Right Atrial-ventricular Dissociation and Entrainment while Pacing from High Right Atrium and Coronary Sinus during Circus Movement Tachycardias BOLIVAR PORTILLO, AGUSTIN CASTELLANOS. JOSE MEIIAS. LIAQAT ZAMAN, NELLY LEON-PORTILLO, and ROBERT J. MYKRBURG From the Hospital General del Sur, Maracaibo, Venezuela and the Division of Cardiology, University of Miami School of Medicine. Miami. Florida. U.S.A. PORTILLO. B., ET AL.: Right atrial-ventricular dissociation and entrainment while pacing from high right atrium and coronary sinus during circus movement tachycardias. Thirteen patients with circus movement tachycardias [CMT] were studied. Twelve had lefi-sided. and one, right-sided, accessory pathways. Entroinmont was possible during overdrive high right atria/ stimulation in 13/13 patients, and during cornnary sinus pacing in 10/12 patients. The minimal pacing rates required/or (his lo occur were 10 to 31 beats/min faster than those of the tachycardias. Short episodes of right atriai-ventricular dissociation occurred while pacing from the high right atrium [6/13 patien(s). but not from the coronary sinus (0/13 patients). It is possible to explain this phenomenon hy postulating the existence of two distinct atrioventricu/ar (AV) nodai inputs (one for right-sided and the other for left-sided impulses); it could also have been an expression of the close distance existing between the AV node and the coronary sinus. Entrainment. by defining a range of paring rates followed by resumption of the tachycardia upon the cessation of stimulation, indicated that /aster rates were needed for the CMT to be interrupted. However, regardless of the pacing rate and pacing site, tachycardia termination occurred when an anterograde impulse was blocked at the. AV node. The information obtained from this study suggests that some patients with drug-resis(ant CMT may benefit from pacing modes capable of terminating the arrhythmia "through entrainment" at the slowest afrial rate at which this is possible. (PACE, Vol. 7. July-August. 1984] entrainmenl, circus movement, tachycardia, atrial pacing, AV dissociation, reentry That overdrive atrial pacing can result in entrain- ment when initiated during circus movement tachycardia (CMT) incorporating an accessory pathway (AP) has been described previously.'"^ However, few studies have dealt with right atrial- ventricular dissociation during stimulation from the high right atrium (HRA) and with entrainmont Supported in part by a grant from CONTREC (Confederacion Transnaciona! de Electmfisiologia y Cardioestimutacitin) Address for reprints: Dr. ARUStin Castellanos. Division of Car- diology (D-39). U/Miami School of Medicine. P.O. Box 016960. Miami. FL 33101. Received December 15. 1983: accepted February 14.1984. during coronary sinus pacing, as will be discussed in this communication. Material and Methods Electrophysiologic studies were performed in 12 patients with CMT involvinga left-sided accessory pathway for retrograde conduction. Six patients had manifest Wolff-Parkinson-White (WPW) syn- drome and 6 had concealed WPW (AP capable of only retrograde conduction). Eight were males and 4 were females. Their ages ranged between 17 and 65 years (Table I). Although organic heart disease was not detected in 8 patients, 3 had congestive cardiomyopathy and 1 had coronary artery dis- 710 )uly-Aunust 1984 PACE. Vol. 7