Longterm effects of cryosurgery in the sheep heart.

This study concerns the longterm effects of both epicardial and endocardial cryosurgery with particular reference to the coronary arteries. Sheep were subjected to epicardial cryosurgery without cardiopulmonary bypass, and to endocardial application with bypass. In both groups the heart was kept beating throughout the operation. Neither cardioplegia nor aortic cross-clamping was used. In the first group applications were made for 5 min directly over or adjacent to a major branch of the left coronary artery. In the second, the cryoprobe was applied for 5 min or until atrioventricular dissociation occurred. No sheep developed late arrhythmias or evidence of myocardial ischaemia. Only minimal arterial changes were observed and all the major coronary arteries remained widely patent. Cryothermia to the heart produced a small discrete lesion without complication. Bright fluorescence of necrotic myocytes was observed in all the immature lesions when sections stained with haematoxylin and eosin were examined under ultraviolet light. This vivid fluorescence clearly delineated the extent of the lesions and persisted while cytoplasmic elements remained. Our results indicate that cryosurgery provides a safe and permanent technique for the surgical treatment of arrhythmias in man, and may safely be used even in proximity to the coronary arteries. Cardioplegia is contraindicated.