High-resolution mapping and histologic examination of long radiofrequency lesions in canine atria

Introduction: Catheter ablation may prevent conduction of multiple atrial w avefronts and/or reduce the critical mass of atrial myocardium required to sustain fibrillation. The purpose of this study was to examine the effect o f radiofrequency (RF) energy application on conduction in canine atria by p erforming high-density epicardial mapping and careful histologic examinatio n of the ablation zone. Methods and Results: RF energy was applied to the right atrial endocardium in nine anesthetized mongrel dogs in an attempt to create a line of conduct ion block spanning the vertical length of a 504-channel epicardial mapping plaque. The mean length and width of the histologically determined ablation zone was 34 +/- 4 and 7.3 +/- 2.6 mm, respectively. No thrombus was presen t. Conduction block that spanned the mapping plaque in 6 of 9 animals was m atched histologically by continuous transmural necrosis in five. In one, on ly a portion of the ablation zone was transmural; the remainder was nide bu t nontransmural. In 2 of 3 animals with conduction, a narrow region was pre sent where continuous transmural necrosis was absent. In the other animal, conduction was present despite continuous transmural necrosis. Conclusion: Conduction block usually occurred when continuous transmural ne crosis was present, and conduction usually persisted when continuous transm ural necrosis was absent. However, important exceptions were observed, incl uding block when the ablation zone was wide but nontransmural, and conducti on despite a thin line of continuous transmural necrosis.