Depression of distal AV conduction following ventricular pacing.

A 61-year-old man presented with symptomatic 2 degree Mobitz II AV block in association with bifascicular block. Ventricular pacing resulted in temporary depression of AV conduction. The extent of pacing-induced AV block varied directly with the duration and rate of ventricular pacing. Intracardiac recordings proved that the site of spontaneous and pacing-induced AV block was distal to the His bundle. Possible mechanisms by which this phenomenon may arise and several implications of practical importance are discussed.