Right, Left, then Right Bundle Branch Block

Report:

Sinus tachycardia 140/min

Second degree AV block

First degree AV block in conducted beats

PR 0.30”

SVEBs, blocked (causing the pauses)

Left bundle branch block

Primary repolarisation changes c/c infarction/ischæmia

Comment:

This is an obvious case of bilateral bundle branch block (BBBB). It is interesting to note that the LBBB has a marked LAD (divisional LBBB) whereas the RBBB had a marked RAD. Maybe the latter was due to LPHB rather than loss of anterior R waves, as reported in Case 265. The conduction appears to have changed not just from bundle branch to bundle branch but also from fascicle to fascicle. It was phenomena like those that demonstrated, before the days of electrophysiology, that the blocks need not be anatomical blocks. Even so, in cases of anterior infarction in particular, they remain markers of severe myocardial disease. It is the loss of myocardium that determines the outcome, not the wiring or the arrhythmias. One could argue here that it is the coronary anatomy which is destiny in ischæmic disease but, in this case at least, le sort s’est prononcé!

The trace looks, superficially, like bigeminy due to a 3:2 block. The conducted PR intervals are all the same, indicating a Möbitz 2 mechanism despite the long PR intervals. This is an illusion: the first P wave in all the pauses is a premature P’ and the preceding blocked sinus P wave notches the preceding ST segment. The following sinus P wave also comes after a slightly longer cycle, reflecting post-ectopic SA depression, even in marked tachycardia.

The blocked SVEBs causing the long cycles are atrial, perhaps even sino-atrial, in origin.

Below (Fig 66a) is a trace in straight 2:1 conduction, with regular ventricular rate 70/min.