Effect of hypothermic anoxic cardioplegia on myocardial contractility

A study was undertaken to ascertain the protective effect of topical hypothermia on the anoxic heart. The presence or absence of myocardial damage was judged by myocardial contractility. The papillary muscle of an excised rabbit heart was detached from the mitral annulus and interposed between a fixed point and a force/displacement transducer. The maximal net developed tension (TNmax) of the papillary muscle with normothermic coronary perfusion was used as an index of myocardial contractility. With each temperature drop of 10 degrees C, the anoxia time that resulted in the same recovery level of TNmax was prolonged by a factor of 2.8. A nomogram was constructed correlating percent of myocardial recovery seen with different degrees of myocardial hypothermia during various anoxic periods. Optimum protection was noted at a myocardial temperature of 18 degrees C.