FUNCTIONAL, METABOLIC AND ULTRASTRUCTURE EVIDENCE FOR IMPROVED MYOCARDIAL PROTECTION DURING SEVERE ISCHEMIC STRESS WITH MBS, A NEW CRYSTALLOID CARDIOPLEGIC SOLUTION

The duration of aortic clamping and the temperature of the arrested he art are two important factors in the overall strategy of myocardial pr otection with cardioplegic solutions. The isolated working rat heart w as used to compare the cardioprotection effects (function, metabolism and ultrastructure) of the new ''extracellular'' crystalloid solution, MBS (containing glucose, aspartate and lactobionate) and St. Thomas' Hospital No. 2 (STH) during prolonged moderate hypothermic ischaemia ( 30 degrees C, 2 hours and 4 hours) with multidose reinfusion (2 min ev ery 30 min interval). All MBS treated hearts (n=9 per group) rapidly r esumed spontaneous regular sinus rhythm (0.8+/-0.2 min) and had simila r high degree of functional recovery (cardiac output: 90.2+/-4.5% & 80 .9+/-3.5%, stroke volume: 89.1+/-4.7% & 81.9+/-3.4% and aortic pressur e: 102.0+/-4.0% & 100.0+/-7.3% of pre-arrest values for 2 hours and 4 hours groups, respectively) during 30 min post-ischaemic reperfusion. In contrast, hearts protected with STH showed significantly (p<0.01) l ess recovery of left ventricular function (cardiac output: 64.3+/-2.9% & 5.5+/-3.9%, respectively) with two of the nine hearts failing to re gain any cardiac pump function after 4 hours. MBS increased lactate ef flux (glycolysis) and completely abolished the progressive increase in the coronary vascular resistance during 4 hours ischaemic arrest. The se improvements were directly related to the significantly (p<0.01) re duced depletion of the myocardial adenosine triphosphate (13.32+/-1.65 vs 2.42+/-0.09 mu mol/g dry wt) and guanosine triphosphate (1.56+/-0. 08 vs 0.74+/-0.04 mu mol/g dry wt) during arrest; to their enhanced re pletion after reperfusion (ATP: 96% vs 36%, TAN: 90% vs 40% and GTP: 6 9% vs 48%); and to the absence of ultrastructural injury to cardiac my ocytes and the microvasculature. We conclude that the new crystalloid cardioplegic solution MBS provides markedly improved myocardial protec tion particularly during severe ischaemic stress.