A "multisite" atrioventricular block.

A 6-year-old child, operated for a perimembranous ventricular septal defect, underwent an electrophysiologic study for the presence of first degree atrioventricular (AV) block and bifascicular block with episodes of type 1 and type 2 second degree AV block. Electrophysiologic study showed a considerable infra-His conduction delay (HV interval 170 ms) and spontaneous phases of infra-His type 1 second degree AV block. During incremental atrial pacing supra-His type 1 second degree AV block and 2:1 infra-His AV block were simultaneously observed and this condition persisted unmodified despite the intravenous injection of atropine. The block distal to the His bundle was considered functional.