Ectopic Foci and Abnormal Conduction – Heart Rate and Electricity

00:01 Now, what happens if you don't get that conduction past the AV node? Remember, Purkinje fibers can beat on their own.

00:12 They beat very slow, though, right? 30 to 40 beats per minute.

00:17 That’s a slow, slow beat.

00:21 But if you don't get enough information, they will take over and beat anyway.

00:26 And these generate ectopic foci, a place in the ventricle, that decides, I didn't get enough information, I don't know when I should beat, I'm just going to beat anyway, you can't stop, I’m beating because, you know, why not? That's what happens.

00:44 They take over their heart rate and they will beat on their own if they don't get enough signal.

00:50 So, unless you get SA node, AV node signals down the ventricular myocytes and the Purkinje fibers will take over beating.

01:00 This causes havoc.

01:03 It makes the QRS complex very wide and creates a process called a premature ventricular complex.

01:12 And these PVCs are seen very often in electrocardiogram.

01:17 And the reason why they happen is because the Purkinje fibers did not get signal from the SA node or the AV node.

01:27 You might ask, at this point, well, why don't they beat on their own anyway? I mean, because, you know, they have that intrinsic rhythm, right, 30 to 40 beats.

01:38 The reason why they normally don't take over beating is because every time an action potential comes through, it resets the clock.

01:48 So, if you have something like a sinoatrial node that beats 60 to 100 times per minute, it's going to reset the clock of the AV node and Purkinje fibers every time it happens.

01:59 So, you'd have to have a block in the system for those other pacemaker cells to take over.