Transient complete atrioventricular block provoked by ventricular pacing in a patient with nonsustained ventricular tachycardia.

A 75-year-old woman with complete left bundle branch block underwent electrophysiological study (EPS) to assess the conduction in the His-Purkinje conduction system and to further investigate the electrical instability in the ventricle, which was suggestive by the findings of nonsustained ventricular tachycardia in ambulatory monitoring. Transient complete atrioventricular (AV) block was provoked by ventricular pacing, and the intracardiac recordings proved that the site of AV block was distal to the His bundle. This phenomenon was not related to the rate or the duration of the ventricular pacing. The transient impairment of the conduction appeared to be due to the fatigue phenomenon in the His-Purkinje system.