Radiology Section - Computed Tomography to Detect Coronary Artery Calcification

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

Electron beam CT (also known as ultrafast CT) uses an electron gun rather than a standard x-ray tube to generate x-rays, thus permitting very rapid scanning. Spiral CT scanning (also referred to as helical CT scanning) also creates images at greater speeds by rotating a standard x-ray tube around the patient such that data are gathered in a continuous spiral or helix rather than individual slices. While both electron beam CT (EBCT) and spiral CT scanning may be valued as an alternative to conventional CT scanning due to their faster throughput, their speed of image acquisition permits unique imaging of the moving heart. For example, the rapid image acquisition time virtually eliminates motion artifact related to cardiac contraction, permitting visualization of the calcium in the epicardial coronary arteries. EBCT software permits quantification of calcium area and density, which are translated into calcium scores. Calcium scores have been investigated as a technique for detecting coronary artery calcification, in both symptomatic patients to determine necessity of coronary angiography and in asymptomatic patients, as a screening technique for coronary artery disease.

Although most of the research regarding imaging of coronary artery calcification has focused on EBCT, spiral CT scanning has also been used for this purpose.  As of 2007, EBCT and multi-detector computed tomography (MDCT) are the primary fast CT methods for measurement of coronary artery calcification.  A fast CT study for coronary artery calcium measurement generally takes 10-15 minutes and requires only a few seconds of scanning time.

Note: The use of contrast-enhanced computed tomographic angiography (CTA) for coronary artery evaluation including evaluation of CAD in an emergent setting or for the diagnosis of CAD is addressed separately in Radiology, Policy No. 46.

POLICY/CRITERIA

The use of computed tomography to detect and quantify coronary artery calcification is considered investigational.

POSITION STATEMENT

This policy addresses the use of electron beam computed tomography (EBCT) for two main indications, namely, as a screening technique for coronary artery disease (CAD) in asymptomatic individuals or for evaluating the necessity of angiography in symptomatic patients.  Each indication is discussed separately below.

EBCT As a Screening Technique for Asymptomatic Patients

The policy for EBCT as a screening technique is based on a 1998 BlueCross BlueShield Association Technology Evaluation Center (TEC) Assessment, which offered the following analysis and conclusions (2):

Two distinct studies reported on the use of EBCT to identify individuals at high risk for coronary artery disease (CAD). Neither study showed that EBCT improved upon the prognostic information from risk factor models such as the Framingham Heart Study or the National Cholesterol Education Program-III (NCEP III). Similarly, neither study compared EBCT against other non-invasive tests such as exercise treadmill testing. Despite the ease with which EBCT may be performed, existing evidence did not establish that EBCT resulted in improved health outcomes by improving prognostic information.

In 2000, the American College of Cardiology and the American Heart Association jointly issued a consensus document on the use of EBCT for the diagnosis and prognosis of coronary artery disease. (3) Regarding the use of EBCT in asymptomatic patients, the executive summary included the following statements:

Because the severity of coronary atherosclerosis is known to be associated with risk of coronary events, coronary artery calcium scores should likewise correlate with risk for coronary events. However, for a test to be most valuable when asymptomatic patients are screened, it should increase the likelihood of coronary heart disease above the probability determined by standard and readily available assessments, such as the Framingham risk model…. The published literature does not completely answer the question of whether the EBCT calcium score is additive to the Framingham score for defining coronary heart disease risk in asymptomatic patients…. Selected use of coronary calcium scores when a physician is faced with a patient with intermediate coronary disease risk may be appropriate. However, the published literature does not clearly define which asymptomatic people require or will benefit from EBCT. Additional appropriately designed studies of EBCT for this purpose are strongly encouraged.

