What Do You Think 16

92-year old, one-eyed cardiothoracic surgeon with labyrinthine degeneration and bilateral foot drop. Plans to cut back his surgical sessions.

Holter monitor shows two nocturnal episodes of bradycardia (yellow highlight):

Both are called 2:1 second degree AV block(red highlight). 

What do you think?

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My first thoughts were the 06:53:12 tracing was non-conducted atrial bigeminy.            

To summarize: Non-conducted atrial ectopic:

• Sinus rhythm (red arrows).
• The P wave is premature (blue arrow).
• The P wave is usually an abnormal appearance.
• The PR intervals before and after the blocked beat are the same (red highlight).
• Compensatory pause (yellow highlight).

Let us relook at the timing of our tracings.

The P-P intervals (red arrows) are near identical in timing with lost P waves in the lower tracing(red-yellow arrow) and the pause about twice the P-P intervals.  

I suggest that the lower tracing is 2:1 AV block with 3:2 sino-atrial block. Both tracings have 2:1 AV (Wenckebach) block and one also sino-atrial Wenckebach sequences. This is called a pan-conduction defect, because of block in both nodes.

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The footprints of typical sino-atrial Wenckebach block.

• Fulfils criteria for Wenckebach block within the sinus node and is “pre-P wave”.
• Progressive fatigue of sino-atrial conduction with sinus block to the atrium.      
• Sinus node “rests” and conduction returns.
• Greatest increase in sino-atrial conduction is typically between the first and second beat with an incremental increase of sino-atrial conduction becoming shorter.
• The P-P interval progressively shortens with each beat of the cycle.

Here is a case of sino-atrial Wenckebach block:

As the incremental increase of sino-atrial conduction becomes shorter(red highlight), so do the P-P intervals with the shortest before the sinus pause (yellow highlight).

Another example of a pan-conduction defect with bundle branch blocks.

This illustration is the “full hand” of conduction system disease. There is sinus rhythm and the QRS shows both left bradycardia dependent (red highlight) and right (yellow highlight)bundle branch block. The Wenckebach AV block sequences, range from long to 2:1, whereas the sino-atrial dropped beats (red shadow arrows) occur irregularly(blue highlight). The feature of the Wenckebach sino-atrial block is that the shortest P-P interval is before the sinus pause (green highlight).

The techs were correct. Both tracings show 2:1 AV block.

It isn’t always what you think it is!!!