Further observations on the ventricular echo phenomenon elicited in the human heart. Is the atrium part of the echo pathway?

SUMMARY In order to answer the question whether the atrium is a link in the pathway of ventricular reciprocation or whether the A-V node itself is the reflection point of the echo, a special stimulation program was followed in six patients in whom ventricular echo beats with stable time relations could be elicited by regular pacing of the right ventricle or by the application of appropriately timed right ventricular premature beats during regular pacing of the right ventricle. In these experiments the atrial septum was stimulated earlier than the expected arrival at the atrium of the retrograde impulse in the course of the echo sequence. The influence of stepwise (steps of 5 msec) advancing of this atrial "preexcitation" on the timing of the ventricular echo beat was studied. We found that the atrial septum could be preexcited without interfering with the ventricular echo beat time relations over a time interval less than 5 msec in one patient, less than 10 msec in one, less than 20 msec in two, and less than 30 msec in two cases. When the time interval needed for the stimulated atrial impulse to reach the atrionodal margin is taken into account, it seems likely that the atrium participated in the echo pathway in the four cases with minimal atrial preexcitation intervals of 20 msec or less, and that in the two cases with a minimal atrial preexcitation intelval of 30 msec the echo reflection point was localized in the upper part of the A-V node. IN RECENT years intracavitary stimulation studies have outlined the conditions favoring the occurrence of the ventricular echo phenomenon in the intact human heart.1-4 The outcome of these studies suggested that the mechanism of reciprocation in the human heart could be explained with the concept of longitudinal dissociation in the upper part of the A-V junction.5-7 These clinical investigations did not give an answer to the question duction Ventricular reciprocation Stimulation experiments whether the atrium is a link in the echo circuit, as advocated by Mendez and co-workers ,8 or whether the point of reflection of the echo is located within the A-V node, as proposed by Mignone and Wallace.9 In six patients with ventricular reciprocation elicited by appropriately timed stimulation of the ventricles, we tried to obtain an answer to this question by stimulaton of the atrium earlier than the excitation of the atrium expected in the course of the …