MYOCARDIAL SUBSTRATE OXIDATION DURING WARM CONTINUOUS BLOOD CARDIOPLEGIA

Background. Although long-chain fatty acids are a major energy substra te utilized by the myocardium, changes in the substrate balance toward a predominating fatty acid utilization could jeopardize the myocardiu m during cardiac operative procedures. Methods. In the present study m yocardial substrate utilization was examined during warm continuous bl ood cardioplegia (4 hours, 37 degrees C), using pigs undergoing cardio pulmonary bypass. Hearts were perfused antegradely in a closed extraco rporeal circuit in which cardioplegic donor blood (hematocrit, 22%) co ntaining C-14-glucose and H-3-oleate was delivered to the heart. Arter ial and coronary sinus blood samples were taken at intervals for deter mination of plasma concentrations of energy substrates, as well as glu cose and oleate oxidation rates ((CO2)-C-14 and (HOH)-H-3 production). Results. The concentration of fatty acids in the cardioplegic perfusa te did not change significantly during the cardiac arrest period. The mean concentration of glucose showed a 30% decline (not significant), whereas the lactate concentration increased from a starting value of 3 .12 +/- 0.27 to 6.31 +/- 0.72 mmol/L at the end (mean +/- standard err or of the mean; n = 8; p < 0.05). Only fatty acid levels showed a sign ificant (positive) arterial-coronary sinus difference. Myocardial oxid ation of oleate varied between 302 +/- 71 and 650 +/- 66 nmol . min(-1 ). heart(-1), whereas the range of variation for glucose oxidation was 144 +/- 64 to 355 +/- 107 nmol . min(-1). heart(-1). However, the cha nges in fatty acid levels and glucose oxidation rates during the cardi ac arrest period were not statistically significant. We calculated tha t overall glucose oxidation accounted for less than 5% of the total ae robic energy production. Conclusions. The present results demonstrate overreliance on fatty acids as a source of energy during warm continuo us blood cardioplegia, consistent with a condition of myocardial insul in resistance.