Perioperative myocardial ischemia and infarction - Identification by continuous 12-lead electrocardiogram with online ST-segment monitoring

Background: Perioperative myocardial ischemia is conventionally monitored using five electrocardiographic leads, with only one precordial lead placed at V-5. This is based on studies from more than a decade ago. The authors reassessed this convention by analyzing data obtained from continuous on-line 12-lead electrocardiographic monitoring. Methods: One hundred eighty-five consecutive patients undergoing vascular surgery were monitored by continuous 12-lead ST-trend analysis during and for 48-72 h after surgery. Cardiac troponin I was measured in the first 3 postoperative days, and cardiac outcome was prospectively recorded. Ischemia was defined as ST deviation, relative to the reference preanesthesia electrocardiogram, of 0.2 mV or more in one lead or 0.1 mV or more in two contiguous leads, lasting more than 10 min. Results: During 11,132 patient-hours of monitoring, 38 patients (20.5%) had 66 transient ischemic events, with all but one denoted by ST-segment depression. Twelve patients (6.5%) sustained postoperative infarction (cardiac troponin I > 3.1 ng/ml). Among the 38 patients with ischemia, lead V-3 most frequently (86.8%) demonstrated ischemia, followed by V-4 (78.9%) and V-5 (65.8%). Among the 12 patients with infarction, V-4. was most sensitive to ischemia (83.3%), followed by V-3 and V-5 (75% each). Combining two precordial leads increased the sensitivity for detecting ischemia (97.4% for V-3 + V-5 and 92.1% for either V-4 + V-5 or V-3 + V-4) and infarction (100% for V-4 + V-5 or V-3 + V-5 and 83.3% for V-3 + V-4). On average, baseline preanesthesia ST was above isoelectric in V-1 through V-3 and below isoelectric in V-5 through V-6. Lead V-4 was closest to the isoelectric level on the baseline electrocardiogram, rendering it most suitable for ischemia monitoring. Conclusions: As a single lead, V-4 is more sensitive and appropriate than V-5 for detecting prolonged postoperative ischemia and infarction. Two precordial leads or more are necessary so as to approach a sensitivity of greater than 95% for detection of perioperative ischemia and infarction.