Does warm antegrade intermittent blood cardioplegia really protect the heart during coronary surgery?

Objective: Intermittent antegrade blood cardioplegia (IABC) has been standardized as a routine technique for myocardial protection in coronary surgery. However, if the myocardium is known to tolerate short periods of ischemia during hypothermic arrest, it may be less tolerant of warm ischemia, so the optimal cardioplegic temperature of intermittent antegrade blood cardioplegia is still controversial. The aim of this study was to compare the effects of warm intermittent antegrade blood cardioplegia and cold intermittent antegrade blood cardioplegia on myocardial pH and different parameters of the myocardial metabolism. Methods: Thirty patients undergoing first-time isolated coronary surgery were randomly allocated into two groups: group 1 (15 patients) received warm (37°C) intermittent antegrade blood cardioplegia and group 2 (15 patients) received cold (4°C) intermittent antegrade blood cardioplegia. The two randomization groups had similar demographic and angiographic characteristics. Total duration of cardiopulmonary bypass (108±17 and 98±21 min) and of aortic cross-clamping (70±13 and 65±15 min) were similar. The cardioplegic solutions were prepared by mixing blood with potassium and infused at a flow rate of 250 ml/min for a concentration of 20 mEq/l during 2 min after each anastomosis or after 15 min of ischemia. Intramyocardial pH was continuously measured during cardioplegic arrest by a miniature glass electrode and values were corrected by temperature. Myocardial metabolism was assessed before aortic clamping ( pre-XCL), 1 min after removal of the clamp ( XCL off) and 15 min after reperfusion (Rep) by collecting coronary sinus blood samples. All samples were analyzed for lactate, creatine kinase (MB fraction), myoglobin and troponin I. Creatine kinase and troponin I were also daily evaluated in peripheral blood during 6 days post-operatively. Results: The clinical outcomes and the haemodynamic parameters between the two groups were identical. In group 1, XCL off and Rep were associated with higher coronary sinus release of lactate (5.5±1.8 and 2.2±0.5 mmol/l) than in group 2 (2.0±0.7 and 1.6±0.3 mmol/l, P