause of acute cardiac injury in
patients with COVID-19. Accordingly, international societies have devised pathways and
protocols to effectively treat COVID-19 patients with ACS, including appropriate and timely use
of resources to ensure the best outcome for the patient while also maintaining provider safety
(99).
There are multiple pathophysiologic mechanisms by which systemic viral infection (by influenza
or SARS-CoV2, for example) may lead to a higher risk of plaque destabilization and ACS (100).
The role of inflammation in the development and progression of atherosclerosis is well
established (101,102). The immune response to acute viral infection and the accompanying surge
of cytokines and inflammatory mediators can lead to localized arterial inflammation which is
more pronounced within coronary plaques (61,103). Entry of viral products into the systemic
circulation, also known as pathogen-associated molecular patterns (PAMPs), can cause innate
immune receptor activation which can cascade into activation of immune cells resident in preexisting
atheromata driving plaque rupture.(104) Viral PAMPs are also believed to activate the
inflammasome, resulting in conversion of pro-cytokines into the biologically active cytokines
(105). In addition, dysregulation of coronary vascular endothelial function by infection and
inflammation may lead to a more vasoconstricted coronary bed (106). All of these changes are
25
putative mechanisms by which COVID-19 infection could lead to destabilization of pre-existing
atherosclerotic plaque driving an acute coronary event.
Myocardial injury secondary to oxygen supply and demand mismatch
Periods of severe physiologic stress in the setting of sepsis and respiratory failure can be
associated with elevations in biomarkers of myocardial injury and strain in some patients, an
entity that confers poorer prognosis.(107-109) The mechanism of such myocardial injury is
thought to be related to a mismatch between oxygen supply and demand, without acute
atherothrombotic plaque disruption, and consistent with a diagnosis of type 2 myocardial
infarction (MI) (100,110). Indeed, patients who suffer from type 2 MI compared to type 1 MI
have higher mortality rates, which may in part be explained by a higher burden of acute and
chronic comorbid conditions in the type 2 MI population (111). Furthermore, type 2 MI on the
background of coronary artery disease (CAD) has a worse prognosis than those patients without
CAD. Given the age and comorbidity profile of patients hospitalized with severe COVID-19, it is
reasonable to assume that this population has a higher risk of underlying non-obstructive CAD,
and therefore the presence of type 2 MI in this population is likely a marker of and contributor to
the poor outcomes of COVID-19 patients with troponin elevations (56).
Systemic hyperinflammatory response with resulting myocardial injury
Perhaps one of the more intriguing mechanisms for cardiac injury in severe COVID-19 patients
stems from the significant systemic inflammatory response. Early reports have demonstrated
severely elevated levels of inflammatory biomarkers and cytokines, including IL-6, C-reactive
protein (CRP), tumor necrosis factor (TNF)-α, interleukin (IL)-2R and ferritin (112). Higher
26
levels of these biomarkers are associated with more severe COVID-19 manifestations and worse
outcomes. A proposed theoretical model of COVID-19 disease progression divides the course
into three overlapping yet distinct stages. In this staging framework, stage I represents early viral
infection with associated constitutional symptoms. In stage II, direct viral cytotoxicity of the
pulmonary system with associated inflammatory activation leads to prominent respiratory system
compromise, associated with dyspnea and ultimately acute respiratory distress syndrome
(ARDS) and hypoxia. With ACE2 receptors serving as an entry-point for viral replication in type
II pneumocytes, the pulmonary system becomes the maiden organ of injury. If the host is unable
to clear the virus via a productive and protective immune response, COVID-19 progresses to
stage III - a hyperinflammatory state associated with profound elevations in inflammatory
biomarkers. Patients who reach stage III have severe COVID-19 manifestations with multiorgan
dysfunction and cytokine storm, with immune dysregulating akin to that seen in cytokine release
syndrome (CRS) associated with chimeric antigen receptor T-cell (CAR-T) therapy (112-116).
This observation is basis for several investigational therapies in COVID-19, including steroids
and anti-inflammatory agents, as discussed later.
Prior studies have shown that cardiomyopathy in sepsis is partially mediated by inflammatory
cytokines such as TNF-α, IL-6, IL-1β, INF-γ and IL-2 (73). Recombinant TNF-α resulted in an
early and sustained LV systolic dysfunction in canines (117). Cultured rat cardiomyocytes
demonstrated reduced contractility when exposed to IL-6 (118). The mechanism may be through
modulation of calcium channel activity with resultant myocardial dysfunction (119-121).
Additionally, nitric oxide (NO) is also believed to be a mediator of myocardial depression in
hyperinflammatory states such as sepsis. Seminal studies found that medium from LPS-activated
27
macrophages suppressed myocyte contractility, a finding reversed with the NO synthase
inhibitor, L-N-monomethyl arginine (122). Finally, recent understanding of the key role of
mitochondrial dysfunction in septic states has raised questions about the role of this entity in
sepsis associated cardiomyopathy (123). Indeed, similar mechanisms are thought to possibly
underly the pathophysiology of stress (Takotsubo) cardiomyopathy as well.
Potential Targeted or Disease Modifying Treatments in SARS CoV2
The preceding review of the viral physiology of SARS-CoV2 and the various potential
mechanisms of injury to the host, serve as the basis for considering specific targeted treatment
and prevention. The following section outlines several current candidate classes of agents,
including a brief discussion of vaccine development (Figure 1).
Nucleotide Analogs - Inhibitors of Viral Genome Replication
The antiviral mechanism of nucleotide analogs is to interfere with RdRp function and viral
genome replication and amplification (Figure 1). There are no CoV-specific drugs available at
this time and so ongoing efforts to employ this drug class against SARS-CoV2 are reliant on preexisting
agents designed for other viral illnesses (124).
The most widely-applied agent in this class against SARS-CoV2 has been remdesivir (125).
Remdesivir functions as a chain terminator of RNA replication, initially designed for use against
Ebola (124). Addition of remdesivir to the growing RNA strand by RdRp blocks the
incorporation of additional nucleotides, thereby halting genome replication (126,127). The agent
has been shown to have in vitro activity against SARS-CoV2, leading to off-label and
28
investigational use around the world (4,125). Multiple randomized-controlled trials are ongoing
in China and the United States for moderate, severe and critical COVID-19 (NCT04292730,
NCT04292899, NCT04252664, NCT04252664, NCT04292730).
Another nucleotide analog for the disruption of RdRp-dependent viral replication is favipiravir,
which has investigational approval in several countries (128,129). Additional agents that are
under study include emtricitabine/tenofovir and ribavirin (128,130).
Protease Inhibitors - Inhibitors of Nonstructural Protein Generation
The antiviral mechanism of action of protease inhibitors is to block viral proteases which cleave
the non-structural proteins from the large, monomeric, replicase as detailed above (Figure 1). As
the maturation of non-structural proteins, such as RdRp, is necessary for viral reproduction, the
pharmacologic impairment of the protease should be effective to stop viral replication.
A randomized control trial of lopinavir-ritonavir, a combination protease inhibitor designed for
HIV treatment, in 199 patients with at least moderate COVID-19 did not significantly alter
clinical improvement or viral clearance (131). While the results of this trial were met with
disappointment, this negative study should not forestall trials and drug development of protease
inhibitors as a therapeutic class, given that this drug was not specifically designed for SARSCoV2
(128).
Indeed, the development of inhibitors specific to SARS-CoV2 main protease is underway. A
class of agents identified using structure-based drug design, α-ketonamide inhibitors, has
demonstrated in vitro efficacy and favorable pharmacokinetics (132). Other candidate protease
29
inhibitors for SARS-CoV2 include danoprevir, a drug originally intended for HCV therapy
(133).
Inhibitors of Membrane Fusion
In order for the viral genome to gain access to cellular machinery for replication, a membrane
fusion event must occur between the viral and endosomal membranes, which are noncovalently
bound by the interaction between the S protein and ACE2. The exact mechanism of membrane
fusion is unknown but appears to be dependent on endosomal maturation and a membrane-bound
host protease, TMPRSS2 (7).
Chloroquine (CQ) / Hydroxychloroquine (HCQ)
The antiviral properties of chloroquine (CQ) were previously observed in HIV and other viruses
(134,135). CQ and HCQ are thought to inhibit endosomal maturation, a process by which
endosomes are translocated from the perimembrane regions of the cell to central hubs (136,137)
(Figure 1). CQ prevented viral replication of SARS-CoV1 in vitro (138). A follow-up study
demonstrated comparable efficacy of HCQ, a less toxic derivative, and suggested that the
mechanism of impaired endosomal maturation indeed applied to SARS-CoV2 infection in vitro
(139). Only poor-quality, non-randomized, unblinded data exists assessing the benefit of HCQ in
COVID-19 (140). While HCQ is being widely used with an FDA emergency authorization,
more data are needed to prove efficacy against SARS-CoV2 in humans. Notably, CQ and HCQ
prolong the QT and may induce arrhythmia; significant caution should be used in starting these
agents in patients with a QTc>500 ms. Concomitant use of other QT prolonging agents is not
recommended.
If you are still looking for tons of info, pls reply to this post.
In the interim period, search for info at:
https://www.ncbi.nlm.nih.gov
Select PMC from the databases dropdown top left then search to get FOC access to literally millions of full-text research papers.
To whet your appetite, I shall try to attach one slightly content-heavy paper herewith [unless it is too large a file for TSR to cope with]
Be in touch!
M
OK too large: I shall try to copy part of content here [brace yourself!]
Journal Pre-proof
COVID-19 for the Cardiologist: A Current Review of the Virology, Clinical
Epidemiology, Cardiac and Other Clinical Manifestations and Potential Therapeutic
Strategies
Deepak Atri, MD, Hasan K. Siddiqi, MD MSCR, Joshua Lang, MD, Victor Nauffal, MD,
David A. Morrow, MD MPH, Erin A. Bohula, MD DPhil
PII: S2452-302X(20)30157-1
DOI: https://doi.org/10.1016/j.jacbts.2020.04.002
Reference: JACBTS 443
To appear in: JACC: Basic to Translational Science
Received Date: 7 April 2020
Accepted Date: 7 April 2020
Please cite this article as: Atri D, Siddiqi HK, Lang J, Nauffal V, Morrow DA, Bohula EA, COVID-19 for
the Cardiologist: A Current Review of the Virology, Clinical Epidemiology, Cardiac and Other Clinical
Manifestations and Potential Therapeutic Strategies, JACC: Basic to Translational Science (2020), doi:
https://doi.org/10.1016/j.jacbts.2020.04.002.
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition
of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of
record. This version will undergo additional copyediting, typesetting and review before it is published
in its final form, but we are providing this version to give early visibility of the article. Please note that,
during the production process, errors may be discovered which could affect the content, and all legal
disclaimers that apply to the journal pertain.
© 2020 Published by Elsevier on behalf of the American College of Cardiology Foundation.
