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In persons with multiple risk factors, high coronary calcium scores (e.g., =75th percentile for age and sex) denote advanced coronary atherosclerosis and provide a rationale for intensified LDL-lowering therapy.
ATP III does not recommend EBCT for indiscriminate screening for coronary calcium in asymptomatic persons, particularly in persons without multiple risk factors. Its predictive power for persons without multiple risk factors has not been determined in prospective studies. (National Heart Lung and Blood Institute, 2002)
Background Computed tomography angiography (CTA), is a noninvasive, radiographic technique that rapidly provides images of the coronary arteries after intravenous injection of a contrast agent. The goal of CTA is to detect heart disease caused by partial or complete blockages in the coronary arteries.
Research Suspected CAD Although diagnostic accuracy is vastly improved with new advances in MSCT, MSCT cannot yet replace coronary angiography for diagnosing CAD in every patient presenting with chest pain, particularly in patients who are considered at high risk for CAD. The appearance of stenoses is still impacted by many factors, e.g., degree of calcification in coronary vessel segments, vessel size, and close anatomical relationship to coronary veins, and CAG may be required before a treatment plan is developed. Other limitations of MSCT include the relatively high radiation dosages and the lack of validated algorithms quantifying the degree of lumen narrowing.
However, diagnostic performance of 16- and 64-slice CT may be sufficient (NPV is maintained at 95% to 99%) to enable the technology to serve as a triage tool for eliminating CAD as a cause of chest pain in patients at low risk for CAD.
Additional research is needed to establish appropriate patient selection criteria, to specify triage parameters, to investigate the impact on patient health outcomes, and to define the role of MSCT in triaging patients for invasive coronary angiography. (Hayes, 2007) For coronary arteries, CTA requires at least a 16-slice CT system to achieve sufficient temporal resolution to image the beating heart. Temporal resolution refers to the imaging modality's effective scan time - that is, whether images are captured fast enough to avoid blurring. However, a 64-slice CT is preferable in cardiac imaging to obtain high-quality diagnostic images. In addition, 64-slice CT has also been shown to provide better specificity and positive predictive value than 16-slice CT in detecting CAD. Although high-end multislice CT is also available as 32- and 40-slice systems, ECRI Institute experts have found that the current U.S. market for CT systems is essentially divided between 16- and 64-slice (including dual-source CT) systems. (ECRI, 2007a) Miller, et al. (2008) conducted a prospective, multicenter study to examine the accuracy of 64-row multidetector CT angiography as compared with conventional coronary angiography in patients with suspected CAD. The study included 291 patients who had been referred for conventional coronary angiography; the majority of patients were white males and the median patient age was 59 years. Of 291 patients, 56% were found to have obstructive CAD. The 64-CT scanner was 93% as accurate as traditional angiography in identifying patients with the highest degree of CAD. Overall, the CT angiograms identified 85% of patients with heart disease and 90% of patients who were disease free. The 64-CT scanner was able to positively predict 91% of patients with the most severe disease and only 83% of patients with less severe disease. CT angiography was able to identify 84% of patients who went on to undergo revascularization versus 82% for conventional angiography. There was virtually no difference noted between CT and conventional angiography in the Cardiac Computed Tomography (CT), Coronary Artery Calcium Scoring and Cardiac CT Angiography - Commercial Medical Management Guideline ability to evaluate diseased vessel segments and diseased vessels. Although, multidetector CT angiography accurately identified the presence and severity of obstructive coronary artery disease, the authors concluded that multidetector CT angiography cannot replace conventional coronary angiography at present.
Pooling the data of more than 800 patients from recent studies analyzing the accuracy of 64-slice CT and dual-source CT for the detection of coronary artery stenoses in patients with suspected coronary artery disease, yields a sensitivity of 89% (95% CI 87-90) with a specificity of 96% (95% CI 96-97) and a positive and negative predictive value of 78% (95% CI 76-80) and 98% (95% CI 98-99), respectively. Most of the available data concerning the detection of coronary stenoses by CT angiography have been obtained in patient groups with suspected CAD and stable symptoms. The consistently high negative predictive value in all studies suggests that CT angiography will be clinically useful to rule out coronary stenoses in this patient group. In patients with a very high pre-test likelihood of disease, the use of CT angiography will most likely not result in a 'negative' scan that would help avoid invasive angiography. Therefore, the use of CT angiography should be restricted to patients with an intermediate pre-test likelihood of CAD. (Schroeder, 2008) The prospective multicenter ACCURACY (Assessment by Coronary Computed Tomographic Angiography (CCTA) of Individuals Undergoing Invasive Coronary Angiography) trial evaluated the diagnostic accuracy of 64-multidetector row CCTA in populations with intermediate prevalence of CAD. Results showed that 64-multidetector row CCTA possessed high diagnostic accuracy for detection of obstructive coronary stenosis at both thresholds of 50% and 70% stenosis.
