Biophysics of the second-generation cryoballoon: cryobiology of the big freeze.

C urrent guidelines recommend antral isolation of the pulmonary veins (PV) as the cornerstone of atrial fibrillation ablation. 1 Although conventional radiofrequency energy has traditionally been used with a point-by-point approach, cryo-ablation has emerged as a viable alternative to radiofrequency energy. The clinical success of cryoablation has been driven by the introduction of the cryoballoon. Cryoenergy has been studied as early as the 1940s using CO 2 gas injected in a probe to produce controlled myocardial tissue damage and studied in a variety of experimental animal models. 2 In these early experiments, cryoinjury was demonstrated to cause sharply demarcated myocardial lesions. In marked contrast to radiofrequency ablation (RFA) lesions, cryolesions result in preservation of tissue architecture, including fibro-cytes and collagen, and there is significantly less damage to large vascular structures or to the endocardium. 3 These characteristics contribute to an increased safety profile compared with RFA, including less thrombogenicity 4 (preserved endo-cardium) and less risk of perforation (preserved tissue structure). Another advantage is that cryomapping may be used by temporarily cooling the tissue to sublethal temperatures to predict possible consequences (ie, AV block) of a prolonged abla-tion. Although safety of point-by-point cryoablation has been demonstrated in clinical studies, long-term efficacy in treating various supraventricular arrhythmias is thought to be reduced when compared with RFA. 5 Moreover, feasibility of creating extensive longitudinal lesions is hampered by slow conductive cooling of the tissue and heat-sink effect from surrounding high-flow vascular areas. Development of cryoballoon technology (with recently introduced more efficient second-generation balloons) has been a game-changer for atrial fibrillation ablation because it allows for rapid cooling of large areas in the left atrium (LA) and has proved to be an effective modality to create permanent lesions in a time-efficient manner. The first randomized, multicenter trial (Cryoballoon ablation of pulmonary veins for paroxysmal atrial fibrillation: first results of the North American Arctic Front [STOP AF] pivotal trial) confirmed the superior efficacy of cryoballoon ablation compared with antiarrhythmic drug treatment. 6 During the past decade, the worldwide experience with cryoballoon abla-tion has grown to >50 000 cases and multiple clinical studies reported an overall comparable efficacy to point-by-point RFA. Procedural time and complication rates with the cryo-balloon seem to be similar to RFA and a final determination of comparative efficacy and safety will await the results of a large European trial (FIRE AND ICE: Comparative Study of Two Ablation Procedures in Patients With Atrial …