Elsevier

American Heart Journal

Volume 151, Issue 6, June 2006, Pages 1139-1146
American Heart Journal

Curriculum in Cardiology
Coronary artery calcium scanning: Clinical paradigms for cardiac risk assessment and treatment

https://doi.org/10.1016/j.ahj.2005.07.018Get rights and content

Background

Coronary artery calcium (CAC) scanning is being increasingly used for cardiac risk assessment in asymptomatic patients, particularly in those with a Framingham 10-year risk of 10% to 20%. Physician awareness of this technology and its appropriate uses and limitations is crucial to appropriate use.

Methods

With the goal of establishing clinical paradigms, this document integrates the results of key published articles, Framingham Risk Score, National Cholesterol Education Program Adult Treatment Plan III guidelines, American College of Cardiology/American Heart Association exercise testing and angiographic guidelines, and the authors' extensive clinical experience.

Results

Coronary artery calcium scanning is best used in the asymptomatic population with a 10% to 20% risk of cardiac events over 10 years, with selected application in higher and lower risk categories. In the 10%-20% risk patient, coronary artery calcium scores >100 or >75th percentile for age and sex transform the moderately high-risk patient to higher risk status with the attendant recommendation for more aggressive therapy; scores from 11 to 100 and <75th percentile are consistent with the 10%-20% 10-year risk status and scores from 0 to 10 and <75th percentile convert the patient to lesser risk categories. If stress testing is planned in the asymptomatic patient, it should be preceded by coronary artery calcium scanning and performed only for scores >400; it should always precede coronary angiography in these patients.

Conclusions

Coronary artery calcium scanning is an important risk assessment tool with direct clinical applications; it is of particular utility in the Framingham 10%-20% 10-year risk population.

Section snippets

Brief overview of CAC

Electron beam computed tomography uses a rotating electron beam to acquire triggered, tomographic x-ray images acquired over 100 milliseconds at 3-mm intervals, in the space of a 30- to 40-second breath-hold, and quantifies the calcified plaque in the epicardial coronary arteries. Multidetector computed tomography uses a rotating gantry with a special x-ray tube and variable number of detectors (from 4 to 64), with images acquired over 165 to 420 milliseconds at 0.5- to 3.0-mm intervals, and

Key studies

The final report of the NCEP guidelines29 made the following recommendation, based on the data of Raggi et al3, 30: “Therefore, measurement of coronary calcium is an option for advanced risk assessment in appropriately selected persons. In persons with multiple risk factors, high coronary calcium scores (e.g., >75th percentile for age and sex) denotes advanced coronary atherosclerosis and provides a rationale for intensified low density lipoprotein (LDL)–lowering therapy.” Raggi et al30

Patient selection

Recommendations for CAC scanning are not based on age and sex alone. Rather, the Framingham Risk Score, which incorporates both age and sex, is recommended as the initial step in selecting the appropriate test populations. Asymptomatic patients in the 10%-20% Framingham 10-year risk category (moderately high risk) comprise the group that presents the greatest challenge to the treating physician and are those in whom the application of CAC scoring is most appropriate. Although this application

Limitations

As with any diagnostic method, CAC testing has limitations. It does not evaluate the degree of coronary stenosis; the specificity for obstructive disease of any CAC >0 is in the 40% range.54 In addition, the specificity of CAC for cardiac events is quite low, as only a minority of patients with CAC experience events. However, the specificity of CAC for the identification of atherosclerosis is nearly 100%. Coronary artery calcium does not visualize soft plaque, and patients with exclusively

Conclusions

The increasing use of CAC scanning for risk assessment is now supported by extensive evidence in appropriately selected patients. Critical to its implementation is the ability of the practitioners to understand the data and the limitations of the test, as outlined in this review, and to appropriately use this knowledge in applying the test results to the care of their patients.

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