Advantages of intermittent blood cardioplegia over intermittent ischemia during prolonged hypothermic aortic clamping.

Ten dogs underwent 2 hours of hypothermic (22 degrees C) aortic clamping. Arrest was produced by ischemia in five dogs, with 150 ml of 22 degrees C unmodified blood reperfused every 20 minutes. Five others underwent cardioplegic arrest (500 cc pH 7.8 blood containing 30 mEq/L KCl, 0.6 mEq/L Ca++) with 150 ml of blood cardioplegia solution replenished each 20 minutes. Seven additional dogs underwent 4 hours of continuous coronary perfusion without ischemia. Continuous coronary perfusion did not change myocardial ATP or water content, but reduced left ventricular contractility (maximum positive dP/dt, peak systolic pressure) 16% (P < 0.05) and decreased left ventricular compliance moderately (50%). Hypothermic ischemic arrest reduced myocardial ATP 39% (P < 0.05), raised myocardial water 3.2% (P < 0.05), reduced compliance 83% (P < 0.05), and depressed left ventricular performance 64% (P < 0.05), despite intermittent reinfusion of unmodified blood each 20 minutes. In contrast, blood cardioplegia reduced postischemic left ventricular compliance only slightly 17%, P < 0.05) and resulted in normal postischemic ATP, water, and contractility.