Protection of the immature myocardium: An experimental evaluation of topical cooling, single-dose, and multiple-dose administration of St. Thomas' Hospital cardioplegic solution

Low cardiac output in infants after cardiac operations continues to be a problem, yet little experimental work has been done to evaluate the various methods of protecting the immature myocardium. In this study, we have used an isolated working heart model to test three methods of myocardial protection in 3- to 4-week-old rabbit hearts: (1) topical cooling, (2) single-dose cardioplegia plus topical cooling, and (3) multiple-dose cardioplegia plus topical cooling. Myocardial temperature was maintained at 10°C during ischemia, and St. Thomas' Hospital solution was used for cardioplegia. Sets of 18 hearts were subjected to 60, 90, or 120 minutes of ischemia, and within each set six hearts were protected by all three methods. After 90 and 120 minutes of ischemia, the percent recovery of aortic flow (expressed as mean ± standard error of the mean) was lower in hearts protected with multiple-dose cardioplegia plus topical cooling (61.5% ± 4.8%, 50.7% ± 14.2%) than in those protected with topical cooling (92.4% ± 5.7%, 94.3% ± 12.8%) or single-dose cardioplegia plus topical cooling (86.4% ± 5.3%, 90.2 ± 3.6%). However, adenosine triphosphate, creatine phosphate, and glycogen levels were adequately preserved in all groups. Both topical cooling and single-dose cardioplegia provide effective protection for the immature rabbit heart during ischemia, but multiple-dose cardioplegia plus topical cooling results in inadequate preservation of hemodynamic function, despite adequate preservation of myocardial high-energy phosphate stores.