EFFECT OF SLOW PATHWAY ABLATION ON VENTRICULAR RATE DURING ATRIAL-FIBRILLATION - DEPENDENCE ON ELECTROPHYSIOLOGICAL PROPERTIES OF THE FAST PATHWAY

Background Catheter ablation of the posteroseptal right atrium has bee n proposed for control of ventricular rate in patients with tachycardi c atrial fibrillation (AF). However, the exact mechanism of rate contr ol is unclear. Because the ablation site corresponds to the location o f the slow pathway in patients with AV nodal reentry tachycardia (AVNR T), we investigated whether selective ablation of this posterior AV no dal input can provide a sufficient reduction in heart rate during AF. Methods and Results In 30 patients with AVNRT, conduction properties o f the AV nodal pathways were determined before and after slow pathway ablation. AF was induced by burst pacing at baseline and after ablatio n, and the mean ventricular cycle length was determined. After slow pa thway ablation, the mean ventricular cycle length during AF increased (449+/-98 versus 515+/-129 milliseconds, P<.01). At baseline, the mean ventricular cycle length correlated with the Wenckebach cycle length of both the slow (r=.90) and fast (r=.86) pathways. After ablation, th e mean ventricular cycle length was extremely well determined by the W enckebach cycle length of the fast pathway (r=.94). However, the slope of the regression line was significantly steeper compared with baseli ne (1.50 versus 0.77, P<.0001), illustrating that the reduction in ven tricular rate was not as evident if the fast pathway had a short Wenck ebach cycle length. Conclusions Selective elimination of the slow path way reduces ventricular rate during AF. However, in patients with a sh ort Wenckebach cycle length of the anterior AV nodal input that causes tachycardic AF, this effect may be insufficient to provide adequate c ontrol of ventricular rate.