Cellular monitoring in open heart surgery. Monitoring of markers for ischemia, free amino acids, glucose and lactate in the myocardial interstitial fluid before, during and after cardiac surgery using microdialysis technique

Abstract

Protection of the myocardium during open-heart surgery is a field of intense development. Numerous protocols have been proposed to minimize ischemia, since the beginning of open-heart surgery more than 40 years ago. Their evaluation is largely based on clinical outcome, since available methods lack the sensitivity required to determine the effects on myocardial oxygenation by small, but sometimes critical, methodological developments. We applied microdialysis to the myocardium with the aim to monitor the degree of ischemia from the concentrations of ASAT, troponin-T, free amino acids, glucose and lactate before, during and after cardioplegia. We also aimed at correlating postoperative events with the concentration of these markers. The myocardium of a mixed group of patients undergoing coronary artery by-pass grafting (CABG) and/or aortic valve surgery was monitored with a flexible microdialysis probe developed in our laboratory. The safety and function of the probe was first examined in an animal model for myocardial ischemia and then confirmed in man. Specific time courses were found in the interstitium for ASAT, troponin-T and several amino acids, during and after cardioplegia. Twenty and 300 times higher peak concentrations than in plasma were recorded in the interstitium for ASAT and troponin-T, respectively. The regulation of glucose and lactate was studied in the myocardial interstitium before, during and after cardioplegia in another group of patients undergoing CABG surgery. Concentrations of glucose and lactate were, to our knowledge, determined for the first time in the myocardial interstitium, with the use of internal calibration. Glucose was not critically reduced during cardioplegia, nor did lactate reach pathologically high concentrations. Even though transient elevations of marker levels coincided with postoperative clinical events in a number of patients, a larger population than was studied would be required for significant correlation. It is concluded that microdialysis sampling of the myocardial interstitial fluid is a safe procedure in clinical use. The approach has a potential for the evaluation of new technology for myocardial protection and for postoperative surveillance