1
COVID-19 for the Cardiologist: A Current Review of the Virology, Clinical Epidemiology,
Cardiac and Other Clinical Manifestations and Potential Therapeutic Strategies
Deepak Atri MD*, Hasan K. Siddiqi MD MSCR*, Joshua Lang MD, Victor Nauffal MD, David
A. Morrow MD MPH, and Erin A. Bohula MD DPhil
Cardiovascular Division, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA
*Denotes co-first authors.
Corresponding Author:
Erin A. Bohula MD DPhil
350 Longwood Ave
First Office Floor
Boston, MA 02115
Email: [email protected]
2
Highlights
- Severe acute respiratory virus-2 (SARS-CoV2), the infection responsible for coronavirus
disease-2019 (COVID-19), has spread globally leading to a devastating loss of life. In a
few short months, the clinical and scientific communities have rallied to rapidly evolve
our understanding of the mechanism(s) of disease and potential therapeutics.
- This review discusses the current understanding of the basis virology of SARS-CoV2 and
the epidemiology, clinical manifestations, including cardiovascular, and mortality of
COVID-19. A detailed review of the viral life cycle and putative mechanism(s) of injury
frames the discussion of possible preventative and therapeutic strategies.
- The ongoing, unprecedented collective effort will, without a doubt, advance our ability to
prevent the spread and optimally care for patients suffering from COVID-19.
Summary
The coronavirus disease-2019 (COVID-19), a contagious disease caused by severe acute
respiratory syndrome coronavirus-2 (SARS-CoV2), has reached pandemic status. As it spreads
across the world, it has overwhelmed healthcare systems, strangled the global economy and led
to a devastating loss of life. Widespread efforts from regulators, clinicians and scientists are
driving a rapid expansion of knowledge of the SARS-CoV2 virus and the COVID-19 disease.
We review the most current data with a focus on our basic understanding of the mechanism(s) of
disease and translation to the clinical syndrome and potential therapeutics. We discuss the basic
virology, epidemiology, clinical manifestation, multi-organ consequences, and outcomes. With a
focus on cardiovascular complications, we propose several mechanisms of injury. The virology
and potential mechanism of injury form the basis for a discussion of potential disease-modifying
therapies.
Key words: COVID-19, SARS-CoV2, Cardiovascular, Virology, Treatments
Abbreviations
ACE2 – angiotensin-converting enzyme 2
ARDS – acute respiratory distress syndrome
CDC – Centers for Disease Control
CFR – case fatality rate
COVID-19 – coronavirus disease-2019
CoV – coronavirus
DIC – disseminated intravascular coagulation
ER - endoplasmic reticulum
hsCRP – high sensitivity c-reactive protein
ICU – intensive care unit
SARS-CoV1 or 2– severe acute respiratory syndrome coronavirus-1 or -2
SOFA – sequential organ failure assessment
TMPSS2 – trasmembrane serine protease-2
3
Introduction
The coronavirus disease-2019 (COVID-19), a contagious disease caused by severe acute
respiratory syndrome coronavirus-2 (SARS-CoV2), has reached pandemic status. As it spreads
across the world, it has overwhelmed healthcare systems, strangled the global economy and led
to a devastating loss of life. In the ongoing wake of COVID-19, the world’s medical and
scientific communities have come together to rapidly expand our knowledge of the pathogenesis,
disease manifestations and possible preventive and therapeutic strategies. Virologists have
looked to related diseases to understand the life cycle of this novel viral infection. Despite being
overwhelmed, through conventional and historically unconventional mechanisms, clinicians
managing patients with COVID-19 have made a concerted effort to rapidly educate colleagues in
expectant regions of the world on lessons learned. The world’s regulatory agencies and
pharmaceutical industry are using emergency mechanisms to expedite access to and study of
therapeutic options. These widespread efforts, drawn from many arenas, are driving a rapid
expansion of collective experience and understanding of COVID-19.
Here, we review this body of work with a focus on our basic understanding of the mechanism(s)
of disease and translation to the clinical syndrome and potential therapeutic options.
Specifically, we discuss the basic virology, epidemiology and clinical manifestations, including
presentation, progression, multi-organ consequences and outcomes. With a focus on the
cardiovascular complications, we propose several potential mechanisms of injury. We discuss a
range of possible therapeutic options in the context of the viral life cycle and possible
mechanisms of injury. Finally, in recognition of the scale of this crisis, we address the ethical
considerations around standards of care in the event of resource scarcity.
4
Basic Virology of SARS-CoV2
Genetics and Structure
Coronaviridae comprise a family of enveloped, single stranded, positive sense, RNA viruses
with comparable genomic organization and functional mechanisms. Coronaviruses (CoV) are
canonically divided into alpha- and beta-, gamma- and delta- genera predicated on genetic
clustering. The alpha- and beta-CoV are known to cause human diseases, such as common
respiratory infections. The SARS-CoV2 and SARS-CoV1 are beta-CoV (1-3). CoV are sonamed
because of the characteristic crown, or corona, of electron density that they exhibit on
transmission electron micrographs. This appearance is thought to be caused by the densely
packed protein that studs the viral membrane and is responsible for receptor binding on targetcell
membranes.
The CoV genome is organized into two parts. Highly conserved with the CoV family, the 5’
terminal end, encodes the replicase - the nonstructural proteins responsible for viral replication
within the cell (1-3). It is translated as one peptide (~790 kDa) from which the constituent
functional proteins are subsequently cleaved. CoV genomes encode 16 nonstructural proteins, as
in SARS-CoV2, and they exhibit a multitude of functions required for viral replication (2,4,5).
Critical proteins for viral replication include the main protease (nsp5), the papain-like protease
(nsp3) and the RNA-dependent RNA polymerase (nsp12, RdRp). The other replicase constituent
proteins repurpose the cellular machinery to facilitate viral replication and to blunt the intrinsic
host immune functions (1,6).
5
The remaining third of the CoV genome encodes the structural proteins and a variety of
accessory proteins (latter not discussed here). The structural proteins are the constituent proteins
of the transmissible viral particle, or virion. The key structural CoV proteins are the nucleocapsid
protein (N) and three transmembrane proteins: the spike protein (S), the membrane protein (M),
and the envelope protein (E) (1-5)(Figure 1). The S protein is responsible for virus-cell receptor
interactions (7-11)(Figure 1). The E and M proteins are responsible for membrane structure and
fusion. The N protein binds viral RNA and mediates its interaction with the S, E, and M proteins
for genome encapsulation (1,12).
Life Cycle
The life cycle of SARS-CoV2 has not been rigorously established; however, given the
considerable sequence homology, it is presumed to be similar to that of SARS-CoV1 and other
CoV (4,5). In general, the CoV life cycle consists of a series of steps that begins with viral
binding to a target cell and culminates in viral reproduction. Knowledge of this process informs
an understanding of viral physiology and also will serve as the basis for discussion of antiviral
therapeutics (8)(Figure 1). The aim of evolving therapeutics will be to break the “links in the
chain” of the viral life cycle in order to forestall the propagation of infection within the cells of
an individual patient.
SARS-CoV2 is known to bind to cells via the same receptor as SARS-CoV1, the membranebound
glycoprotein Angiotensin Converting Enzyme 2 (ACE2) (4). It has not been observed to
bind other CoV receptors, namely dipeptidyl peptidase 4 (DPP4) or aminopeptidase N (APN)
(4,13). After binding of ACE2, the virus is internalized via endocytosis without access to the
6
host intracellular compartment until a membrane fusion event occurs (4)(Figure 1). This process
is mediated, at least in part, by another membrane bound protease known as transmembrane
serine protease 2 (TMPRSS2), which cleaves the S protein as a necessary step of membrane
fusion (7). Interestingly, the protease activity of the CoV receptors, ACE2, DPP4 and APN, does
not seem necessary for membrane fusion (14).
Upon membrane fusion, the viral RNA genome enters the intracellular compartment. At this
point, the viral RNA may be translated into its encoded structural and nonstructural proteins. The
translation of the nonstructural proteins, or replicase, results in the production of a single massive
polypeptide chain, from which the sixteen constituent nonstructural proteins are cleaved. This
process is initially mediated by intracellular proteases, and then further propagated by the
function of the CoV main protease and papain-like protease (1). Another replicase protein, the
RNA-dependent RNA polymerase (RdRp) is responsible for the replication and amplification of
the viral genome (15). During this process, mutations may be acquired by errors in replication
and recombination events (1).
Upon amplification of the viral RNA, more viral structural and nonstructural proteins may be
generated. Viral structural proteins, because of their transmembrane nature (with the exception of
the N protein), are targeted to the ER membrane with appropriate signal sequences. Viral RNA,
bound by N protein, interacts with the structural proteins on the membrane of the ER and Golgi
apparatus before another membrane fusion event on these membranes results in viral budding
and exocytosis (1,8,12).
7
Importantly, the precise molecular differences that account for the important clinical differences
between SARS-CoV2 and SARS-CoV1 infections, such as prolonged latency, widely variable
symptoms, a possible predisposition for individuals with pre-existing cardiovascular conditions,
and a predilection for myocardial complications, remain unclear.
Pathogenesis: Angiotensin-Converting Enzyme 2
SARS-CoV2, SARS-CoV, and HCoV-NL63, a virus that causes a mild respiratory infection, are
all known to employ ACE2 as a receptor (3,4,16,17). Given the functions of ACE2 in the
cardiovascular system, the importance of angiotensin-directed pharmacology in cardiovascular
disease and the apparent propensity for severe illness among patients with COVID-19 with
cardiovascular comorbidity, the ACE2 molecule has been the subject of much attention (18).
Indeed, major clinical societies have issued consensus statements on the use of ACE inhibitors
(ACEi) and angiotensin-receptor blockers (ARBs) in the setting of the COVID-19 pandemic, as
discussed later (19).
Angiotensin-Converting enzyme 2 (ACE2) is a single-pass transmembrane protein with protease
activity that cleaves the vasoconstrictor angiotensin II into the vasodilator angiotensin 1-7 (20-
23). In doing so, it functions as a counter-regulatory enzyme to the functions of ACE1, which
generates angiotensin II (20). In humans, the protein has a broad pattern of expression and has
been found in the lung epithelium (in particular the type II pneumocyte), the myocardium, the
endothelium, the GI tract, bone marrow, kidneys and spleen among other tissues; potentially
explaining the multi-organ injury observed with SARS-CoV2 infection (24). Another relevant
8
feature of Ace2 gene expression is its encoding on the X chromosome, which may account for
possible sex differences observed in the epidemiology of COVID-19 (25).
In animal models of acute respiratory distress syndrome (ARDS), due to chemical pneumonitis,
overwhelming sepsis, endotoxemia, or influenza, Ace2KO mice have more severe acute lung
injury (ALI) relative to their wild-type counterparts as evaluated histologically and by measures
of elastance (26-28). The phenotype of increased elastance was rescued by administration of
recombinant human ACE2, which affirms a causal link between Ace2 deficiency and a more
profound state of ALI (26,28). Additionally, the administration of losartan, an angiotensin II
type-1 receptor (AT1R) blocker mitigated the exacerbating effects of SARS-CoV spike protein in
an animal model of ARDS (29). Losartan also abrogated the severity of ALI due to influenza in
mice (27,28).
