Myocardial metabolism assessed by microdialysis: a prospective randomized study in on- and off-pump coronary bypass surgery.

Objective: The aim of the study was to compare energetic metabolism in the myocardium during coronary surgery with and without cardiopulmonary bypass by means of microdialysis.
Methods: Twenty-six low-risk patients were prospectively randomized to off-pump versus on-pump surgery. Microdialysis was used to sample myocardial interstitial fluid during and for 23 hours after surgery.
Results: Preoperative characteristics and clinical outcome were similar in both groups. Blood glucose and lactate did not differ between groups throughout the observation time. During surgery, intramyocardial levels of glucose, pyruvate and urea were unaffected in off-pump patients, while the same substances significantly decreased (p<0.05) in on-pump patients during cardioplegic arrest, and increased during reperfusion. Interstitial lactate levels were higher during off-pump surgery (p<0.05). From 3 to 15 hours after surgery, intramyocardial concentrations of glucose, urea and lactate were higher in off-pump patients (p<0.001), while pyruvate was higher in on-pump patients (p<0.01). Intramyocardial lactate/pyruvate ratio never differed between groups. Postoperatively, cumulative blood release of troponin-T was significantly higher in the on-pump group (p<0.005).
Conclusions: Microdialysis could demonstrate significant differences in energetic metabolism between the two groups. Our data confirm and might help in explaining the lower release of myocardial ischemic markers after off-pump surgery.
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