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The sensitivity for a significant stenosis in evaluable segments was 307 of 372 (83%) with 4-slice CT, 1023 of 1160 (88%) with 16-slice CT, and 165 of 176 (94%) with 64-slice CT. Average specificity was 93% or greater with all multidetector CT. Seventy-eight percent of segments were evaluable with 4-slice CT, 91% with 16-slice CT, and 100% with 64-slice CT. Stenoses in proximal and mid-segments were shown with a higher sensitivity than distal segments. Left main stenosis was identified with high sensitivity with all multidetector CT, but sensitivity in other vessels increased with an increasing number of detectors. (Stein, 2006) A technology assessment report on contrast-enhanced CTA by the Blue Cross Blue Shield Association Technology Evaluation Center (TEC) concluded that the available evidence is inadequate to determine whether CTA improves the net health outcome or is as beneficial as established alternatives for diagnosis of coronary artery stenosis or for evaluation of acute chest pain in the ER. The report evaluated seven studies that compared CTA to angiography for diagnosis of coronary artery stenosis, ranging in size from 30 to 84 patients. In 5 studies reporting a per-patient analysis, the sensitivity of CTA in identifying a 50% stenosis ranged from 88-100%, with 4 of 5 studies reporting sensitivities of at least 95%. Specificity ranged from 86-100%. In a per-segment analysis, sensitivity ranged from 79-99%, and specificity ranged from 95-98%.
The robust visualization and classification of anomalous coronary arteries make CT angiography a first-choice imaging modality for the investigation of known or suspected coronary artery anomalies. Radiation dose must be considered often in the young patients, and measures to keep dose as low as possible must be employed. (Schroeder, 2008) As opposed to magnetic resonance imaging, which also permits the analysis of coronary anomalies in tomographic images, CT requires radiation and a contrast agent. However, the high resolution of the datasets (permitting analysis even of small details) and the speed of image acquisition make it reasonable to use CT as one of the first-choice imaging modalities in the workup of known and suspected coronary anomalies. (Budoff, 2006) Professional Societies/Government Organizations American College of Cardiology (ACC) The American College of Cardiology Foundation (ACCF), together with key specialty societies, published appropriateness criteria for cardiac computed tomography (CCT). For the 39 indications for CCT, 13 were found to be appropriate, 12 were uncertain, and 14 inappropriate.
Appropriate: test is generally acceptable and is a reasonable approach for the indication.
Uncertain: test may be generally acceptable and may be a reasonable approach for the indication. Uncertainty also implies that more research and/or patient information is needed to classify the indication definitively.
Inappropriate: test is not generally acceptable and is not a reasonable approach for the indication.
(Hendel, 2006) Available at: http://content.onlinejacc.org/cgi/reprint/48/7/1475.pdf. Accessed April 7, 2009.
As a follow-up to the 2006 multisociety clinical guideline (Hendel, 2006), the Society of Cardiovascular Computed Tomography (SCCT) and the North American Society for Cardiac Imaging (NASCI) published a consensus statement detailing the utility and appropriateness of CTA in everyday clinical practice. (Poon, 2007) American Heart Association (AHA) In a scientific statement (Budoff, 2006), the AHA made the following recommendations on CT angiography of the
Class IIa Recommendations (Weight of evidence/opinion is in favor of usefulness/efficacy). CTA is reasonable for:
1. Assessment of obstructive disease in symptomatic patients.
2. Assessment of known and suspected coronary anomalies.
Class IIb Recommendations (Usefulness/efficacy is less well established by evidence/opinion) CTA might be reasonable
1. Follow-up after bypass surgery.
Class III Recommendations (Not useful/effective and in some cases may be harmful) CTA is not recommended for:
Cardiac Computed Tomography (CT), Coronary Artery Calcium Scoring and Cardiac CT Angiography - Commercial Medical Management Guideline
1. Follow-up of percutaneous coronary intervention (stent placement).
2. Assessment of noncalcified plaque (NCP) to track atherosclerosis or stenosis over time.
3. Screening in asymptomatic persons for atherosclerosis (noncalcific plaque).
4. Use of hybrid scanning to assess cardiovascular risk or presence of obstructive disease.
American College of Radiology (ACR, 2006b) Indications for contrast-enhanced cardiac CT include, but are not limited to, the diagnosis, characterization, and/or
1. Arterial and venous aneurysms.
2. Atherosclerotic disease.
3. Traumatic injuries of arteries and veins.
4. Arterial dissection and intramural hematoma.
5. Arterial and venous thromboembolism
6. Vascular congenital anomalies and variants.
7. Vascular interventions (percutaneous and surgical, e.g., angioplasty, coronary stenting, coronary bypass grafts [CABGs], ablation therapy for cardiac dysrhythmia, valve surgery, aortic root replacement, pacemaker placement planning,).
