Radiology Section - Contrast Enhanced Computed Tomographic Angiography (CTA) for Coronary Artery Evaluation

IMPORTANT REMINDER

Regence Medical Policies are developed to provide guidance for members and providers regarding coverage in accordance with contract terms. Benefit determinations are based in all cases on the applicable contract language. To the extent there may be any conflict between the Medical Policy and contract language, the contract language takes precedence.

PLEASE NOTE: Contracts exclude from coverage, among other things, services or procedures that are considered investigational or cosmetic. Providers may bill members for services or procedures that are considered investigational or cosmetic. Providers are encouraged to inform members before rendering such services that the members are likely to be financially responsible for the cost of these services.

DESCRIPTION

Contrast-enhanced computed tomographic angiography (CTA) is a noninvasive imaging study that requires the use of intravenously administered contrast material and high-resolution, high-speed CT machinery to obtain detailed images of the coronary blood vessels.

The various computed tomographic (CT) imaging devices used to assess coronary arteries include but are not limited to electron beam CT (also known as ultrafast CT) and  helical CTs including multi-detector row CT (MDCT) and multi-slice CT (MSCT).

POLICY/CRITERIA

Note:  This policy only addresses the use of CTA in the evaluation of coronary arteries and does not address the use of CTA for evaluation of cardiac structure and function (e.g. cardiac masses, emergent evaluations of aortic dissection, suspected pulmonary embolism, and structural morphology.)

The use of electron beam CT or helical CT to detect coronary artery calcification is addressed in a separate policy, Radiology 6, Computed Tomography to Detect Coronary Artery Calcification.

1. Anomalous Coronary Artery Mapping

   Contrast-enhanced computed tomographic angiography (CTA) for evaluation of congenital anomalous (native) coronary arteries in symptomatic patients may be considered medically necessary when conventional angiography is unsuccessful or equivocal.

2. Evaluation of Coronary Artery Disease

Contrast-enhanced computed tomographic angiography (CTA) of the coronary arteries is considered investigational for the diagnosis and screening of coronary artery disease (CAD) including but not limited to:

1. Evaluation of chest pain in an emergency room setting
2. Diagnosis of CAD in coronary artery bypass grafts
3. Diagnosis of CAD after percutaneous stent placement
4. Delineation of coronary artery anatomy prior to a cardiovascular procedure

POSITION STATEMENT

• CTA appears to effectively determine the origin and course of coronary arteries in cases when conventional angiography is unsuccessful.
• It is uncertain if CTA can reliably diagnose the presence or severity of CAD.
• Evidence is insufficient to determine whether a CTA diagnostic strategy provides greater benefits and/or lesser harms than comparative approaches for the evaluation of CAD.
• Currently, the “gold standard” for evaluating the presence and severity of CAD is invasive coronary angiography.  Other tests used to diagnose CAD in low to intermediate risk patients include the exercise treadmill test (ETT), the nuclear stress test, and stress echocardiography. How CTA should be used in the context of these other diagnostic protocols has not been well defined.
• In patients who are found to need invasive treatment, an intervention can be done efficiently at the time of angiography, thus avoiding the need for both CTA and angiography.  High risk patients are more likely to require intervention, but which high risk patient has not been well established.

Effectiveness

Mapping congenital anomalous coronary arteries

Several studies have shown that CTA may be able to map the origin and direction of anomalous arteries when conventional angiography cannot.(2-6) Anomalous coronary arteries are an uncommon finding at angiography, occurring in approximately 1% of coronary angiograms completed for evaluation of chest pain. Given the incidence and severity of this rare condition, the present level of evidence is sufficient to support the use of CTA for the presurgical mapping of anomalous coronary arteries when conventional angiography is unsuccessful or equivocal.

Validity of CTA for the Diagnosis or Screening of CAD

The majority of studies examining sensitivity, specificity, and positive and negative predictive values of CTA have significant limitations that do not allow conclusions to be made about the effectiveness of this test for evaluation of CAD.(6-33,45-47) Limitations include one or more of the following:

• Inadequate Study Power  

Studies were not adequately powered to prove equivalence between CTA and conventional angiography. Sample sizes were not determined in advance.

• Potential Bias:

CTA for diagnosis of CAD has largely been evaluated in preselected, high risk patients who were scheduled for angiography.  The ability of CTA to diagnose and prevent angiography in patients with a low to intermediate risk, for which CTA use is proposed, is still unknown. Safety and efficacy for the low to intermediate risk population may be different than for those patients already scheduled for angiography.

Subjects were convenience samples, limited to patients who agreed to be in the study, subjects scheduled for elective surgery, or availability of the research staff. These studies may represent selection bias.

Diagnostic performance was analyzed and reported per vessel or per segment rather than per patient. While vessel or segment-based analyses might be useful in determining treatment decisions about single vessels, decisions about whether to undergo invasive angiography are not made on a vessel-by-vessel basis, but based on all cardiac vessels in the patient as a whole.