Importantly, the 99% negative predictive value at the patient and vessel level establishes CCTA as an effective noninvasive alternative to invasive coronary angiography to rule out obstructive coronary artery stenosis. (Budoff, 2008) Hausleiter, et al reported the results of the CACTUS trial, a prospective, blinded study that investigated the diagnostic value of coronary MSCT angiography in patients with an intermediate pre-test probability for having CAD when compared with invasive angiography. Of 243 enrolled patients, 129 and 114 patients were studied by 16- and 64-slice CT angiography, respectively. The overall sensitivity, negative predictive value, and specificity for CAD detection by MSCT were 99% (95% CI, 94-99%), 99% (95% CI, 94-99%), and 75% (95% CI, 67-82%), respectively. On a per-segment basis, the use of 64-slice CT was associated with significantly less inconclusive segments (7.4 vs. 11.3%, P 0.01), resulting in a trend to an improved specificity (92 vs. 88%, P = 0.09). In addition, the investigators concluded that 64slice CT appears to be superior for CAD detection when compared with 16-slice CT. (Hausleiter, 2007) A meta analysis of 29 studies compared multislice spiral computed tomography (MSCT) with conventional invasive coronary angiography (CA) for the diagnosis of coronary artery disease (CAD). The per-segment analysis pooled the results from 27 studies corresponding to a cumulative number of 22,798 segments. Among unassessable segments, 4.2% were excluded from the analysis and 6.4% were classified at the discretion of the investigators, underscoring the shortcomings of MSCT. With this major limitation, the per-segment sensitivity and specificity were 81% (95% confidence interval [CI] 72% to 89%) and 93% (95% CI 90% to 97%), respectively, with positive and negative likelihood ratios of 21.5 (95% CI 13.1 to 35.5) and 0.11 (95% CI 0.06 to 0.21), respectively, and positive and negative predictive values of 67.8% (95% CI 57.6% to 78.0%) and 96.5% (95% CI 94.7% to 98.3%), respectively. The per-patient analysis showed an increased sensitivity of 96% (95% CI 94% to 98%) but a decreased specificity of 74% (95% CI 65% to 84%).
Multislice spiral computed tomography has shortcomings difficult to overcome in daily practice and, at the more clinically relevant per-patient analysis, continues to have moderate specificity in patients with high prevalence of CAD.
Studies evaluating the diagnostic performance of the newest generation of MSCT, including patients with low to moderate CAD prevalence, will be critical in establishing the clinical role of this emerging technology as an alternative to CA. (Hamon, 2006) Sun and Jiang conducted a systemic review of the literature and a meta-analysis, evaluating 4- 16- or 64-slice CTA compared with conventional invasive angiography. A total of 47 studies (67 comparisons) were included in the metaanalysis. Results demonstrated assessable segments for CTA in the detection of CAD were 74%, 92%, and 97% with 4-, 16- and 64-slice scanners, respectively. The authors reported separate pooled sensitivity and specificity data for the Cardiac Computed Tomography (CT), Coronary Artery Calcium Scoring and Cardiac CT Angiography - Commercial Medical Management Guideline diagnostic accuracy of 4-, 16- and 64-slice MSCT using coronary angiography as the reference standard. MSCT pooled sensitivity was 76% for 4-slice CT (20 studies) 82% for 16-slice CT (19 studies) and 92% for 64-slice CT (7 studies).
Pooled specificity was 93% for 4-slice CT, 95%, for 16-slice and 94% for 64-slice. (Sun, 2006) Schuijf et al. (2006) conducted a meta-analysis to compare the diagnostic performance of MRI with 4- to 16-slice CT for noninvasive coronary angiography. Overall, 51 studies (28 MRI and 23 MSCT) were included that had been published between January 1990 and January 2005. Based on this analysis, MSCT was superior to MRI for the detection or exclusion of hemodynamically significant CAD. Diagnostic performance for 16-slice CT was as follows (prevalence of CAD ranged from 50% to 98%; median 67%): sensitivity 85%, specificity 94%, PPV 71%, NPV 97%.
A meta-analysis by Stein et al, including 33 studies (4-slice n=15; 8-slice n=2; 16-slice n=15; 64-slice n=1) reported the diagnostic accuracy by a patient and segmental analysis. Average sensitivity for patient-based detection of significant (50% or or =50%) stenosis was 61 of 64 (95%) with 4-slice CT, 276 of 292 (95%) with 16-slice CT, and 47 of 47 (100%) with 64-slice CT. Average specificity was 84% for 4-slice CT, 84% for 16-slice CT, and 100% for 64-slice CT.