Myocardial preservation in the neonate. Beneficial effects of cardioplegia and systemic hypothermia on piglets undergoing cardiopulmonary bypass and myocardial ischemia.

This study examined anatomic differences between the adult and the newborn heart as they relate to myocardial preservation and compared standard techniques of myocardial preservation used in operations for congenital heart disease. The biventricular endocardial surface area/ventricular mass ratios were calculated in 10 neonatal (2.5 +/- 0.2:1) and 10 adult (0.6 +/- 0.1:1) pigs (p less than 0.001). Three groups of neonatal pigs underwent 1 hour of global myocardial ischemia while being supported by cardiopulmonary bypass. Myocardial protection was by deep systemic hypothermia (group 1), moderate systemic hypothermia and cardioplegia (group 2), or by deep systemic hypothermia and cardioplegia (group 3). Left ventricular end-systolic pressure-dimension and end-diastolic pressure-dimension relationships were measured before and after cardiopulmonary bypass. Septal temperatures remained below 20 degrees C in groups 1 and 3 but rose above 20 degrees C in group 2. Groups 1 and 2 had moderate and mild ventricular stiffening, respectively, whereas group 3 showed no diastolic dysfunction. Ventricular contractility was increased (p less than 0.05) in group 3. Techniques for myocardial preservation used during operations for congenital heart disease must consider the large endocardial surface area/mass ratio and the rewarming effects of systemic blood. The combination of deep systemic hypothermia and cardioplegia provided superior myocardial protection compared with the other techniques tested.