Is protection of ischemic neonatal myocardium by cardioplegia species-dependent?

Abstract

Hypothermia combined with pharmacologic cardioplegia protects the globally ischemic adult heart, but this benefit may not extend to children, resulting in poor postischemic recovery of function and increased mortality. The relative susceptibilities to ischemia modified by hypothermia alone and by hypothermia plus cardioplegia were assessed in isolated perfused neonatal (3- to 4-day-old) rabbit and pig hearts. Hearts were perfused aerobically with Krebs buffer solution in the working mode for 30 minutes and aortic flow was recorded. This was followed by 3 minutes of hypothermic (14° C) coronary perfusion with either Krebs or St. Thomas’ Hospital cardioplegic solution No. 2 followed by hypothermic (14° C) global ischemia (rabbits 2, 4, and 6 hours; pigs 2 and 4 hours). Hearts were reperfused for 15 minutes in the Langendorff mode and 30 minutes in the working mode, and recovery of postischemic aortic flow was measured. Hypothermia alone provided excellent protection of the ischemic neonatal rabbit heart, with recovery of aortic flow after 2 and 4 hours of ischemia at 91% ±4% and 87% ±5% (mean ± standard deviation) of its preischemic value. Recovery after 6 hours of ischemia was depressed to 58% ±9% of its preischemic value. Ischemic neonatal pig hearts protected with hypothermia alone recovered 94% ±3% of preischemic aortic flow after 2 hours; none was able to generate flow after 4 hours. St. Thomas’ Hospital solution No. 2 decreased postischemic aortic flow after 4 hours of ischemia in rabbit hearts from 87% ±5% to 70% ±7% (p