Pediatric myocardial protection: Where do we stand?

doi:10.1016/j.jtcvs.2004.03.017 T he objectives of every cardiac operation, whether adult or pediatric, are technical success and absence of iatrogenic injury from inadequate myocardial protection. To obtain the best results, the surgeon should select a method of protection only after learning how the cardioplegic method was developed, as well as how to benefit from its advantages, and how to avoid inappropriate use by recognizing the disadvantages. The choice for protection is similar to the selection of a structural technique for surgical repair of an underlying cardiac lesion. Failure of either modality is unacceptable, because both are equally important if the patient is to receive the full benefit from the surgical correction. Improved myocardial protection is not a phase of surgical development; it is intrinsic to the repair of congenital cardiac defects. Despite major advances in the technical aspects of surgical repair, pediatric myocardial protective techniques remain relatively unchanged. Moreover, there are currently few articles in the major journals on pediatric myocardial protection. This would imply that current techniques provide optimal and complete preservation of the pediatric heart and that there is little need for further research to improve protection methods. However, pediatric patients continue to need mechanical assist devices, as well as prolonged inotropic support or an open chest despite a “technically perfect repair.” Moreover, perioperative myocardial damage with low cardiac output remains the most common cause of morbidity and death after repair of congenital lesions. Cardiac damage from inadequate myocardial protection can prolong hospital stay and result in delayed myocardial fibrosis, leading to cardiac dysfunction months to years later. Protection of the immature heart is further complicated by a reduced response to inotropic agents relative to the adult heart. Thus preservation of myocardial function in immature hearts assumes even greater importance, because a perioperative insult is both less well tolerated and more difficult to treat. In general, most changes in pediatric myocardial protection have been derived from the adult cardiac experience. However, in view of the structural, functional, and metabolic differences, extrapolation of adult cardioprotective strategies to the pediatric patients is fundamentally imprudent and potentially harmful. Myocardial protective strategies and cardioplegia solutions must be studied in the immature heart if pediatric protection is to be truly optimized. In this issue, Modi and associates report a randomized clinical trial comparing crystalloid with blood cardioplegia in pediatric patients. Demonstrating differences between cardioplegic techniques is often difficult in the clinical setting because, unlike in the experimental laboratory where variables can be precisely controlled and measured, patients are not uniform, and the measurements of damage are less precise. In the experimental laboratory all hearts are subjected to the same preintervention stress, they undergo identical periods of ischemia, their anatomy is not altered, and postoperative measurements are precise and sensitive to detect damage. This makes it easy to demonstrate differences in protection strategies. In contrast, hearts in clinical studies are all different before surgery, they are anatomically altered (repaired), during surgery their crossclamp times are varied, and the postoperative measurements are far less precise. This makes it much more difficult to demonstrate clinical differences unless they are profound, even though significant myocardial damage may have occurred.