The protective effect of
cardioplegia upon neonatal myocardium during
ischemia has not been clearly established. This study evaluated the effects of
cardioplegia on left ventricular function in isolated working neonatal rabbit hearts (aged 1 week) subjected to 120 minutes of global
ischemia at 28 degrees C. Four groups were studied: Group 1,
hypothermia alone; Group 2, intermittent washout with an oxygenated noncardioplegic
solution; Group 3, multidose
cardioplegia; Group 4, single-dose
cardioplegia. After
ischemia, cardiac output was reduced to 72% +/- 5% (mean +/- standard error of the mean) of control (p less than 0.02) in Group 1 and to 56% +/- 4% in Group 2 (p less than 0.001). In contrast, there was no significant reduction from baseline cardiac output in those animals receiving
cardioplegic solution (Group 3, 93% +/- 6%, and Group 4, 97% +/- 4%). Group 2 hearts demonstrated significantly worse recovery of cardiac output and stroke volume than all other groups. After
ischemia, the first derivative of left ventricular pressure fell to 73% +/- 13% of control in Group 1 (p less than 0.1) and to 89% +/- 5% in Group 2 (p less than 0.05). However, the first derivative of left ventricular pressure was restored to control values in Group 3 (118% +/- 11%) and Group 4 (114% +/- 9%). When compared to baseline,
creatine kinase was higher 30 minutes after reperfusion in Group 1 (40 +/- 8 versus 143 +/- 32 IU/L/gm, p less than 0.05) and in Group 2 (39 +/- 7 versus 163 +/- 33 IU/L/gm, p less than 0.05).
Creatine kinase remained unchanged from baseline in Groups 3 and 4. This study demonstrates excellent preservation of left ventricular function in the neonatal rabbit heart protected with
cardioplegic solution. In contrast, neither
hypothermia alone nor intermittent washout with an oxygenated noncardioplegic
solution was effective in preventing myocardial dysfunction. As in adults, the administration of
cardioplegic solution preserves ventricular function during
ischemia in neonatal hearts.