8. Vascular infection, vasculitis, and collagen vascular diseases.
9. Sequelae of ischemic coronary disease (myocardial scarring, ventricular aneurysms,thrombi).
10. Cardiac tumors and thrombi.
11. Pericardial diseases.
12. Cardiac functional evaluation, especially in patients in whom cardiac function may not be assessed by magnetic resonance imaging(automatic implantable defibrillator, pacemaker, general MRI contraindications, etc.) or echocardiography (e.g., poor acoustic window).
In a statement on noninvasive cardiac imaging, ACR described cardiac CT as a proven and important imaging modality for the detection and characterization of cardiac disease. CT may be used as either the primary modality for detecting disease or as an adjunct to other imaging modalities to better characterize disease and help assess change over time. CT can be used to assess both cardiac structure and function, as well as evaluate disease processes within the field of view but outside of the heart and pericardium. (Weinreb, 2005) U.S. Preventive Services Task Force (USPSTF) The USPSTF recommends against routine screening with resting electrocardiogram (ECG), exercise treadmill test (ETT), or electron beam computerized tomography (EBCT) scanning for coronary calcium, either to determine the presence of severe coronary artery stenosis (CAS) or to predict coronary heart disease (CHD) events in adults at low risk. This recommendation was supported by at least fair evidence that screening asymptomatic adults for CHD is ineffective or that harms outweigh benefits. The USPSTF found insufficient evidence to recommend for or against routine screening with ECG, ETT or EBCT scanning for coronary calcium, either to determine the presence of severe CAS or to predict CHD events in adults at increased risk. (USPSTF, 2004) Agency for Healthcare Research and Quality (AHRQ) AHRQ prepared a technology assessment report for the Medicare Coverage Advisory Committee (MCAC) on noninvasive imaging tests (NITs) for coronary artery disease. The authors identified 29 studies using 16-slice or greater multi-detector computed tomography (MDCT) assessing coronary CTA for evaluation of coronary arteries. These studies were generally small, performed at single centers, and often did not include information that would serve to provide confident assessments of the key questions. In particular, the authors did not identify any studies evaluating the clinical impact of diagnostic strategies including CTA compared with strategies that did not include this technique. The vast majority of CTA studies were performed on 16-MDCT scanners, with 6 studies using 64-MDCT scanners for CTA. To provide a clearer picture of the most recent and thus most relevant literature, only the 64-array MDCT studies along with Cardiac Computed Tomography (CT), Coronary Artery Calcium Scoring and Cardiac CT Angiography - Commercial Medical Management Guideline the 5 prospective 16-array MDCT studies that enrolled at least 100 patients were selected for detailed review. The report concluded that at present, there is limited evidence regarding test performance of NITs for identifying, quantifying, or otherwise characterizing coronary artery stenoses. The available evidence provides preliminary data on the ability of coronary CTA using at least 16-slice MDCT technology to detect obstructive coronary artery lesion in the proximal to mid coronary arteries. The evidence regarding detection of coronary lesions in branch vessels or distal coronary arteries remains unclear and may well improve as the technology improves. Studies conducted to date primarily fall into the "proof of concept" category with study patients having a high pre-test probability of CAD. Patients providing suboptimal images were often excluded from calculations of test accuracy. Future work will need to examine these tests in larger, less selected populations representing the clinical settings in which they are actually expected to be used. The effect of biases in selection of study patients and in the publication of accuracy results for these tests was not assessed in this preliminary analysis. With regard to electron beam computed tomography (EBCT) the authors stated that to date, this technology has not achieved the level of resolution required to image coronary artery anatomy directly. Further, its role in clinical screening for CAD remains controversial. (Matchar, 2006)