Brain-Stem CVA: SA Wenckebach

Report:

Sinus rhythm 56 – 100/min

Sino-atrial exit block, Möbitz 1

Minor T wave changes

Lead V4 missing

Comment:

At first, seeing the typical grouping with acceleration before the pause, one thinks of AV Wenckebach. But there is no PR interval prolongation, no blocked P waves. It’s the entire P-QRS sequence which accelerates, and then a P wave is missing, with predictable consequences.

There is a (visually) difficult differential diagnosis for this: the shortest cycles could be due to atrial premature beats, except the putative P’ waves look the same as sinus P waves. If they were sinus extrasystoles, one could not exclude them, except that I have never seen in them in sustained trigeminy. Or, the pauses could be due to buried blocked P’ waves, except that T waves do not look suspiciously distorted in any way.

The phenomenon persisted (Fig 283a below) but, fortunately for the patient, ICU priorities lay elsewhere.

Overpage is another patient, 82 year old also with a brain-stem CVA. He has the more usual pattern, of sinus bigeminy, almost invariably due to SA block (3:2 Wenckebach exit block). The LAHB does not affect his outlook but then again, neither does the SA block. Most likely his CVA was due to prior episodes of AF (below).