TERMINATION OF ATRIOVENTRICULAR NODAL REENTRANT TACHYCARDIA BY PREMATURE STIMULATION FROM ABLATING CATHETER - A RELIABLE GUIDE TO IDENTIFY SITE FOR SLOW-PATHWAY ABLATION

Background Slow-pathway ablation is currently used more frequently to control atrioventricular nodal reentrant tachycardia (AVNRT). However, in patients with the common type of AVNRT, successful ablation of the slow pathway can be difficult and time-consuming. We tested a simple method to predict a site for slow-pathway ablation in patients with AVNRT of the common variety. Methods and Results Twenty patients with symptomatic common AVNRT (13 women and 7 men; mean age, 41+/-21 years) were included in the study. Once the AVNRT had a stable cycle length (+/-10 ms) for at least 20 cycles, single extrastimuli were delivered from the ablating catheter tip beginning with 20 ms less than the tachycardia cycle length and decrementing by 10 ms until tachycardia terminated or loss of capture occurred at the pacing site. The pacing protocol was performed systematically in a stepwise fashion at four adjacent sites starting from the posterior/inferior interatrial septum near the tricuspid annulus and moving progressively more anteriorly. The pacing protocol was then repeated in the same sequence, followed by delivery of radiofrequency current at each site to determine its effect at sites where AVNRT could not be terminated with a pacing protocol. AVNRT could be terminated in the anterograde direction from at least one site in 19 patients. Tachycardia could be terminated at two or more adjacent sites in 5 patients. The longest atrial coupling interval at the site of tachycardia termination was 67+/-27 ms (range, 30 to 130 ms) less than the AVNRT cycle length. Resetting of subsequent His bundle depolarization (H-2), producing an H-H-2 interval prolongation of 26+/-24 ms (range, 10 to 80 ms), occurred in 17 patients before termination of the tachycardia. In 18 of the 19 patients, the slow pathway was successfully ablated at the site at which AVNRT was terminated at the longest atrial coupling interval. Conclusions Termination of tachycardia in the anterograde direction at the longest atrial coupling interval by extrastimuli delivered from the ablating catheter can be helpful for identification of an optimal site for slow-pathway ablation in patients with the common variety of AVNRT.