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

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Abstract
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.

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