Myocardial metabolism and efficiency after warm continuous blood cardioplegia

Background. Warm continuous blood cardioplegia (WCBCP) has been recommended during prolonged cardiac arrest to minimize functional deterioration. Myocardial metabolism and efficiency after this cardioplegic modality are not well described. Methods. Substrate oxidation, blood now, and myocardial function were measured before, during, and after 3 hours of WCBCP in 7 pigs. Results. Free fatty acid and glucose oxidation decreased by 60% +/- 3.8% and 94% +/- 1.2%, respectively, during cardioplegia (both p < 0.05) and increased to 62% +/- 28% and 122% +/- 62% of baseline during the early recovery phase (p < 0.05 for glucose). One hour after WCBCP oxidation rates were similar to baseline. The transient postcardioplegic increase in substrate oxidation was associated with a 43% +/- 23% elevation of oxygen consumption (MVO2) compared with baseline and a 62% +/- 18% increase in myocardial blood flow. Cardiac output and mean arterial pressure did not change significantly after WCBCP, although myocardial function (stroke work, left ventricular end-systolic pressure, end-diastolic pressure, contractility, and efficiency) was depressed (p < 0.05). End-diastolic pressure and contractility improved from early to late phase of recovery, whereas the other indicators of ventricular function remained depressed. Conclusions. Myocardial substrate oxidation was preserved after 3 hours of WCBCP, although ventricular function was moderately impaired. Thus, WCBCP with a seemingly normal substrate and oxygen supply was associated with a reduced cardiac efficiency. (C) 2000 by The Society of Thoracic Surgeons.