Critical atrial site for ablation of pacing-induced atrial fibrillation in the normal dog heart

Introduction: Radiofrequency catheter ablation (RFA) has been used recently to treat atrial fibrillation (AF). The purpose of this study was to investigate a new approach to preventing AF by RFA. Methods and Results: In open chest, anesthetized dogs, AF (lasting > 30 sec) was induced after burst stimulation, and electrophysiologic parameters were recorded before and after RFA. In group 1 (9 dogs) we performed selective and combined slow and fast pathway RFA, whereas in group 2 (11 dogs) RFA was applied as a linear lesion at the mid-atrial septum between the inferior vena cava and the fossa ovalis. After ablation, the Wenckebach cycle length was significantly prolonged only in group 1 (194 ± 23 vs 282 ± 35 msec. P = 0.002), whereas the interval between the stimulus (S) artifact applied at the high right atrium to the His bundle (H) (SH interval) prolonged to the same extent in both groups (162 ± 14 vs 146 ± 45 msec, P = NS); group 1 due to an A-H prolongation whereas in group 2 it was due to an intra-atrial conduction delay. In group 1 AF still remained inducible, although with a longer mean R-R interval (215 ± 16 vs 433 ± 88 msec, P <0.05). No instance of complete AV block developed. In group 2, sustained AF was noninducible in 10 dogs and its duration was markedly shorter in the remaining one (8 sec). Gross anatomy and histology did not reveal any damage inside of Koch's triangle, and particularly to the compact AV node. Conclusion: These findings suggest that RFA at the mid- atrial septum prevents AF in the normal dog heart. This approach might also be successful in those clinical settings in which the atrial septum plays a critical role in the maintenance of sustained AF.