Intraoperative Detection of Myocardial Ischemia with an ST Segment Trend Monitoring System

The purpose of this study was to assess the use of a modified microcomputer-based electrocardiograph (ECG) to determine its value as an aid in the intraoperative detection of myocardial ischemia. The modification of the commercially available exercise/arrhythmia monitoring ECG permitted summing the absolute values of ST segment deviations 0 point + 60 msec) from the isoelectric line for three selected ECG leads. The system provided a trend line of ST segment changes as well as electronic storage of the ECG complexes. The authors report the use of the system during cardiovascular surgical procedures in which V5, AVF, and -V1 (on the back opposite to V1) were chosen as an orthogonal lead set. The simple trend line was found to be a sensitive indicator that alerted the anesthesiologist to subtle ST segment changes not easily recognized on conventional ECG monitors. Intraoperative ECG monitoring provides rhythm and rate information, but generally fails to diagnose adequately those episodes of myocardial ischemia that result in subtle ST segment changes. This inability is due primarily to limitations of the equipment and techniques commonly employed. Most monitors do not permit simultaneous display of multiple leads and often limit lead selection. The low-frequency response of the ECG amplifiers of many monitors designed for the operating room, or any ECG amplifier in the monitor mode, is unsuited for the accurate assessment of ST segment changes (1–3). Frequently, placement of the more sensitive V5 electrode is difficult or impossible because of the site of surgery, thus less optimal but more convenient sites are used. Even when V5 or bipolar leads such as CM5, CB5, or CS5 are observed with a diagnostic bandwidth amplifier, the limitations inherent in conventional single-lead monitoring systems often preclude diagnosis of early ischemic events (1). The technology necessary to simultaneously monitor multiple leads and provide sensitive indicators of ST segment changes has been developed for exercise stress testing, but has not been adopted for intraoperative use. This report describes our experience with a microprocessor-based prototype of a system that is capable of trending ST-segment changes.