ADVERSE-EFFECTS OF CRYSTALLOID CARDIOPLEGIA AND SLOW COOLING FOR PROTECTION OF IMMATURE RAT HEARTS

Background. Studies on the benefit of methods for protection of the hy pertrophied immature myocardium are rare and controversial. Methods. W e assessed the effects of (1) rapid cooling by topical hypothermia alo ne, (2) slow prearrest cooling by coronary perfusion hypothermia, and (3) cardioplegic cardiac arrest with St. Thomas' Hospital solution no. 2 for protection of isolated immature rat hearts (age, 28 days) durin g 8 hours of global ischemia at 10 degrees C. Myocardial hypertrophy w as induced noninvasively by lifelong feeding of a low iron diet. Recov ery of left ventricular function, metabolism, and myocardial fine stru cture were assessed. Results. In hypertrophied hearts, protection by t opical hypothermia alone resulted in significantly improved postischem ic recoveries of maximum left ventricular pressure and rate of pressur e rise compared with the method of slow cooling or application of card ioplegia (40.6 +/- 5.0% and 38.1% +/- 5.9%, mean +/- standard error of the mean; p < 0.05). The same pattern of recovery was observed among nonhypertrophied control hearts. Regardless of the method of protectio n, hypertrophied hearts revealed a significantly larger interstitial s pace at the end of reperfusion than control hearts. In hypertrophied h earts, postischemic adenosine triphosphate concentrations were higher with topical hypothermia alone for protection than with the other meth ods. Conclusions. Rapid cooling by topical hypothermia alone provides superior protection of hypertrophied immature rat hearts as compared w ith slow prearrest cooling. Application of St. Thomas' Hospital cardio plegic solution no. 2 does not improve protection and even hinders pos tischemic functional recovery.