Since the release of the ACC/AHA Consensus Document in 2000, several potentially relevant publications were identified that examined screening in asymptomatic individuals.  Although it was well established previously that calcium scores predicted future coronary events, studies showing incremental predictive value beyond that of standard risk prediction were lacking.  Recent prospective studies demonstrated evidence for predictive capacity of calcium scores in addition to assessment of traditional risk factors.  In a study of 1,029 asymptomatic adults with at least one coronary risk factor, Greenland and colleagues showed that a calcium score of >300 predicted increased risk of cardiac events within Framingham risk categories. (4) A study by Arad and colleagues showed similar findings in a population-based sample of 1,293 subjects who had both traditional risk factors and calcium scores evaluated at baseline. (5)  A study by Taylor and colleagues studied the association of the Framingham risk score and calcium scores in a young military population (mean age 43 years). (6)  Although only nine acute coronary events occurred, calcium scores were associated with risk of events while controlling for the risk score.  LaMonte and colleagues also analyzed the association of calcium scores and CHD events in 10,746 adults. (7)  In this study, coronary risk factors were self-reported. During a mean follow-up of 3.5 years, 81 CHD events occurred. Similar to the other studies, the relationship between calcium scores and CHD events remained after adjustment for other risk factors.

Although a growing body of literature now addresses the relationship of traditional risk factors, calcium scores, and risk of coronary heart disease, more knowledge is needed about how calcium scores should be integrated into treatment guidelines. Current treatment guidelines for coronary disease prevention recommend specific treatment based on prediction of coronary disease risk. Thus, solid information is needed on how such a risk predictor produces accurate predictions. The cited studies enrolled different populations, assessed different traditional risk factors, and assessed different coronary disease outcomes. Different calcium score cutoffs were analyzed in the studies. Given the variation in the studies, it is difficult to know the magnitude of increased risk conferred by a given calcium score. The results of the study by Greenland and colleagues suggest that a high calcium score as defined as a score >300 does not change risk appreciably for those with Framingham risk scores less than 10% or greater than 20%. (4)  Given that there is no direct evidence that risk stratification using calcium scores in addition to traditional risk assessment improves patient outcomes, a consensus approach that integrates existing evidence with a modeling approach to predicting patient outcomes could aid in determining whether EBCT is of value. Given that the ACC/AHA has already produced a consensus document on EBCT that recognized the need for the type of evidence that has recently been published, it is likely that they will revisit this issue. (3)

In February 2004, the United States Preventive Services Task Force (USPSTF) released updated guidelines for screening for coronary artery disease which included an assessment of EBCT for coronary artery calcium. (8) Two indications for EBCT were addressed:

• The USPSTF recommended against routine screening with EBCT for coronary artery calcium to detect the presence of either severe coronary artery stenosis (CAS) or the prediction of coronary heart disease events in adults at low risk for CHD.  Evidence for EBCT for this indication was limited. In the absence of evidence that such detection by EBCT among adults at low risk for CHD events ultimately results in improved health outcomes, and because false-positive tests are likely to cause harm, including unnecessary invasive procedures, over-treatment, and labeling, the USPSTF concluded that the potential harms of routine screening for CHD in this population exceeded the potential benefits.

• The USPSTF found insufficient evidence to recommend for or against routine screening with EBCT scanning for coronary calcium for either the presence of severe CAS or the prediction of CHD events in adults at increased risk for CHD events.  Among adults at increased risk for CHD events, the USPSTF found inadequate evidence to determine the extent to which the added detection offered by EBCT (beyond that achieved with conventional CHD risk factor assessment) would result in interventions that lead to improved health outcomes.  Although there was limited evidence to determine the magnitude of harms from screening this population, harms from false-positive tests (i.e., unnecessary invasive procedures, over-treatment, and labeling) were likely to occur.  As a result, the USPSTF could not determine the balance between benefits and harms of screening this population for CHD.

In summary, the additional studies published since the 1998 TEC Assessment do not yet establish a clear role for EBCT in coronary disease risk stratification in asymptomatic patients, nor have any studies shown that clinical outcomes can be favorably altered by the use of screening EBCT.

EBCT as a Diagnostic Study in Symptomatic Patients

The 1998 TEC Assessment determined that while EBCT was an effective method of selecting symptomatic patients for angiography, no studies made direct comparisons with other non-invasive tests such as single photon computed tomography (SPECT) or echocardiography. (2) The evidence suggested that EBCT was not as effective as SPECT.  The TEC Assessment concluded that evidence was inadequate to determine whether EBCT was as effective as other commonly used tests such as echocardiography.

Regarding the use of EBCT in symptomatic individuals, the ACC/AHA executive summary included the following statement: "The majority of the members of the Writing Group would not recommend EBCT for diagnosing obstructive coronary artery disease because of its low specificity (high percentage of false-positive results), which can result in additional expensive and unnecessary testing to rule out a diagnosis of coronary artery disease." (3)  The 1999 ACC/AHA Coronary Angiography Guideline committee reached a similar conclusion.

