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Coronary Calcium Scores

Coronary artery calcium scores are calculated based on imaging of the arteries, which visualize calcium deposits in the arteries.

Arterial calcification – Calcified plaque results when there is a build-up of fat and other substances under the inner layer of the artery. This material can calcify which signals the presence of atherosclerosis, a disease of the vessel wall, also called coronary artery disease (CAD).

The presence and extent of coronary arterial calcification (CAC) can predict the presence of coronary artery stenosis (narrowing), but in general it is a better marker of the extent of coronary atherosclerosis than the severity of stenosis.

Indications

Most of the clinical studies that examined the relationship between CAC and coronary artery stenosis have been performed in patients with chest pain who were referred for x-ray coronary angiography.

The 2010 American College of Cardiology/American Heart Association (ACC/AHA) guidelines on screening for coronary artery disease indicated that measurement of coronary artery calcification is reasonable (level of evidence B) for cardiovascular risk assessment in asymptomatic adults at Framingham intermediate risk (10 to 20 percent 10-year risk). The guidelines noted that measurement of CAC “may be reasonable” for patients at low to intermediate risk (6 to 10 percent 10-year risk). It was not recommended for patients at low (<6 percent, 10-year risk) or high risk.

Scoring of CAD Lesions

The Agatston score is calculated in the following way

Each slice taken using an ultrafast CT is analyzed and weighted values are assigned to the highest density of calcification as measured by houndsfield units. A score of 1 is given for 130-199 HU, 2 is given for 200-299, 3 for 300-399 and 4 for 400 or greater (the whiter the lesion, the higher the HU). The weighted score is then multipied by the area of the calcification.

Example: coronary calcification in the LAD measuring 4 square millimeters with a peak density of 250 HU. The score would therefore be 8 (4mm^2 times 2 weighted score). The total score is the sum of all the slices.

Classification of CAD by calcium score:

Calcium Score Presence of CAD
0 No evidence of CAD
1-10 Minimal evidence of CAD
11-100 Mild evidence of CAD
101-400 Moderate evidence of CAD
Over 400 Extensive evidence of CAD

 

Predictive value of the Agatston Score

Positive Test:

Agatston Scores above 400 have increased occurrence of coronary procedure and events of myocardial infarction or cardiac death within 2-5 years after the Calcium Score Scan is performed. Examples of coronary procedures include:

  • bypass
  • stent placement
  • angioplasty

Negative Test:

This does not exclude the presence of atherosclerosis in one’s coronary arteries. It means there is simply minimal atherosclerosis. Predicts a very low likelihood of having a MI or cardiac death in the next 2-5 years.

In a study of 1764 patients with suspected CHD, as the Agatston CAC score varied from >20th percentile to >75th percentile for age, the sensitivity fell from 97 to 81 percent in men and from 98 to 76 percent in women but the specificity increased up to 77 percent. Patients with no CAC had a probability of stenosis of less than 1 percent.

Calcium vs Stenosis

  • Can you have a low calcium score and still have severe obstruction (i.e a 20% score leading to 90% obstruction)?

Yes, without contrast enhancement coronary artery calcification scoring through CT has a low sensitivity for detecting plaques without significant calcification and in one study, the cross-sectional plaque area found on histologic examination was approximately five times greater than the calcification area measured by electron beam computed tomography (EBCT)

Sensitivity and specificity of CAC score

Highly sensitive for the presence of ≥50 percent angiographic stenosis but only moderately specific, especially in individuals over 60 years of age. Both sensitivity and specificity vary with the degree of CAC.

USE OF CAC SCORE – Recommendations

  1. Use for CV risk assessment in intermediate risk patients as determined by their Framingham score when the result will reasonably alter management goals
    1. recommended against those who are classified in either the low or high score group
  2. Asymptomatic patients  with a high CAC score should undergo radionuclide stress testing
  3. CAC should not be used to monitor pharmacologic therapy or initiate preventative therapy

References:

Gerber, T.C., Kramer, C.M. (2014, October 10). Diagnostic and prognostic implications of coronary artery calcification detected by computed tomography. UpToDate. Retrieved from http://www.uptodate.com/contents/diagnostic-and-prognostic-implications-of-coronary-artery-calcification-detected-by-computed-tomography


http://circ.ahajournals.org/content/108/8/e50.full

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