PROTECTION OF THE CHRONIC HYPOXIC IMMATURE RAT-HEART DURING GLOBAL-ISCHEMIA

The benefit of cardioplegic cardiac arrest for the protection of immat ure myocardium is controversial. We therefore investigated the efficac y of (1) topical hypothermia alone, (2) slow cooling by coronary perfu sion hypothermia, and (3) cardioplegic cardiac arrest for the protecti on of isolated immature rat hearts (28 days) during 8 hours of global ischemia at 10 degrees C. The study was conducted in hearts from rats that were kept hypoxemic by lifelong exposure to simulated high altitu de. Left ventricular function, endothelial function, the metabolic sta tus, and the extent of myocardial injury were all assessed. Topical hy pothermia provided superior protection in hypoxic hearts, with recover y of the maximum developed left ventricular pressure by 70.6% +/- 18.0 % (mean +/- standard deviation) of its preischemic value (p < 0.01 ver sus slow cooling and versus cardioplegic protection). The same pattern of recovery was observed among control hearts. The degree of recovery of endothelial function after sole topical hypothermia measured 54% /- 36% in hypoxic hearts and 62% +/- 37% in control hearts, but was no t recordable in any of the other groups. Creatine kinase leakage and t he myocardial high-energy content did not differ significantly among a ny of the groups. Rapid cooling by topical hypothermia alone provides superior protection in chronic hypoxic, immature rat hearts versus the protection conferred by slow cooling. St. Thomas' Hospital cardiopleg ic solution II does not afford additional protection. Endothelial inju ry caused by cold asanguineous perfusates, including cardioplegia, int erferes with the recovery of vascular function, which, in turn, may li mit mechanical function.