In regard to the counter-regulatory properties of ACE1 and ACE2, the effects of Ace2-deficiency
appear to be rescued by Ace1-deficiency in mice. For example, the effects of Ace2-deficiency to
result in more severe ALI are abrogated by Ace1-deficiency. Ace2KO mice demonstrated more
severe ALI than Ace2KO;Ace1+/-, with further reduction in severity observed in Ace2KO;Ace1-/-
(26). This dose-responsiveness also implies causation. Comparable effects were seen with
myocardial dysfunction, as Ace2KO;Ace1+/- and Ace2KO;Ace1-/- had no evidence of the
contractile deficit observed in Ace2KO mice (30). Of note, in each of the above cases, however,
the animal models were constitutive knockout systems (rather than lineage-specific or inducible
knockout). Thus, the ACE2-expressing cell that mediates each phenotypic abnormality has not
been determined.
9
SARS-CoV2 is able to utilize ACE2 isoforms from swine, bats, civets and humans suggesting a
mechanism whereby the virus may have been initially transmissible from species to species and,
with mutation, evolved into a novel pathogen (4). Notably, murine ACE2 is not a functional
receptor for SARS-CoV2; thereby requiring transgenic expression of human ACE2 if mice are to
be used as a research model (4).
ACE2 undergoes cleavage by the membrane-bound protease ADAM17; resulting in the release
of soluble ACE2 into the blood stream (31). The effects of soluble ACE2 are unclear in humans,
however it appears to have favorable effects on lung function in models of ARDS, influenza, and
RSV infection (26,28,32). Soluble ACE2 has been studied in a phase II trial of ARDS, but largescale,
well-powered clinical outcomes trials are needed (33). Research is ongoing to determine
whether soluble ACE2 may act as a specific therapeutic to SARS-CoV2 in the role of a decoy
receptor, as discussed later (34).
Finally, given the necessity of ACE2 for viral infection, the role of ACE inhibitors (ACEi) or
angiotensin receptor blockers (ARBs) in COVID-19 has drawn intense attention. Importantly,
the ACE2 enzyme itself is not inhibited by ACEi/ARB use (21). ACEi or ARB exposure may
result in ACE2 protein upregulation in animal models; however not all animal models exhibit
this effect. The existing epidemiology of COVID-19 among patients taking ACEi or ARB is
confounded by cardiovascular comorbidities which may alter ACE2 and angiotensin II
expression (18). At this time, it is unclear if ACEi or ARBs use influences receptor expression
and whether variable expression impacts the propensity for or severity of SARS-CoV2 infection.
10
Transmission
Exposure to the Huanan seafood market was common among the earliest cases contributing to
the SARS-CoV2 epidemic in China suggesting that this was a zoonotic disease with an
intermediate animal host (non-aquatic animals were sold in the market) (35). Genomic analyses
have identified approximately 87% DNA sequence homology between SARS-CoV2 and two
SARS-like CoV isolated from Chinese horseshoe bats, bat-SL-CoVZC45 and bat-SLCoVZXC21,
in the Zhejiang province in China (36). Notably, no bats are sold in the market and
at the onset of the outbreak in December most bat species in Wuhan would be hibernating. Thus,
similar to SARS-CoV1 and MERS-CoV, while bats may be the natural reservoir for SARSCoV2,
there is likely an unidentified intermediate animal host responsible for animal-to-human
transmission. Despite closure of the Huanan market on January 1, 2020, the epidemic continued
to expand and case clusters with no exposure to the market were reported indicating the
occurrence of human-to-human transmission (37).
Akin to other respiratory viruses, SARS-CoV2 spreads primarily through small respiratory
droplets that are expelled from infected individuals and can travel approximately 3-6 feet. The
virus can exist in nature on surfaces and can last for up to 4 hours on copper, 24 hours on
cardboard and up to 72 hours on plastic and stainless steel surfaces leading to fomite
transmission (38). In fact, the Japanese National Institute of Infectious Disease reported detection
of SARS-CoV2 RNA on surfaces in the cabins of symptomatic and asymptomatic passengers on
the Diamond Princess up to 17 days after they were vacated (39). Live virus has also been
isolated and cultured from fecal specimens raising the possibility of oro-fecal transmission,
11
though corroborating clinical evidence for this method of transmission is lacking (40). Airborne
transmission may be facilitated in healthcare settings where aerosol-producing interventions are
being performed including endotracheal intubation, bronchoscopy, suctioning, nebulizer
treatment, non-invasive positive pressure ventilation and delivery of oxygen via a high-flow
nasal cannula. These transmission data support the clinical recommendations that airborne
precautions, including use of N-95 masks, should be implemented in these aerosol-producing
settings whereas standard droplet precautions should be used during all other encounters with
infected individuals (41).
In a fully susceptible population, reflected by early stages of the epidemic in China, studies have
estimated a basic reproductive number (Ro) of 2.38 for SARS-CoV2, meaning that every infected
individual is likely on average to spread the virus to 2 to 3 other individuals (42). An outbreak
will continue to increase in size if the Ro>1. For context, seasonal influenza has an Ro of 1.5 (43).
Substantial transmission from asymptomatic hosts has facilitated the widespread transmission of
SARS-CoV2 and contributed to its pandemic potential (42). A study from Singapore with
extensive contact tracing identified 7 clusters of cases where secondary spread of the infection
occurred 1-3 days prior to symptom development in the source patient (44). Thus, containment
measures aimed solely at isolating symptomatic individuals are inadequate. Furthermore, contact
tracing efforts should take in to account the pre-symptomatic contagious period to
comprehensively capture all potentially exposed individuals. Ro is not a static measure and
interventions including self-quarantine, contact isolation, social distancing and enhanced hygiene
measures have proven to be effective in China. Following implementation of such measures in
12
China, the Ro steadily decreased from 2.38 prior to January 23rd to 0.99 during the period of
January 24-February 8, 2020 (42).
Epidemiology and Clinical Manifestations of SARS-CoV2
Epidemiology
The burden of the SARS-CoV2 virus has evolved rapidly since it first appeared in Wuhan, China
in December 2019. What began as a few case reports of atypical pneumonia now spans the globe
as a pandemic. At present, most published data come from China and form the basis for our
understanding of the epidemiology of COVID-19. In the largest published registry to date, the
Chinese Centers for Disease Control and Prevention (CDC) reported high-level details for patient
characteristics, severity of manifestations and survival in 72,314 cases of putative (47%) and
confirmed (63%) COVID-19 (45). In this population, predominantly identified by the presence
of symptoms (~99%), <2% of cases occurred in children < 19 years of age suggesting that
children either are either resistant to infection or rarely symptomatic. Of confirmed cases, most
(87%) were mild, defined by no or mild pneumonia, 14% were severe with significant infiltrates
or signs of respiratory compromise and 5% were critical with respiratory failure (e.g. mechanical
ventilation), shock or multiorgan system failure.
The first confirmed case of COVID-19 in the US was identified on January 20, 2020 and the US
has now surpassed all other countries in the absolute number of cases. However, given the rapid
and recent onset of the burden, there are few published data reflecting the experience with
COVID-19 in the US. In an early snap shot from the US CDC in 4,226 confirmed cases with
symptoms or exposure, only 5% occurred in those under the age of 20 (46).
13
While data are rapidly accumulating, much of the epidemiology of this virus remains unknown.
Most publications are small, single center studies, and detail the clinical characteristics,
complications and outcomes in the subset of patients who were hospitalized. As a result of the
limitations on testing and the data suggesting that many infected individuals may be
asymptomatic, the true burden of infected individuals is unclear and underestimated (42,47). Not
only does the variable manifestation of symptoms hamper public health initiatives to trace and
isolate infected individuals, but also it limits our ability to accurately estimate infectivity,
symptom burden, and non-fatal and fatal complication rates in the overall population of infected
individuals. With that caveat, the published data provide insights into the more vulnerable, atrisk
populations who require hospitalization. While the individual studies are small, the
predictors of more severe manifestations and poor outcomes have been generally consistent as
detailed below.
Clinical Presentation / Syndrome
In a multi-center case series of 1,099 hospitalized patients from China, the most common
symptoms were fever in up to 90%, followed by cough, fatigue, sputum production, and
shortness of breath (48). Less common symptoms included headache, myalgias, sore throat,
nausea, vomiting, and diarrhea. The American Association of Otolaryngology has recently
highlighted anosmia and dysgeusia as possible symptoms of disease as well (49). The median
incubation period, or time from probable exposure to first symptom, was 4 days (IQR 2-7) (48).
Another report detailed that 99% of infected patients develop symptoms within 14 days (50).
Common lab derangements on admission included lymphopenia, elevations in c-reactive protein,
14
lactate dehydrogenase, liver transaminases and d-dimer (48). Notably, procalcitonin was rarely
elevated (48). These data are generally consistent across multiple smaller studies, several of
which noted elevations in other inflammatory markers, such as IL-6, ferritin and ESR (51-55).
Evidence of cardiac or kidney injury at admission was variable across studies, but tended to be
absent upon hospitalization (48,51-53,56). Chest computed tomography at the time of admission
was abnormal in 87% of patients with ground glass opacities or local or patchy “shadowing”
(48).
Disease Progression
Many of the more severe manifestations, such as ARDS, acute kidney injury (AKI) and
myocardial injury, tend to occur as many as 8-14 days after the onset of symptoms and portend
worse outcomes (53). Within a hospitalized population, rates of ICU admission range between
26-32% across most studies (35,48,51-53,57). Several studies have identified older age and
baseline burden of comorbidity, such as diabetes, hypertension, prior coronary disease and prior
lung disease, as predictors of more significant disease progression with higher rates of ARDS,
AKI, cardiac injury, ICU admission and death (51-53,58,59). Increases in markers of
inflammation, coagulation, and cardiac injury also correlate with disease severity and rise
throughout the course of the disease (53,54,56). In hospitalized populations, the timing of death
occurred at a median of 16-19 days after illness onset (53,58). The median time from symptom
onset to discharge in survivors was around 3 weeks (53).
Non-Cardiovascular Clinical Manifestations
Respiratory Failure
15
The most prominent complication of COVID-19 is respiratory failure. As previously described,
the majority of patients have no or mild symptoms (45). In hospitalized patients, respiratory
symptoms are common and range in severity from cough (60-80%) or dyspnea (19-40%) to
ARDS (17-42%) (51-53,56,57). ARDS rates were only 3.2% in the largest case series, but this
may be an underestimate due to a short average follow up time of 12 days, with the vast majority
of patients remaining hospitalized at the end of study (48). ARDS tends to occur ~1-2 weeks
into illness and is often precipitous and protracted (51,53,57). For these reasons, and to avoid
risk of provider infection with emergent intubation, professional societies recommend early
intubation in the event of respiratory decline (41). Intubation was required in 10-33% in the
various Chinese series; however, rates of high-flow nasal cannula and non-invasive mechanical
ventilation also were high (35,51-53). These therapies are believed to result in aerosolization
and are generally not recommended – consequently, more patients will be intubated when unable
to be supported by nasal cannula or a non-rebreather mask (41). Older age, baseline
hypertension, diabetes, high fever, lymphopenia, injury to other organs (e.g. AKI, ALI), and
elevated d-dimer and inflammatory markers were predictors of ARDS; advanced age,
neutropenia, elevated d-dimer and inflammation are associated with higher mortality in those
with ARDS (51). Development of ARDS, along with acute cardiac injury, was an independent
predictor of death (56). Importantly, hypoxemic respiratory failure is the leading cause of death
in COVID-19, contributing to 60% of deaths (58).
