Möbitz 2 Block

Report:

Sinus rhythm

First degree AV block

PR 0.22”

Second degree AV block, Möbitz 2

Left posterior hemiblock

Right bundle branch block

Comment:

The fixity of the PR interval rules out Möbitz 1 (Wenckebach) mechanism for the AV block. Almost invariably, in Möbitz 2 block, there is, like here, associated evidence of intraventricular conduction defect(s) - RBBB + LPHB in this case. One could call this BBBB or bi- or trifascicular block; I feel these terms are only justified in a specific context where they convey additional meaning or emphasis. Not routinely: they sound hollow and somewhat showy.

Trifascicular would here mean that the PR interval prolongation is attributable to impaired conduction in the anterior superior division of the left bundle branch – the remaining conducting bundle. This is not provable by standard electrocardiography.

Below (Fig 66a) is the ECG following the permanent pacemaker implantation. It is difficult to see that the unit contributes to the ventricular complexes at all; it senses but does not capture.

Shortening the sensing AV interval would make the unit pace; lenthening it would abolish the battery-wasting spikes. In this setting RBBB complexes perform better than paced LBBB-like ones would. The AV interval should be lenthened to avoid pacing.