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The specification asks for the role of AVN and the bundle of His and I don’t think I know these.
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Also, how can the use of ECG’s aid the diagnosis of diseases ? Do we look at irregularities in the ecg of a person ?
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Jpw1097
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(Original post by CurrentlyAtLevel)
The specification asks for the role of AVN and the bundle of His and I don’t think I know these.
Name:  C9F6FB29-A88A-4182-9017-34C5D97DE272.jpeg
Views: 94
Size:  106.5 KB
Also, how can the use of ECG’s aid the diagnosis of diseases ? Do we look at irregularities in the ecg of a person ?
The heart muscle is myogenic - that means it will beat on its own with no external stimulus.
The AV node has a slow conduction velocity, so this creates a delay. This delay allows the atria to finish contracting and emptying into the ventricles before the ventricles start contracting. From the AV node, the depolarisation spreads through the bundle of his (in the interventricular septum) and then through Purkinje fibres into the ventricular walls, causing the ventricles to contract from the apex upwards.
ECGs are very complex you only need a basic understanding. So make sure you know about the typical ECG trace (P wave, QRS complex, T wave and what they mean). Also make sure you're able to work out the heart rate from an ECG strip. And just be aware that ECGs can show irregularities in the conduction system such as arrhythmias (i.e. irregular heart rhythms), heart block, atrial fibrillation as well as things like a myocardial infarction (heart attack). ECG interpretation is difficult and takes many years to master, you only need the very basics.
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(Original post by Jpw1097)
The heart muscle is myogenic - that means it will beat on its own with no external stimulus.
The AV node has a slow conduction velocity, so this creates a delay. This delay allows the atria to finish contracting and emptying into the ventricles before the ventricles start contracting. From the AV node, the depolarisation spreads through the bundle of his (in the interventricular septum) and then through Purkinje fibres into the ventricular walls, causing the ventricles to contract from the apex upwards.
ECGs are very complex you only need a basic understanding. So make sure you know about the typical ECG trace (P wave, QRS complex, T wave and what they mean). Also make sure you're able to work out the heart rate from an ECG strip. And just be aware that ECGs can show irregularities in the conduction system such as arrhythmias (i.e. irregular heart rhythms), heart block, atrial fibrillation as well as things like a myocardial infarction (heart attack). ECG interpretation is difficult and takes many years to master, you only need the very basics.
Thank you.
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(Original post by Jpw1097)
The heart muscle is myogenic - that means it will beat on its own with no external stimulus.
The AV node has a slow conduction velocity, so this creates a delay. This delay allows the atria to finish contracting and emptying into the ventricles before the ventricles start contracting. From the AV node, the depolarisation spreads through the bundle of his (in the interventricular septum) and then through Purkinje fibres into the ventricular walls, causing the ventricles to contract from the apex upwards.
ECGs are very complex you only need a basic understanding. So make sure you know about the typical ECG trace (P wave, QRS complex, T wave and what they mean). Also make sure you're able to work out the heart rate from an ECG strip. And just be aware that ECGs can show irregularities in the conduction system such as arrhythmias (i.e. irregular heart rhythms), heart block, atrial fibrillation as well as things like a myocardial infarction (heart attack). ECG interpretation is difficult and takes many years to master, you only need the very basics.
Hi again. I was just reading about a few of the heart conditions we might be faced with and I came across Tachycardia; when the heart rate is too high. I have a question, if the heart rate is too high, is the blood pressure high or low ? It makes sense for it to be high because the heart rate is high but if the heart rate is high then doesn’t that mean less blood will be pumped out ( less volume ) so less pressure ?
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Hi again. I was just reading about a few of the heart conditions we might be faced with and I came across Tachycardia; when the heart rate is too high. I have a question, if the heart rate is too high, is the blood pressure high or low ? It makes sense for it to be high because the heart rate is high but if the heart rate is high then doesn’t that mean less blood will be pumped out ( less volume ) so less pressure ?
That's a very good question. Let's work through it.
BP = CO x SVR, where BP is blood pressure, CO is cardiac output and SVR is systemic vascular resistance (i.e. how constricted the blood vessels are).
CO = HR x SV (cardiac output = heart rate x stroke volume; stroke volume is the volume of blood ejected into the aorta in one minute).
Therefore BP = HR x SV x SVR.

According to this equation, if the heart rate goes up, the cardiac output (volume of blood ejected into the aorta in one minute) goes up and therefore the blood pressure goes up, provided everything else stays the same. In reality, as the heart rate increases, baroreceptors will detect the rise in blood pressure and will cause blood vessel walls to relax and dilate, as well as decrease the strength of the contraction of the heart, thereby lowering the blood pressure - allowing the blood pressure to remain more or less constant. This is known as the baroreflex.
However, when the heart rate gets too high (say around 180 bpm), diastole is significantly shortened which reduces the time for filling of the ventricles such that the heart begins to pump out less blood (so the stroke volume and therefore cardiac output goes down). Some arrhythmias can cause heart rates to reach this sort of level and they can cause loss of consciousness.
So the answer to your question is it depends on how high the heart rate is. If its just a bit high, BP may go up (but may not due to the reflexes keeping blood pressure constant). If the heart rate is very high, filling of the ventricles is impaired and so cardiac output and blood pressure fall - this can cause loss of consciousness (also known as syncope) due to a fall in blood flow to the brain.
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