Preservation of ATP, ultrastructure, and ventricular function after aortic cross-clamping and reperfusion: Clinical use of blood potassium cardioplegia

Abstract

Multidose blood cardioplegia (potassium 30 mEq/L, pH 7.4, normal calcium) in combination with profound myocardial hypothermia (<20° C) was studied in 24 patients undergoing cardiac operations during the period August to December, 1978. Serial myocardial biopsies were obtained to assess preservation of myocardial adenosine triphosphate (ATP) and ultrastructure during cross-clamping and after reperfusion. Cardiac output was measured serially before and after bypass. Several technical details were found to be of crucial importance: monitoring myocardial temperature and avoiding rewarming, topical hypothermia, volume and frequency of cold blood injection, and monitoring of injectate pressure. Patients could be divided into two groups: Group I (17 patients) had optimal myocardial protection with mullidose reinjections into the aortic root or coronary arteries every 20 to 30 minutes, maintenance of myocardial temperature below 20° C, and absence of electrocardiographic activity during cross-clamping. Seven patients (Group II) were noted to have inadequate myocardial preservation because of technical errors occurring during cross-clamping: failure to reinject the solution frequently, presence of electrocardiographic activity, and myocardial temperature above 28° C. Aortic occlusion time was not significantly different in the two groups (77 ± 8 SE minutes versus 91 ± 16 SE minutes, p > 0.05). Following unclamping and after 30 minutes of reperfusion, only mild changes were noted in the myocardial ultrastructure in Group I, whereas severe changes approaching irreversibility were noted in the mitochondria of Group II patients. Myocardial ATP levels in Group I patients were elevated both at the end of cross-clamping (↑54% ± 15%, p < 0.005) and following 30 minutes of reperfusion C↑8% ± 10%, p > 0.05). In contrast, ATP levels at similar intervals in Group 11 patients were markedly depressed (↓44% ± 9%, p < 0.005; ↓57% ± 11%, p < 0.005). Postoperative cardiac outputs were unchanged in Group I and significantly depressed in Group II (p < 0.02). These data indicate that, with proper technique, cold blood potassium cardioplegia combined with topical hypothermia is a superior method of myocardial protection.