Asynchronous conduction in the human His bundle.

2 patients with symptoms of paroxysmal AV block showed widening, splitting, slurring and decreasing amplitude of the His potential. Concomitantly, this was followed by different patterns of bundle branch block. In one of the patients it was obvious that a left bundle branch block was related to a Wenckebach phenomenon in the His bundle, and in the other patient different bundle branch block patterns were related to the occurrence of the intra-His bundle conduction delay. It is suggested that the present electrophysiological findings reflect asynchronous conduction in the His bundle causing a critical conduction delay in parts of the bundle branches leading to bundle branch block.