Physiologic observations of the heart six months after ischemic normothermic cardioplegia

The late effects of normothermic ischemic cardioplegia were studied in four experimental groups of dogs subjected to intervals of aortic cross-clamping during cardiopulmonary bypass. Groups which had zero, 20, 30, or 40 minutes of aortic cross-clamping, respectively, were studied 6 months later for cardiac performance and morphology. The immediate operative mortality rate of animals subjected to 40 minutes of ischemia was 65 percent, compared to 22 percent in controls. There were no late deaths in any group Compliance, histology, biochemical determination of deoxyribonucleic acid: ribonucleic acid, and Vmax determinations after cross-clamping revealed no differences between the experimental groups. Open chest isovolumetric contraction curves showed decreased experimental groups. Open chest isovolumetric contraction curves showed decreased function in the 40 minute ischemia group at the extreme levels of cardiac stress. These results suggest that under the conditions of this study normothermic cardiac ischemia of greater than 30 minutes in duration results in a high initial mortality rate (65 percent) and leads to compromise of cardiac function under stress in the late postoperative period.