Is this third degree AV block or NOT?

A pt c/o syncope. Complete heart block (CHB) or not?

Image 1

This is only a 10 sec strip of a very exciting rhythm. I intentionally printed this portion for the great visual display of the complexes. What the h@*#% is happening here?

In understanding these kinds of rhythms it is worthhile to watch this video blog of Dr. Ken G. - 

The question being asked is that is this CHB or not? If you watched the videp then it is very clear that this is not CHB because some of the sinus impulses were conducted to the ventricle.

The short answer for this strip is advance or high grade AV block. This patient eventually got a pacemaker.

What is happening here?

1. Look for the P

Image 2

Here a caliper is of utmost importance because you have to march it out. Start at the obvious P to P. Here you can use the P to P between QRS # 4 and 5 or 5 and 6. Whichever you like. Marked in red arrows are the obvious P's. The blue arrows are the P's hidden from view (buried in the QRS or distorting the T waves.) Thus, this is sinus rhythm (~ 94 bpm). 

2. Which one P waves were conducted?

Image 3

QRS #4,5 and 6 are likely captured beats. But there is more. The morphology of the QRS are different. QRs #4 is conducted with a right bundle branch block (RBBB) morphology (aberancy). QRS #5 is cconducted normally. QRS #6 looked like a morphology between the normal-looking QRS and the wide QRS. So, QRS #6 looked like a fusion beat (F).

During this event, there is a 2:1 conduction.

Measuring the R to R helps

Image 4

The wide QRS beats are obviously not captured beats considering the variable PR interval. Added to that is if you measure the R to R, it will help. R2R3, R7R8 are equal. As well as R6R7. Thus, going back, we are saying that R6 or QRS 6 is a fusion beat.So, R2,R3, R7 and R8 are venticular escape beats.

The mysterious R1

The RR interval of R1R2 is < than R2R3 (and the rest). If you also look closely at the morphology using lead II, R1 morhology is different from the rest of the wide QRs beats. we do not have enough information but we can probably assume that this could also be a captured beat (abberant is morphology).

So, we have here advance or high grade AV block. During capture it showed RBBB-aberrancy and fusion beats.

Image 5

*In the words of Dr. K Wang, in ECG interpretation there are alternative explanations.