Martin G. Wong

Intraoperative myocardial ischemia: localization by continuous 12-lead electrocardiography

Based primarily on results obtained during exercise treadmill testing, electrocardiographic (ECG) leads II and V5 are the suggested optimal leads for detecting intraoperative myocardial ischemia. However, these recommendations have not been validated in this setting using all 12 ECG leads. Accordingly, the authors studied 105 patients with known or suspected coronary artery disease (CAD) undergoing noncardiac surgery with general anesthesia by continuously recording the 12-lead ECG intraoperatively in all patients. The average duration of monitoring was 8.2 ± 2.7 h (mean ± SD). Ischemic episodes (i.e., ± 1-mm horizontal or downsloping ST depression, ± 1.5-mm slowly upsloping ST depression or ± 1.5-mm ST of 51 ischemic episodes, 45 involved ST depression alone, and the remaining six involved both ST depression and elevation. ST segment changes occurred in a single lead only in 134 episodes, while multiple leads were involved in 37 episodes. Lead sensitivity was estimated assuming that all St segment changes were true positive responses. Sensitivity using a single lead was greatest in V5 (75%) and V4 (61%), and intermediate in II, V3 and V6 (33%, 24%, and 37%, respectively). The remaining seven leads demonstrated very low sensitivity (2–14%) or exhibited no ischemic changes (I and a V1). Combining leads V4 and V5 increased sensitivity to 90%, while the standard clinical combination, II and V5, was only 80% sensitive. Sensitivity increased to 96% by combining II, V4, and V5. The further addition of V2 and V3 (five leads) increased sensitivity to 100%. This study confirms previous recommendations for the routine use of a V5 lead (either uni- or bipolar) in all patients at risk for ischemia. V4 is more sensitive than lead II, and should be considered as a second choice. However, lead II, superior for detection of atrial dysrhythmias, is more easily obtained with conventional monitors. The use of all three would appear to be the optimal arrangement for most clinical needs, and is recommended if the clinician has the capability.

Perioperative myocardial ischemia in patients undergoing noncardiac surgery—II: Incidence and severity during the 1st week after surgery☆

Because of the importance of postoperative myocardial ischemia and because substantial physiologic changes can occur for prolonged periods postoperatively, the incidence, severity and temporal course of myocardial ischemia were studied in 100 high risk patients during the 1st week after major noncardiac surgery. Electrocardiographic (ECG) changes consistent with ischemia were continuously monitored using ambulatory solid state ECG in the 100 patients with or at risk for coronary artery disease. Ischemic episodes were defined as reversible ST segment depression greater than or equal to 1 mm or elevation greater than or equal to 2 mm above the baseline value, with the baseline adjusted for respiratory and positional variation and temporal drift. All ischemic episodes were confirmed by three independent blinded investigators using hard-copy recordings. Total ECG monitoring time was 10,445 h. Twenty-seven patients (27%) developed 437 episodes of ischemia during the 1st week after surgery. The total duration of ischemia was 18,658 min, or 1.8 min of ischemia/h monitored. Ischemia was most severe during the early (days 0 to 3) versus late (days 4 to 7) postoperative period: 284 versus 153 episodes; 2.2 versus 1.2 min of ischemia/h. The greatest severity occurred on postoperative day 3: 109 episodes, 3.4 min of ischemia/h monitored, 1.5 mm mean ST change and 130 min mean duration. However, in 8% of patients, severe episodes also occurred late: postoperative day 6 = 44 episodes, 1.7 min of ischemia/h monitored, 1.3 mm mean ST change (59% greater than or equal to 2 mm) and 92 min mean duration. Most ischemic episodes (57%) were associated with tachycardia.(ABSTRACT TRUNCATED AT 250 WORDS)

The “Natural History” of Segmental Wall Motion Abnormalities in Patients Undergoing Noncardiac Surgery

Intraoperative segmental wall motion abnormalities (SWMA) detected by transesophageal echocardiography (TEE) are sensitive, but not always specific, markers of myocardial ischemia. To determine their incidence, characteristics, and relation to postoperative cardiac morbidity, we continuously recorded the left ventricular short-axis view and 12-lead ECG in 156 high-risk patients undergoing non-cardiac surgery. Monitoring was clinically blinded. Wall motion was scored at predefined clinical, hemodynamic, and ECG events and at periodic intervals (26 +/- 11 samples per patient). We detected 44 episodes of new or worsened SWMA in 32 patients (20%). The severity of most episodes was limited to severe hypokinesis (24/44, 55%) followed by akinesis (16/44, 36%) and dyskinesis (4/44, 9%). The remaining 124 patients had normal wall motion or only mild hypokinesis (56/156, 36%) or chronic SWMA (68/156, 44%). The incidence of new SWMA did not differ for patients with known coronary artery disease (CAD) and those with cardiac risk factors only (22% vs. 19%, P = not significant), although CAD patients had a significantly greater incidence of chronic SWMA (62% vs. 41%, P = 0.02). The incidence of new or worsened SWMA was significantly greater during aortic vascular surgery (38% vs. 17%, P = 0.05). Approximately 40% of all new TEE changes occurred in the absence of either an apparent clinical event or a significant change in systolic blood pressure or heart rate. Ten patients had new or worsened SWMA persisting until the end of surgery, 8 with new akinesis, only 1 developing myocardial infarction. The distribution of new or worsened SWMA and significant intraoperative ST-T changes (n = 19) in this cohort was discordant: temporal overlap between modalities was present in only 5 patients. Major cardiac complications occurred in 5 patients (3.2%), all of whom underwent peripheral vascularization. All patients with cardiac complications and new or worsened SWMA also had intraoperative or early postoperative ST-T changes. We conclude that: 1) continuous TEE recording with offline analysis in this high-risk group of patients revealed a relatively low incidence of new or worsened SWMA (20%), most episodes of which were characterized by severe hypokinesis (55%); 2) episodes were more common in patients undergoing aortic vascular surgery; 3) approximately 40% of episodes were unaccompanied by clinical events or significant hemodynamic changes; 4) episodes were poorly correlated with postoperative cardiac complications; and 5) the discordant relation between TEE and ECG changes observed here necessitates careful monitoring of the ECG when TEE is used clinically.