The relationship between myocardial temperature and recovery after experimental cardioplegic arrest.

The aim of this study was to determine the temperature for optimal myocardial preservation during cardioplegic arrest. In isolated canine hearts perfused by a support dog, functional and metabolic recovery was measured after cardioplegic arrest using the St. Thomas' Hospital solution. The temperature range, -2 degrees to 37 degrees C, was studied using a 2 hour arrest period. A 6 hour arrest period was used to enhance differences in the range 4 degrees to 20 degrees C. Cooling to -2 degrees C produced severe mitochondrial damage seen on electron microscopy and zero recovery of function. Reperfusion after 2 hours of arrest at 4 degrees or 15 degrees C was followed by complete functional and metabolic recovery. As the temperature during arrest was raised above 20 degrees C, recovery decreased markedly, culminating in ischemic contracture at 37 degrees C. The severe stress of 6 hours of arrest revealed further increases in protection conferred by stepwise cooling to 4 degrees C. In diseased hearts, long periods of ischemia are less well tolerated than in the normal hearts used in this study. Therefore, the additional protection conferred by cooling to 4 degrees C is of clinical importance. The conclusion is that during cardioplegic arrest, provided freezing is avoided, the lower the myocardial temperature, the better is the protection against ischemia.