UTILITY OF MYOCARDIAL PROTECTION METHODS IN IMMATURE RAT HEARTS SUBJECTED TO LONG-TERM HYPOXIA

This study examines the efficacy of three methods for myocardial prote ction during 8 hours of global ischema at 10-degrees-C in immature (28 days) rat hearts subjected to lifelong hypoxia afforded by exposure t o simulated high altitude. Hearts in group 1 were protected by rapid t opical cooling alone, in group 2 by slow pre-arrest cooling with Krebs -Henseleit solution plus topical cooling and in group 3 by coronary pe rfusion with St. Thomas' Hospital cardioplegia No 2 (STS 2) plus topic al cooling. Hearts in groups 4-6 served as controls without hypoxia an d were protected accordingly. Parameters of myocardial function (left ventricular pressure, LVP), the metabolic status (myocardial concentra tion of ATP and creatine phosphate) and endothelial function (response to the vasodilator acetylcholine) were measured. Myocardial protectio n by rapid topical cooling alone resulted in equal - or significantly improved - postischemic recovery of LVP and endothelial function compa red with slow pre-arrest cooling or additional protection with STS 2. The data advocate topical cooling for myocardial protection during sur gical correction of cyanotic congenital cardiac disease in early infan cy. In this age group, coronary perfusion with cold crystalloid soluti ons appears to aggravate ischemic endothelial injury.