Myocardial metabolic monitoring with the microdialysis technique during and after open heart surgery

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Abstract
Background: Post-operative ischemia after coronary artery bypass grafting (CABG) is well described but effective intervention requires immediate diagnosis. One possible way of increasing efficacy of peri-operative myocardial monitoring is using the microdialysis technique. Methods: In 30 patients undergoing routine CABG, a microdialysis catheter was inserted in the left heart in an area of abnormal ventricular contraction. A second catheter was placed in normal tissue of the right ventricle. Microdialysis measurements were performed at time intervals before, during and 24 h after cardiopulmonary bypass (CPB) and retrospectively compared with standard clinical monitoring and clinical course. Results: During CPB, both ventricles showed signs of poor tissue oxygenation. Glycerol was significantly higher in the left myocardium (146 ± 67 vs. 72 ± 36 μmol/l) and the glucose/lactate ratio (GLR), as a marker of nutritional disorder of the right ventricle (41 ± 15% vs. 67 ± 17%, P < 0.05), had significantly better values at this time point. Myocardial lactate concentrations were significantly higher in the dyskinetic segments (2.82 ± 0.81 vs. 1.5 ± 0.81 μM). During this period, no abnormal clinical standard monitoring results were observed. Post-operative significantly increased lactate/pyruvate ratios of three patients were clinically associated with peri-operative myocardial infarction (108 ± 67 vs. 38 ± 9, P < 0.05). The lactate/pyruvate ratio started rising before any other standard monitoring tools showed abnormal values. Conclusions: Peri-operative microdialytic measurements of parameters related to ischemia can be safely performed in a clinical setting, resulting in faster and more reliable detection of ongoing or new ischemia.

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