Current issues of ACP Journal Club are published in Annals of Internal Medicine


Etiology

Cardiac events after peripheral vascular surgery

ACP J Club. 1993 Jan-Feb;118:25. doi:10.7326/ACPJC-1993-118-1-025


Source Citation

Raby KE, Barry J, Creager MA, et al. Detection and significance of intraoperative and postoperative myocardial ischemia in peripheral vascular surgery. JAMA. 1992 Jul 8:268:222-7.


Abstract

Objective

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

Design

Cohort analytic study.

Setting

Brigham and Women's Hospital in Boston.

Patients

115 patients (mean age 67 y, 77 men) having peripheral arterial surgery who were thought to be at an acceptably low cardiac risk by independent cardiologists blinded to preoperative monitoring results. Exclusion criteria were thoracic, upper-extremity, trauma, or emergency surgery; baseline electrocardiographic (ECG) findings that precluded monitor interpretation; and unwillingness to wear a monitor for up to 72 hours.

Assessment of risk factors

Ambulatory ECG monitoring for at least 24 hours preoperatively, throughout the intraoperative period, and for up to 72 hours post-operatively. An episode of myocardial ischemia was defined as a ST-segment depression that was planar or downsloping, of ≥ 1 mm as compared with baseline, present for 0.06 seconds beyond the J point, and present in consecutive beats for ≥ 60 seconds. Tracing results were confirmed by an experienced reader blinded to patient information.

Main outcome measures

Postoperative cardiac events, including death from a cardiac cause, myocardial infarction, unstable angina, and ischemic pulmonary edema as determined by independent cardiologists.

Main results

23 patients (20%) had preoperative ischemia, 21 patients (18%) had intraoperative ischemia, and 35 patients (30%) had postoperative ischemia. A total of 16 cardiac events occurred. In multivariate logistic regression analysis, preoperative ischemia was the only independent risk factor for postoperative cardiac events (P < 0.001). All 14 patients with postoperative ischemia and events also had preoperative ischemia. Preoperative ischemia was highly correlated with both intraoperative and postoperative ischemia.

Conclusions

Preoperative ischemia was a risk factor for postoperative cardiac events in patients undergoing peripheral arterial surgery. Postoperative ischemia preceded events in patients with preoperative ischemia.

Sources of funding: In part, W.K. Kellogg Foundation; National Institutes of Health; American Heart Association.

For article reprint: Dr. K.E. Raby, Cardiovascular Division and the Division of Clinical Epidemiology, Brigham and Women's Hospital, 75 Francis Street, Boston, MA 02115, USA. FAX 617-732-7134.


Commentary

There are 2 reasons for assessing the risk for cardiac death in a patient having peripheral vascular surgery. The first is to determine the risk-to-benefit ratio for the procedure. Despite small numbers of events and discontinuous patient selection, Raby and colleagues found that preoperative ischemia predicted an increased likelihood of postoperative cardiac complications. Conversely, the absence of perioperative ischemia predicted a low (< 2%) likelihood of postoperative events similar to the results of more expensive thallium and exercise testing. But are technical assessments better than clinical descriptors? In this study, age > 70 years, diabetes, or a history of coronary disease was found in 88% of those who had cardiac events, a sensitivity comparable with ECG monitoring. Moreover, the positive predictive value of preoperative ischemia for cardiac morbidity and mortality was 61%. We can, therefore, identify patients who are unlikely to have events but not those who will.

The second reason for assessing risk is to identify treatable medical hazards. Perioperative cardiac events are rare, and most occur in the immediate postoperative period. Severe coronary artery disease is clearly a risk factor, but those postsurgical physiologic events that initiate the formation of a thrombus on existing atheromas are unknown. Further, neither angioplasty, nor bypass surgery, nor medical therapy has been proved to reduce the incidence of postoperative myocardial infarction.

The low incidence of fatal postoperative myocardial infarction (2.5% to 5%) in acceptable-risk patients with peripheral vascular disease, the poor positive predictive value of preoperative ECG monitoring, and our uncertain ability to prevent postoperative myocardial infarction argue that routine preoperative ECG monitoring may not be ripe for general application.

John S. Kizer, MD
University of North CarolinaChapel Hill, North Carolina, USA