Intravasal microdialysis as a novel technique to monitor metabolism in myocardial ischemia and critical illness

Abstract

Rapid detection of post-operative myocardial ischemia is of great value in the treatment of patients undergoing cardiac surgery. With the methods readily available in modem thoracic intensive care units post-operative myocardial ischemia is difficult to detect, and the risk of myocardial ischemia and other complications after cardiac surgery is particularly high in patients with concurrent co-morbidity.

The investigations in this thesis were undertaken with the objective to develop and evaluate the technique of intravasal microdialysis in respect to monitoring energy metabolites during myocardial ischemia/reperfusion and critical illness. Moreover, the clinical applicability of intravasal microdialysis and the possibility to detect post-operative adverse events in high-risk patients undergoing cardiac surgery has been evaluated.

Myocardial ischemia was detected by increased levels of lactate and glycerol as well as an increased lactate/pyruvate-ratio in microdialysate from the great cardiac vein. Intravasal microdialysis in the great cardiac vein was shown to be superior to intramyocardial microdialysis in detecting regional myocardial ischemia. The total myocardial outflow of taurine, aspartate, glutamate, hypoxanthine, inosine and guanosine were correlated to the infarction size. In models of critical illness (i.e. gut ischemia, endotoxin shock and hemorrhagic shock) the outflow patterns of energy metabolites in the splanchnic area showed a distinctive pattern depending on the cause of critical illness. Intravasal microdialysis in patients undergoing cardiac surgery was demonstrated as safe and reliable and no major changes in the levels of energy metabolites were detected in patients where no adverse events were seen.

Taken together these findings demonstrate the usefulness of intravasal microdialysis to monitor cardiac surgery patients, both in high-risk cases and standard elective cases where rapid detection and treatment of post-operative myocardial ischemia would be of great value.