TEC Assessment Index

Contrast-Enhanced Cardiac Computed Tomographic Angiography in the Diagnosis of Coronary Artery Stenosis or for Evaluation of Acute Chest Pain

Assessment Program
Volume 21, No. 5
August 2006

Executive Summary

Background
Coronary artery disease is currently diagnosed using angiography, an invasive procedure with risk of complications. Contrast-enhanced computed tomography angiography (CTA) is a noninvasive method of visualizing the coronary arteries, which might be useful in various clinical scenarios in which coronary artery disease is under consideration.

Objective
The objective of this Assessment is to determine the usefulness of CTA as a substitute for coronary angiography for two indications: 1) in the diagnosis of coronary artery stenosis, and 2) in the evaluation of acute chest pain in the emergency room (ER). Uses of CTA for other indications are not addressed in this Assessment.

Search Strategy
MEDLINE® was searched (via PubMed) through June 2006 to identify all articles pertaining to use of contrast-enhanced cardiac CT angiography.

Selection Criteria
Studies that evaluated 32- or greater row CTA and compared CTA to angiography for diagnosis of coronary artery stenosis, and any study evaluating CTA for patients with acute chest pain in the ER were selected.

Main Results
Seven studies compared CTA to angiography for diagnosis of coronary artery stenosis, ranging in size from 30 to 84 patients. These studies enrolled essentially convenience samples of consecutive patients scheduled to undergo angiography, and thus may be subject to spectrum bias. No study specifically studied a lower-risk subset of those patients referred for angiography, which is the target population for this procedure. A high prevalence of coronary stenosis was noted in all studies. In 5 studies reporting a per-patient analysis, 3 studies excluded patients with indeterminate test results.  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%. Four of these studies excluded either patients or segments from the analysis.

Two studies evaluated the use of CTA for patients with acute chest pain in the ER. The sample sizes of the studies were 31 and 69. The studies used a mixed reference standard of angiography, clinical data, and noninvasive testing, which allows a calculation of sensitivity and specificity, but does not allow a comparison of performance to an alternative strategy. No alternative strategies for diagnosis were evaluated. Sensitivity of CTA was 83% and 96%, and specificity was 89% and 96%. It is unknown whether this indicates better or worse performance than an alternative strategy.

Author's Conclusion and Comments
The studies evaluating the use of CTA in comparison to angiography are relatively small studies from single centers.* Their major failing is that they enrolled convenience samples of patients being referred for angiography. The results from these studies may not generalize to lower-risk populations. In addition, such studies only directly address the question of whether CTA can accurately triage patients already referred for angiography. The use of CTA as part of the initial workup of chest pain or possible angina is not addressed at all in these kinds of studies. However, analyzing the information from these studies solely from the perspective of sensitivity and specificity in identifying a specific amount of coronary stenosis may shortchange the potential utility of CTA. Visualizing the coronary anatomy may provide useful prognostic information for optimally managing patients even if no direct referral to angiography results. However, in order to demonstrate improved patient outcomes, valid prognostication tied to improved management and outcomes must be demonstrated. Clinical trials comparing patients undergoing CTA as part of their diagnostic workup compared to patients not undergoing CTA may be required to demonstrate improved patient outcomes. There is no evidence except in the ER regarding the use of CTA in the early workup of patients in whom CAD is being considered.

Current published studies of CTA in the management of acute chest pain in the ER are clearly inadequate to determine utility. No comparator strategy was specified in any study, and there was no solid reference standard for diagnosis. Clinical trials may be necessary to demonstrate utility in this setting.

Based on the available evidence, the Blue Cross and Blue Shield Association Medical Advisory Panel made the following judgments about whether CTA for screening or diagnostic evaluation of the coronary arteries meets the Blue Cross and Blue Shield Association Technology Evaluation Center (TEC) criteria.

1. The technology must have final approval from the appropriate governmental bodies.

Multiple manufacturers have received U.S. Food and Drug Administration (FDA) 510(k) clearance to market MDCT machines equipped with at least 16 detector rows and at least two models of EBCT machines have been cleared through FDA 510(k) clearance. Intravenous iodinated contrast agents used for cardiac CTA have also received FDA approval.

2. The scientific evidence must permit conclusions concerning the effect of the technology on health outcomes.

Current studies are inadequate to determine the effect of CTA on health outcomes for the diagnosis of coronary artery stenosis in patients referred for angiography or for evaluation of acute chest pain in the ER.

3. The technology must improve the net health outcome; and
4. The technology must be as beneficial as any established alternatives.

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.

5. The improvement must be attainable outside the investigational settings.

Whether use of CTA improves health outcomes has not been established in the investigational setting.

Based on the above, CTA as a substitute for coronary angiography in the diagnosis of coronary artery stenosis does not meet the TEC criteria. CTA in the evaluation of acute chest pain in the emergency room also does not meet the TEC criteria.

*As this Assessment went to press, a multicenter trial of 16-row CTA was published (Garcia et al. 2006). This trial is summarized in the "Review of Evidence" as an addendum to the summary of the 2005 TEC Assessment (which was limited to 16-row technology or greater); however, its results do not change the conclusions of this Assessment. 

TEC Assessment Index

KEYWORDS: DiagnosticImaging (category); CardiovascularMedicine (category); acute; aneurysm; angina; angiography; atherosclerosis; atherosclerotic; CAD; calcification; cardiac; chest pain; computed tomography; contrast enhanced; contrast-enhanced; convenience samples; conventional angiography; coronary artery disease; coronary artery stenosis; coronary artery; coronary syndrome; CTA; decision tree; detector; diagnostic accuracy; EBCT; electron beam; emergency room; ER; false; heart; indeterminate; ionizing; ischemia; ischemic; MDCT: multidetector; medical management; multislice; multiplanar; myocardial; negative; noninvasive; reference standard; spectrum bias; stenosis; tomographic; true; ultrafast; unenhanced; unstable angina; value; vessel; vessel-based