Bradycardia-Dependent RBBB

Report:

Sinus/atrial rhythm

Shifting pacemaker

First degree AV block

Second degree AV block, Möbitz I

Blocked SVEBs, ?reentry of atrial origin

Bradycardia-dependent right bundle branch block

Comment:

This is the same patient as in Case 1.

All the long pauses are terminated by RBBB complexes, each of which has a reasonably conductible PR interval. Junctional escape beats - again with RBBB aberrancy - cannot be excluded in view of the rather irregular atrial activity.

Some of the blocked P waves are too premature to be considered subject to Wenckebach block of the preceding rhythm. They may, in view of the prevailing 1o AV block, be reentry beats of atrial origin.

Below (Fig 6a) is a strip with faster sinus (or atrial) rate, showing the RBBB failing to develop in pauses shorter than in the original strips. Thus the patient has two critical rates - one for tachycardia- and one for bradycardia-dependent RBBB.

Fig 6b shows this patient’s agonal tracings, retaining rate-dependent RBBB to the end. Some incomplete RBBB complexes follow the fully-blown ones, both in sinus beats and in SVEBs.