CORRESPONDENCE: LETTER TO THE EDITOR
Value of Multislice Computed Tomography Coronary Angiography in Suspected Coronary Artery Disease
Khurram Nasir, MD, MPH*,
Matthew J. Budoff, MD,
Leslee J. Shaw, PhD and
Roger S. Blumenthal, MD
* MGH Cardiac MRI PET CT Program, Massachusetts General Hospital, Harvard Medical School, 165 Charles River Plaza 400, Boston, Massachusetts 02114 (Email: knasir{at}partners.org).
We read with great interest the recent study by Pundziute et al. (1) and congratulate the investigators for demonstrating the utility of multislice computed tomography (MSCT) findings in predicting coronary artery disease (CAD) events. In all patients, a coronary artery noncontrast scan was performed to determine coronary artery calcification (CAC) scores followed by contrast-enhanced computed tomography angiography (CTA). In this study, a strong trend (p = 0.06) was found on univariate analysis between CAC scores and CAD events. Conversely, CAC scores were not used in multivariate analysis as they did not reach a level of significance (p  0.05).
In our experience, determination of CAD risk with CAC scores as a continuous variable in standard parametric analyses is extremely challenging owing to high frequency of zero scores resulting in a highly skewed distribution. The approach of assessing the hazard ratio for CAD events in a sample size of 100 patients for 1-U increase in CAC score, as in this study, would result in significant loss of information, would reduce the analytic power, and somewhat bias the findings, primarily because of the nonlinear nature of risk across the CAC range (2). Therefore, largely in standard clinical practice and in outcome studies, CAC scores are more appropriately employed as categorical variables (3–5), based on cutoffs that approximate underlying burden of coronary atherosclerosis.
In addition, a 100% event-free survival was observed in patients without any abnormalities on CTA, highlighting an excellent negative predictive value; this is reassuring and in agreement with previous studies demonstrating similar results with absence of CAC (6,7). Also of note is the finding that the 25th to 75th percentile of CAC score among patients who had an event ranged from 122 to 552. It appears that those with scores <100, let alone in the absence of CAC, did not suffer events.
These findings also raise a critical question. Can we potentially use information from the CAC scores to best identify individuals who may need further evaluation with CTA, which is definitely a more advanced and informative technique, but also associated with higher cost, is more time-consuming, and has potential risks from higher ionizing radiation and need for intravenous contrast? Based on findings from current and previous studies, we believe that performing CTA in the setting of zero CAC on a noncontrast CT may not further provide significant prognostic information for future CAD events. As a result, low CAC scores and/or absence of CAC could serve as a cost-effective, initial filter before selecting patients who would benefit from further evaluation with CTA (8). However, performing CTA among those with intermediate to high CAC scores may potentially identify those at higher risk for events.
Furthermore, to better comprehend the independent prognostic significance of MSCT as a prognostic modality predicting CAD, we encourage the researchers to 1) identify the relationship of increasing CAC burden on the initial noncontrast scans with CAD events based on standard cutoffs (e.g., 0, 1 to 10, 11 to 100, >100) rather than using it as a continuous variable; 2) assess whether information gained from subsequent CTA provides prognostic information above and beyond CAC score categories obtained on noncontrast scan; and 3) most importantly, describe whether there is any added value of performing a CTA among those with low CAC and/or CAC = 0 in predicting CAD events. We believe similar studies employing multimodal imaging in conjunction with outcome data will improve our understanding of the appropriate utilization of sensitive imaging markers in assessing future CAD risk in a more effective manner.
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Footnotes
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Please note: None of the authors have a conflict of interest with this study. Dr. Budoff is with the Speakers’ Bureau of Pfizer and GE Healthcare and Dr. Shaw receives grant support from GE Healthcare.
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References
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- Pundziute G, Schuijf JD, Jukema JW, et al. Prognostic value of multislice computed tomography coronary angiography in patients with known or suspected coronary artery disease J Am Coll Cardiol 2007;49:62-70.[Abstract/Free Full Text]
- Reilly MP, Wolfe ML, Localio AR, Rader DJ. Coronary artery calcification and cardiovascular risk factors: impact of the analytic approach Atherosclerosis 2004;173:69-78.[CrossRef][ISI][Medline]
- Taylor AJ, Bindeman J, Feuerstein I, Cao F, Brazaitis M, O’Malley PG. Coronary calcium independently predicts incident premature coronary heart disease over measured cardiovascular risk factors: mean three-year outcomes in the Prospective Army Coronary Calcium (PACC) project J Am Coll Cardiol 2005;46:807-814.[Abstract/Free Full Text]
- Raggi P, Shaw LJ, Berman DS, Callister TQ. Prognostic value of coronary artery calcium screening in subjects with and without diabetes J Am Coll Cardiol 2004;43:1663-1669.[Abstract/Free Full Text]
- Arad Y, Goodman KJ, Roth M, Newstein D, Guerci AD. Coronary calcification, coronary disease risk factors, C-reactive protein, and atherosclerotic cardiovascular disease events: the St. Francis Heart Study J Am Coll Cardiol 2005;46:158-165.[Abstract/Free Full Text]
- Georgiou D, Budoff MJ, Kaufer E, Kennedy JM, Lu B, Brundage BH. Screening patients with chest pain in the emergency department using electron beam tomography: a follow-up study J Am Coll Cardiol 2001;38:105-110.[Abstract/Free Full Text]
- Keelan PC, Bielak LF, Ashai K, et al. Long-term prognostic value of coronary calcification detected by electron-beam computed tomography in patients undergoing coronary angiography Circulation 2001;104:412-417.[Abstract/Free Full Text]
- Budoff MJ, Achenbach S, Blumenthal RS, et al. Assessment of coronary artery disease by cardiac computed tomography: a scientific statement from the American Heart Association Committee on Cardiovascular Imaging and Intervention, Council on Cardiovascular Radiology and Intervention, and Committee on Cardiac Imaging, Council on Clinical Cardiology Circulation 2006;114:1761-1791.[Free Full Text]
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