SELECTIVE TRANSCATHETER ABLATION OF THE FAST AND SLOW PATHWAYS USING RADIOFREQUENCY ENERGY IN PATIENTS WITH ATRIOVENTRICULAR NODAL REENTRANT TACHYCARDIA

Background. The safety and efficacy of selective fast versus slow pathway ablation using radiofrequency energy and a transcatheter technique in patients with atrioventricular nodal reentrant tachycardia (AVNRT) were evaluated. Methods and Results. Forty-nine consecutive patients with symptomatic AVNRT were included. There were 37 women and 12 men (mean age, 43 +/- 20 years). The first 16 patients underwent a fast pathway ablation with radiofrequency current applied in the anterior/superior aspect of the tricuspid annulus. The remaining 33 patients initially had their slow pathway targeted at the posterior/inferior aspect of the right interatrial septum. The fast pathway was successfully ablated in the initial 16 patients and in three additional patients after an unsuccessful slow pathway ablation. A mean of 10 +/- 8 radiofrequency pulses were delivered; the last (successful) pulse was at a power of 24 +/- 7 W for a duration of 22 +/- 15 seconds. Four of these 19 patients developed complete atrioventricular (AV) block. In the remaining 15 patients, the post-ablation atrio-His intervals prolonged from 89 +/- 30 to 138 +/- 43 msec (p < 0.001), whereas the shortest 1:1 AV conduction and effective refractory period of the AV node remained unchanged. Ten patients lost their ventriculoatrial (VA) conduction, and the other five had a significant prolongation of the shortest cycle length of 1:1 VA conduction (280 +/- 35 versus 468 +/- 30 msec, p < 0.0001). Slow pathway ablation was attempted initially in 33 patients and in another two who developed uncommon AVNRT after successful fast pathway ablation. Of these 35 patients, 32 had no AVNRT inducible after 6 +/- 4 radiofrequency pulses with the last (successful) pulse given at a power of 36 +/- 12 W for a duration of 35 +/- 15 seconds. After successful slow pathway ablation, the shortest cycle length of 1:1 AV conduction prolonged from 295 +/- 44 to 332 +/- 66 msec (p < 0.0005), the AV nodal effective refractory period increased from 232 +/- 36 to 281 +/- 61 msec (p < 0.0001), and the atrio-His interval as well as the shortest cycle length of 1:1 VA conduction remained unchanged. No patients developed AV block. Among the last 33 patients who underwent a slow pathway ablation as the initial attempt and a fast pathway ablation only when the former failed, 32 (97%) had successful AVNRT abolition with intact AV conduction. During a mean follow-up of 6.5 +/- 3.0 months, none of the 49 patients had recurrent tachycardia. Forty patients had repeat electrophysiological studies 4-8 weeks after their successful ablation, and AVNRT could not be induced in 39 patients. Conclusions. These data suggest that both fast and slow pathways can be selectively ablated for control of AVNRT. Slow pathway ablation, however, by obviating the risk of AV block, appears to be safer and should be considered as the first approach.