Evaluation of myocardial protection by cardioplegic solutions and hipothermia in anoxic hearts. An experimental study. This investigation was performed in a group of 20 dogs submitted to myocardial anoxia by cross-clamping of the ascending aorta for sixty minutes under extracorporeal circulation, followed by reperfusion for 360 minutes. Ultrastructural changes of the myocardium were studied. The animals were divided into 4 groups of 5 dogs each. In the first group (control), myocardial anoxia was induced in normothermia and no cardioplegic solution was administered. In the second group, the body temperature was reduced to 28ºC before the onset of myocardial anoxia, and no cardioplegic solution was used. In the third and fourth groups, in addition to 28ºC systemic hypothermia, coronary infusion of 4ºC cardioplegic solutions were performed immediately and after 30 minutes of clamping of the aorta. The cardioplegic solutions utilized have NaCl, KCl, CaCl2, Lidocaine, Verapamil, NaHCO3, MgSO4 and the infusion vehicle was 5% glucose solution in Group III, and blood in Group IV. Biopsies for freeze-fracture replication were obtained from the anterior wall of the left ventricle, before and after 60 minutes of myocardial anoxia, and 360 minutes after reperfusion. The alterations in sarcolemma and celular organeles due to anoxia or myocardial reperfusion was observed, specially through the diminution and aggregation of intramembranous particles in its P surface. We may conclude that both cardioplegic solutions used, associated to hipothermia, protect efficiently the myocardial cells against anoxia. It was not possible, however, to demonstrate any superiority of the blood solution over an acellular solution. Systemic hypothermia as a single method was not sufficient to offer good protection to the anoxic myocardium. The animals of Group I (control) showed severe compromise of the structure and function of the myocardium.
myocardial protection; myocardial protection