Evaluation of a novel cryoablation system: In vivo testing in a chronic porcine model

Objective: Cryoablation is commonly used at present in the surgical treatment of atrial fibrillation (AF). However, there have been few studies examining the efficacy of the commonly used ablation devices. This report compares the efficacy of two cryoprobes in creating transmural endocardial lesions on the beating heart in a porcine model for chronic AF. Methods: In six Hanford miniature swine, the right atrial appendage and the inferior vena cava were isolated using a bipolar radiofrequency clamp to create areas of known conduction block. A connecting ablation line was performed endocardially via a purse string with the novel malleable 10-cm Cryo1 probe for 2 minutes at-40 C. Additional ablation lines were created with the Cryo1 and the 3.5-cm 3011 Maze Linear probe on the right and the left atrial wall. Epicardial activation mapping was performed before and immediately after ablation as well as 14 days postoperatively. Histologic examination was performed 14 days postoperatively. Results: Transmural lesions were confirmed in 83/84 cross-sections (99%) for the Cryo1 probe and in 40/41 cross-sections (98%) for the 3011 Maze Linear probe. There was no difference between the devices in lesion width (mean ± SD, Cryo1, 10.7 ± 3.5 mm; 3011, 10.0 ± 3.9 mm; P = 0.31), lesion depth (Cryo1, 4.5 ± 1.7 mm; 3011, 4.6 ± 1.5 mm; P = 0.74), or atrial wall thickness (Cryo1, 4.5 ± 1.8 mm; 3011, 4.7 ± 1.7 mm; P = 0.74). There was a conduction delay across the right atrial ablation line (20 ± 2 milliseconds vs 51 ± 8 milliseconds, P < 0.001) that remained unchanged at 14 days (51 ± 8 milliseconds vs 52 ± 10 milliseconds, P = 0.88). Conclusions: The Cryo1 probe created transmural lesions on the beating heart, resulting in sustained conduction delay. Both probes had a similar performance in lesion geometry in this chronic animal model.