The optimal flow rate during reperfusion after hypothermic ischemic arrest

This experiment was designed to determine the optimal flow rate during early reperfusion after ischemic arrest for one hour at 28 degrees C of myocardial temperature, assessed by cardiac function, biochemistry and fine structure of the left ventricle. Under cardiopulmonary bypass (CPB) at a flow rate of 80 ml/kg/min, the ascending aorta was clamped for one hour at 28 degrees C of myocardial temperature in 19 mongrel dogs. After the aorta was declamped, the perfusion pressure was maintained at 50 mmHg and dogs were divided into 3 groups by flow rate of 50 (Group A), 80 (Group B) and 150 ml/kg/min (Group C) for 15 min of reperfusion. The left ventricular function was measured and calculated before the institution of CPB and 30 and 60 min after the declamping of the aorta. Myocardial isoenzymes (m-GOT, MB-CPK) in the coronary sinus venous blood were measured. Myocardial adenosine triphosphate (ATP), creatine phosphate (CP) and water content were measured by the samples of the epicardial and endocardial layers of the left ventricle and the ventricular septum at the end of experiment. The subendocardium of the left ventricle was examined by electron microscopy. Mortality rates were 1/6 (16.7%) in Group A, 2/7 (28.6%) in Group B and 4/6 (66.7%) in Group C. The myocardial water content was the lowest, and ATP was significantly higher in Group A compared to others. Left ventricular endodiastolic pressure was the lowest and the ultrastructure was well maintained in Group A. These data suggest that a high flow rate is detrimental to myocardial recovery during early reperfusion, and the optimal flow rate during early reperfusion after ischemic arrest (60 min, 28 degrees C) appears to be 50 ml/kg/min.