LETTER TO THE EDITOR
Evaluating coronary artery disease—where does EBCT fit in?: Reply
David M. Shavelle, MDa and
Matthew J. Budoff, MDb
a Division of Cardiology, Box 356422, University of Washington, Seattle, Washington 98195, USA
b Saint John’s Cardiovascular Research Center, 1124 West Carson Street, RB-2, Torrance, California 90502, USA
dshav{at}u.washington.edu Budoff{at}flash.net
We appreciate the comments of Drs. Sheppard and Eisenberg regarding our recent publication evaluating the use of electron beam computed tomography (EBCT) in symptomatic patients undergoing exercise stress testing and coronary angiography (1). The study population was indeed at high risk for coronary artery disease (CAD) as all patients were symptomatic with presumed ischemic chest pain and were referred for coronary angiography by their treating physicians. This population would therefore not be reflective of patients referred for EBCT to exclude the presence of CAD. By assuming a disease prevalence of 20%, compared to the prevalence of 69% in our study, Drs. Sheppard and Eisenberg found EBCT to have a negative predictive value of 98%, indicating an excellent ability to exclude CAD. Using values for sensitivity and specificity from a meta-analysis (2), they found technetium-stress testing to have the highest positive likelihood ratio among the testing methods, indicating a superior ability to diagnose CAD in this lower-risk population. We agree with these calculations and conclusions, but we stress that our patient population was significantly different from one with a disease prevalence of 20%. Therefore, our study did not evaluate a patient population referred to EBCT for the purpose of screening for CAD.
A significant limitation of our report was the relatively low sensitivity and specificity for technetium-stress testing. As outlined in the Discussion section, possibilities for this include imaging defects secondary to diaphragmatic and/or breast attenuation, the lack of electrocardiograph (ECG)-gating and delayed image acquisition after injection of the nuclear tracer agent. However, as Drs. Shepard and Eisenberg point out, another significant issue is the relatively small number of patients in our study (n = 97), which may be the main reason for these findings.
The suggestion that exercise echocardiography may be the best noninvasive diagnostic test because of its highest positive likelihood ratio (3.7) is possible, but this modality was not evaluated in our study.
The 95% confidence intervals (CIs) for the characteristics of each testing method are shown in Table 1. As Drs. Sheppard and Eisenberg suggest, the CIs for several of the testing methods are relatively wide. We agree that additional, larger studies are needed to further evaluate the utility of EBCT coronary scanning.
Dr. Danias points out similar concerns to Drs. Shepard and Eisenberg regarding the low sensitivity and specificity for technetium-stress testing. As discussed previously, this is clearly a limitation of our study and could potentially be resolved by evaluating a larger number of patients. Dr. Danias also expresses concern over the 27 patients who had a positive EBCT scan and a negative treadmill-ECG and were therefore classified as having a negative "test" for the combined approach (EBCT combined with treadmill-ECG). The mean coronary calcium (CC) score for these patients as determined by the Agatston method (3) was 394, range 1 to 1420. For this combined approach, a positive EBCT was defined as a CC score >0 in order to maximize sensitivity. Raising the CC score cutoff would lower sensitivity and raise specificity, as shown in Table 3 of our article (1). We agree with Dr. Danias that our study did not include a cost-effectiveness analysis, which would be useful in further determining the utility of EBCT in the evaluation of symptomatic patients. However, EBCT does have a relatively low cost, and other studies have documented its benefit in the diagnostic evaluation of patients with symptoms suggestive of CAD (4,5).
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References
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1. Shavelle DM, Budoff MJ, LaMont DH, Shavelle RM, Kennedy JM, Brundage BH. Exercise testing and electron beam computed tomography in the evaluation of coronary artery disease. J Am Coll Cardiol. 2000;36:32–38[Abstract/Free Full Text]
2. Fleischmann KE, Hunink MG, Kuntz KM, Douglas PS. Exercise echocardiography or exercise SPECT imaging? A meta-analysis of diagnostic test performance. JAMA. 1998;280:913–920[Abstract/Free Full Text]
3. Agatston A, Janowitz W, Hildner F, Zusmer N, Viamonte M Jr, Detrano R. Quantification of coronary artery calcium using ultrafast computed tomography. J Am Coll Cardiol. 1990;15:827–832[Abstract]
4. Kajinami K, Seki H, Takekoshi N, Mabuchi H. Noninvasive prediction of coronary artherosclerosis by quantification of coronary artery calcification using electron beam computed tomography: comparison with electrocardiographic and thallium exercise stress test results. J Am Coll Cardiol. 1995;26:1209–1221[Abstract]
5. LaMont DH, Budoff MJ, Shavelle DM, Brundage BH, Hager JM. Coronary calcium scanning identifies patients with false positive stress tests. (abstr)Circulation. 1997;96:306I
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