Cardioplegia for the immature myocardium. A comparative study in the neonatal rabbit.

This study examined the effect of hypothermia (15 degrees C) alone or combined with various cardioplegic solutions on functional recovery of the neonatal heart after 120 minutes of global ischemia in an isolated working rabbit heart model. Control hearts were preserved with hypothermia alone, and groups 1 to 6 were given different hyperkalemic crystalloid cardioplegic solutions. Each cardioplegic solution differed in Na+ and Ca++ content. Aortic flow, coronary flow, cardiac output, heart rate, peak systolic pressure, and stroke work were measured before ischemia and after 35 and 45 minutes of reperfusion. There were no statistical differences in hemodynamic recovery in the six groups in which cardioplegia was used. However, hearts preserved with multidose hyperkalemic cardioplegia showed significantly better recovery of cardiac output (86% versus 75%; p less than 0.05), coronary flow (88% versus 72%; p less than 0.05), and stroke work (86% versus 75%; p less than 0.05) than those preserved with hypothermia alone. These results suggest that hypothermic hyperkalemic cardioplegia improves preservation of the neonatal rabbit heart but that variations in Ca++ and Na+ content appear not to provide further myocardial protection.