Efficiency of cardioplegia in the presence of coronary occlusion

Myocardial tissue pH and temperatures (MT) were continuously measured in dogs on total cardio-pulmonary bypass (CPB) after acute distal coronary artery occlusion. Measurements were performed in a collateralized area with myocardial blood flow (MBF) ranging from 20 to 80 ml/100 g-min (microspheres). Immediately after coronary artery occlusion the aorta was clamped and the heart perfused with a cardioplegic solution (Bretschneider HP, 41 ml/kg, 4 degrees C). Prolonged regional fibrillation was observed and MT fell to 20 degrees C in 10 min in the low perfusion area (LPA) and in 2 min in the control area (CA). Whereas MTs were practically identical 15 min after termination of cardioplegic perfusion the magnitude of H+ accumulation continued to be greater in the LPA. During blood reperfusion with the coronary snare released MBF was significantly lower in the LPA as opposed to the CA indicating a microcirculatory derangement. Accordingly the bipolar ECG revealed signs of regional ischemia even after 30 min of reperfusion. We conclude that myocardial protection may be inadequate in areas located distal to coronary occlusion. This is true not only in cases of acute severe ischemia but also when collateral resistance is sufficiently high to impede the flow of cold viscous cardioplegic solutions. Results derived from intermittent MT measurements may be erroneous because intramyocardial heat equilibration may mask the inhomogeneous cardioplegic perfusion.