Myocardial protection for neonates and infants.

This report reviews developmental differences between mature and immature myocardium. These differences, which are structural, biochemical, and functional, probably explain the differences which are observed between mature and immature myocardium with respect to resistance to ischemia. Although there are some clinical reports and also laboratory reports suggesting that immature myocardium ist more susceptible to ischemic 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 cardiac surgery though it per se is rarely a cause of death. Factors which exacerbate postoperative low cardiac output include mechanical factors such as distention and retraction, injury to coronary artery branches or direct injury to the myocardium with a ventriculostomy, as well as various perfusion and reperfusion factors such as pH. A recently completed prospective clinical trial at our hospital has revealed that cardiac output is consistently higher with pH stat relative to alpha stat. The ideal recipe for cardioplegia for immature myocardium remains poorly defined. The age at which the transition occurs to mature myocardium also remains to be defined in humans.