Experimental Demonstration of Concealed AV Conduction in the Human Heart

Artificial pacing of patients with Stokes-Adams disease provided an opportunity to study experimentally the ways of operation of concealed antegrade or retrograde conduction, or both, in the AV junction.With a catheter electrode in the right atrium the classical experiment of Lewis and Master was repeated, revealing, during a 2:1 ventricular response to an atrial tachycardia, the delaying effect of seemingly blocked atrial impulses on subsequent AV conduction.Shifting the position of a single premature atrial impulse within a constant driving cycle of the atria produced graded effects of “blocked” atrial impulses on AV junctional refractoriness, permitting an estimation of the duration of the “phase of concealed AV conduction.”Interpolation of such premature atrial impulses into successive driving cycles resulted in “repetitive concealed conduction.”In an artificially produced atrial parasystole there was observed “concealed discharge” of a subsidiary (escaping) AV junctional pacemaker by an apparently nonconducted atrial impulse.With a catheter electrode in the right ventricle in a case of advanced AV block, concealed retrograde conduction of pacer stimuli disturbed the rhythmicity of a spontaneous AV junctional pacemaker.In a case of advanced AV block with preservedretrograde conduction (unidirectional block), evidence of penetration of the upper AV junction by the “blocked” antegrade impulse was found.With electrodes implanted in the left ventricle in a case of advanced AV block, concealed retrograde conduction of the artificial pacemaker stimuli enhanced antegrade conduction by transiently changing an area of unidirectional block to one of supernormal conduction.Thus, all known manifestations of concealed atrioventricular and ventriculo-atrial conduction, occurring spontaneously in clinical records or induced in animal experiments, were artificially reproduced in the human heart.