ELECTROPHYSIOLOGY OF THE ATRIO-AV NODAL INPUTS AND EXITS IN THE NORMAL DOG HEART - RADIOFREQUENCY ABLATION USING AN EPICARDIAL APPROACH

Ablation of Atrionodal Connections. Introduction: We studied the effec ts of selective and combined ablation of the fast (FP) and slow pathwa y (SP) on AV and VA conduction in the normal dog heart using a novel e picardial ablation technique. Methods and Results: For FP ablation, ra diofrequency current (RFC) was applied to a catheter tip that was held epicardially against the base of the right atrial wall. SP ablation w as performed epicardially at the crux of the heart. Twenty-three dogs were assigned to two ablation protocols: FP/SP ablation group (n = 17) and SP/FP ablation group (n = 6). In 12 of 17 dogs, FP ablation prolo nged the PR interval (97 +/- 10 to 149 +/- 22 msec, P < 0.005) with no significant change in anterograde Wenckebach cycle length (WBCL). Sub sequent SP ablation performed in 8 dogs further prolonged the PR inter val and the anterograde WBCL (117 +/- 22 to 193 +/- 27, P < 0.005). Co mplete AV block was seen in 1 of 8 dogs, whereas complete or high-grad e VA block was seen in 6 of 8 dogs. In the SP/FP ablation group, SP ab lation significantly increased WBCL with no PR changes. Combined SP/FP ablation in 6 dogs prolonged the PR interval significantly, but no in stance of complete AV block was seen. VA block was found in 50% of the se cases. Histologic studies revealed that RFC ablation affected the a nterior and posterior atrium adjacent to the undamaged AV node and His bundle. Conclusion: Using an epicardial approach, combined ablation o f the FP and SP AV nodal inputs can be achieved with an unexpectedly l ow incidence of complete AV block, although retrograde VA conduction w as significantly compromised.