Myocardial substrate uptake and oxidation during and after routine cardiacsurgery

Objective: This study was designed to clarify whether myocardial substrate uptake and oxidation change after a period of hypothermic cardioplegic arre st during coronary artery bypass grafting procedures. Methods: In 30 patien ts arterial and coronary sinus blood was sampled and coronary sinus flow me asurements were performed before and after sternotomy and 10 minutes, 20 mi nutes, 50 minutes, and 6 hours after release of the aortic crossclamp, Meas urement of free fatty acids, lactate, glucose, oxygen content, and carbon d ioxide content in arterial and coronary sinus blood allowed calculations of myocardial substrate use, respiratory quotients, and myocardial oxidation rates of carbohydrates and fat, Results: Uptake of free fatty acids and lac tate was significant throughout the study and did not change in association with release of the crossclamp, Free fatty acid and lactate uptake measure d 6 +/- 4 mu mol/min and 23 +/- 26 mu mol/min, respectively, before crosscl amping compared with 8 +/- 7 mu mol/min and 19 +/- 21 mu mol/min, respectiv ely, after release of the clamp. Glucose uptake was significant only during the first hour after crossclamp release and increased from 7 +/- 50 to 28 +/- 34 mu mol/L after crossclamp release, Myocardial oxygen consumption did not change significantly (0.5 +/- 0.2 mmol/L compared with 0.35 +/- 0.2 mm ol/L) after release of the crossclamp, Myocardial oxygen extraction ratio d ecreased from 58% +/- 8% to 41% +/- 13% after crossclamp release. Respirato ry quotient increased after crossclamp release (0.85 +/- 0.2 compared with 1.00 +/- 0.2), which implies that carbohydrate oxidation increased at the e xpense of free fatty acid oxidation, Conclusion: We conclude that hypotherm ic cardioplegic arrest during coronary artery bypass graft operations is as sociated with a transiently increased uptake and oxidation of carbohydrates during the immediate reperfusion phase.