Myocardial Uptake and Release of Substrates in Type II Diabetics Undergoing Coronary Surgery

OBJECTIVE: Knowledge about myocardial metabolism in diabetic patients is limited, and even more so in association with myocardial ischaemia and cardiac surgery. This study investigates myocardial substrate utilization in type II diabetic patients after elective coronary artery bypass graft surgery (CABG). DESIGN: Myocardial substrate utilization in 10 type II diabetic patients was assessed during the first hours after elective CABG with the coronary sinus catheter technique. RESULTS: No significant myocardial uptake of carbohydrates was observed. Free fatty acids were extracted throughout the study period but uptake was not related to arterial levels. As arterial levels of beta-hydroxybutyric acid tended to increase a significant myocardial uptake emerged. The average extraction rate of beta-hydroxybutyric acid was 31% with a peak of 42%. A comparable extraction rate of glutamate was also found whereas alanine was released from the heart. CONCLUSION: Free fatty acids were the main source of energy for the heart whereas uptake of carbohydrates was restricted. The high extraction rates of beta-hydroxybutyric acid and glutamate suggest an adaptive role for these substrates during this unfavourable metabolic state for the post-ischaemic diabetic heart.