Microelectrode Studies on Retrograde Concealment of Multiple Premature Ventricular Responses

Abstract

Retrograde concealment of serially evoked premature ventricular responses was studied in an isolated preparation of rabbit atria and ventricles. Transmembrane potentials were recorded simultaneously from single cells within the atrioventricular (A-V) node and ventricular specialized conduction system, together with atrial and ventricular bipolar electrograms. In these experiments, retrograde conduction delays and block occurred within the ventricles, between ventricular muscle and the Purkinje-bundle branch system, between the bundle branch and His bundle, and within the A-V node. The ventricular specialized conduction system was found to be a major location of retrograde conduction delays and block. Many examples of retrograde concealment and block, previously interpreted as due to A-V nodal mechanisms, almost certainly result instead from mechanisms operating within the ventricular specialized conduction system. Antegrade and retrograde block of sequentially evoked premature responses occurred within the A-V node. Reentry "echo" responses occurred in many experiments following premature stimulation of the atria, the ventricles, or both.