Renal injury
Estimates vary as to the incidence of acute kidney injury in COVID-19, ranging between 0.5-
15% (35,48,52,53,56,59). Among hospitalized patients the rates of proteinuria (43.9%) and
16
hematuria (26.7%) appear to be even higher (59). Acute kidney injury occurs in the first few
days after admission in patients with baseline chronic kidney disease, and after 7-10 days in
patients with normal baseline renal function (59). Mechanisms of renal injury have been
hypothesized to include both acute tubular necrosis (ATN), direct cytotoxic effects of the virus
itself, and immune-mediated damage (59).
Liver injury
Transaminitis is common with an incidence of 21-37%, and as high as 48-62% of patients who
are critically ill or who do not survive (35,48,53). Acute liver injury, defined as either alanine
aminotransferase or aspartate aminotransferase greater than three times the upper limit of
normal, occurs less frequently, and was reported to occur in 19.1% (n=4) of 21 patients who
were admitted to an ICU in Washington State (55).
Cardiovascular Manifestations
Cardiac injury
Numerous studies have reported acute cardiac injury as an important manifestation of COVID-
19. In studies published to date, acute cardiac injury was variably defined as either cardiac
troponin elevation >99th percentile alone or a composite of troponin elevation, ECG or
echocardiographic abnormalities (52-56,58). Importantly, many aspects of this endpoint remain
undefined including the frequency and severity of associated structural abnormalities. The
reported rate of cardiac injury varies between studies, from 7% to 28% of hospitalized patients, a
number which is likely partially dependent upon the definition used and the severity of cases at
the hospital from which the data was drawn (52-54,56). Notably, patients with evidence of
17
cardiac injury tend to be older with more comorbidities, including baseline hypertension,
diabetes, coronary heart disease, and heart failure (54,56). Across all studies, cardiac injury is
associated with worse outcomes, including ICU admission and death (52-54,56). Based on serial
assessment of troponin, researchers in China reported that the median time to the development of
acute cardiac injury was 15 days (IQR 10 -17) after illness onset, occurring after the
development of ARDS (53). Of note, early cardiac injury has been reported, even in the absence
of respiratory symptoms (60). In a case series by Shi et al, the mortality rate for those
hospitalized with subsequent evidence of cardiac injury was significantly higher than those
without cardiac injury (51.2% vs 4.5%, p<0.001) and, along with ARDS, was an independent
predictor of death (56). The magnitude of troponin elevation correlates modestly with the degree
of hsCRP elevation (54). Dynamic increases in troponin were associated with a higher mortality
rate (54,61). Importantly, the mechanism of cardiac injury may be multifactorial, including
demand-ischemia, toxicity from direct viral injury, stress, inflammation, microvascular
dysfunction or plaque rupture, as discussed later (Central Illustration).
Arrhythmia
Arrhythmias have been noted in several published reports. In a case series of 138 hospitalized
patients with COVID-19, 16.7% (n=23) developed an unspecified arrhythmia during their
hospitalization (52); higher rates were noted among patients admitted to the ICU (44.4%, n=16).
A case series of 187 hospitalized patients provided insight into specific arrhythmias, reporting
sustained ventricular tachycardia or ventricular fibrillation amongst 5.9% (n=11) of the patients
(54). These findings are consistent with arrhythmias documented in influenza, which has been
known to cause both AV node dysfunction and ventricular arrhythmias (62).
18
Heart failure, cardiogenic shock and myocarditis
Heart failure and myocardial dysfunction have been described in COVID-19 (53,55,58,60,63). In
a case series of 191 patients, heart failure was noted as a complication of COVID-19 in 23%
(n=44) of all patients and among 52% (n=28) of non-survivors, though the definition of heart
failure was not clearly detailed (53). A smaller series of 21 elderly, critically-ill patients in
Washington State reported incident systolic dysfunction and cardiogenic shock in 7 patients
(33%).(55) Outside of this series, the incidence of cardiogenic shock has not been reported.
Two case reports have documented cardiogenic shock in the setting of an elevated troponin, ST
elevations, a reduction in left ventricular systolic function and no obstructive coronary disease in
patients with COVID-19.(60,63) One report confirmed fulminant myocarditis by cardiac
MRI.(60) Neither patient underwent endomyocardial biopsy. Both were treated with inotropes
and steroids with recovery of LV function. The potential etiologies of the clinical myocarditis
are discussed in detail below (Central Illustration). In one case series from China, myocardial
damage or heart failure contributed to 40% of deaths overall with 7% attributed to solely to
circulatory failure without respiratory failure.(58)
Thrombosis
One of the prominent findings replicated across most early studies of COVID-19 includes
disarray of the coagulation and fibrinolytic system. Hospitalized patients with moderate and
severe COVID-19 and those with poorer outcomes are noted to have prolonged prothrombin
time (PT), elevated D-dimer, and activated partial thromboplastin time (APTT).(35,53,54,64) In
the context of a clinical picture that is consistent with disseminated intravascular thrombosis, it is
19
reasonable to speculate that COVID-19 would be associated with venous or arterial thrombi,
however the incidence has not been published. A pathology report from SARS-CoV1
demonstrated fibrin thrombi in 17 of 20 patients examined with 12 of them showing pulmonary
infarcts (65). One preliminary case report, which has not been peer-reviewed, from a COVID-19
patient described autopsy findings of microthrombi in the pulmonary vasculature (66). While
empiric anticoagulation is being used in some centers (Personal communication Lorenzo
Grazioli, Papa Giovanni XXIII hospital in Bergamo, Italy), the absence of published data
documenting thrombotic events in COVID-19, routine use of anticoagulation is not
recommended without evidence a thrombotic indication (67).
Mortality
COVID-19 has a lower estimated case fatality rate (CFR) than its predecessors, SARS-CoV1 and
MERS-CoV which were 9.4% and 34.4%, respectively (68). However, given the high global
burden of infection seen in COVID-19 compared to SARS and MERS, the absolute number of
fatalities is staggeringly high, crossing 70,000 fatalities at the time of this review (69). CFR
estimates have been challenging with SARS-CoV2, as populations have not been widely
screened for infection – leading to an underestimate of the denominator and probable
overestimate of the CFR. Crude, unadjusted estimates for the global CFR are ~5% at the time
writing with notable variation by country: Italy 11.9% (13,155 deaths), Spain 9.0% (9,387
deaths), South Korea 1.7% (169 deaths), China 4.1% (3312 deaths), Iran 6.4% (3036 deaths),
Germany 1.2% (931 deaths) and the United States 2.3% (5,137 deaths) (69). Regional and
national differences in CFR may be a result of multiple factors, including a) variable testing of
the general and asymptomatic/mildly symptomatic population, b) differing age across countries,
20
c) variable health care system resources and preparedness as well as d) widely different public
health measures for virus control. Importantly, as healthcare capacity is exceeded, a large
number of deaths may occur because of limited availability of critical care resources, such as
mechanical ventilation. When adjusted for underlying demography and under-ascertainment of
cases, the CFR rate was estimated to be 1.4% in China.(70)
The general pattern of fatalities across the age groups appears to be consistent throughout the
world. In general, greater age is associated with greater risk of severe disease as well as death.
According to the Chinese CDC report of over 70,000 cases, the age-related CFR was as follows:
<1% in age <50 years, 1.3% in age 50-59 years, 3.6% in age 60-69 years, 8% in age 70-79 years,
and 14.8% in age 80 years and greater (45). This steep increase in age-related mortality was also
observed in Italy, the US and South Korea (46,71,72). In fact, age, along with markers of
disease severity (d-dimer and sequential organ failure assessment [SOFA] score) were the only
independent predictors of mortality in one study (53).
Multiple associations have been reported between baseline characteristics and comorbid
conditions with mortality in COVID-19. In univariate analyses of predictors of death, Zhou and
colleagues reported that age, coronary heart disease, diabetes, hypertension, respiratory rate,
SOFA score, elevated WBC, lymphocyte count, creatinine, lactate dehydrogenase, high
sensitivity troponin I, D-dimer, and elevated inflammatory markers such as ferritin, IL-6 and
procalcitonin were associated with death (53). However, in multivariable modeling only age
(OR 1·10 [95% CI 1·03–1·17] per year increase), SOFA score (OR 5.7 [95% CI 2.6-12.2]) and
elevated D-dimer (18.4 [95% CI 2.6 - 128.6]) remained independent predictors of mortality as
21
described above (53). In another multivariate analysis of 416 patients from Wuhan, after
controlling for age, baseline cardiovascular, pulmonary, and renal disease, only presence of
cardiac injury and development of ARDS were significantly associated with mortality (4.3 [95%
CI, 1.9-9.5] and 7.9 [95% CI, 3.7-16.7], respectively).(56) It should be noted, however, that
both of these complications tend to occur in older individuals.(56,73)
Putative Mechanisms of Cardiovascular Manifestations in SARS-CoV2
As mentioned in prior sections, COVID-19 patients present with highly variable acuities of
disease and disease progression. Cardiac injury is a common feature of the disease process, and
40% of patients die with myocardial injury as a proximate finding (58). While multiple therapies
are currently under development and in trials for treatment of COVID-19, as discussed in a later
section, understanding the mechanism(s) of cardiac disease will be vital to effective and timely
targeted treatment of this syndrome and its devastating sequelae. Here we propose several
putative mechanisms of COVID-19-induced cardiovascular disease (Central Illustration).
Direct viral myocardial injury
The presence of ACE2 receptors on the myocardium and vascular endothelial cells provides a
theoretical mechanism for direct viral infection of the heart with resultant myocarditis. Reports
have documented clear cases of myocarditis syndromes (60,63). However, to date there no
reports of biopsy proven SARS-CoV2 viral myocarditis with viral inclusions or viral DNA
detected in myocardial tissue. The closely related SARS-CoV1 has been documented to cause a
viral myocarditis with detection of viral RNA in autopsied hearts (74,75). In light of the shared
22
host cell entry receptor between SARS-CoV2 and CoV1, a direct viral myocardial entry and
resulting injury is plausible with SARS-CoV2 as well (76).
