Testing: Coronary artery calcium to risk stratify in primary prevention

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What the test entails

  • Single Computer tomography (CT) scan of the chest using either electron beam CT (EBCT) or multidetector CT (MDCT)
  • A radiologist or cardiologist evaluates the CT images and quantifies calcification of the coronary arteries (a marker of atherosclerotic plaque buildup) using the Agatston score

Evidence

A 2004 meta-analysis identified the coronary artery calcium (CAC) score as an independent risk factor for coronary artery disease events (coronary death, non-fatal MI or revascularization)

  • CAC score: odds ratio (OR) for coronary heart disease event
    • No calcification (0): OR 1 (reference)
    • Low (1-100): OR 2.1
    • Medium (101-400): OR 5.4
    • High (>400): OR 10

The Multi-Ethnic Study of Atherosclerosis (MESA) population-based cohort provides the best evidence for use of the coronary artery calcium (CAC) score in risk stratification.

  • In a primary prevention cohort that included patients with a low (<5%), intermediate (5-20%) and high (>20%) 10-year risk of CVD based on the Framingham risk score, the CAC score was a statistically significant predictor of coronary or total CV events, but added little extra accuracy to the Framingham risk score used alone.
    • Indescriminate testing is the main limitation of these results. There is little value in obtaining a CAC score in a patient who is at low risk of a CV event based on their risk factors. Similarly, a CAC score is unlikely to reclassify a patient with a high Framingham score down into a low-risk category that doesn't warrant treatment.
  • To account with the limitations of the above study, the MESA investigators evaluated the performance of the CAC score (& other novel risk markers) in a sub-cohort of 1330 patients without diabetes with an "intermediate" Framingham score (10-year risk of coronary artery disease of 5-20%) over a median follow-up period of 7.6 years.
    • Addition of CAC score to the Framingham risk score correctly reclassified
      • ~25% of patients from an intermediate- to high-risk group (i.e. changed their estimated 10-year risk of a coronary event from 5-20% to >20%)
      • ~40% of patients from the intermediate- to low-risk group

Bottom line

  • Patients who should NOT get CAC scoring (low likelihood of altering management)
    • Low Framingham score
    • High Framingham score
    • Patients already receiving primary prevention therapies
    • Patients who have already made a decision for/against medical therapy for primary prevention
  • Patients for whom CAC scoring could be useful
    • Intermediate Framingham score + patient undecided about initiating therapy, or wishing for further stratification
    • High Framingham score + undecided about therapy
  • Clinicians can integrate the CAC score with traditional clinical risk factors to estimate a patient's 10-year CV risk using this calculator.

 

Prepared by: Ricky Turgeon BSc(Pharm), ACPR, PharmD

Last updated: 9 Sept 2016

Calcified LAD