Eleven patients with an accessory pathway and reciprocating tachycardia were studied using both fixed rate atrial pacing and the atrial extrastimulus technique. Six of the patients had an accessory pathway that conducted in both the anterograde and retrograde direction; but the effective refractory period of their accessory pathway in the anterograde direction was relatively long and was greater than the longest coupling intervals that initiated atrial echoes. Five patients had an accessory pathway that conducted only in the retrograde direction. The extrastimulus technique could be used with stimulation sites near to and remote from the accessory pathway in 10 of the 11 patients. Atrial echoes were initiated by a single atrial extrastimulus at both sites in 7 of the 10 patients, and in each patient the upper limit of the echo zone was longer with stimulation at the site near the accessory pathway. In the other three patients atrial echoes were initiated only during stimulation at the site near the acessory pathway because either atrial refractoriness or atrioventricular nodal refractoriness was encountered before the echo zone was entered during stimulation at the site remote from the accessory pathway. Differences in the longest cycle length that initiated an atrial echo during fixed rate atrial pacing were similarly demonstrated in three patients. In these three patients, pacing at the site near the accessory pathway initiated echoes at a longer cycle length than pacing at the site remote from the accessory pathway. In three other patients the electrophysiologic characteristics of atrioventricular conduction prevented a demonstration of these differences. Catheter position is an important variable in the initiation of atrial echoes in patients with accessory pathways.
Bibliographical noteFunding Information:
From the Division of Cardiology, Duke University Medical Center, Durham, North Carolina. This study was supported in partb y GrantR R-30f rom the General Clinical Research Center Branch, Division of Research Resources and by Grant HL 151901 from the National Institutes of Health, Bethesda, Maryland. This work was done in part during the tenure of Dr. Benditt as a Fellow of the Medical Research Council of Canada. Dr. Prttchett is the recipient of Young Investigator Research Award lR23 HL21347-01 from the National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland. This work was done during Dr. Gallagher’s tenure as an Established lnvestioator for the American Heart Association, Dallas,?exas. Manuscript received April 18, 1978; revised manuscript received June i3. 1978, ac- cepted June 14, 1978. Address for reprints: Edward L. C. Pritchett, MD, PO Box 3477, Duke University Medical Center, Durham, North Carolina 27710.