Focal Transcatheter Cryoablation: Is a Four-Minute Application Still Required?

Transcatheter Cryoablation. Introduction: The standard 4-minute application time for transcatheter cryoablation was determined in the 1990s when the system employed less potent chlorofluorocarbon refrigerants. The current refrigerant, nitrous oxide, generates substantially colder temperatures, with a faster cooling rate. Methods and Results: We conducted a preclinical study on 32 mongrel dogs with stratified randomization of right atrial, right ventricular, and left ventricular chambers to 2-minute versus 4-minute application times using 8-mm electrode tip cryocatheters (Freezor Max, Medtronic CryoCath LP, Montreal, Canada). Animals were sacrificed one month after the procedure. Three-dimensional morphometric analyses were conducted in a blinded fashion. A total of 193 identified ablation lesions were processed for histological analyses, 102 with 2-minute applications and 91 with 4-minute applications. Ablation lesion surface area (167.8 +/- 21.6 mm(2) vs. 194.3 +/- 22.6 mm(2), P = 0.40), maximum depth (4.4 +/- 0.2 mm vs. 4.5 +/- 0.2 mm, P = 0.71), and volume (125.7 +/- 69.5mm(3) vs. 141.0 +/- 83.5mm(3), P = 0.25) were similar between groups. Overall, 90.2% of ablation lesions in the right atrium were transmural, 45.6% in the right ventricle, and 2.4% in the left ventricle, with no differences between 2-minute and 4-minute application times (P = 0.55). Thrombus was detected on the endocardial surface of 0.0% and 3.3% of ablation lesions created with 2-minute and 4-minute application times, respectively (P = 0.10). Conclusion: Single 2-minute and 4-minute application times result in catheter ablation lesions of similar size using the modern cryoablation system with nitrous oxide as a refrigerant. While these findings suggest the potential to reduce the standard 4-minute application time, further studies are required to compare clinical efficacy.