CORRESPONDENCE: LETTER TO THE EDITOR
Reply
W. Bob Meijboom, MD,
Matthijs F.L. Meijs, MD,
Joanne D. Schuijf, MD, PhD,
Maarten J. Cramer, MD, PhD,
Nico R. Mollet, MD, PhD,
Carlos A.G. van Mieghem, MD,
Koen Nieman, MD, PhD,
Jacob M. van Werkhoven, MD,
Gabija Pundziute, MD,
Annick C. Weustink, MD,
Alexander M. de Vos, MD,
Francesca Pugliese, MD,
Benno Rensing, MD, PhD,
J. Wouter Jukema, MD, PhD,
Jeroen J. Bax, MD, PhD,
Mathias Prokop, MD, PhD,
Pieter A. Doevendans, MD, PhD,
Myriam G. Hunink, MD, PhD,
Gabriel P. Krestin, MD, PhD and
Pim J. de Feyter, MD, PhD*
* Department of Cardiology and Radiology, Erasmus Medical Center, Room Hs 227 ‘s Gravendijkwal 230, P.O. Box 2040, 3015 GD Rotterdam, the Netherlands (Email: p.j.defeyter{at}erasmusmc.nl).
Coronary multidetector computed tomography (MDCT) is a relatively recent noninvasive diagnostic modality. The first 4-slice computed tomography (CT) scan was introduced in 1999; since then the technique has undergone rapid technological improvements, with introduction of 64-, 128-, 256-, and 320-slice MDCT scanners that have resulted in better, high-quality coronary images. Coronary CT has an enormous appeal, not only because of the sometimes spectacular and seductive cardiac images—this noninvasive diagnostic modality may potentially be able to replace invasive coronary angiography. This might have led to initial over-enthusiasm that prompted use of this new technique in many clinical situations, although the necessary evidence to support this was lacking.
However, in the meantime, many CT studies have been published, and together with 3 large-sized multicenter studies it has been clearly shown that: 1) coronary MDCT is reliable to rule out the presence of significant coronary stenoses in patients with suspected coronary artery disease; and 2) the current state-of-the-art CT technique cannot replace invasive coronary angiography (1–3). We agree with Drs. Min and Berman that the ability of CT to exclude disease is important for patients. But we also know that coronary CT is not perfect. Several issues, including radiation exposure, calcifications, and arrhythmias, are still problematic for coronary CT scanning. Initially coronary MDCT was associated with a rather high radiation exposure; new protocols (prospective electrocardiogram [ECG]-triggered acquisition) or radiation exposure-reducing technology (ECG gated tube modulation) have now achieved acceptable radiation exposure—as low as 2 to 3 mSv (4). Coronary calcification causing misinterpretation of the presence and severity of coronary stenoses remains a significant problem that can only be alleviated by better CT detector technology that significantly improves the spatial resolution. Very recently the Gemstone scintillator technology has been introduced that, in an ideal phantom setting, significantly improved the spatial resolution up to 230 µm. Also the problems of significant cardiac arrhythmias (atrial fibrillation), which are still problematic for cardiac CT, will be resolved by new CT technology that needs only 1 heartbeat to acquire data for coronary imaging. Another problem, raised by Dr. Nicol and colleagues, is overestimation of visual assessment of the severity of CT coronary stenoses, which has in the past also been a problem with invasive coronary angiography. Accurate automated contour-detection algorithms developed for coronary MDCT might resolve this issue. Another important issue raised by Dr. Nicol and colleagues is the mismatch between CT anatomy imaging and functional imaging. The assumption that a significant stenosis defined as >50% luminal diameter is hemodynamically significant is not always confirmed by myocardial perfusion imaging or invasive coronary stenosis pressure measurements (fractional flow reserve), and in particular a significant mismatch between anatomical severity of a stenosis and functional severity of a stenosis often occurs in intermediate lesions (5,6). However, increasing the severity of a stenosis to a cutoff level of 70% will result in a better agreement with myocardial perfusion imaging as suggested by Dr. Nicol and colleagues, but the price to be paid is lower sensitivity and consequent decrease in negative predictive value, which is considered 1 of the major strengths of coronary CT imaging. We agree with Dr. Nicol and colleagues that more studies are required to define the most acceptable cutoff level of the severity of a stenosis (50% vs. 70%) either determined by visual or automated contour detection algorithms.
Importantly, only scant information is available about the role of noninvasive coronary anatomy information as compared with functional information obtained by exercise ECG stress testing, stress echocardiography, or single-photon emission computed tomography. It is always difficult for a new diagnostic modality to establish its role among already available diagnostic modalities, and it will take time to provide scientific evidence to demonstrate the diagnostic performance and value of the new technique in various clinical situations and even more time to establish its cost-effectiveness. Although we are still enthusiastic about the potential of coronary CT, we are also aware of the fact that more scientific evidence should become available before we can recommend widespread use of this exciting new diagnostic modality.
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1. Miller JM, Rochitte CE, Dewey M, et al. Diagnostic performance of coronary angiography by 64-row CT N Engl J Med 2008;359:2309-2311.[CrossRef][Web of Science][Medline]2. Budoff MJ, Dowe D, Jollis JG, Gitter M, Sutherland J, Halamert E. Diagnostic performance of 64-multidetector row coronary computed tomographic angiography for evaluation of coronary artery stenosis in individuals without known coronary artery disease: results from the prospective multicenter ACCURACY (Assessment by Coronary Computed Tomographic Angiography of Individuals Undergoing Invasive Coronary Angiography) trial J Am Coll Cardiol 2008;52:1724-1732.[Abstract/Free Full Text] 3. Meijboom WB, Meijs MF, Schuijf JD, et al. Diagnostic accuracy of 64-slice computed tomography coronary angiography: a prospective, multicenter, multivendor study J Am Coll Cardiol 2008;52:2135-2144.[Abstract/Free Full Text] 4. Herzog BA, Husmann L, Burkhard N, et al. Accuracy of low-dose computed tomography coronary angiography using prospective electrocardiogram-triggering: first clinical experience Eur Heart J 2008;29:3037-3042.[Abstract/Free Full Text] 5. Schuijf JD, Wijns W, Jukema JW, et al. Relationship between noninvasive coronary angiography with multi-slice computed tomography and myocardial perfusion imaging J Am Coll Cardiol 2006;48:2508-2514.[Abstract/Free Full Text] 6. Meijboom WB, Van Mieghem CAG, Pelt N, et al. Comprehensive assessment of coronary artery stenoses: computed tomography coronary angiography versus conventional coronary angiography and correlation with fractional flow reserve in patients with stable angina J Am Coll Cardiol 2008;52:636-643.[Abstract/Free Full Text]
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