Adverse effect of prearrest hypothermia in immature hearts: rate versus duration of cooling

It has been suggested that rapid cooling before the induction of arrest may be harmful to the newborn myocardium. The objective of this study was twofold: (1) to evaluate whether prearrest rapid cooling is indeed detrimental to myocardial recovery and (2) if so, to evaluate whether the adverse effect of prearrest hypothermia is dependent on the rate of cooling or the total duration of cold perfusion. After an initial stabilization period isolated Langendorff hearts (n = 5 per group) from neonatal piglets (5 to 7 days old) were randomized to four groups: group 1, 5 minutes of rapid cooling to 15 degrees C; group 2, 20 minutes of slow cooling to 15 degrees C; group 3 and group 4, rapid and slow cooling, respectively, with the addition of St. Thomas cardioplegic solution. All groups were then subjected to 2 hours of ischemia at 15 degrees C followed by 30 minutes of reperfusion at 38.5 degrees C. Post-ischemic recovery of left ventricular developed pressure was significantly greater in group 1 versus group 2 (80% +/- 3% versus 61% +/- 2%; p less than 0.05) and in the presence of cardioplegia, group 3 versus group 4 (72% +/- 3% versus 57% +/- 3%; p less than 0.05). The increase in left ventricular end-diastolic pressure was significantly less in group 1 versus group 2 (8% +/- 5% versus 33% +/- 7%; p less than 0.01). Myocardial adenosine triphosphate content recovery correlated with ventricular recovery.(ABSTRACT TRUNCATED AT 250 WORDS)