Nonarrhythmogenicity of therapeutic cryothermic lesions of the myocardium

There is increasing interest in the application of surgical methods to the treatment of refractory ventricular tachyarrhythmias (VT). Cryothermic ablation is one of the more promising techniques. However, there is clinical concern that a cryothermic lesion may lead to later arrhythmias. Previous studies have shown that dogs with nonhomogeneous, transmural infarctions are susceptible to VT initiation using programmed electrical stimulation (PES). The purpose of this study was to compare the incidence of inducing VT in dogs with transepicardial cryothermic myocardial damage (Group A) versus dogs with nonhomogeneous transmural infarctions resulting from 2-hr occlusion of the left anterior descending coronary artery (LAD) and subsequent reperfusion (Group B). Twelve dogs in each group were studied 10-14 days later using PES with unipolar cathodal ventricular pacing and two ventricular extrastimuli. Initiation of VT was attempted from at least six normal intramyocardial sites in each dog along the distribution of the LAD and in close proximity (less than or equal to 1 cm) to areas of chronically cryoablated damaged tissue. All dogs survived the initial procedure. VT was not inducible in any dog in Group A. Histological as well as electrophysiological evaluation, including determination of regional excitability thresholds and refractory periods employing strength-interval curves, revealed that all of the Group A dogs had homogeneous transmural infarcts with variable subendocardial sparing. In conclusion (1) cryothermal injury produces homogeneous damage; and (2) the lesion produced is not arrhythmogenic at 7-14 days.