The metabolic consequences of blood and crystalloid cardioplegia

Twenty-seven patients undergoing elective coronary revascularization were evaluated by the following metabolic studies: coronary blood flow and vascular resistance, myocardial oxygen consumption and extraction, and lactate and potassium extraction, uptake and release. Patients were divided into two groups, 14 having crystalloid potassium (25 mEq/l) and 13 blood potassium (25 mEq/l) cardioplegic arrest. The groups were comparable in terms of preoperative demographic characteristics and the duration of cardioplegic arrest, which averaged 63.8 minutes in the crystalloid group and 65.6 minutes in the blood group. There were obvious differences in the effects of the two cardioplegic solutions during administration. Crystalloid cardioplegia had a significantly higher infusion rate and, accordingly, a lower vascular resistance, whereas blood cardioplegia provided increased oxygen use during administration. The amount of lactate released during cardioplegic infusion was greater in the crystalloid than in the blood group, while the amount of potassium absorbed by the heart was greater with blood. During reperfusion, coronary blood flow, vascular resistance and myocardial oxygen consumption were not significantly different in the two groups. The myocardial oxygen extraction, as manifested by a narrowed arteriovenous oxygen difference, was decreased compared with control in both groups during early reperfusion, and the extraction curves for both groups returned to control values by 20 minutes. Myocardial lactate release occurred in both groups during early reperfusion and there was no significant distinction between the two groups. Potassium release occurred during reperfusion in both groups, but significantly more potassium was released in the blood group than in the crystalloid group. We conclude that both methods of myocardial preservation provide adequate protection for 1 hour of ischemic arrest and nearly equal depression in oxygen use. Crystalloid cardioplegia allows greater lactate production during the arrest interval, whereas blood allows a greater potassium absorption by the heart during arrest but releases more potassium during reperfusion.