Cryosurgical ablation of the atrioventricular node-His bundle: Long-term follow-up and properties of the junctional pacemaker

We used a cryosurgical technique to ablate the atrioventricular (AV) node-His bundle in twenty-two selected patients with disabling supraventricular trachyarrhythmias unresponsive to medical managment. Successful AV block was achieved in seventeen. There was no intraoperative mortality and surgery revealed that the subsidiary pacemaker had a narrow QRS complex morphology and a mean cycle length of 1244 msec. Isoproterenol (1-4 μg/min i.v.) significantly increased (p < 0.01) the rate of the subsidiary pacemaker (mean maximum response 1008.3 msec); atropine (2 mg i.v.) had no effect on its rate. The significant (p = 0.024) increase (mean cycle length 1430 msec). Treadmill exercise in seven patients did not result in the subsidiary pacemaker exceeding the rate of the implanted demand pacemaker set at 70 beats/min. The properties of the subsidiary pacemaker suggest an intra-Hisian site of impulse formation.