Uniform myocardial protection by cold potassium-induced cardioplegia for coronary artery bypass.

Cold potassium solution (4 C) is used to induce cardioplegia during coronary artery bypass surgery. When 1,000 ml of the cold solution are introduced through the root of the aorta, the temperature of the myocardium drops to about 7 C within a few minutes. At this level of hypothermia, ischemia can be tolerated for at least 2 h, the surgical field is rendered quiet and dry, and the safety and precision of the procedure are increased. This method, however, does not provide uniform cooling of the myocardium and some areas remain less protected than others. The temperatures in the different areas of the myocardium are measured directly with needle thermistors and the "warm" areas are cooled in turn, in descending order of myocardial temperature. Saphenous vein grafts are anastomosed to the arteries in these warm areas and additional cold solution is instilled through the graft until the temperature drops to 7 C. The coronary artery bypass, and any other required surgical procedure, is then performed. To maintain hypothermia, small amounts of cold solution are infused at intervals through the root of the aorta and through the appropriate graft. With this method of cooling, the operative mortality rate in a series of 200 high-risk patients with coronary artery disease in whom there was at least one factor predisposing to perioperative mortality and/or infarction was only 3%.