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.

Fig 64a.

Fig 65. 79 year old man with permanent pacemaker, in Casualty with symptomatic tachycardia. The symptoms were not too severe, since he signed himself out and returned home.