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 electr ophysiological study (EPS) to assess the conduction in the His-Purkinje con duction system and to further investigate the electrical instability in the ventricle, which was suggestive by the findings of nonsustained ventricula r tachycardia in ambulatory monitoring. Transient complete atrioventricular (AV) block was provoked by ventricular pacing, and the intracardiac record ings proved that the site of AV block was distal to the His bundle. This ph enomenon was not related to the rate or the duration of the ventricular pac ing. The transient impairment of the conduction appeared to be due to the f atigue phenomenon in the His-Purkinje system.