Iatrogenous 1o AV Block

Report:

Sinus rhythm 62/min 1

DDD (universal) pacemaker

Atrial-sensing, ventricular-pacing mode 3

Atrial under-sensing in V1-3, with atrial + ventricular paced complex 3

Long A-V interval 0.30” 3

Comment:

In programming the A-V sequential pacemakers one often prolongs the A-V interval in order to allow the native QRS complex to appear instead of the paced one: it saves the pacemaker’s battery from producing ventricular spikes seen in paced, fusion and pseudofusion beats. With one exception, it also allows more effective ventricular contraction, avoiding the LBBB activation sequence of the paced beats. The latter may be important in patients with advanced LV failure.

This patient was that exception: his native beats (below) all had LBBB morphology anyway! Not only that: the pacemaker paced the ventricle – using its battery – even at AV interval of 300 ms. Why, then, such a long A-V interval? Dr. Johnson had the answer: ignorance, Madam, pure ignorance!

The P wave not sensed by the atrial electrode is the one closest to the preceding R wave; perhaps that’s why it was ignored by the pacemaker. We do not know the programmed PVARP: perhaps it was long enough to make that P wave a non-wave. Later on, the atrial electrode failed completely and the pacemaker was converted to a VVI one.