Letter by Gaibazzi Regarding Article, “Usefulness of 64-Slice Cardiac Computed Tomographic Angiography for Diagnosing Acute Coronary Syndromes and Predicting Clinical Outcome in Emergency Department Patients With Chest Pain of Uncertain Origin”
To the Editor:
I congratulate the authors of the interesting article, “Usefulness of 64-Slice Cardiac Computed Tomographic Angiography for Diagnosing Acute Coronary Syndromes and Predicting Clinical Outcome in Emergency Department Patients With Chest Pain of Uncertain Origin,” for their well-conducted study.1
In the Clinical Implications section, the authors state “MDCT [multidetector computed tomographic] scanning has the potential to change clinical practice with respect to ED [emergency department] triage in patients with chest pain of uncertain origin.” I hope this is not going to happen, since my point is that it would be very unfortunate.
The interest in clinical use of MDTC for coronary artery disease detection has been overinflated in the last few years, driven by equipment vendors for obvious, nonscientific reasons, as is typical for any new technology. MDCT is able to show nice-looking pictures of the coronaries, and a negative scan can approximate 100% of negative predictive power for coronary artery disease, but when used in chest pain units, the information it adds is trivial in comparison with low-cost, well-established imaging modalities.
In fact, stress echocardiography has demonstrated exceptionally high negative predictive power in multicenter studies with large samples, such as the Stress Pharmacological Echocardiography in Emergency Department (SPEED) trial,2 with negative predictive power of 98.8% for all cardiovascular events and 99.6% for “hard” cardiovascular events. Conversely, a positive MDCT scan (presence of >50% coronary stenosis) often presents a diagnostic dilemma in that MDCT is not able to address the functional significance of a stenosis. In case of a positive result, a stress test becomes mandatory before or after diagnostic coronary angiography, making the initial MDCT scan once again redundant (“a costly picture”).
Even more important, patient radiation exposure tends to be understated or “forgotten” in clinical studies and in clinical practice. This exposure represents a serious downside to this imaging modality, with the 10 to 20 mSv exposure dose of the scan corresponding to 1 new (fatal or nonfatal) cancer for every 1000 to 500 scans, according to the latest estimate of the authoritative Biological Effects of Ionizing Radiation Seventh Committee, released in 2005 from the US National Research Council.3
So what is the role of MDCT scanning in the chest pain unit? Do we need a 1% gain in negative predictive power (from 99% to 100%) paid for by radiation exposure and unbelievably higher financial costs? Long-term risks should be included in the risk–benefit assessment of our procedures.
Rubinshtein R, Halon DA, Gaspar T, Jaffe R, Karkabi B, Flugelman MY, Kogan A, Shapira R, Peled N, Lewis BS. Usefulness of 64-slice cardiac computed tomographic angiography for diagnosing acute coronary syndromes and predicting clinical outcome in emergency department patients with chest pain of uncertain origin. Circulation. 2007; 115: 1762–1768.
Health Risks From Exposure to Low Levels of Ionizing Radiation: Biological Effects of Ionizing Radiation Seventh Committee, Phase 2 (2006). Available at: http://books.nap.edu/openbook.php?isbn=030909156X. Accessed August 18, 2007.