How are the results of a CT scan interpreted for cardiac assessment?

Updated: Nov 20, 2018
  • Author: Richard S Krause, MD; Chief Editor: Barry E Brenner, MD, PhD, FACEP  more...
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Answer

The amount of calcium seen in coronary vessels on CT scanning is usually expressed as a calcium score ("Agatston score"), which is based on the area and the density of the calcified plaques. A typical report provides a calcium score for the major coronary arteries as well as a total score. A test result is considered to be positive if any calcification is detected within the coronary arteries. A positive test result is nearly 100% specific for atheromatous coronary plaque but not highly correlated with obstructive disease. A negative test result has a 96-100% negative predictive value (NPV) for obstructive lesions. Scores of less than 10, 11-99, 100-400, and above 400 have been proposed to categorize individuals into groups having minimal, moderate, increased, or extensive amounts of calcification, respectively.

Conversely, a study by Rosen et al found that "although there is a significant relationship between the extent of calcification and mean degree of stenosis in individual coronary vessels, 16% of the coronary arteries with significant stenosis had no calcification at baseline." [27]

Calcium scores greater than 1000 have been associated with significant increases in morbidity and mortality independent of other risk factors. Scores greater than 100 are consistent with a high risk (>2% annually) of a coronary event within 5 years. The amount of calcification can give, to some extent, an indication of the overall amount of atherosclerosis. In addition, a greater amount of calcification and a higher calcium score increase the likelihood that coronary angiography will detect significant coronary artery stenosis. However, there is not a 1-to-1 relationship between a high score and the presence of coronary artery stenosis. In other words, a positive scan result indicates atherosclerosis but not necessarily significant stenosis. [28]

Individuals with calcium scores greater than 400 have an increased occurrence of coronary procedures (bypass, stent placement, angioplasty) and events (myocardial infarction [MI] and cardiac death) within the 2-5 years after the test. Individuals with very high scores (>1000) have a 20% chance of suffering a MI or cardiac death within a year. Even among elderly patients (>70 y), who frequently have calcification, a calcium score greater than 400 was associated with a higher risk of death. In one study, patients with calcium scores greater than 1000 were found to have a relative risk of death at 5 years of 4.03 (95% confidence interval [CI], 2.52-6.40). However, calcium scores reflect overall risk and cannot be used to diagnose the presence of a specific obstructing lesion. [29]


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