Atrial-Sensing Pacemaker Fails to Pace

Report:

V1 and V3 reversed 1

Sinus rhythm 94-100/min 0.5

Ventriculophasic sinus arrhythmia 2

Atrial-sensing ventricular pacemaker 2

Complete failure to pace 1

2:1 and 3:2 AV block, Möbitz 2 2

Right bundle branch block 1

Borderline ST segment depression V3-4 0.5

Comment:

Sometimes it is difficult to tell between atrial bigeminy and ventriculophasic sinus arrhythmia, where sinus P waves sandwiching a QRS are closer together than those with nothing between them. Looking at all the leads, the latter is more likely; slight difference obtains from the location of P waves immediately after T waves, possibly superimposed on U waves. The origin of the ventriculophasic effect remains unknown40.

A single episode of 3:2 conduction allows one to inspect two consecutive conducted P waves and diagnose Möbitz 2 block – rarer and more interesting , therefore overdiagnosed, than Möbitz 1 (Wenckebach). The presence of RBBB makes type 2 block even more likely.

The pacing spikes are obviously “married” to the P waves. They remain faithful, but ineffectual: there are no captures.

Below (Fig 64a) , there’s a sample of the patient’s pre-implantation ECGs, showing transition from 2:1 to 1:1 conduction, again with ventriculophasic sinus arrhythmia.