The Neonatal Heart: Developmental Differences, Response to Ischemia, and Protection during Cardiopulmonary Bypass

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Abstract
(J. Extra-Corpor. Tech. 18[4] p. 208–218 Winter 1986) Accompanying the advent of open heart surgery was the need to better understand the relationship between ischemic damage and cell viability. Corrective cardiac surgical procedures necessitate a flacid, bloodless field to provide the surgeon optimal exposure. This interruption of blood flow, however, has many deleterious effects. A non-homogeneous cascade of events is produced that, if allowed to proceed unchecked, will ultimately lead to cell death. The time period of interrupted flow to the myocardium is referred to as ischemia, and results in certain cellular perturbations that are dependent on both temporal and temperature related factors. The effects of ischemia have been studied extensively, both clinically and in the laboratory, utilizing various techniques that almost exclusively employ the adult myocardium as a model. The resultant information has been broadly applied in formulating methods of myocardial protection across all ages. Cardiovascular physiology, however, is directly dependent upon the developmental state of the myocyte, showing changes in mechanical function, structure, and response to pharmacologic intervention throughout ontogeny. Therefore, a better understanding of the inherent differential characteristics must be considered in optimizing a plan for the ideal method of myocardial preservation in newborn hearts. This review will attempt to highlight some of the major developmental differences in the neonate, the effects of ischemia on the immature heart, and methods of myocardial protection during cardiopulmonary bypass.

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