2:1 AV Block in Bad Company

Report:

Sinus rhythm 74/min

2:1 second degree AV block

Right axis deviation (RAD) +120o

Left posterior hemiblock

Right bundle branch block

Ventriculophasic sinus arrhythmia

Comment:

The patient had no history of heart disease and had been on cimetidine 400 mg BD. The drug is more often implicated in sinoatrial disorders65, but there is at least one report of its association with AV block66. There is, to my knowledge, no evidence that cimetidine (or ranitidine) can cause ventricular conduction deficits.

What is seen here is often loosely called trifascicular block. Presumably, the 2:1 (and also the associated 1o block in conducted beats) results from a lesion in the remaining conducting fascicle, in this instance the superior-anterior one. There could be a nodal block as well, although the rhythm strips below (Fig 103a) favour, despite the prolonged PR interval, a Möbitz 2 mechanism. One can never be sure without a bundle of His recording: it’s best to describe what’s present and leave it at that. What’s present here is enough to warrant a permanent pacemaker, which was duly implanted.

LPHB is not, per se, a purely electrocardiographic diagnosis: RVH has to be excluded clinically, since it is a major cause of right axis deviation. In this context, however, RVH would be most unlikely.

Fig 103a. Lesser degree of AV block type 2 apparent despite prolonged (but identical) PR intervals. The AV node may be involved in a panconduction disease even if it is not responsible for more than 1o AVB in this case.

Fig 404. Same lady as in previous Case 103, half an hour later.