Another hypothesized mechanism of direct viral injury to the myocardium is through an
infection-mediated vasculitis. The ACE2 receptor is highly expressed in arterial and venous
endothelial cells (24). There are pathologic data from SARS-CoV1 showing evidence of
vasculitis with monocyte and lymphocyte infiltration, vascular endothelial cell injury and stromal
edema in the heart (77). Either direct viral entry into myocardial endothelial cells could trigger a
vasculitis or presence of virus could lead to an indirect immunological response and resulting
hypersensitivity reaction (78,79). This insult would be associated with myocardial injury and
perhaps even overt myocardial dysfunction in COVID-19.
Microvascular injury
Micro- and macro-thromboses were observed in autopsy evaluations of 3 patients who died from
SARS-CoV1 (80). A prominent finding of SARS-CoV2 is disarray of the coagulation and
fibrinolytic system, with >70% of non-survivors meeting criteria for DIC (81). It may be
hypothesized that myocardial injury is a result of microthrombus formation in the myocardial
vasculature in the setting of a hypercoagulable state like DIC.
Infections and sepsis are a leading cause of DIC in general (82). The exact mechanism of DIC in
the setting of sepsis and ARDS is complex, but is generally thought to be related to an immunemediated
exhaustion of the coagulation and fibrinolytic systems promoting bleeding and
thrombosis in the same patient (83). Endothelial injury and inflammatory cytokines, such as IL23
6 and TNF-alpha, upregulate tissue factor expression, driving a pro-thombotic state (84-87).
Dysregulation of antithrombin III, plasminogen activator inhibitor type 1 (PAI-1) and protein C
in the setting of significant inflammation and sepsis promote an anti-coagulated state (88-90).
Furthermore, platelet activation also ensues in the context of sepsis and inflammation, further
tipping the fine balance of the coagulation system (91-94). In summary, the hyperinflammation
and immune activation seen in severe COVID-19 infection is likely sufficient to trigger DIC,
microvascular dysfunction and myocardial injury.
Stress cardiomyopathy
The role of stress (Takotsubo) cardiomyopathy in COVID-19 related cardiac injury is not known
at this time, with no cases in the literature currently. However, several of the proposed
mechanisms of COVID-19 related cardiac injury detailed in this review are also thought to be
implicated in the pathophysiology of stress cardiomyopathy, particularly those of microvascular
dysfunction, cytokine storm and sympathetic surge (95).
Acute coronary syndrome
Any discussion of myocardial injury would be incomplete without addressing the issue of acute
coronary syndrome (ACS) and myocardial infarction (MI). The current published experience
does not detail the incidence of ACS or epicardial plaque rupture as a mechanism for the acute
cardiac injury observed in COVID-19. However, there is historical precedent for an association
between infection and an elevated risk of ACS. Epidemiologic studies have shown that
hospitalization for pneumonia is associated with a higher risk for atherosclerotic events (96).
Influenza infection has been well studied and shown to have a temporal association with
24
cardiovascular complications and acute coronary syndrome (97,98). Annual vaccination against
seasonal influenza was associated with a 36% lower rate of major adverse cardiovascular events
in a meta-analysis of clinical trials evaluating this question (97). Therefore, viral infection is
associated with an increased risk for coronary events and prevention with a reduction in this risk.
Therefore, it is plausible that ACS will also be an important cause of acute cardiac injury in
patients with COVID-19. Accordingly, international societies have devised pathways and
protocols to effectively treat COVID-19 patients with ACS, including appropriate and timely use
of resources to ensure the best outcome for the patient while also maintaining provider safety
(99).
There are multiple pathophysiologic mechanisms by which systemic viral infection (by influenza
or SARS-CoV2, for example) may lead to a higher risk of plaque destabilization and ACS (100).
The role of inflammation in the development and progression of atherosclerosis is well
established (101,102). The immune response to acute viral infection and the accompanying surge
of cytokines and inflammatory mediators can lead to localized arterial inflammation which is
more pronounced within coronary plaques (61,103). Entry of viral products into the systemic
circulation, also known as pathogen-associated molecular patterns (PAMPs), can cause innate
immune receptor activation which can cascade into activation of immune cells resident in preexisting
atheromata driving plaque rupture.(104) Viral PAMPs are also believed to activate the
inflammasome, resulting in conversion of pro-cytokines into the biologically active cytokines
(105). In addition, dysregulation of coronary vascular endothelial function by infection and
inflammation may lead to a more vasoconstricted coronary bed (106). All of these changes are
25
putative mechanisms by which COVID-19 infection could lead to destabilization of pre-existing
atherosclerotic plaque driving an acute coronary event.
Myocardial injury secondary to oxygen supply and demand mismatch
Periods of severe physiologic stress in the setting of sepsis and respiratory failure can be
associated with elevations in biomarkers of myocardial injury and strain in some patients, an
entity that confers poorer prognosis.(107-109) The mechanism of such myocardial injury is
thought to be related to a mismatch between oxygen supply and demand, without acute
atherothrombotic plaque disruption, and consistent with a diagnosis of type 2 myocardial
infarction (MI) (100,110). Indeed, patients who suffer from type 2 MI compared to type 1 MI
have higher mortality rates, which may in part be explained by a higher burden of acute and
chronic comorbid conditions in the type 2 MI population (111). Furthermore, type 2 MI on the
background of coronary artery disease (CAD) has a worse prognosis than those patients without
CAD. Given the age and comorbidity profile of patients hospitalized with severe COVID-19, it is
reasonable to assume that this population has a higher risk of underlying non-obstructive CAD,
and therefore the presence of type 2 MI in this population is likely a marker of and contributor to
the poor outcomes of COVID-19 patients with troponin elevations (56).
Systemic hyperinflammatory response with resulting myocardial injury
Perhaps one of the more intriguing mechanisms for cardiac injury in severe COVID-19 patients
stems from the significant systemic inflammatory response. Early reports have demonstrated
severely elevated levels of inflammatory biomarkers and cytokines, including IL-6, C-reactive
protein (CRP), tumor necrosis factor (TNF)-α, interleukin (IL)-2R and ferritin (112). Higher
26
levels of these biomarkers are associated with more severe COVID-19 manifestations and worse
outcomes. A proposed theoretical model of COVID-19 disease progression divides the course
into three overlapping yet distinct stages. In this staging framework, stage I represents early viral
infection with associated constitutional symptoms. In stage II, direct viral cytotoxicity of the
pulmonary system with associated inflammatory activation leads to prominent respiratory system
compromise, associated with dyspnea and ultimately acute respiratory distress syndrome
(ARDS) and hypoxia. With ACE2 receptors serving as an entry-point for viral replication in type
II pneumocytes, the pulmonary system becomes the maiden organ of injury. If the host is unable
to clear the virus via a productive and protective immune response, COVID-19 progresses to
stage III - a hyperinflammatory state associated with profound elevations in inflammatory
biomarkers. Patients who reach stage III have severe COVID-19 manifestations with multiorgan
dysfunction and cytokine storm, with immune dysregulating akin to that seen in cytokine release
syndrome (CRS) associated with chimeric antigen receptor T-cell (CAR-T) therapy (112-116).
This observation is basis for several investigational therapies in COVID-19, including steroids
and anti-inflammatory agents, as discussed later.
Prior studies have shown that cardiomyopathy in sepsis is partially mediated by inflammatory
cytokines such as TNF-α, IL-6, IL-1β, INF-γ and IL-2 (73). Recombinant TNF-α resulted in an
early and sustained LV systolic dysfunction in canines (117). Cultured rat cardiomyocytes
demonstrated reduced contractility when exposed to IL-6 (118). The mechanism may be through
modulation of calcium channel activity with resultant myocardial dysfunction (119-121).
Additionally, nitric oxide (NO) is also believed to be a mediator of myocardial depression in
hyperinflammatory states such as sepsis. Seminal studies found that medium from LPS-activated
27
macrophages suppressed myocyte contractility, a finding reversed with the NO synthase
inhibitor, L-N-monomethyl arginine (122). Finally, recent understanding of the key role of
mitochondrial dysfunction in septic states has raised questions about the role of this entity in
sepsis associated cardiomyopathy (123). Indeed, similar mechanisms are thought to possibly
underly the pathophysiology of stress (Takotsubo) cardiomyopathy as well.
Potential Targeted or Disease Modifying Treatments in SARS CoV2
The preceding review of the viral physiology of SARS-CoV2 and the various potential
mechanisms of injury to the host, serve as the basis for considering specific targeted treatment
and prevention. The following section outlines several current candidate classes of agents,
including a brief discussion of vaccine development (Figure 1).
Nucleotide Analogs - Inhibitors of Viral Genome Replication
The antiviral mechanism of nucleotide analogs is to interfere with RdRp function and viral
genome replication and amplification (Figure 1). There are no CoV-specific drugs available at
this time and so ongoing efforts to employ this drug class against SARS-CoV2 are reliant on preexisting
agents designed for other viral illnesses (124).
The most widely-applied agent in this class against SARS-CoV2 has been remdesivir (125).
Remdesivir functions as a chain terminator of RNA replication, initially designed for use against
Ebola (124). Addition of remdesivir to the growing RNA strand by RdRp blocks the
incorporation of additional nucleotides, thereby halting genome replication (126,127). The agent
has been shown to have in vitro activity against SARS-CoV2, leading to off-label and
28
investigational use around the world (4,125). Multiple randomized-controlled trials are ongoing
in China and the United States for moderate, severe and critical COVID-19 (NCT04292730,
NCT04292899, NCT04252664, NCT04252664, NCT04292730).
Another nucleotide analog for the disruption of RdRp-dependent viral replication is favipiravir,
which has investigational approval in several countries (128,129). Additional agents that are
under study include emtricitabine/tenofovir and ribavirin (128,130).
Protease Inhibitors - Inhibitors of Nonstructural Protein Generation
The antiviral mechanism of action of protease inhibitors is to block viral proteases which cleave
the non-structural proteins from the large, monomeric, replicase as detailed above (Figure 1). As
the maturation of non-structural proteins, such as RdRp, is necessary for viral reproduction, the
pharmacologic impairment of the protease should be effective to stop viral replication.
A randomized control trial of lopinavir-ritonavir, a combination protease inhibitor designed for
HIV treatment, in 199 patients with at least moderate COVID-19 did not significantly alter
clinical improvement or viral clearance (131). While the results of this trial were met with
disappointment, this negative study should not forestall trials and drug development of protease
inhibitors as a therapeutic class, given that this drug was not specifically designed for SARSCoV2
(128).
Indeed, the development of inhibitors specific to SARS-CoV2 main protease is underway. A
class of agents identified using structure-based drug design, α-ketonamide inhibitors, has
demonstrated in vitro efficacy and favorable pharmacokinetics (132). Other candidate protease
29
inhibitors for SARS-CoV2 include danoprevir, a drug originally intended for HCV therapy
(133).
Inhibitors of Membrane Fusion
In order for the viral genome to gain access to cellular machinery for replication, a membrane
fusion event must occur between the viral and endosomal membranes, which are noncovalently
bound by the interaction between the S protein and ACE2. The exact mechanism of membrane
fusion is unknown but appears to be dependent on endosomal maturation and a membrane-bound
host protease, TMPRSS2 (7).
