Relative vulnerability of neonatal and adult hearts to ischemic injury

To clarify the controversy over whether the neonatal heart is more or less susceptible to global ischemia than the adult heart, the time interval between the onset of ischemia and the beginning of contracture (TIC) was compared in neonatal (n = 6, 3 to 5 days old) and adult (n = 6, 4 to 5 months old) pig hearts. A comparison of the myocardial concentrations (mumol/g wet weight) of ATP, glycogen, lactate, and glucose-6-phosphate (G-6-P) was also done. The anesthetized animals underwent a sternotomy, and control right ventricular myocardial biopsy samples were taken. The heart of each was rapidly excised and placed in a 37 degrees C substrate-free Krebs-Henseleit bath. A compliant balloon was placed in the left ventricle to record pressure changes. Time to onset and peak TIC were recorded and additional proximal right ventricular biopsy samples were taken. Data were recorded as mean +/- SEM. Results demonstrated that neonatal hearts had a significantly shorter (p less than .05) TIC (29.5 +/- 1.7 min) than adult hearts (43.0 +/- 2.9 min) and exhibited more rapid lactate accumulation (2.5 +/- 0.5 to 22.1 +/- 3.0, p less than .001) and an increase in G-6-P (0.07 +/- 0.03 to 0.34 +/- 0.07, p less than .01) with a nonsignificant decline in myocardial glycogen (23.3 +/- 12.1 to 17.4 +/- 4.0, p greater than .05). Our findings indicate that neonatal hearts are more sensitive than adult hearts to global ischemia, which has potential implications for myocardial protection in pediatric cardiac surgery.