The safety and efficacy of multiple consecutive cryo lesions in canine pulmonary veins-left atrial junction

Objective. The purpose of the study is to evaluate the safety and efficacy of multiple cryo lesions in canine pulmonary veins-left atrial junction. Background. The use of radiofrequency to achieve electrical isolation of the pulmonary veins (PVs) has been associated with PV stenosis. No information is currently available concerning the safety and the electrophysiological effects of multiple and consecutive cryo applications at the PV-left atrial junction. Methods. Liquid N₂O was delivered into semi-compliant 15 to 22-mm-diameter balloons. In 13 dogs weighing 34 ± 2 kg, one to four consecutive cryo lesions were randomly applied to each PV for 3 minutes in 6-minute intervals. The pre- and post-PV sizes were recorded by angiography. Electrogram activity and pacing thresholds were recorded before and after cryo. PV patency and the PV-atrial tissue characteristics were evaluated grossly and histologically. Results. Pacing capture was not possible with 10 mA postablation in 26/46 (57%) electrodes, and in 20 (43%) electrodes pacing threshold increased from 1.6 ± 1.7 mA to 7.8 ± 3.2 mA. The total elimination of recorded electrograms was noted in 22%, 29%, and 18% following 1, 2, and 3 cryo lesions respectively. After 4 lesions this value increased to 53%. No significant changes in PV diameter were recorded in any of the veins pre vs the terminal study. The PVs and PV-atrial interface tissue were soft, compliant, and without collagen or cartilaginous tissue. There was no hemoptysis in any of the dogs. Conclusion. In this study, cryo balloon technology is effective and safe regardless of the number of lesions applied and the freezing temperatures achieved. Four consecutive cryo applications result in a significant increase in pacing threshold and a decrease in activity of local atrial electrograms.