00:01
Now again, as I mentioned before, sinus node dysfunction
is much less common than atrioventricular node dysfunction.
00:08
So, the interruption in the electro conduction system usually occurs in or near the AV node
and there are three levels of block.
00:17
One is benign or relatively benign. One is more serious and one is very serious,
and we call them first-degree AV block, second-degree AV block
and third-degree or complete heart block and we'll talk about each of these now in more detail.
00:32
So, here, we see first-degree AV block and you can see, look on the top strip.
00:40
There is a - you can hardly see the first P-wave, but let's look at the second beat.
00:45
There's a P-wave, then there's a QRS.
00:48
But look at how long the pause is between the P-wave and the QRS and the next beat as well.
00:54
It's taking a long time for the electrical impulse to get through the AV node.
00:59
So, remember that the normal PR interval is 0.2 seconds or five little boxes.
01:05
In this case, the PR interval is actually 9.5 little boxes or 0.38 seconds
and we call this first-degree AV block, usually asymptomatic; the patients don't notice it.
01:18
Here is another example of first-degree AV block.
01:21
You'll notice, again, normal PR intervals, are 3 to 5 little boxes, 0.12-0.20 seconds.
01:28
In this case it's a six and a half little boxes or 0.26 seconds, in other words, first-degree AV block.
01:35
Another example, not as severe as the last one.