Performance of an Irrigated Bipolar Radiofrequency Ablation Clamp on Explanted Human Hearts

Background: Bipolar radiofrequency (RF) clamps are commonly used during surgical ablation for atrial fibrillation (AF). This study examined the efficacy of an irrigated bipolar RF clamp to create transmural lesions in an ex vivo human heart model. Methods: Ten donor hearts, turned down for transplantation, were explanted and arrested with cold cardioplegia. The ablations of the Cox Maze IV procedure were performed using the Cardioblate LP (Medtronic, Inc) irrigated bipolar RF clamp. In the first 5 hearts, each lesion was created with a single application of RF, whereas in the remaining 5 hearts, each lesion was created with a double application of RF without unclamping. Each lesion was cross-sectioned and stained with 2,3,5-triphenyl-tetrazolium chloride to assess ablation depth and transmurality. Results: A total of 100 lesions were analyzed. In the single-ablation group, 222 of 260 sections (85%) and 37 of 50 lesions (74%) were transmural. The efficacy improved significantly in the double-ablation group, in which 348 of 359 sections (97%, P < .001) and 46 of 50 lesions (92%, P = .017) were transmural. Overall, in nontransmural lesions, the epicardial fat thickness was significantly greater (1.69 ± 0.70 mm vs 0.45 ±0.10 mm, P < .001) than the transmural lesions. Conclusions: A single ablation on human atrial tissue with an irrigated bipolar RF clamp was insufficient to reliably create transmural lesions, but a double ablation significantly increased the lesion and section transmurality. Nontransmural lesions were associated with significantly thicker layers of epicardial fat, which likely decreased tissue energy delivery due to the higher resistance of fat to current flow.