Detrimental effects of multidose hypothermic cardioplegia in the neonatal heart: the role of the frequency of cardioplegic infusions.

In the neonatal rabbit heart, multidose crystalloid cardioplegia is protective against normothermic ischemia, but its beneficial effects are lost under hypothermia. In order to determine the relationship between myocardial protection and the number of cardioplegic infusions administered during the ischemic period, we examined the effects of an increasing number of infusions on postischemic recovery at three temperatures (37 degrees, 20 degrees, or 10 degrees C). Isolated working hearts from rabbits aged 7-10 days were perfused aerobically (37 degrees C) for 20 min before infusion of St. Thomas' Hospital cardioplegic solution at the selected temperature. At each temperature, the cardioplegic solution was given either as a single 2-min infusion (single-dose) or as repeated 2-min infusions (multidose) at various intervals. Following the ischemic period, hearts were reperfused (15 min Langendorff, 20 min working) before assessment of the recovery of function. Ischemic durations (selected to result in approximately 55%-70% recovery in the single-dose group at each temperature) were 1, 10, or 18 h at 37 degrees, 20 degrees, and 10 degrees C. At 37 degrees C, there was a positive correlation between postischemic recovery and the number of infusions during the ischemic period. However, at 20 degrees or 10 degrees C the relationship was reversed and recovery was depressed with increasing number of infusions.(ABSTRACT TRUNCATED AT 250 WORDS)