Both the BCBSA TEC Assessment and the ACC/AHA Expert Consensus Document focused on the use of EBCT for detecting coronary artery calcification. While spiral CT scanning has been used for the same purpose, there are minimal data regarding this application and there are inadequate data to determine whether calcium scores derived from spiral CT imaging are equivalent to those derived from EBCT imaging. Most importantly, limitations in the data regarding EBCT noted in both the TEC Assessment and ACC/AHA document also apply to spiral CT scanning.

A May 2006 updated search of the MEDLINE database did not identify any new clinical study data that alter the above conclusions.

In 2006, the American Heart Association (AHA) issued a scientific statement (9) on the use of cardiac computed tomography. Most of the document reviewed the utility of calcium scoring for the use of determining prognosis and diagnosis. In addition to reviewing a large body of evidence regarding calcium scoring, clinical recommendations were also offered. No indications received a class I  recommendation, i.e., evidence and/or agreement that the procedure is useful and effective. Several indications received a class IIb recommendation, which means that there is conflicting evidence and/or a divergence of opinion regarding usefulness or efficacy. The “b” qualifier indicates usefulness/efficacy is less well established. The indications that received such a IIb recommendation were:

• Patients with chest pain with equivocal or normal electrocardiograms and negative cardiac enzymes
• Determining the etiology of cardiomyopathy
• Symptomatic patients, in the setting of equivocal treadmill or functional tests
• Asymptomatic patients with intermediate (e.g., 10–20% 10-year risk) risk of coronary artery disease

Four indications received a class III recommendation, which means that there is evidence that the procedure or treatment is not useful or possibly harmful. These indications were:

• Low-risk (<10% 10-year risk) and high-risk (>20% 10-year risk) asymptomatic patients
• Establishing the presence of obstructive disease for revascularization in asymptomatic persons
• Serial imaging for assessment of progression of coronary calcification
• Hybrid nuclear and CT imaging

The 2006 AHA scientific statement (9) also cited several other studies showing an association between calcium scores and coronary artery disease (CAD) events after adjustment for traditional risk factors. The report recognized that despite growing evidence that calcium scores are an independent predictor of CAD; studies have not demonstrated improved clinical outcomes as a result of calcium score screening. This scientific statement reflected these uncertainties in the utility of calcium scoring in their clinical guideline statements.

A 2007 clinical consensus document co-written by the American College of Cardiology Foundation (ACCF) and the AHA (10) reviewed much of the same evidence as the 2006 AHA scientific statement. It should be noted that this type of consensus document represents the best attempt of the ACCF and AHA to inform clinical practice where rigorous evidence is not yet available. Thus formal grading of evidence and classification of clinical recommendations are not reported in this type of document. This document essentially concludes that the indications receiving a IIb recommendation in the 2006 scientific statement “may be reasonable”.

In summary, studies published do not establish a clear role for EBCT in coronary disease risk stratification in asymptomatic or symptomatic patients, nor have any studies shown that clinical outcomes can be favorably altered by the use of computed-tomography-based determination of coronary artery calcification in screening for coronary artery disease. Guideline statements based on this evidence reflect the uncertain role of EBCT by not giving strong endorsement to the test.

Additional studies published since the last policy update show similar relationships between coronary artery calcification and coronary disease events (11,12). These studies are all qualitatively similar to other studies previously referenced, showing some independent predictive capability of coronary artery calcium score with a graded association between coronary calcium scores and coronary disease events. In a study by Elkeles and colleagues calcium scores were predictive of future coronary events in asymptomatic subjects with type 2 diabetes.(13)

There has been one randomized, controlled trial of EBCT published. O’Malley and colleagues randomized 450 subjects to receive EBCT or not, and assessed outcomes one year later for change in Framingham Risk Score. (14) Thus, EBCT was to be used as a guide to refine risk in patients and possibly provide motivation for behavioral change. The study was not powered for clinical endpoints. EBCT did not produce any benefits in terms of a difference in Framingham risk score at one year.

