Detection of Myocardial Ischemia during Anesthesia

Abstract

Depression, elevation or pseudo-normalization of the electrocardiographic ST-T-segment, are by far the most accepted indicators of myocardial ischemia during anesthesia.Classically, a change of 0.1 mV, measured 80 ms after the maximal R-wave, is the minimal criterion to establish the diagnosis (1). If the electrocardiogram (ECG) is not recorded on paper such small changes are likely to pass undetected. When the different electrocardiographic leads were compared in association with exercise testing, it was found that approximately 90% of all changes suggesting subendocardial ischemia were seen in the V5 lead (2). This lead reflects metabolic changes occurring in the area of the myocardium perfused by the left anterior (LAD) and circumflex (CX) arteries (3). During anesthesia, ischemia in this part of the myocardium is also likely to result in the most severe cardiovascular dysfunction and the highest incidence of early postoperative reinfarction and deaths (4). Monitoring of the V5 lead has consequently been recommended as the minimal requirement for patients with cardiovascular disease, subjected to anesthesia and surgery (5). The use of microprocessor operated oscilloscopes, which graphically present a summary of the ST-T-segments from a multiple lead ECG, have recently been reported to improve the diagnosis of myocardial ischemia (6). As yet, there are however no studies performed in anesthetized patients reporting on the relationship between ECG changes and metabolic changes occuring in the monitored area of the myocardium.