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 pr ovides superior myocardial protection, especially in the ischemically stressed heart, However, the superiority of blood over crystalloid car dioplegia in the pediatric population is unproved, Furthermore, becaus e many pediatric hearts undergo a preoperative stress such as hypoxia, it is important to compare the different methods of protection in bot h normal and hypoxic hearts, Methods: Twenty neonatal piglets were sup ported by cardiopulmonary bypass and subjected to 70 minutes of cardio plegic arrest. Of 10 nonhypoxic hearts, five (group 1) were protected with blood cardioplegia and five (group 2) with crystalloid cardiopleg ia (St, Thomas' Hospital solution), Ten other piglets underwent 60 min utes of ventilator hypoxia (inspired oxygen concentration 8% to 10%) b efore cardioplegic arrest, Five (group 3) were then protected with blo od cardioplegia and the other five (group 4) with crystalloid cardiopl egia. Myocardial function was assessed by means of pressure volume loo ps and expressed as a percentage of control, Coronary vascular resista nce was measured with each infusion of cardioplegic solution, Results: No difference waas noted between blood (group 1) or crystalloid cardi oplegia (group 2) in nonhypoxic hearts regarding systolic function (en d-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 c rystalloid cardioplegia (group 4) by preserving systolic function (end -systolic elastance 106% vs 40%; p < 0.05) and preload recruitable str oke work (103% vs 10%; p < 0.05); reducing diastolic stiffness (153% v s 240%; p < 0.05) and myocardial tissue edema (79.6% vs 80.1%); and pr eserving vascular function, as evidenced by unaltered coronary vascula r resistance (p < 0.05), Conclusion: This study demonstrates that (1) blood or crystalloid cardioplegia is cardioprotective in hearts not co mpromised by preoperative hypoxia and (2) blood cardioplegia is superi or to crystalloid cardioplegia in hearts subjected to the preoperative stress of acute hypoxia.