[Cryosurgical ablation of the atrioventricular conduction system--experimental study for the determination of the appropriate ablation site and the long term follow-up results with clinical application].

In a series of experimental studies in dogs, we determined the exact site for the disruption of the atrioventricular conduction system by cryosurgical ablation which does not disturb the intraventricular conduction. The long-term symptomatic effects were evaluated in 9 patients with supraventricular tachycardia. In a total of 15 adult mongrel dogs, a thoracotomy was performed under pentobarbital anesthesia that was maintained during the procedure with artificial ventilation and cardiopulmonary bypass. The body temperature was maintained at 37 degrees C and throughout each experiment, the ECG was recorded by the conventional limb lead method while monitoring and recording the His bundle potentials from the catheter-electrode introduced via the internal carotid artery. The location in which the maximum His bundle potential was recorded was determined by intraoperative His bundle mapping through the right atrial incision. Cryoablation was performed by using -60 degrees C probes with a 5 mm tips. In 5 dogs (experiment A), we compared the effect of cryoablation at 2 different points on the interatrial septum, which were either 10 mm (10 mm point) or 5 mm (5 mm point) away from the site of the largest His bundle potential to the direction of the coronary sinus ostium. The two ablations were performed successively at 20 minute intervals. A second group consisting of 10 dogs, received cryoablation only at the 5 mm point (experiment B). In experiment A, atrioventricular block (AV block) was inconsistently achieved following cryoablation at the 10 mm point, whereas at the 5 mm point, the procedure was 100% successful in obtaining AV block without affecting the QRS morphology or H-V interval. In experiment B, we confirmed the reliability of the 5 mm point. Following cryoablation at the 5 mm point, coagulation necrosis in the region from the AV node to the penetrating portion of the His bundle were observed by pathological examination, however, the damage was only mild at the branching portion of the His bundle. Cryoablation was performed at the 5 mm point in 9 subjects. In all of these cases, complete AV block was successfully produced to terminate the tachycardias. The R-R interval of the escape rhythm in these patients gradually prolonged, and stabilized at 1500-1600 ms 3 years following the operation. In the long-term electrophysiological studies, all subjects had A-H block, and there were no subjects with prolonged H-V intervals observed. We conclude that cryoablation at the 5 mm point is an appropriate and effective choice for the treatment of supraventricular tachycardias.