More than you probably wish to know about the heart's electrical function

It's a lot headier than most of us would prefer to have to deal with, but...have at it if you're inclined:

[www.cvphysiology.com]

Quote
gloaming
It's a lot headier than most of us would prefer to have to deal with, but...have at it if you're inclined:

You might be interested studying in the atrial effective refractory period (AERP).

"In electrocardiography, during a cardiac cycle, once an action potential is initiated, there is a period of time that a new action potential cannot be initiated. This is termed the effective refractory period (ERP) of the tissue. This period is approximately equal to the absolute refractory period (ARP), it occurs because the fast sodium channels remain closed until the cell fully repolarizes. During this period, depolarization on adjacent cardiac muscles does not produce a new depolarization in the current cell as it has to refract back to phase 4 of the action potential before a new action potential can activate it. ERP acts as a protective mechanism and keeps the heart rate in check and prevents arrhythmias, and it helps coordinates muscle contraction. Anti-arrhythmic agents used for arrhythmias usually prolong the ERP. For the treatment of atrial fibrillation, it is a problem that the prolongation of the ERP by these agents also affects the ventricles, which can induce other types of arrhythmias. Source


"The period from the start of the QRS complex to the peak of the T wave is of particular interest
when it comes to atrial fibrillation. During this period (the effective refractory period or ERP)
myocyte depolarization can not be triggered by stimulus originating from rogue atrial cells thus
preventing afib from being initiated. However, atrial fibrillation can be triggered during the last
half of the T wave (relative refractory period or RRP) making it highly desirable that the ERP is as
long as possible and the RRP as short as possible. Several medications aim to exploit this fact
by acting to extend the ERP so that the RRP (the vulnerable period) becomes as short as
possible. This is particularly important in the case of the AV node as during the ERP the node
can not be stimulated and thus in essence filters out the erratic atrial impulses. " Source

Various things such as autonomic nervous and electrolyte status can shorten or lengthen ERP. Generally for afib, you'd like to lengthen the ERP (to a point).

Oy, I'm getting a headache. It's complicated stuff. Takes a younger brain than mine to get a solid grip on it. But, I'll keep pluggin' away...

Thanks, George.