Ultrastructural and biochemical changes of human papillary heart muscle during different methods of induced cardiac arrest.

To determine the protective effects of different methods of cardioplegia, studies on ATP/lactate levels and ultrastructure were performed in human papillary muscles obtained during mitral valve replacement. In group I (n = 5), plain ischemic arrest in hypothermia (systemic venous temperature = 24 degrees C) was accomplished. In group II (n =12), the heart was arrested by injection cardioplegia using magnesium-aspartate-procaine at systemic venous and myocardial temperatures of 24 degrees C. In group III (n = 12) Bretschneider infusion cardioplegia at systemic venous and myocardial temperatures of 26 degrees C and 19 degrees C respectively was applied. With regard to ultrastructural changes there were no clearcut differences in the three methods of hypothermic cardiac arrest after 60 minutes of ischemia. Ischemic changes tended to be slightest in group III (infusion cardioplegia). ATP decay and lactate increase were significant in group I and moderate to minimal in groups II and III after the same period of time. It is concluded that for aortic cross-clamp times up to 60 minutes, body hypothermia and injection cardioplegia using magnesium-aspartate-procaine at a myocardial temperature of 24 degrees C provide adequate protection of the myocardium. For ischemia times beyond 70 minutes, profound myocardial hypothermia below 20 degrees C is preferred.