Meta-analysis: Noninvasive imaging provides risk stratification before vascular surgery
ACP J Club. 1996 Sept-Oct;125:44. doi:10.7326/ACPJC-1996-125-2-044
Shaw LJ, Eagle KA, Gersh BJ, Miller DD. Meta-analysis of intravenous dipyridamole-thallium-201 imaging (1985 to 1994) and dobutamine echocardiography (1991 to 1994) for risk stratification before vascular surgery. J Am Coll Cardiol. 1996 Mar 15;787-98. [PubMed ID: 8613604]
To determine the prognostic value of preoperative pharmacologic stress imaging for risk stratification of patients having vascular surgery.
Published studies were identified in MEDLINE using the terms radionuclide imaging, dipyridamole, preoperative, and coronary artery disease (1985 to 1994) and dobutamine, echocardiography, and preoperative (1990 to 1994).
Peer-reviewed English-language studies that provided cardiac event rates classified by noninvasive test results were selected. Studies of nonvascular surgery were excluded. 10 studies on dipyridamole-thallium-201 myocardial perfusion imaging included 1994 patients, and 5 studies on dobutamine echocardiography included 445 patients.
A quality assessment grade (A to D) was assigned to each study. Studies that could be generalized to various patients and had no important methodologic flaws (grade A) and those that were more narrowly generalized with a few well-described methodologic flaws (grade B) were included. Extracted data were study design, clinical and test characteristics, and study end points (cardiac death, myocardial infarction [MI], recurrent ischemia, and congestive heart failure).
Results of dipyridamole-thallium-201 imaging were normal in 36% of patients, fixed perfusion defects were seen in 24% of patients, and 40% of patients had ≥ 1 reversible defects. For normal results, fixed defects, and reversible defects, cardiac event rates were 3%, 11%, and 18%, respectively; for cardiac death or MI, rates were 1%, 7%, and 9%, respectively. The summary odds ratio for prediction of any cardiac event by dipyridamole-thallium-201 imaging was 3.5 (95% CI 2.5 to 4.8); for cardiac death or MI, the odds ratio was 3.9 (CI 2.5 to 5.6). The pretest probability of coronary disease was correlated with the positive predictive value of a reversible thallium-201 defect (r = 0.70). The positive predictive value of an abnormal test result increased 6-fold between patients with the lowest to highest pretest probability of coronary artery disease. In 5 studies of dobutamine stress echocardiography, cardiac event rates ranged from 4% to 29%. Approximately one third of the patients had a dobutamine-induced ischemic response (range 3% to 50%). Cardiac event rates were 0.4% in patients with a normal response and 26% for patients with a new wall motion abnormality. The summary odds ratio for prediction of any cardiac event was 27.4 (CI 13.0 to 57.7) and was 14.4-fold (CI 5.3 to 39.2) greater for cardiac death or nonfatal MI.
Pharmacologic stress imaging is useful in predicting operative risk in patients having vascular surgery. The accuracy of the tests is affected by pretest disease prevalence.
Source of funding: Department of Veterans Affairs.
For article reprint: Dr. D.D. Miller, Division of Cardiology, Saint Louis University Health Sciences Center, 3635 Vista at Grand Boulevard, 14th Floor, Cardiology, St. Louis, MO 63110, USA. FAX 314-268-5108.
The meta-analysis by Shaw and colleagues provides no new information about the appropriateness of dipyridamole-thallium-201 imaging. It does, however, validate the use of dobutamine echocardiography as an equally accurate method of stratifying patients having vascular surgery who are at intermediate risk (1 to 2 of the following risk factors: age > 70 y, congestive heart failure, diabetes, angina, Q-waves on electrocardiogram, ST depression, or ventricular arrhythmia) (1) into high- and low-risk groups. A concern of all studies in this meta-analysis was that enrolled patients were "consecutive series," which means that only patients referred for the test in question were included. Physicians who do preoperative consultations have no way of knowing how many patients were referred, how many had immediate invasive cardiac testing or procedures, or how many were evaluated as low-risk and sent immediately to surgery. At present, the algorithm proposed by Palda, Detsky, and the American College of Physicians (2, 3) for risk stratification is the preferred tool for cardiac evaluation of patients scheduled for vascular surgery. This algorithm identifies risk categories based on the Modified Cardiac Risk Index (4). Intermediate risk (3% to 15% risk for perioperative cardiac events) patients can be further stratified on the basis of dipyridarnole-thallium-201 imaging or stress echocardiography. Any positive test result is classified as high-risk; a normal test classifies the patient as low-risk.
Elizabeth Kozak, MD
Butterworth HospitalGrand Rapids, Michigan, USA