Calculating heart rate from an ECG

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joann_e
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#1
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How would I go about calculating the heart rate per min from an ECG?
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Nirgilis
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Moved to life science help for you
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Revenged
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(Original post by joann_e)
How would I go about calculating the heart rate per min from an ECG?
Count the complex on the bottom strip and times by six.
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sleepybear
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They should give you a length of time for the ECG strip. Count the number of QRS complexes in that strip.

Say they gave length of time as 10 seconds and there were 14 QRS complexes:

14 complexes in 10 seconds
x complexes in 60 seconds.

You multiplied the 10 by 6 to get 60 seconds, so multiply 14 by 6 to get x.

84 beats per min

So you can do the same for anything.. eg: time given 3 seconds. 5 QRS complexes in the strip:

5 complexes in 3 seconds
x complexes in 60 seconds

You multiplied the 3 by 20 to get 60 seconds, so multiply 5 by 20 to get x.

100 beats per min
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Friar Chris
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#5
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(Original post by joann_e)
How would I go about calculating the heart rate per min from an ECG?

Assuming it's in sinus rhythm, you need to know what speed the 'paper' was - this will be printed on the ECG. Or rather, these days, it's just a 'speed' usually as it's not printed onto paper directly but it's printed off a digital monitor.

Once you know what speed the ECG is at - usually 25mm/s - you can calculate the heart rate by measuring the R-R interval. At 25mm/s there are, conveniently, five 5mm squares per second, meaning there are... 300 per minute (0.2s per square). This simplifies matters when the speed is 25mm/s, as it means you can simply divide 300 by however many of the 'large' 5mm squares there are between each R wave to produce the beats per minute.

For a totally precise reading or if the speed is different, you just have to measure in millimetres and do the maths: what is the R-R interval in mm - so how much time is that based on the graph speed - and then divide 60 seconds by the time of the interval.



Easy peasy, until you start considering the rhythm; if it is irregular, you generally estimate by taking an average like sleepbear described above, by using the rhythm strip. This is usually from lead II, a full-length readout often on the bottom of the prinout which isn't just a short sample for assessment of the content, but a longer strip so you can look at the rhythm. For simple arrhythmias like AF where the R-R interval has no consistency or meaningful pattern, an average of a 6-second span would generally suffice: count the number of beats in 6 seconds on the rhythm strip, and multiply by 10 for your estimate.
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DanielDaniels
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#6
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#6
(Original post by Friar Chris)

Assuming it's in sinus rhythm, you need to know what speed the 'paper' was - this will be printed on the ECG. Or rather, these days, it's just a 'speed' usually as it's not printed onto paper directly but it's printed off a digital monitor.

Once you know what speed the ECG is at - usually 25mm/s - you can calculate the heart rate by measuring the R-R interval. At 25mm/s there are, conveniently, five 5mm squares per second, meaning there are... 300 per minute (0.2s per square). This simplifies matters when the speed is 25mm/s, as it means you can simply divide 300 by however many of the 'large' 5mm squares there are between each R wave to produce the beats per minute.

For a totally precise reading or if the speed is different, you just have to measure in millimetres and do the maths: what is the R-R interval in mm - so how much time is that based on the graph speed - and then divide 60 seconds by the time of the interval.



Easy peasy, until you start considering the rhythm; if it is irregular, you generally estimate by taking an average like sleepbear described above, by using the rhythm strip. This is usually from lead II, a full-length readout often on the bottom of the prinout which isn't just a short sample for assessment of the content, but a longer strip so you can look at the rhythm. For simple arrhythmias like AF where the R-R interval has no consistency or meaningful pattern, an average of a 6-second span would generally suffice: count the number of beats in 6 seconds on the rhythm strip, and multiply by 10 for your estimate.
Sorry for randomly appearing

Question: How can I calculate HR from PR interval? say 0.24 s
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Friar Chris
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#7
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(Original post by Daniel Atieh)
Sorry for randomly appearing

Question: How can I calculate HR from PR interval? say 0.24 s
You can't. The PR interval is simply the time between the start of atrial/SAN depolarisation and the start of ventricular depolarisation; it doesn't give you any information on how frequently the SAN is depolarising or whether there's any heart block (and, therefore, whether there's 1:1 conduction of SAN/atrial depolarisation to each ventricular systole*).

A lengthened PR interval implies some degree of heart block (whether of a congenital, structural/ischaemic or chemical origin); the heart rate is not determined by this, merely the ventricular response time to the initial depolarisation.

*Heart rate is, by definition, based upon ventricular systole.
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DanielDaniels
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#8
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(Original post by Friar Chris)
You can't. The PR interval is simply the time between the start of atrial/SAN depolarisation and the start of ventricular depolarisation; it doesn't give you any information on how frequently the SAN is depolarising or whether there's any heart block (and, therefore, whether there's 1:1 conduction of SAN/atrial depolarisation to each ventricular systole*).

A lengthened PR interval implies some degree of heart block (whether of a congenital, structural/ischaemic or chemical origin); the heart rate is not determined by this, merely the ventricular response time to the initial depolarisation.

*Heart rate is, by definition, based upon ventricular systole.
Seriously thanks a bunch, Friar
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DanielDaniels
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#9
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(Original post by Friar Chris)
You can't. The PR interval is simply the time between the start of atrial/SAN depolarisation and the start of ventricular depolarisation; it doesn't give you any information on how frequently the SAN is depolarising or whether there's any heart block (and, therefore, whether there's 1:1 conduction of SAN/atrial depolarisation to each ventricular systole*).

A lengthened PR interval implies some degree of heart block (whether of a congenital, structural/ischaemic or chemical origin); the heart rate is not determined by this, merely the ventricular response time to the initial depolarisation.

*Heart rate is, by definition, based upon ventricular systole.
Another question if you don't mind please.

This appeared in my previous exam and I am still thinking about it. Not quite sure about the wording, but it went something like this: CG records 1) complete depolarisation and complete repol. OR 2) incomplete depol. and incomplete repol. OR 3) complete depol and incomplete repol OR 4) incom. depol. and comp repol.

Shall I go with 1?
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Bloom <3
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#10
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#10
Hi guys
Can any of you confirm if we have to learn how to interpret ECG of heart attacks,atrial fibrillation and ventricular fibrillation for A2 unit 5 paper edexcel
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Andrea Denby
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#11
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#11
Thanks, I wanted to understand it and this is very helpful!
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