Feasibility of closed heart discrete cryomodification of atrioventricular conduction. Electrophysiologic effects in the canine heart.

Discrete cryosurgical modification of atrioventricular conduction abolishes refractory atrioventricular node reentry tachycardia with preservation of antegrade atrioventricular nodal conduction. This procedure presently requires cardiopulmonary bypass. To modify atrioventricular conduction without cardiac surgery, we evaluated the electrophysiologic effects of cryolesions applied to the peri-nodal area in the closed heart in 16 dogs before operation, during cryothermic exposure, and at 1 hour and 3 hours after operation. The electrophysiologic effects were evaluated in 10 of the 16 dogs at 2 weeks postoperatively. The dogs were given general anesthetics, and a cryoprobe was introduced into the right atrial cavity through the right atrial appendage. Cryolesions (-60 degrees C) were placed at nine to eleven preselected points around the perinodal area guided by electrodes on the tip of the cryoprobe. Postoperatively, there were significant prolongations of the atrio-His interval, Wenckebach's point, effective refractory period, and functional refractory period of the atrioventricular node. Atrial echo beats were eliminated or decreased in frequency. There was also a significant increase in retrograde ventriculoatrial conduction time. In the long-term observation period the atrio-His intervals remained significantly prolonged in comparison with the preoperative values, the atrial echoes progressively decreased, and ventriculoatrial conduction was absent in five of seven animals. A serendipitous atrioventricular node reentry tachycardia that was inducible in one animal with dual atrioventricular node conduction pathways was successfully eliminated and was not inducible at 2 weeks postoperatively. Complete atrioventricular block occurred during attempts to produce greater atrio-His prolongation in three of the 16 animals and persisted in two for the 2-week period of observation. Closed heart intracardiac cryomodification of atrioventricular conduction is feasible, with the cryoprobe in normothermic blood, producing changes in atrioventricular conduction similar to the open cardiac procedure.