Significance of His Bundle Recordings with Short H-V lntervals

¹ Section of Cardiology, Department of Medicine, University of Miami School of Medicine, and the Cardiopulmonary Laboratory, Veterans Administration Hospital, Miami, Florida

The H-V interval was defined as the time elapsed between activation of His bundle and ventricular muscle. "Shortening" of this interval had a different significance in various pathologic conditions. For instance, in the presence of late ventricular extrasystoles a short H-V interval merely indicated that part of the ventricles had been depolarized by the ectopic focus before than by the impulse traversing the His bundle. This interval was also shortened in ventricular preexcitation due to a total (Kent bundle) or partial (Mahaim bundle) bypass of the normal A-V conducting system. When only the A-V node was bypassed (James bundle) the H-V interval was not short. Extrasystoles arising in the posterior division of the left branch produced retrograde activation of His bundle ahead of the ventricles. Pseudoshortening of the H-V interval occurred if the His bundle was depolarized after the onset of the QRS complex in the, surface electrogram but before the electrogram in the HBE leads.