Despite
hypothermia, pediatric cardiac surgeons continue to experience difficulties in providing adequate myocardial protection in newborns. This study examines the effects of deep
hypothermia on neonatal heart tolerance to
ischemia by measuring metabolic responses and the time to onset of
ischemic contracture, or "stone heart." After control right ventricular biopsy specimens were obtained, hearts of newborn pigs (n = 36) were excised and placed in temperature-regulated
baths: 37.5 degrees +/- 0.5 degrees C (n = 9), 19.0 degrees +/- 0.5 degrees C (n = 14), and 12.0 degrees +/- 0.5 degrees C (n = 13). With a compliant balloon in the left ventricle to measure pressure, time to onset of
ischemic contracture (greater than 2-mm Hg rise) was recorded, and sequential biopsies were done. Data indicated
hypothermia significantly (p less than 0.001) prolonged time to onset of
ischemic contracture from 29.5 +/- 1.7 minutes (mean +/- standard error of the mean) at normothermia to 150.0 +/- 6.4 minutes at 19 degrees C and to 283.8 +/- 46.4 minutes at 12 degrees C.
Lactate buildup at 30 minutes of
ischemia was significantly reduced by 70% with
hypothermia. Decline in
adenosine triphosphate level was significantly reduced by 50% (19 degrees C) and 75% (12 degrees C) with
hypothermia. More importantly, a subgroup of hearts in each
hypothermia group (n = 5 per group) was identified by 38% to 48% lower
adenosine triphosphate stores before
ischemia compared with the group means.(ABSTRACT TRUNCATED AT 250 WORDS)