Gap in bundle-branch conduction elicited by programmed His bundle stimulation.

The gap phenomenon in right bundle-branch conduction was elicited during programmed stimulation of the His bundle. Premature beats with short and long coupling intervals showed undisturbed intraventricular conduction, while the premature beat with intermediate coupling interval blocked within the right bundle branch. The electrophysiologic mechanism of "supernormal" conduction of the earliest beats was conduction delay at a proximal site within the His bundle which allowed recovery of the right bundle branch. This study shows that programmed His bundle stimulation is a valuable method in analyzing conduction characteristics of the distal atrioventricular conduction system in cases where atrioventricular nodal refractoriness would preclude this by atrial stimulation.