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


Diagnosis

Single-photon emission tomography was accurate for investigating coronary artery disease

ACP J Club. 1991 Jan-Feb;114:20. doi:10.7326/ACPJC-1991-114-1-020


Source Citation

Mahmarian JJ, Pratt CM, Cocanougher MK, Verani MS. Altered myocardial perfusion in patients with angina pectoris or silent ischemia during exercise as assessed by quantitative thallium-201 single-photon emission computed tomography. Circulation. 1990 Oct;82:1305-15.


Abstract

Objective

To determine whether patients who have silent ischemia during exercise testing differ in reversible perfusion defects from patients who have chest pain.

Design

Independent, blinded comparisons of quantitative single-photon emission computed tomography (SPECT), electrocardiography, and coronary angiography (the criterion standard for diagnosis of coronary artery stenosis) in describing coronary artery disease.

Setting

Exercise testing laboratory in Texas, USA.

Patients

356 consecutive patients aged 29 to 83 years (59% men) were referred for exercise SPECT. 18% were asymptomatic. Patients who had had previous coronary revascularization procedures were excluded.

Description of test and diagnostic standard

Just before the end of symptom-limited treadmill exercise, patients were injected intravenously with thallium-201. Within 5 minutes, SPECT was begun with a gamma camera. Tomographic images were assessed visually and by computer. Coronary angiography (diagnostic standard) was done a mean of 5.1 days before or 2.8 days after SPECT. All tests were interpreted by experts blinded to the angiographic findings, and inter-observer and intra-observer agreements were at least 80%.

Main outcome measures

Coronary artery disease was diagnosed if angiography indicated the patient had stenosis of > 50% of ≥ 1 coronary arteries. The presence, site, and size of perfusion defects were measured by visual and quantitative SPECT. Ischemia was measured by electrocardiogram during exercise testing.

Main results

Of 356 patients, 52 (15%) had chest pain during exercise. Of 219 patients with stenoses of > 50%, no significant differences existed between those with chest pain (30 patients [14%]) and those without (189 patients [86%]) in extent, distribution, or severity of stenoses. Quantitative SPECT identified 190 (sensitivity 87%) of those with stenoses of > 50%. Specificity was 88% (64 of 73 patients). {The likelihood ratio of a positive test was 7.04 and the likelihood ratio of a negative test was 0.15.}* Mean perfusion defect size was 21% ± 15% for patients with significant coronary artery disease; size was not related to pain. On visual scintigraphy 118 (54%) patients with coronary artery disease had reversible perfusion defects. These were not significantly related to chest pain. In comparison with exercise electrocardiography, which detected 88 (40%) patients with ischemia, scintigraphy was better (P < 0.001).

Conclusion

Chest pain during exercise testing was a poor indicator of coronary artery disease with abnormally perfused myocardium. Single-photon emission tomography was a sensitive and specific method of investigating coronary artery disease compared with angiography and stress electrocardiography.

Source of funding: National Institutes of Health.

Address for article reprint: Dr. M. S. Verani, Department of Internal Medicine, Baylor College of Medicine, The Methodist Hospital, 6535 Fannin, F-905, Houston, TX 77030, USA.

*Numbers calculated from data in article.


Commentary

The results of the study by Mammarian and colleagues confirm what is now well known, that asymptomatic coronary artery disease is far more prevalent than symptomatic coronary artery disease. However, a great deal of difference exists between coronary artery stenosis and active ischemia. For example, the authors emphasize the high sensitivity rate of thallium-201 SPECT (87%) in diagnosing silent ischemia, but only 54% (118 of 219) of these patients had a reversible perfusion defect. Thus, if one were to use presence of reversible perfusion defect (which is the accepted criterion for diagnosis of myocardial ischemia on thallium-201) as evidence of myocardial ischemia, only 54% would be diagnosed by SPECT findings. Although the authors state that "all thallium-201 abnormalities in patients without previous history of myocardial infarction should presumably reflect only viable myocardium," they fail to provide evidence to support this concept. More important, the authors themselves point out that patients with chest pain had a lower heart rate, lower blood pressure, and lower double product, suggesting that these patients did indeed have earlier onset of ischemia.

Among patients with asymptomatic coronary artery disease, we do not know whether abnormal SPECT findings are associated with poor prognosis. Although the authors speculate that the scintigraphic results of the study support the claims of prognostic studies, which showed that the presence of symptomatic or asymptomatic ischemia during exercise identifies patients at high risk for cardiac events, they provide no follow-up data that documents the rate of these events in their patients. It is necessary to do careful follow-up studies of patients found to have evidence of ischemia by new techniques such as SPECT to determine the clinical role of these tests.

Prakash C. Deedwania, MD
University of California, San FranciscoFresno, California, USA