Chloroquine (CQ) / Hydroxychloroquine (HCQ)
The antiviral properties of chloroquine (CQ) were previously observed in HIV and other viruses
(134,135). CQ and HCQ are thought to inhibit endosomal maturation, a process by which
endosomes are translocated from the perimembrane regions of the cell to central hubs (136,137)
(Figure 1). CQ prevented viral replication of SARS-CoV1 in vitro (138). A follow-up study
demonstrated comparable efficacy of HCQ, a less toxic derivative, and suggested that the
mechanism of impaired endosomal maturation indeed applied to SARS-CoV2 infection in vitro
(139). Only poor-quality, non-randomized, unblinded data exists assessing the benefit of HCQ in
COVID-19 (140). While HCQ is being widely used with an FDA emergency authorization,
more data are needed to prove efficacy against SARS-CoV2 in humans. Notably, CQ and HCQ
prolong the QT and may induce arrhythmia; significant caution should be used in starting these
agents in patients with a QTc>500 ms. Concomitant use of other QT prolonging agents is not
recommended.
2nd half:
Camostat
Camostat is a protease inhibitor approved for the treatment of chronic pancreatitis. Camostat
appears to inhibit TMPRSS2 in proteomic and in vitro studies (7,141). A randomized, placebocontrolled
trial is underway for this agent in COVID-19 (NCT04321096) (Figure 1).
Neutralizing Antibodies and Decoy Proteins
Neutralizing antibodies are designed to bind virions, preventing viral exposure or binding to host
cells (Figure 1). Plasma from patients who have recovered from SARS-CoV2 may contain anti-
SARS-CoV2 IgG antibodies. In a small, single-arm trial of convalescent plasma in COVID-19
patients with ARDS, all had clinical improvement with 3/5 patients weaning from the ventilator
(142). Additional trials are ongoing to better define the safety and efficacy of this strategy.
Isolation of SARS-CoV2 specific neutralizing antibodies with clonal techniques is an appealing
strategy to provide targeted therapy, potentially with lower risk of adverse events. Strategies
currently under investigation include antibodies cloned from convalescent serum of individuals
recovered from SARS-CoV2 or SARS-CoV1 and synthetic antibodies. It is unclear whether
differences in the S proteins of SARS-CoV1 and SARS-CoV2 may limit the effectiveness of
antibodies cloned from patients convalescent to SARS-CoV1 (9). Synthetic antibodies represent
an exciting, novel therapeutic avenue. One strategy being explored is to fuse ACE2 to Fc IgG,
with the hypothesis that this synthetic antibody would serve as a decoy receptor, preventing
cellular binding of the virion (143).
31
In a similar vein, studies are ongoing of decoy proteins that are designed to act as viral “sinks”.
There is preliminary success with this strategy using soluble human ACE2 (34) (Central
Illustration).
Anti-Inflammatory Therapy
Advanced stages of COVID-19 have been likened to cytokine storm syndromes with nonspecific
widespread immune activation (114). Elevated levels of inflammatory biomarkers, such
as IL-6 and hsCRP, identify patients at high risk of progressing to severe disease and death (53).
Immunomodulatory and anti-inflammatory therapy have been used, despite limited data, in
patients with evidence of hyperinflammation in an effort to curb pathologic immune activation.
Corticosteroids
Corticosteroids have been used in several, severe viral respiratory infections including influenza,
SARS-CoV and MERS-CoV with limited benefit and, in some instances, evidence of delayed
viral clearance and increased rates of secondary infection and mortality (144). A retrospective
analysis of 84 patients with ARDS secondary to SARS-CoV2 observed an association with
improved survival in patients who received solumedrol (51). In the absence of robust evidence,
major professional society guidelines do not recommend routine use of corticosteroids in
treatment of COVID-19 but rather restricting its use to patients with other indications for
steroids, such as refractory shock or advanced ARDS (41). Clinical trials are ongoing to
examine the safety and efficacy of corticosteroids in hospitalized non-critically ill COVID-19
patients (Clinical Trials.gov ID: NCT04273321) and in those with ARDS (Clinical Trials.gov
ID: NCT04323592).
32
IL-6 Inhibitors
Elevation of IL-6 in patients with severe COVID-19 has prompted consideration of use of IL-6
inhibitors (Tocilizumab, Siltuximab) extrapolating from treatment of cytokine release syndrome
(145). Tociluzimab, a recombinant humanized monoclonal antibody, and Siltuximab, a chimeric
monoclonal antibody, both bind soluble and membrane bound IL-6 receptors resulting in
inhibition of IL-6-mediated signaling. In one preprint case series from China, 21 patients with
severe or critical COVID-19 treated with tocilizumab experienced a salutary effect with
resolution of fever, improved oxygenation, improvement in lung opacities on chest CT,
resolution of lymphopenia and a reduction in CRP levels within a few days of therapy in the
absence of any significant reported adverse events (146). In this preliminary report, 19 patients
were discharged alive and 2 remained hospitalized at the time the case series was published.
Several randomized clinical trials of tocilizumab in treatment of severe COVID-19 infection are
ongoing (NCT04317092; NCT04306705).
Azithromycin
Azithromycin, a macrolide antibiotic, has long been touted for its anti-inflammatory effect and
has been used as adjunctive therapy in treatment of community acquired pneumonia and chronic
obstructive pulmonary disease exacerbations (147). Limited data suggest that adjunctive
azithromycin in moderate-severe ARDS is associated with improved outcomes (148). A small
non-randomized study showed that combination azithromycin and hydroxychloroquine was
associated with more effective SARS-CoV2 clearance in COVID-19 patients compared with
either monotherapy with hydroxychloroquine or standard of care; however, numerous limitations
33
of this study render the data uninterpretable (140). QT interval monitoring is prudent especially
when used in combination with hydroxychloroquine. Several randomized clinical trials assessing
the combination of hydroxychloroquine/chloroquine with azithromycin across the severity
spectrum of COVID-19 are ongoing or about be launched (NCT04321278, NCT04322396,
NCT04322123, NCT04324463).
Other Anti-Inflammatory Therapies
JAK-2 inhibitors inhibit receptor mediated-endocytosis leading to the hypothesis that it might
prevent cellular entry of the SARS-CoV2 (Figure 1). Additionally, this class of agents have antiinflammatory
effects by inhibiting cytokine release (149). An agent in the class, baricitinib, is
being studied in an open-label non-randomized pilot study in patients with COVID-19
(NCT04320277). Currently, a 3-arm randomized control trial is being launched to compare
anakinra monotherapy, emapalumab monotherapy and standard of care (NCT04324021).
Anakinra is a recombinant monoclonal antibody that blocks IL-1 receptors. It has been used to
treat autoimmune conditions including juvenile idiopathic arthritis as well as recurrent
pericarditis. Emapalumab is a fully human anti-gamma interferon monoclonal antibody that has
been approved by the FDA for treatment of primary hemophagocytic lymphohistiocytosis, a
disease reminiscent of the hyperinflammatory state seen in advanced COVID-19. Finally,
colchicine, a microtubule polymerization inhibitor and anti-inflammatory drug, is being tested in
a large randomized clinical trial of ambulatory COVID-19 patients (NCT04322682).
Other Therapies
Angiotensin Converting Enzyme Inhibitors & Angiotensin Receptor Blockers
34
ACE-2 receptor mediated endocytosis of SARS-CoV2 is central to the viral life cycle.
Conflicting data exist regarding the effect of renin-angiotensin-aldosterone-inhibitors (RAASi),
including ACE-I and ARB, on ACE2 activity/levels in various human tissues and the resultant
susceptibility to infection with SARS-CoV2 (18). The totality of the available data is
insufficient to recommend cessation of ACE-I/ARB in individuals with an existing indication for
life-prolonging therapy with these drugs and major societies have strongly recommended
continuation of ACE-I/ARB therapy. An open label randomized trial is on the way to examine
the effect of prophylactic ACE-I/ARB withdrawal in COVID-19 naive individuals with essential
hypertension as the sole indication for treatment on the risk of infection and subsequent
complications (NCT04330300). Based on the pre-clinical data described earlier in this review,
two paired trials are currently underway examining losartan therapy in COVID-19 who are
ambulatory (NCT04311177) and hospitalized (NCT04312009).
Statins
The anti-inflammatory pleiotropic effects of statins have been cultivated in different pathologic
states. Statins have been shown in murine models of acute lung injury and in humans to
attenuate the inflammatory component of acute lung injury (150,151). A multi-center
randomized trial of simvastatin in patients with versatile causes of ARDS showed no difference
as compared to placebo in ventilator free days, multi-organ failure and mortality (152). A
subsequent study, subphenotyping the trial population in to hyper vs. hypoinflammatory ARDS,
found a statistically significant improvement in survival with simvastatin in the
hyperinflammatory group (153). A post-hoc analysis of the JUPITER trial observed a reduction
35
in incident pneumonia with rosuvastatin (154). The benefit of statin therapy in the
hyperinflammatory state in advanced COVID-19 is unknown.
Vaccines Against SARS-CoV2
As discovery of a safe and efficacious vaccine again SARS-CoV2 is clearly the aspiration for
preventative strategies, intense efforts are ongoing employing numerous approaches with
accelerated testing. It is believed that all 4 structural proteins, E, M, N and S proteins, may serve
as antigens for neutralizing antibody and CD4+CD8+ T cell responses (155). Based on the
experience with SARS-CoV1 vaccine development, it seems that the most promising candidates
target the S protein, which induces humoral and protective cellular immunity (8).
Encouragingly, administration of full-length or the ACE2-receptor binding domain of the S
protein of SARS-CoV1 induced highly potent neutralizing antibodies that conveyed protective
immunity in animal models (156,157).
Potential delivery strategies include inactivated or attenuated virus, subunit vaccines, viral
vectors, DNA or RNA-based vaccines (158). Live attenuated viral vaccines are likely to induce
significant immune response but may carry risk of disease, particularly in immunosuppressed
individuals. Inactivated “whole” viral or subunit vaccines are relatively easy to develop, but do
not induce immediate or complete immunity, typically requiring multiple doses to promote
humoral, but often not cellular, immunity. Immunity may also wane over time, requiring booster
dosing. Viral vector-based vaccines would employ other viruses, such as the vaccina virus (a
poxvirus used for the smallpox vaccine) or adenovirus, to display SARS-CoV2 antigens. This
strategy can promote robust cytotoxic T cell responses but may fail in the face of the pre-existing
36
immunity to or toxicity of the viral vector (159). Nucleic acid-based strategies, which work
through delivery of DNA or RNA that are translated by host machinery to produce viral protein
antigens, are relatively simple to design but may be limited by toxicity and/or stability concerns.
Of note, at this time, there are no approved DNA or RNA vaccines for humans. Most
approaches to SARS-CoV2 are in pre-clinical development, with several early trials of RNA
(NCT04283461) and viral-vector (NCT04299724, NCT04313127, NCT04276896) vaccine
strategies ongoing.
