Experimental study of cryofreezing energy applications on the ventricular myocardium using sheep hearts

BACKGROUND: Cryofreezing energy has been utilized to abolish arrhythmogenic substrates of various kinds of tachyarrhythmias. However, systematic electrophysiological and histological investigations of cryothermia have never been performed. The aim of this study was to clarify those aspects using sheep beating hearts. METHODS: A total of eight adult sheep were utilized under total anesthesia, and a pericardial cradle was made by opening the pericardium. Eight epicardial plaque electrodes were sutured on the epicardial surface of the left ventricle 2∼3 cm apart from each other. A cryoprobe was inserted through a vent made in the left ventricular apex, and positioned so as to locate the probe tip at a site just opposite the center of the epicardial plaque electrodes. Ventricular electrograms and pacing threshold were measured during endocardial freezing. The volume of the necrotized lesion created by the cryofreezing was measured in the excised hearts after staining. RESULTS: The cryoprobe tip temperature was lowered to -50°C for 10 minutes. A significant increase in the pacing threshold and significant reduction in the ventricular electrograms were observed after endocardial freezing. The transmurality of the necrotized lesions varied depending on the situation of the cryoapplications, and the lesion depth and volume were significantly larger in the transmural lesions; however, there was no significant difference between the transmural and nontransmural lesions regarding the lesion width. CONCLUSIONS: Endocardial cryofreezing could provoke significant electrophysiological and injurious effects on the ventricular myocardium in the goat heart. Transmural cryolesions could be created when cryoprobe was appropriately applied.