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Accuracy and Value of 64-Slice Coronary Computed Tomographic Angiography
Abstract & Commentary
By Harold L. Karpman, MD, FACC, FACP, Clinical Professor of Medicine, UCLA School of Medicine. Dr. Karpman reports no financial relationship to this field of study.
Synopsis: Compared with invasive coronary angiography, coronary computed tomographic angiography demonstrated high diagnostic accuracy for detection of obstructive coronary stenosis and a 99% negative predictive value.
Source: Budoff MJ, et al. 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.
Coronary computed tomographic angiography (CCTA) has emerged as a promising non-invasive method for the detection and exclusion of obstructive coronary artery disease (CAD).1 Unfortunately, early studies were potentially skewed because they were performed in subjects with high pretest likelihoods of CAD (i.e., frequently in patients with abnormal coronary calcium [CAC] scores and often with heavily calcified coronary artery segments, which diminished accuracy) and not in other groups such as those with a low or intermediate pretest likelihood of CAD. More recent studies with the newer 64-multidetector computed tomography (MDCT) scanners have demonstrated significant improvement in CCTA diagnostic accuracy compared with the older generation CT scanners.2 Miller and her colleagues very recently compared CCTA to invasive coronary angiography (ICA) and concluded that CCTA accurately identified the presence and severity of obstructive coronary artery disease, but that the negative and positive predictive values suggested that CCTA was not yet ready to replace ICA in patients with suspected coronary artery disease.3
Because a prospective multicenter trial evaluating the diagnostic accuracy of 64-multidetector row CCTA accuracy in patients without known CHD or with only an intermediate CHD risk score had not yet been reported, Budoff and his colleagues mounted a multicenter study at 16 sites in patients with only an intermediate CAD risk score. A total of 230 subjects complaining of chest pain were referred for ICA. Coronary artery calcium scores, CCTAs, and ICAs were obtained from all patients. CCTA was found to have a high diagnostic accuracy for detection of obstructive coronary artery stenosis in the patients with both 50% and 70% stenotic lesions (95% and 94% sensitivity), but most importantly, the negative predictive value was 99% in all patients, thereby establishing CCTA as an effective non-invasive alternative to ICA to rule out obstructive coronary artery stenosis in patients with chest pain.
The results of the ACCURACY (Assessment by Coronary Computed Tomographic Angiography of Individuals Undergoing Invasive Coronary Angiography) trial provide the first prospective multicenter data evaluating the diagnostic performance of current generation 64-multidetector row CCTA compared with the results of non-emergency ICA in symptomatic individuals without known CAD and with only an intermediate CAD risk score. When compared to a conventional angiogram, the diagnostic accuracy of CCTA in this study proved to be superb, recognizing the fact that the spatial resolution of a conventional angiogram is still somewhat superior because artifacts such as those produced by cardiac motion and focal calcifications are of minimal or no concern when performing and interpreting a conventional angiogram.
It is equally important to recognize that the negative predictive value of 99% on CCTA suggests that one of its important long-term values may be its ability to accurately predict the presence and severity of coronary artery obstructive disease, especially in the low or intermediate CAD risk subject. But not to be overlooked, the real importance of CCTA may lie not just in its value in defining the presence and degree of coronary artery stenosis, but rather in its unique ability to non-invasively evaluate the character of coronary artery plaques.4 As improvements in temporal and spatial resolution occur because of improving hardware and software technology, the presence of non-calcified, ulcerated, complex/ mixed, and other plaque morphology will undoubtedly become more accurately defined and become part of every CCTA report. Eventually, this knowledge will permit us to carefully evaluate plaque severity and characteristics thereby improving prognostic capability. Of course, the coronary artery calcium score will also provide incremental prognostic information when estimating the severity of coronary artery stenosis.5
In summary, the ACCURACY trial is an important milestone in evaluating the diagnostic accuracy of CCTA with respect to obstructive CAD using a simple, non-invasive imaging technique that has the important capability of probably being able to accurately define plaque morphology and characteristics. As these abilities become more refined, CCTA may prove to be of inestimable value in the diagnosis and treatment of CAD and perhaps may even prove to have a diagnostic and therapeutic impact similar to that which echocardiography had when it was first introduced into clinical practice more than 30 years ago. The extremely high negative predictive values of CCTA and CAC scores will help the clinician assess chest pain occurring in low or intermediate CAD risk patients. Finally, it should be noted that recent technological improvements in 64- and 128 multidetector row imaging units have permitted the reduction of radiation exposure to one-tenth of previous radiation dosage; therefore, the indications for the use of this technology will undoubtedly broaden and grow in the very near future.
1. Hamon M, et al. Diagnostic performance of multislice spiral computed tomography of coronary arteries as compared with conventional invasive coronary angiography: A meta-analysis. J Am Coll Cardiol 2006;48: 1896-1910.
2. Hamon M, et al. Coronary arteries: Diagnostic performance of 16- versus 64-section spiral CT compared with invasive coronary angiographymeta-analysis. Radiology 2007;245:720-731.
3. Miller JM, et al. Diagnostic performance of coronary angiography with 64-row CT. N Engl J Med 2008; 359:2324-2336.
4. Hoffmann U, et al. Noninvasive assessment of plaque morphology and composition in culprit and stable lesions in acute coronary syndrome and stable lesions in stable angina by multidetector computed tomography. J Am Coll Cardiol 2006;47:1655-1662.
5. Keelan PC, et al. Long-term prognostic value of coronary calcifications detected by electronic-beam computed tomography in patients undergoing coronary angiography. Circulation 2001;104:412-417.