Myocardial protection in normal and hypoxically stressed neonatal hearts: the superiority of blood versus crystalloid cardioplegia

OBJECTIVES: Blood cardioplegia predominates in the adult because it provides superior myocardial protection, especially in the ischemically stressed heart. However, the superiority of blood over crystalloid cardioplegia in the pediatric population is unproved. Furthermore, because many pediatric hearts undergo a preoperative stress such as hypoxia, it is important to compare the different methods of protection in both normal and hypoxic hearts. METHODS: Twenty neonatal piglets were supported by cardiopulmonary bypass and subjected to 70 minutes of cardioplegic arrest. Of 10 nonhypoxic hearts, five (group 1) were protected with blood cardioplegia and five (group 2) with crystalloid cardioplegia (St. Thomas' Hospital solution). Ten other piglets underwent 60 minutes of ventilator hypoxia (inspired oxygen concentration 8% to 10%) before cardioplegic arrest. Five (group 3) were then protected with blood cardioplegia and the other five (group 4) with crystalloid cardioplegia. Myocardial function was assessed by means of pressure volume loops and expressed as a percentage of control. Coronary vascular resistance was measured with each infusion of cardioplegic solution. RESULTS: No difference was noted between blood (group 1) or crystalloid cardioplegia (group 2) in nonhypoxic hearts regarding systolic function (end-systolic elastance 104% vs 103%), diastolic stiffness (156% vs 159%), preload recruitable stroke work (102% vs 101%), or myocardial tissue edema (78.9% vs 78.9%). Conversely, in hearts subjected to a hypoxic stress, blood cardioplegia (group 3) provided better protection than crystalloid cardioplegia (group 4) by preserving systolic function (end-systolic elastance 106% vs 40%; p < 0.05) and preload recruitable stroke work (103% vs 40%; p < 0.05); reducing diastolic stiffness (153% vs 240%; p < 0.05) and myocardial tissue edema (79.6% vs 80.1%); and preserving vascular function, as evidenced by unaltered coronary vascular resistance (p < 0.05). CONCLUSION: This study demonstrates that (1) blood or crystalloid cardioplegia is cardioprotective in hearts not compromised by preoperative hypoxia and (2) blood cardioplegia is superior to crystalloid cardioplegia in hearts subjected to the preoperative stress of acute hypoxia.