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Etiology

Postoperative ischemia was associated with cardiac events

ACP J Club. 1993 Sept-Oct;119:56. doi:10.7326/ACPJC-1993-119-2-056


Source Citation

Landesberg G, Luria MH, Cotev S, et al. Importance of long-duration postoperative ST-segment depression in cardiac morbidity after vascular surgery. Lancet. 1993 Mar 20;341:715-9.


Abstract

Objective

To determine whether preoperative, intraoperative, and postoperative myocardial ischemia are associated with increased risk for postoperative cardiac events in patients having major vascular surgery.

Design

Cohort analytic study.

Setting

A university hospital in Israel.

Patients

151 patients (mean age 66 y, 112 men) having elective or semi-elective major vascular surgery. Patients from the emergency department who had immediate surgery were excluded.

Assessment of risk factors

Continuous electrocardiographic (ECG) recordings for 1 day preoperatively, throughout the intraoperative period, and for 1 day postoperatively. Ischemic episodes were defined as either ST-segment depression (down-sloping or horizontal ST depression of > 0.1 mV, lasting > 60 s, and separated from a previous ischemic episode by ≥ 60 s) or ST elevation (≥ 0.2 mV at the J point). Tracing results were examined by a cardiologist blinded to patient information. Cardiac risk was calculated according to the Detsky multifactorial cardiac risk index. Serum creatine kinase and MB isoenzyme values were measured before surgery, during surgery, and every 6 hours for 24 hours after surgery.

Main outcome measures

Postoperative cardiac events, including myocardial infarction (MI), congestive heart failure (CHF), and unstable angina as determined by 2 independent cardiologists.

Main results

41 patients (27%) had preoperative ischemia, 26 patients (17%) had intraoperative ischemia, and 59 patients (39%) had postoperative ischemia. A total of 13 cardiac events occurred: 6 patients with MI (5 were non-Q-wave infarctions), 5 with CHF, and 2 with unstable angina. Most adverse cardiac events (77%) began within 24 hours of surgery, with the most delayed occurring 72 hours after surgery. In univariate analysis, the Detsky cardiac risk index, preoperative and intraoperative ischemia, and postoperative ischemia of > 2 hours duration were risk factors for postoperative cardiac events. In multivariate logistic regression analysis, postoperative ischemia of > 2 hours duration was the only independent risk factor for postoperative cardiac events (odds ratio 21.7, P = 0.001). 8 of 10 patients with postoperative ischemia for > 4 hours had a postoperative cardiac event, and all patients with postoperative MI had postoperative ischemia for > 5 hours. All prognostically important postoperative ischemia was signaled by ST depression rather than ST elevation.

Conclusion

Postoperative ischemia of > 2 hours duration was a risk factor for cardiac events in patients having major vascular surgery.

Source of funding: Not stated.

For article reprint: Dr. G. Landesberg, Department of Anesthesiology and Critical Care Medicine, Hebrew University-Hadassah Medical Center, Jerusalem, Israel 91120. FAX 972-2643-4434.


Commentary

These results appear to contradict the conclusion of Raby and colleagues (1) that preoperative ischemia detected by ECG monitoring is the best predictor of postoperative MI. But, the results of the 2 studies are remarkably similar. The incidences of MI were 4.0% and 7.8% in the Landesberg and Raby studies, respectively; the sensitivities of postoperative ischemia for MI were 100% and 88%, with positive predictive values (PPVs) of 10% and 23%. Postoperative ischemia was present for an average of 14 hours before the 6 MIs in Landesberg's series and for 8 hours before 8 of 9 MIs in Raby's series.

The difference between the studies lies in Raby and colleagues' chance finding of a slightly greater specificity for preoperative ischemia compared with Landesberg and colleagues' finding of a lower sensitivity for the same observation. This statistical difference is not worth the nit-picking. The real issue is whether ECG monitoring or any other modality measured before surgery can predict more accurately than clinical descriptors which patient will have a postoperative MI. So far the answer is no. The presence of ≥ 1 of the 3 risk factors, age > 70 years, diabetes, or a history indicative of coronary artery disease (CAD), is found in 80% to 90% of those who will have a cardiac event, but the PPV of these risk factors for MI is only 5% to 10%. The parallel issue is whether any preoperative intervention, such as coronary artery bypass grafting or angioplasty with their attendant risks, or any medical treatment, such as aspirin, anticoagulants, or the liberal use of narcotics, can lower the incidence of postoperative MI in high-risk patients. No rigorously proven answers exist.

Patients with any evidence for CAD have about a 5% to 10% risk for postoperative MI and are likely candidates for postoperative monitoring. Prolonged postoperative ischemia (> 2 to 4 h) indicates that an intracoronary clot may be forming. Perhaps these few patients are candidates for some acute intervention such as angioplasty.

John S. Kizer, MD
University of North Carolina at Chapel HillChapel Hill, North Carolina, USA


Reference

1. Raby KE, Barry J, Creager MA, et al. Detection and significance of intraoperative and postoperative myocardial ischemia in peripheral vascular surgery. JAMA. 1992;268:222-7.