Crisis Standards of Care and Ethical Resource Allocation
Estimates suggest that, as has happened in Italy and Spain, the burden of COVID-19 will far
outstrip the healthcare capacity in the US and globally with insufficient availability of hospital
and ICU bed capacity, healthcare providers and specific therapeutic or supportive interventions,
such as mechanical ventilation and renal replacement (160). For this reason, organizations, such
as the Italian Society of Anesthesia, Analgesia, Resuscitation and Intensive Care (SIAARTI) and
individual healthcare institutions are developing guidance for allocation of resources in the event
that adequate, additional resources cannot be obtained (161). These efforts are building off of a
set of principles established in the wake of the 2009 H1N1 pandemic.
At that time, the US Department of Health and Human Services commissioned the Institute of
Medicine (IOM) to provide expert guidance on implementing alternative standards of healthcare
in the setting of a disaster. In their report, the IOM defined the principles of “crisis standards of
care”, defined as a substantial change in usual healthcare operations, including the level of care
possible to deliver, in the setting of a pervasive or catastrophic disaster.(162) Notably, this
37
framework recognizes that “the formal declaration that crisis standards of care are in operation
enables specific legal/regulatory powers and protection for healthcare providers in the necessary
task of allocating and using scarce medical resources.” Appreciating the distress associated with
allocation of scarce medical resources, the IOM recommend that the process be guided by seven
ethical principles: fairness, duty to care, duty to steward resources, transparency, consistency,
proportionality and accountability (162).
Working with these principles, ethicists have come to a general consensus that the goal is to
maximize benefit while maintaining equity, objectivity and transparency (160,163).
Maximizing benefit ideally involves preserving the most lives as well as the most life-years,
acknowledging the importance of prognosis. While the practical application of these principles
is challenging, there appears to be general agreement across the literature on a number of
concepts (160,163,164) Most recommend development of a triage or scoring system that
accounts for acute and pre-morbid prognosis in order to allocate scarce resources to those who
are most likely to benefit. The scoring system should utilize objective clinical information, in
order to minimize the need for clinical judgement and the risk of introducing inconsistency and
bias. The use of the system - and the determination that stems from it - should be transparent to
providers, patients and families. Triage should be applied broadly to all patients requiring a
particular resource, not just those suffering from the pandemic disease (e.g. applies to decision to
use VA ECMO in patients with myocarditis due to COVID-19 and cardiogenic shock from a
non-COVID-19 etiology). A random system (e.g. lottery) should be used to break “ties” in cases
with a similar estimated prognosis, rather than a first-come-first serve approach. Importantly,
many advocate that an independent triage physician make the determination to remove the
38
burden from the bedside healthcare team. The triage physician may be supported, as necessary,
by a triage committee, comprised of experts in the area of ethics and relevant medical fields.
Areas of controversy include whether there should be priority allowed for healthcare providers.
Some ethicists argue that they should not be prioritized as that are unlikely to recovery in a time
frame that would allow them to continue their professional responsibilities.(163) Others argue
that granting priority recognizes the assumption of risk and also encourages ongoing
participation in patient care (160). Along the same line, an argument has also been made to
prioritize research participation (160).
The optimal tool for prognostication also remains elusive. The sequential organ failure
assessment (SOFA) score has been suggested as quantitative assessment of acute illness severity;
however, there is a recognition that this tool may not be well calibrated to all populations and
could lead to inaccurate assessments of prognosis (165,166).
The value of pre-determination of this framework with community and provider engagement,
establishment of legal authority and logistic and operational preparedness is clear. Nevertheless,
acknowledging the prospect of large-scale rationing of healthcare is heartbreaking and foreign to
most civilian healthcare providers in developed countries.
Summary
In just a few short months, SARS-CoV2 has spread across the world with distressing speed,
threatening global economic and individual health and well-being. Many regional healthcare
39
systems are overwhelmed and under-resourced, forcing clinicians and administrators to make
previously unthinkable decisions regarding allocation of medical care. However, in the wake of
this devastation, clinicians and scientists have rallied together to rapidly evolve our
understanding of all aspects of SARS-CoV2 infection, from the basic virology, to the human
manifestations to therapeutic and preventative strategies. This unprecedented collective effort
will, without a doubt, advance our ability to prevent the spread and optimally care for patients
suffering from COVID-19.
Acknowledgments
The authors would like to acknowledge Andrew Karaba, MD, PhD for his review of the
manuscript.
40
Figure Legends
Figure 1: Putative SARS-CoV2 Life Cycle and Therapeutic Targets.
The SARS2-CoV2 virus binds to the ACE2 receptor on the host cell membrane. Endocytosis is
believed to be mediated, in part, by JAK-2. Membrane fusion occurs between the mature
endosome and virion with facilitation by the transmembrane serine protease 2 (TMPRSS2)
resulting in release of the SARS-CoV2 RNA into the intracellular space. The RNA is translated
by host machinery to produce the replicase and structural proteins. Host and SARS-CoV2
proteases cleave the replicase to in non-structural proteins, including the RNA-dependent RNA
polymerase (RdRp). RdRp mediates SARS-CoV2 RNA replication and amplification. SARSCoV2
transmembrane proteins (S, E and M) are shuttled via the endoplasmic reticulum and
Golgi apparatus to the forming viral capsids. Viral assembly occurs with addition of the viral
RNA and N protein through association with the transmembrane viral proteins. Exocytosis
results in release of the newly synthesized viral particle.
41
Central Illustration: Potential Mechanisms of Myocardial Injury in COVID-19
MI denotes myocardial infarction; ASCVD, atherosclerotic cardiovascular disease; DIC,
disseminated intravascular coagulation.
42
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147. Zimmermann P, Ziesenitz VC, Curtis N, Ritz N. The Immunomodulatory Effects of Macrolides-A
Systematic Review of the Underlying Mechanisms. Frontiers in immunology 2018;9:302.
148. Kawamura K, Ichikado K, Takaki M, Eguchi Y, Anan K, Suga M. Adjunctive therapy with
azithromycin for moderate and severe acute respiratory distress syndrome: a retrospective,
propensity score-matching analysis of prospectively collected data at a single center.
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149. Richardson P, Griffin I, Tucker C et al. Baricitinib as potential treatment for 2019-nCoV acute
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The New England journal of medicine 2014;371:1695-703.
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differential response to simvastatin: secondary analysis of a randomised controlled trial. The
Lancet Respiratory medicine 2018;6:691-698.
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58
Camostat
Camostat is a protease inhibitor approved for the treatment of chronic pancreatitis. Camostat
appears to inhibit TMPRSS2 in proteomic and in vitro studies (7,141). A randomized, placebocontrolled
trial is underway for this agent in COVID-19 (NCT04321096) (Figure 1).
Neutralizing Antibodies and Decoy Proteins
Neutralizing antibodies are designed to bind virions, preventing viral exposure or binding to host
cells (Figure 1). Plasma from patients who have recovered from SARS-CoV2 may contain anti-
SARS-CoV2 IgG antibodies. In a small, single-arm trial of convalescent plasma in COVID-19
patients with ARDS, all had clinical improvement with 3/5 patients weaning from the ventilator
(142). Additional trials are ongoing to better define the safety and efficacy of this strategy.
Isolation of SARS-CoV2 specific neutralizing antibodies with clonal techniques is an appealing
strategy to provide targeted therapy, potentially with lower risk of adverse events. Strategies
currently under investigation include antibodies cloned from convalescent serum of individuals
recovered from SARS-CoV2 or SARS-CoV1 and synthetic antibodies. It is unclear whether
differences in the S proteins of SARS-CoV1 and SARS-CoV2 may limit the effectiveness of
antibodies cloned from patients convalescent to SARS-CoV1 (9). Synthetic antibodies represent
an exciting, novel therapeutic avenue. One strategy being explored is to fuse ACE2 to Fc IgG,
with the hypothesis that this synthetic antibody would serve as a decoy receptor, preventing
cellular binding of the virion (143).
31
In a similar vein, studies are ongoing of decoy proteins that are designed to act as viral “sinks”.
There is preliminary success with this strategy using soluble human ACE2 (34) (Central
Illustration).
Anti-Inflammatory Therapy
Advanced stages of COVID-19 have been likened to cytokine storm syndromes with nonspecific
widespread immune activation (114). Elevated levels of inflammatory biomarkers, such
as IL-6 and hsCRP, identify patients at high risk of progressing to severe disease and death (53).
Immunomodulatory and anti-inflammatory therapy have been used, despite limited data, in
patients with evidence of hyperinflammation in an effort to curb pathologic immune activation.
Corticosteroids
Corticosteroids have been used in several, severe viral respiratory infections including influenza,
SARS-CoV and MERS-CoV with limited benefit and, in some instances, evidence of delayed
viral clearance and increased rates of secondary infection and mortality (144). A retrospective
analysis of 84 patients with ARDS secondary to SARS-CoV2 observed an association with
improved survival in patients who received solumedrol (51). In the absence of robust evidence,
major professional society guidelines do not recommend routine use of corticosteroids in
treatment of COVID-19 but rather restricting its use to patients with other indications for
steroids, such as refractory shock or advanced ARDS (41). Clinical trials are ongoing to
examine the safety and efficacy of corticosteroids in hospitalized non-critically ill COVID-19
patients (Clinical Trials.gov ID: NCT04273321) and in those with ARDS (Clinical Trials.gov
ID: NCT04323592).
32
IL-6 Inhibitors
Elevation of IL-6 in patients with severe COVID-19 has prompted consideration of use of IL-6
inhibitors (Tocilizumab, Siltuximab) extrapolating from treatment of cytokine release syndrome
(145). Tociluzimab, a recombinant humanized monoclonal antibody, and Siltuximab, a chimeric
monoclonal antibody, both bind soluble and membrane bound IL-6 receptors resulting in
inhibition of IL-6-mediated signaling. In one preprint case series from China, 21 patients with
severe or critical COVID-19 treated with tocilizumab experienced a salutary effect with
resolution of fever, improved oxygenation, improvement in lung opacities on chest CT,
resolution of lymphopenia and a reduction in CRP levels within a few days of therapy in the
absence of any significant reported adverse events (146). In this preliminary report, 19 patients
were discharged alive and 2 remained hospitalized at the time the case series was published.
Several randomized clinical trials of tocilizumab in treatment of severe COVID-19 infection are
ongoing (NCT04317092; NCT04306705).
Azithromycin
Azithromycin, a macrolide antibiotic, has long been touted for its anti-inflammatory effect and
has been used as adjunctive therapy in treatment of community acquired pneumonia and chronic
obstructive pulmonary disease exacerbations (147). Limited data suggest that adjunctive
azithromycin in moderate-severe ARDS is associated with improved outcomes (148). A small
non-randomized study showed that combination azithromycin and hydroxychloroquine was
associated with more effective SARS-CoV2 clearance in COVID-19 patients compared with
either monotherapy with hydroxychloroquine or standard of care; however, numerous limitations
33
of this study render the data uninterpretable (140). QT interval monitoring is prudent especially
when used in combination with hydroxychloroquine. Several randomized clinical trials assessing
the combination of hydroxychloroquine/chloroquine with azithromycin across the severity
spectrum of COVID-19 are ongoing or about be launched (NCT04321278, NCT04322396,
NCT04322123, NCT04324463).
