Intraoperative detection of myocardial ischemia in high-risk patients: electrocardiography

Because acute segmental wall motion abnormalities (SWMAs) of the left ventricle are highly sensitive and specific indicators of myocardial ischemia, this study compared the incidence and significance of ischemia, as detected by two-dimensional transesophageal echocardiography and surface electrocardiography, during anesthesia and surgery in patients at high risk of myocardial ischemia. During surgery, 24 of the 50 patients studied had new SWMAs, whereas only six had ST segment changes. All patients with ST segment changes also had new SWMAs: in three instances, SWMAs occurred before the ST segment change, and in three instances, they occurred simultaneously. All three patients who had intraoperative myocardial infarctions also had persistent intraoperative SWMAs, whereas only one patient had ST segment changes. Ten healthy patients requiring noncardiovascular surgery were monitored similarly; none of these had SWMAs, ST segment changes, or myocardial infarction. This study demonstrates the superiority of two-dimensional transesophageal echocardiography over electrocardiography for the intraoperative detection of myocardial ischemia. Furthermore, when new SWMAs persist to the conclusion of surgery, myocardial infarction is likely to have occurred. Circulation 72, No. 5, 1015-1021, 1985. DESPITE THE AVAILABILITY of aggressive intraoperative cardiac monitoring and therapy, myocardial ischemia and infarction remain common causes of perioperative morbidity and mortality.1 2 The standard surface electrocardiogram (ECG) may not reveal subendocardial ischemia.3 Even severe transmural ischemia may go undetected if only a single electrocardiographic lead is monitored,4 if excessive filtration is used, or if signal standardization is inappropriate. Furthermore, electrocardiographic monitoring for the detection of ischemia may be impossible if certain conduction disturbances or paced rhythms are present.5 6 Nevertheless, the ECG remains the monitor most commonly used to diagnose intraoperative myocardial ischemia. From the Departments of Anesthesia and Medicine, Division of Cardiology, University of California, San Francisco. Supported by NIH grants No. IR23GM-28502-03 and NIA 1 PO 1 AG03104-02,3 and the Anesthesia Research Foundation. Address for correspondence: Michael K. Cahalan, M.D., Department of Anesthesia, University of California, Third and Parnassus Avenues, Room S436, San Francisco, CA 94109. Presented in part at the annual meetings of the Society of Cardiovascular Anesthesiologists and the American Society of Anesthesiologists in 1984. Vol. 72, No. 5, November 1985 In 1935 Tennant and Wiggers7 demonstrated that acute coronary ligation results in paradoxical motion in the ischemic area. Subsequently, wall motion abnormalities have been shown to occur within seconds of the onset of regional ischemia,8-' simultaneously with regional lactate production, 12 but before (and even in the absence of) changes on the surface ECG.'3 Because two-dimensional echocardiography reliably detects segmental wall motion abnormalities (SWMAs),'4 this technique may be a more sensitive measure of intraoperative myocardial ischemia than electrocardiography. However, precordial echocardiographic methods are impractical during surgery. In contrast, two-dimensional transesophageal echocardiography can be used during surgery and has been shown to provide safe, reproducible images of the left ventricle.S'5 16 To compare the incidence of myocardial ischemia, as detected by the occurrence of new SWMAs on echocardiograms, with the incidence as detected by ST segment changes on ECGs, we studied patients at high risk of myocardial ischemia during anesthesia and surgery. Furthermore, we tested whether these 1015 by gest on N ovem er 2, 2017 http://ciajournals.org/ D ow nladed from