VENTRICULAR RATE DURING ATRIAL-FIBRILLATION BEFORE AND AFTER SLOW-PATHWAY ABLATION - EFFECTS OF AUTONOMIC BLOCKADE AND BETA-ADRENERGIC STIMULATION

Background Radiofrequency catheter modification of AV conduction can b e used to control the ventricular rate during atrial fibrillation both in the baseline state and during exercise. Slow-pathway ablation has been suggested to be the mechanism for this response. The purpose of t his study was to determine the effect of slow-pathway ablation on the ventricular rate in atrial fibrillation during autonomic blockade and sympathetic stimulation in patients with AV nodal reentrant tachycardi a (AVNRT). Methods and Results Thirty-five patients undergoing slow-pa thway radiofrequency ablation for AVNRT were assigned to autonomic blo ckade (0.2 mg/kg propranolol and 0.04 mg/kg atropine; n=14) or isoprot erenol (2 mu g/min; n=21). Atrial fibrillation was induced before and after slow-pathway radiofrequency ablation. During autonomic blockade, the mean ventricular cycle length (448+/-34 versus 525+/-103 ms, P<.0 1) and maximum ventricular cycle length (640+/-105 versus 798+/-226 ms , P=.04) were prolonged after ablation, whereas the minimum ventricula r cycle length did not change significantly (361+/-42 versus 403+/-83 ms, P=.05). During isoproterenol infusion, the mean ventricular cycle length (375+/-52 versus 390+/-61 ms, P=.2), maximum ventricular cycle length (520+/-88 versus 537+/-106 ms, P=.3), and minimum ventricular c ycle length (307+/-59 versus 298+/-33 ms, P=.4) did not change signifi cantly after slow-pathway ablation. Conclusions Slow-pathway ablation slows the ventricular rate during atrial fibrillation under conditions of autonomic blockade but not during sympathetic stimulation. Therefo re, slow-pathway ablation alone cannot account for the clinical result s obtained with radiofrequency modification of AV conduction in patien ts with atrial fibrillation.