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(Circulation. 1996;94:1023-1026.)
© 1996 American Heart Association, Inc.

Articles

Ventricular Rate During Atrial Fibrillation Before and After Slow-Pathway Ablation

Effects of Autonomic Blockade and ß-Adrenergic Stimulation

S. Adam Strickberger, MD; Raul Weiss, MD; Emile G. Daoud, MD; Rajiva Goyal, MD; Frank Bogun, MD; K. Ching Man, DO; Fred Morady, MD

the Division of Cardiology, Department of Internal Medicine, University of Michigan Medical Center, Ann Arbor.

Background Radiofrequency catheter modification of AV conduction can be 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 this 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 tachycardia (AVNRT).

Methods and Results Thirty-five patients undergoing slow-pathway radiofrequency ablation for AVNRT were assigned to autonomic blockade (0.2 mg/kg propranolol and 0.04 mg/kg atropine; n=14) or isoproterenol (2 µg/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<.01) and maximum ventricular cycle length (640±105 versus 798±226 ms, P=.04) were prolonged after ablation, whereas the minimum ventricular 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 cycle length (307±59 versus 298±33 ms, P=.4) did not change significantly 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. Therefore, slow-pathway ablation alone cannot account for the clinical results obtained with radiofrequency modification of AV conduction in patients with atrial fibrillation.

Key Words: catheter ablation • ablation • atrium • fibrillation

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