Myocardial protection in cyanotic neonatal lambs

To investigate the susceptibility of cyanotic neonatal myocardium to ischemia and the effectiveness of cardioplegia for protection, we induced cyanosis in 2- to 5-day-old lambs (n = 16) by connecting the left atrial appendage to the main pulmonary artery with a 4 mm polytetrafluoroethylene graft, which produced an arterial oxygen tension of 34.1 +/- 1.2 torr. Seven to 10 days after creation of the model, isolated perfused hearts from cyanotic animals were subjected to 2 hours of ischemia with topical cooling or crystalloid cardioplegia (K = 30 mEq/L) for myocardial protection (both at 15 degrees C). Identical studies were performed on hearts from 16 normoxemic neonatal lambs 5 to 14 days old. The overall effect of cyanosis was to produce a significant impairment in recovery of maximum developed pressure (p less than 0.05) after ischemia. The overall effect of cardioplegia was to produce a significant improvement in recovery of maximum developed pressure, developed pressure at V10 (the balloon volume to produce an end-diastolic pressure of 10 mm Hg during the preischemic period), and peak rate of pressure rise at V10 (p less than 0.05). The protective effect of cardioplegia was more prominent in cyanotic hearts than in normoxemic hearts for recovery of maximum of peak rate of pressure rise and peak rate of pressure rise at V10 (p less than 0.05). End-diastolic pressure at V10 and the diastolic stiffness constant at 10 and 20 mm Hg were all significantly higher after ischemia in the cyanotic hearts than in the normoxemic hearts (p less than 0.05). We conclude that in neonatal hearts cyanosis may increase the vulnerability to ischemia and cardioplegia appears to enhance the recovery of systolic but not diastolic function in these hearts.