LETTER TO THE EDITOR
Stress testing and electron beam computed tomography for evaluation of patients with suspected coronary artery disease
Peter G. Danias, MD, PhDa
a Beth Israel Deaconess Medical Center, 330 Brookline Avenue, Boston, Massachusetts 02215, USA
pdanias{at}caregroup.harvard.edu
I read with interest the study by Shavelle et al. (1) on the value of exercise testing and electron beam computed tomography (EBCT) in the evaluation of coronary artery disease (CAD). The investigators report that when applied to a population referred for angiography, EBCT has a sensitivity of 96% and a specificity of 47% for detection of significant CAD (defined as  50% diameter stenosis), and they conclude that "Electron beam computed tomography has a higher diagnostic ability than either treadmill ECG or technetium-stress for the detection of obstructive angiographic CAD." They also suggest that a combination of EBCT (for optimal sensitivity) with ECG stress testing (for improved specificity and functional information) might be the preferred approach for evaluating patients with suspected CAD.
Both these conclusions have to be viewed with skepticism: The sensitivity of nuclear stress testing in their study (78%) is low, almost equal to that of treadmill ECG (76%). When a broader definition of "positive scan results" was used (either fixed or reversible perfusion defects), the sensitivity was even lower (75%). Other than a typographic error, I can see no explanation to this paradox. Several studies have demonstrated that nuclear stress testing has a significantly higher sensitivity for detection of CAD than hereby presented. Even in the meta-analysis that the investigators quote (2), an almost 10% higher sensitivity (87%) was reported, despite the inclusion of several older studies and some with a stricter definition of "significant CAD" (70% diameter stenosis).
The investigators identify a number of reasons that could explain the lower than expected specificity of nuclear testing in their study, including the absence of ECG-gating and the high likelihood of attenuation-induced defects. However, the low sensitivity in the study is not adequately explained: If both fixed and reversible defects were considered as abnormal, the underestimation of reversibility that the authors quote (3,4) (and which has been described for assessment of myocardial viability) should not underestimate the sensitivity for detection of CAD. Moreover, the potential Tc-99m redistribution that the researchers consider as a source of decreased test sensitivity is minimal (3,5), if any at all (6,7), and is unlikely to completely normalize significant perfusion defects. In any case, the reference that Shavelle et al. quote (8) to support their contention that redistribution might account for their low Tc-99m stress test sensitivity does not address this issue.
Finally, the combined assessment of EBCT and treadmill ECG should be evaluated with caution. In the Shavelle et al. study, 27 patients with a positive EBCT scan, one third of all positive EBCT scans, were considered as having a negative "test." What was the severity of coronary calcification in these patients? Should not the extent of calcification also be taken into account, if a combined test approach were to be used?
The utility of EBCT as a research tool is unquestionable. However, the clinical utility of EBCT, and for that matter any diagnostic test, should be judged on its incremental value above and beyond existing tests, or by the demonstration of a lower cost with at least equal diagnostic and prognostic value. The fact that EBCT has relatively low cost does not necessarily mean that it is also a cost-efficient technique. The study by Shavelle et al. (1) does not include a cost-efficiency analysis, and until newer data are available, the clinical role of EBCT (or EBCT plus treadmill ECG) for evaluation of patients with suspected CAD remains uncertain.
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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. (see comments)JAMA. 1998;280:913–920[Abstract/Free Full Text]
3. Dilsizian V, Arrighi JA, Diodati JG, et al. Myocardial viability in patients with chronic coronary artery disease. Comparison of 99mTc-sestamibi with thallium reinjection and [18F]fluorodeoxyglucose. Circulation. 1994;89:578–587[Abstract/Free Full Text]
4. Maurea S, Cuocolo A, Nicolai E, Salvatore M. Improved detection of viable myocardium with thallium-201 reinjection in chronic coronary artery disease: comparison with technetium-99m-MIBI imaging. J Nucl Med. 1994;35:621–624[Abstract/Free Full Text]
5. Li QS, Solot G, Frank TL, Wagner HN Jr, Becker LC. Myocardial redistribution of technetium-99m-methoxyisobutyl isonitrile (SESTAMIBI). J Nucl Med. 1990;31:1069–1076[Abstract/Free Full Text]
6. Glover DK, Okada RD. Myocardial kinetics of Tc-MIBI in canine myocardium after dipyridamole. Circulation. 1990;81:628–637[Abstract/Free Full Text]
7. Okada RD, Glover D, Gaffney T, Williams S. Myocardial kinetics of technetium-99m-hexakis-2-methoxy-2-methylpropyl-isonitrile. Circulation. 1988;77:491–498[Abstract/Free Full Text]
8. DePuey EG, Parmett S, Ghesani M, Rozanski A, Nichols K, Salensky H. Comparison of Tc-99m sestamibi and Tl-201 gated perfusion SPECT. J Nucl Cardiol. 1999;6:278–285[CrossRef][Medline]
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