Patterns of myocardial metabolism during cardiopulmonary bypass and coronary perfusion

There is widespread uncertainty about methods of coronary perfusion during prosthetic replacement of the aortic valve with cardiopulmonary bypass. These methods range from no perfusion at all (with periods of ischemia ranging from 30 to 60 min or longer, with or without hypothermia) to intermittent or continuous perfusion of one or both coronary arteries. Coronary perfusion may be from branch lines from the arterial perfusion circuit or through separate cannulas and separate pumps. There is similar widespread variation in reported operative mortality rates, ranging from less than 5% to between 10 and 15%. In this investigation several indices of myocardial metabolism were measured while techniques of perfusion were varied. Variables included intermittent versus continuous perfusion, perfusion at different flow rates, and a comparison of fibrillating and nonfibrillating hearts during bypass. To obtain a reliable measurement of changes in myocardial metabolism with operation, measurements were performed not only during bypass but for 72 hr afterward.