Other Anti-Inflammatory Therapies
JAK-2 inhibitors inhibit receptor mediated-endocytosis leading to the hypothesis that it might
prevent cellular entry of the SARS-CoV2 (Figure 1). Additionally, this class of agents have antiinflammatory
effects by inhibiting cytokine release (149). An agent in the class, baricitinib, is
being studied in an open-label non-randomized pilot study in patients with COVID-19
(NCT04320277). Currently, a 3-arm randomized control trial is being launched to compare
anakinra monotherapy, emapalumab monotherapy and standard of care (NCT04324021).
Anakinra is a recombinant monoclonal antibody that blocks IL-1 receptors. It has been used to
treat autoimmune conditions including juvenile idiopathic arthritis as well as recurrent
pericarditis. Emapalumab is a fully human anti-gamma interferon monoclonal antibody that has
been approved by the FDA for treatment of primary hemophagocytic lymphohistiocytosis, a
disease reminiscent of the hyperinflammatory state seen in advanced COVID-19. Finally,
colchicine, a microtubule polymerization inhibitor and anti-inflammatory drug, is being tested in
a large randomized clinical trial of ambulatory COVID-19 patients (NCT04322682).
Other Therapies
Angiotensin Converting Enzyme Inhibitors & Angiotensin Receptor Blockers
34
ACE-2 receptor mediated endocytosis of SARS-CoV2 is central to the viral life cycle.
Conflicting data exist regarding the effect of renin-angiotensin-aldosterone-inhibitors (RAASi),
including ACE-I and ARB, on ACE2 activity/levels in various human tissues and the resultant
susceptibility to infection with SARS-CoV2 (18). The totality of the available data is
insufficient to recommend cessation of ACE-I/ARB in individuals with an existing indication for
life-prolonging therapy with these drugs and major societies have strongly recommended
continuation of ACE-I/ARB therapy. An open label randomized trial is on the way to examine
the effect of prophylactic ACE-I/ARB withdrawal in COVID-19 naive individuals with essential
hypertension as the sole indication for treatment on the risk of infection and subsequent
complications (NCT04330300). Based on the pre-clinical data described earlier in this review,
two paired trials are currently underway examining losartan therapy in COVID-19 who are
ambulatory (NCT04311177) and hospitalized (NCT04312009).
Statins
The anti-inflammatory pleiotropic effects of statins have been cultivated in different pathologic
states. Statins have been shown in murine models of acute lung injury and in humans to
attenuate the inflammatory component of acute lung injury (150,151). A multi-center
randomized trial of simvastatin in patients with versatile causes of ARDS showed no difference
as compared to placebo in ventilator free days, multi-organ failure and mortality (152). A
subsequent study, subphenotyping the trial population in to hyper vs. hypoinflammatory ARDS,
found a statistically significant improvement in survival with simvastatin in the
hyperinflammatory group (153). A post-hoc analysis of the JUPITER trial observed a reduction
35
in incident pneumonia with rosuvastatin (154). The benefit of statin therapy in the
hyperinflammatory state in advanced COVID-19 is unknown.
Vaccines Against SARS-CoV2
As discovery of a safe and efficacious vaccine again SARS-CoV2 is clearly the aspiration for
preventative strategies, intense efforts are ongoing employing numerous approaches with
accelerated testing. It is believed that all 4 structural proteins, E, M, N and S proteins, may serve
as antigens for neutralizing antibody and CD4+CD8+ T cell responses (155). Based on the
experience with SARS-CoV1 vaccine development, it seems that the most promising candidates
target the S protein, which induces humoral and protective cellular immunity (8).
Encouragingly, administration of full-length or the ACE2-receptor binding domain of the S
protein of SARS-CoV1 induced highly potent neutralizing antibodies that conveyed protective
immunity in animal models (156,157).
Potential delivery strategies include inactivated or attenuated virus, subunit vaccines, viral
vectors, DNA or RNA-based vaccines (158). Live attenuated viral vaccines are likely to induce
significant immune response but may carry risk of disease, particularly in immunosuppressed
individuals. Inactivated “whole” viral or subunit vaccines are relatively easy to develop, but do
not induce immediate or complete immunity, typically requiring multiple doses to promote
humoral, but often not cellular, immunity. Immunity may also wane over time, requiring booster
dosing. Viral vector-based vaccines would employ other viruses, such as the vaccina virus (a
poxvirus used for the smallpox vaccine) or adenovirus, to display SARS-CoV2 antigens. This
strategy can promote robust cytotoxic T cell responses but may fail in the face of the pre-existing
36
immunity to or toxicity of the viral vector (159). Nucleic acid-based strategies, which work
through delivery of DNA or RNA that are translated by host machinery to produce viral protein
antigens, are relatively simple to design but may be limited by toxicity and/or stability concerns.
Of note, at this time, there are no approved DNA or RNA vaccines for humans. Most
approaches to SARS-CoV2 are in pre-clinical development, with several early trials of RNA
(NCT04283461) and viral-vector (NCT04299724, NCT04313127, NCT04276896) vaccine
strategies ongoing.
Crisis Standards of Care and Ethical Resource Allocation
Estimates suggest that, as has happened in Italy and Spain, the burden of COVID-19 will far
outstrip the healthcare capacity in the US and globally with insufficient availability of hospital
and ICU bed capacity, healthcare providers and specific therapeutic or supportive interventions,
such as mechanical ventilation and renal replacement (160). For this reason, organizations, such
as the Italian Society of Anesthesia, Analgesia, Resuscitation and Intensive Care (SIAARTI) and
individual healthcare institutions are developing guidance for allocation of resources in the event
that adequate, additional resources cannot be obtained (161). These efforts are building off of a
set of principles established in the wake of the 2009 H1N1 pandemic.
At that time, the US Department of Health and Human Services commissioned the Institute of
Medicine (IOM) to provide expert guidance on implementing alternative standards of healthcare
in the setting of a disaster. In their report, the IOM defined the principles of “crisis standards of
care”, defined as a substantial change in usual healthcare operations, including the level of care
possible to deliver, in the setting of a pervasive or catastrophic disaster.(162) Notably, this
37
framework recognizes that “the formal declaration that crisis standards of care are in operation
enables specific legal/regulatory powers and protection for healthcare providers in the necessary
task of allocating and using scarce medical resources.” Appreciating the distress associated with
allocation of scarce medical resources, the IOM recommend that the process be guided by seven
ethical principles: fairness, duty to care, duty to steward resources, transparency, consistency,
proportionality and accountability (162).
Working with these principles, ethicists have come to a general consensus that the goal is to
maximize benefit while maintaining equity, objectivity and transparency (160,163).
Maximizing benefit ideally involves preserving the most lives as well as the most life-years,
acknowledging the importance of prognosis. While the practical application of these principles
is challenging, there appears to be general agreement across the literature on a number of
concepts (160,163,164) Most recommend development of a triage or scoring system that
accounts for acute and pre-morbid prognosis in order to allocate scarce resources to those who
are most likely to benefit. The scoring system should utilize objective clinical information, in
order to minimize the need for clinical judgement and the risk of introducing inconsistency and
bias. The use of the system - and the determination that stems from it - should be transparent to
providers, patients and families. Triage should be applied broadly to all patients requiring a
particular resource, not just those suffering from the pandemic disease (e.g. applies to decision to
use VA ECMO in patients with myocarditis due to COVID-19 and cardiogenic shock from a
non-COVID-19 etiology). A random system (e.g. lottery) should be used to break “ties” in cases
with a similar estimated prognosis, rather than a first-come-first serve approach. Importantly,
many advocate that an independent triage physician make the determination to remove the
38
burden from the bedside healthcare team. The triage physician may be supported, as necessary,
by a triage committee, comprised of experts in the area of ethics and relevant medical fields.
Areas of controversy include whether there should be priority allowed for healthcare providers.
Some ethicists argue that they should not be prioritized as that are unlikely to recovery in a time
frame that would allow them to continue their professional responsibilities.(163) Others argue
that granting priority recognizes the assumption of risk and also encourages ongoing
participation in patient care (160). Along the same line, an argument has also been made to
prioritize research participation (160).
The optimal tool for prognostication also remains elusive. The sequential organ failure
assessment (SOFA) score has been suggested as quantitative assessment of acute illness severity;
however, there is a recognition that this tool may not be well calibrated to all populations and
could lead to inaccurate assessments of prognosis (165,166).
The value of pre-determination of this framework with community and provider engagement,
establishment of legal authority and logistic and operational preparedness is clear. Nevertheless,
acknowledging the prospect of large-scale rationing of healthcare is heartbreaking and foreign to
most civilian healthcare providers in developed countries.
Summary
In just a few short months, SARS-CoV2 has spread across the world with distressing speed,
threatening global economic and individual health and well-being. Many regional healthcare
39
systems are overwhelmed and under-resourced, forcing clinicians and administrators to make
previously unthinkable decisions regarding allocation of medical care. However, in the wake of
this devastation, clinicians and scientists have rallied together to rapidly evolve our
understanding of all aspects of SARS-CoV2 infection, from the basic virology, to the human
manifestations to therapeutic and preventative strategies. This unprecedented collective effort
will, without a doubt, advance our ability to prevent the spread and optimally care for patients
suffering from COVID-19.
Acknowledgments
The authors would like to acknowledge Andrew Karaba, MD, PhD for his review of the
manuscript.
40
Figure Legends
Figure 1: Putative SARS-CoV2 Life Cycle and Therapeutic Targets.
The SARS2-CoV2 virus binds to the ACE2 receptor on the host cell membrane. Endocytosis is
believed to be mediated, in part, by JAK-2. Membrane fusion occurs between the mature
endosome and virion with facilitation by the transmembrane serine protease 2 (TMPRSS2)
resulting in release of the SARS-CoV2 RNA into the intracellular space. The RNA is translated
by host machinery to produce the replicase and structural proteins. Host and SARS-CoV2
proteases cleave the replicase to in non-structural proteins, including the RNA-dependent RNA
polymerase (RdRp). RdRp mediates SARS-CoV2 RNA replication and amplification. SARSCoV2
transmembrane proteins (S, E and M) are shuttled via the endoplasmic reticulum and
Golgi apparatus to the forming viral capsids. Viral assembly occurs with addition of the viral
RNA and N protein through association with the transmembrane viral proteins. Exocytosis
results in release of the newly synthesized viral particle.
41
Central Illustration: Potential Mechanisms of Myocardial Injury in COVID-19
MI denotes myocardial infarction; ASCVD, atherosclerotic cardiovascular disease; DIC,
disseminated intravascular coagulation.
42
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