MYOCARDIAL PROTECTION FOR NEONATES AND INFANTS

This report reviews developmental differences between mature and immat ure myocardium. These differences, which are structural, biochemical, and functional, probably explain the differences which are observed be tween mature and immature myocardium with respect to resistance to isc hemia. Although there are some clinical reports and also laboratory re ports suggesting that immature myocardium ist more susceptible to isch emic injury than mature myocardium, it is our impression at Children's Hospital, Boston, that immature myocardium is in fact more resistant to ischemia. A decrease in cardiac output is frequently seen after car diac surgery though it per se is rarely a cause of death. Factors whic h exacerbate postoperative low cardiac output include mechanical facto rs such as distention and retraction, injury to coronary artery branch es or direct injury to the myocardium with a ventriculostomy, as well as various perfusion and reperfusion factors such as pH. A recently co mpleted prospective clinical trial at our hospital has revealed that c ardiac output is consistently higher with pH stat relative to alpha st at. The ideal recipe for cardioplegia for immature myocardium remains poorly defined. The age at which the transition occurs to mature myoca rdium also remains to be defined in humans.