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.