Occasionally, beats will actually -- extra beats will actually develop in the AV node itself.
These are so-called 'nodal extra systoles'. They also have a narrow QRS
but there's no abnormal P wave before the abnormal beat.
They originate in the upper AV nodal region.
They're not very common. Much more common are atrial premature beats.
And here we see some examples.
You'll notice that the first three marked with an arrow have no P waves before the extra systoles.
So, you'll notice first beat, there's no P wave in front of it.
Then when we have a normal beat. The second beat, P wave, QRS, and T.
There's another beat there, no P wave. Then the fourth beat, P wave, QRS, and T.
And there's another extra beat with no P wave and so forth. It continues through out.
So, these without a P wave are nodal extra systoles.