Reporting was limited to evaluable coronary artery segments only with up to 12% of these segments being excluded from analysis. In patients with bypass grafts or stents, evaluation was unreliable or impossible in 13-26% of the segments due to vascular clips or calcification artifacts.   Exclusion of these segments from analysis could confound sensitivity and specificity results. 

Results for the technical validity of CTA, including the sensitivity, specificity, and positive and negative predictive values are inconsistent between studies ranging from a sensitivity of 86% to 100% and a specificity of 49% to 100%.

In patients with in-stent restenosis, measurements of diameter were smaller on MDCT by 16% to 27% compared with conventional angiography. It is not known how this difference might influence clinical management of the patient.

Clinical Utility Of CTA for the Diagnosis and Treatment of CAD

The clinical utility of CTA depends on how the results of the study can be used to benefit patient management.  The available evidence has not demonstrated that CTA can improve patient outcomes to a greater extent than currently available tests for the following reasons:

There is only one randomized controlled clinical trial that addresses the use of CTA in a clinical setting. This trial evaluated the ability CTA compared to standard nuclear stress testing to assess the severity and extent of coronary stenosis in symptomatic patients treated in the emergency room.(34)   This study had significant flaws and failed to demonstrate that CTA was superior to nuclear stress testing for the following reasons:

• There was no clearly defined primary end point stated in advance
• Although the study authors concluded the interventions were equivalent, the study was not sufficiently powered to support this conclusion.
• 94.7% of patients evaluated with nuclear stress testing were able to be discharged to home compared to only 67% of subjects who were discharged directly home due to CTA findings alone. 
• For intermediate stenosis or for non-diagnostic CTA, a stress test was performed in addition to CTA, resulting in a second radiation exposure in 24% of the MSCT arm.
• 4% of the MSCT arm required a third radiation exposure.

Other studies evaluating the clinical utility of this test include non-randomized case series with the following limitations: (35-42)

• Within the emergency department, the accuracy of the diagnosis was not dependent on CTA.  Final diagnosis and treatment planning were dependent on the combination of clinical data, radionuclide testing, coronary angiography, and stress echocardiography.
• No alternative strategy for making a diagnosis was specifically defined in the study.
• Within the setting of bypass graft assessment, no information is provided about patient symptoms or how the evidence of graft occlusion affected patient management.
• One large case series reported CTA decreased the rate of normal conventional cardiac angiography by 4.7% during a two-year period which was statistically significant, but of modest magnitude. In the same setting, accuracy achieved was less than desirable with a false-negative rate of 10%. (43)

In summary, larger studies are needed to evaluate low- to intermediate- risk patients and to compare how clinical management of these patients is impacted with the use of CTA.

Safety

There are significant safety considerations with use of CTA for the evaluation of coronary arteries including the following:

• CTA has as much as 2-3 times the level of radiation exposure compared to conventional angiography
• False positive or false negative results may lead to unnecessary treatment (invasive angiography) or conversely, to inaction when treatment is warranted
• The presence of dense arterial calcifications or an intracoronary stent can interfere with imaging quality and lead to the need for repeat testing
• The use of beta blockers, required for MSCT to slow the heart rate, may present a risk under certain clinical situations. The use of high contrast medium may impair renal function under certain clinical situations.

Appropriateness criteria have recently been published for both CTA and cardiac magnetic resonance imaging (CMRI).(44) These criteria were developed using a consensus process that compared the expected benefit of the test with the expected negative consequences. Although a number of scenarios were judged as appropriate for use of CTA in evaluating coronary arteries, an evidence-based review process was not required to make decisions about expected benefits or harms.

REFERENCES

1. BlueCross and BlueShield Association Medical Policy Reference Manual, Policy No. 6.01.43
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6. BlueCross and BlueShield Association Technology Evaluation Center (TEC) Assessment,  Contrast-enhanced cardiac computed tomography angiography for coronary artery evaluation, 2005; Vol. 20 No. 4 http://blueweb.bcbs.com/global_assets/special_content/tec_assessments/vol20/20_ 04.pdf (Verified 05/17/09)
7. BlueCross and BlueShield Association Technology Evaluation Center (TEC) Assessment, Contrast-Enhanced Cardiac Computed Tomographic Angiography in the Diagnosis of Coronary Artery Stenosis or for Evaluation of Acute Chest Pain,  2006; Vol. 21, No. 5 http://blueweb.bcbs.com/global_assets/special_content/tec_assessments/vol21/21_ 05.pdf (Verified  05/17/09)
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20. Sun Z, Jiang W. Diagnostic value of multislice computed tomography angiography in coronary artery disease: a meta-analysis. Eur J Radiol 2006; 60(2):279-86
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CROSS REFERENCES

Computed Tomography to Detect Coronary Artery Calcifications, Regence Medical Policy Manual, Radiology, Policy No. 6

Radiology Section Table of Contents