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.