A gap still remains in the literature regarding the incremental predictive capability of coronary calcium beyond traditional risk prediction, and whether this incremental predictive capability can translate into improved decision making and improved patient outcomes. Direct evidence in the form of a clinical trial, or rigorous indirect evidence in terms of decision modeling does not appear to be available. The essential issue still remains, of how to properly integrate such predictive capability into a coherent practice guideline which can be expected to improve patient outcomes.

REFERENCES

1. BlueCross and BlueShield Association Medical Policy Reference Manual, Policy No. 6.01.03
2. BlueCross and BlueShield Association Technology Evaluation Center (TEC) Assessment, Diagnosis and Screening for Coronary Artery Disease with Electron Beam Computer Tomography, 1998;  Vol.13, No.27
3. O'Rourke RA, Brundage BH, Froelicher VF et al. American College of Cardiology/American Heart Association expert consensus document on electron beam computed tomography for the diagnosis and prognosis of coronary artery disease. J Amer Coll Card 2000;36:326-40
4. Greenland P, LaBree L, Azen SP et al. Coronary artery calcium score combined with Framingham score for risk prediction in asymptomatic individuals JAMA 2004;291(2):210-5
5. Arad Y, Goodman KJ, Roth M et al. Coronary calcification, coronary disease risk factors, C-reactive protein, and atherosclerotic cardiovascular disease events: the St. Francis Heart Study.  J Am Coll Cardiol 2005;46(1):158-65
6. Taylor AJ, Bindeman J, Feuerstein I et al. Coronary calcium independently predicts incident premature coronary heart disease over measured cardiovascular risk factors: mean three-year outcomes in the Prospective Army Coronary Calcium (PACC) project.  J Am Coll Cardiol 2005;46(5):807-14
   
7. LaMonte MJ, FitzGerald SJ, Church TS et al. Coronary artery calcium score and coronary heart disease events in a large cohort of asymptomatic men and women.  Am J Epidemiol 2005;162(5):421-9
8. www.ahrq.gov/clinic/uspstf/uspsacad.htm (Verified 09/22/09)
9. Budoff MJ, Achenbach S, Blumenthal RS et al. Assessment of coronary artery disease by cardiac computed tomography: a scientific statement from the American Heart Association Committee on Cardiovascular Imaging and Intervention, Council on Cardiovascular Radiology and Intervention, and Committee on Cardiac Imaging, Council on Clinical Cardiology. Circulation 2006; 114(16):1761-91. Available online at http://circ.ahajournals.org/cgi/content/full/114/16/1761  (Verified 09/22/09)
10. Greenland P, Bonow RO, Brundage BH et al. ACCF/AHA 2007 clinical expert consensus document on coronary artery calcium scoring by computed tomography in global cardiovascular risk assessment and in evaluation of patients with chest pain: a report of the American College of Cardiology Foundation Clinical Expert Consensus Task Force (ACCF/AHA Writing Committee to Update the 2000 Expert Consensus Document on Electron Beam Computed Tomography) developed in collaboration with the Society of Atherosclerosis Imaging and Prevention and the Society of Cardiovascular Computed Tomography. J Am Coll Cardiol 2007; 49(3):378-402
11. Lakoski SG, Greenland P, Wong ND et al. Coronary artery calcium scores and risk for cardiovascular events in women classified as "low risk" based on Framingham risk score: the multi-ethnic study of atherosclerosis (MESA). Arch Intern Med 2007; 167(22):2437-42
12. Budoff MJ, Shaw LJ, Liu ST et al. Long-term prognosis associated with coronary calcification: observations from a registry of 25,253 patients. J Am Coll Cardiol 2007; 49(18):1860-70
13. Elkeles RS, Godsland IF, Feher MD et al. Coronary calcium measurement improves prediction of cardiovascular events in asymptomatic patients with type 2 diabetes: the PREDICT study. Eur Heart J 2008; 29(18):2244-51
14. O’Malley PG, Feuerstein IM, Taylor AJ. Impact of electron beam tomography, with or without case management, on motivation, behavioral change, and cardiovascular risk profile: a randomized controlled trial. JAMA 2003; 289(17):2215-23

CROSS REFERENCES

Contrast-Enhanced Computed Tomographic Angiography (CTA) for Coronary Artery Evaluation, Regence Medical Policy Manual, Radiology, Policy No. 46

Regence ConsumerTx: CT Scans for Coronary Artery Calcium Scoring

Radiology Section Table of Contents