Ventricular Echoes

These experiments were designed to examine further the concept of a dual pathway for AV transmission in the heart, and to determine whether or not the atrium is a necessary link in the reentry pathway used for a ventricular echo. Studies were performed on anesthetized and awake dogs with recording electrodes implanted on the atrium, bundle of His, and right ventricle. When paired stimuli (V1V2) were applied to the ventricle with an appropriate delay, the second stimulated beat was followed by a nonstimulated ventricular echo. The echo response was of supraventricular origin. During paired stimulation with echoes, stimulation of the atrium prior to arrival of the retrograde response to V2 produced a propagated ventricular beat in advance of the expected echo. Stimulation of the atrium immediately after an echo was associated with apparent supernormal AV conduction. These observations support the conclusion that the AV node can be dissociated functionally into at least two pathways. It was possible to render the atrium refractory without abolishing the echo. This finding indicates that the atrium per se does not participate in the reentry path used for ventricular echo.