DECREASING MYOCARDIAL PH REFLECTS ISCHEMIA DURING CONTINUOUS WARM RETROGRADE CARDIOPLEGIC ARREST

Warm continuous retrograde cardioplegia is thought to prevent myocardi al ischemia. We tested this hypothesis by subjecting canine hearts to 2 hours of either antegrade or retrograde perfusion with normothermic blood cardioplegia. Ischemic alterations were evaluated through the me asurement of myocardial pH, tissue levels of adenosine triphosphate an d lactate, and the preservation of left ventricular contractility. Ant egrade perfusion resulted in uniformly positive changes in the myocard ial pH in both ventricles, preserved levels of adenosine triphosphate, and small increases in the myocardial lactate levels. In contrast, re trograde perfusion caused the myocardial pH to decrease, especially in the right ventricle. Tissue lactate levels rose to a significantly gr eater extent during retrograde perfusion and adenosine triphosphate le vels declined, although not to a statistically significant degree. Fin ally, myocardial function, as assessed by the preload recruitable work area, was preserved (103% +/- 20% of baseline) in the antegrade group but was markedly diminished (33% +/- 6%) in retrogradely perfused lef t ventricles 35 minutes after the aortic cross-clamp was removed. Thes e data suggest that ischemic metabolism and the subsequent alteration of myocardial function take place despite continuous retrograde perfus ion with normothermic blood cardioplegia.