Distal atrioventricular conduction system function.

This article addresses electrophysiologic evaluation of the distal AV conduction system in patients with chronic bifascicular block. It was formerly thought that progression to complete AV block was a common cause of morbidity and even sudden death in this condition, and it was hoped that electrophysiologic evaluation, including measurement of the H-V interval, would facilitate prospective identification and prophylactic treatment of patients prone to these complications. However, a decade of clinical investigation has revealed that progression to complete AV block is rare and that although cardiovascular mortality, including sudden death, is substantial, this mortality usually relates to underlying organic heart disease. The current role for electrophysiologic studies in chronic bifascicular block is limited to delineation of the site of electrocardiographically documented second- or third-degree AV block and to the evaluation of unexplained syncope.