Optimal myocardial and reperfusate temperature in global ischemia induced in rats

Abstract

Topical cardiac hypothermia is widely accepted and affords a measure of protection of the myocardium in cardiac surgery. As the most suitable temperature for such a preservation remains controversial, we prepared an animal model to carry out related experiments. An isolated working rat heart preparation was used to compare the hearts divided into three groups according to different temperatures during ischemia and reperfusion. During ischemia, the hearts in groups A and C were preserved at 5°C and the hearts in group B at 15°C. After one hour of ischemia, the hearts in groups A and B were reperfused at 27°C and rewarmed gradually to 34°C. The hearts in group C were reperfused at 20°C and rewarmed to 34°C. Following 50 min of reperfusion, cardiac output recovery was significantly better in group C, compared to group A ( P < 0.02) and group B ( P < 0.001). The hearts in group B released a significant large amount of lactate compared with the hearts in group A ( P < 0.005) and group C ( P < 0.001). The total amount of creatine phosphokinase (CPK) release during reperfusion was 1.14 ± 0.27 in group A, 1.26 + 0.22 in group B, and 0.49 ± 0.09 IU/heart in group C, respectively. These data show that (1) cold exposure at 5°C has no deleterious effect on myocardial function, (2) myocardial preservation at 5°C has more beneficial effects on depressing the myocardial metabolism than at 15°C, and (3) additional myocardial protection was obtained by lowering the perfusate temperature at the early reperfusion period.