What is a Coronary Calcium Score?
A coronary calcium score is a reliable marker of coronary atherosclerosis burden that quantifies calcification in coronary arteries, providing powerful risk prediction for future cardiovascular events and mortality. 1
Definition and Measurement
The coronary calcium score, most commonly expressed as the Agatston score, is obtained through an electrocardiogram-gated multidetector computed tomography (CT) scan that measures calcification in the coronary arteries. This score:
- Quantifies calcific lesions with CT density >130 Hounsfield units and area >1 mm² 1
- Uses a weighting factor (1-4) based on peak calcium density 1
- Calculates total score by summing scores of all calcified lesions 1
- Can be expressed as a percentile adjusted for sex and race 1
The radiation dose for coronary calcium scoring is relatively low (approximately 0.37 mSv), which is slightly lower than a screening mammography 1.
Clinical Significance
Indicator of Atherosclerosis
- Coronary calcification indicates atherosclerosis of coronary arteries 1
- The extent of calcification correlates with total coronary plaque burden 1
- CAC represents only about 20% of the total atherosclerosis burden 1
- CAC should be viewed primarily as a marker of atherosclerosis, not as an indicator of stenosis severity 1
Risk Stratification
Coronary calcium score provides powerful risk stratification:
- Score of 0: Highly favorable prognosis with annual risk <1% for cardiac death or MI 1
- Scores 1-99: Mild calcification
- Scores 100-399: Moderate calcification
- Scores ≥400: Severe calcification with significantly increased risk 1, 2
A score ≥400 is associated with significantly increased risk for major adverse cardiovascular events (MACE), including unstable angina, myocardial infarction, need for percutaneous intervention, and heart failure 2.
Clinical Applications
Risk Assessment in Asymptomatic Individuals
- Superior to traditional risk factor assessments for predicting cardiovascular events 1
- Particularly useful for reclassifying patients with intermediate (7.5% to <20%) or borderline (5% to <7.5%) 10-year risk 1
- Can help guide decisions about preventive therapies like statins 1
"The Power of Zero"
A calcium score of zero has exceptional negative predictive value:
- <0.5% annual mortality rate, even in patients with possible CAD symptoms 1
- Observed mortality <1% yearly for >15 years in asymptomatic patients 1
- Stronger indicator of low risk than traditional risk factors 1
Important Caveats
Not for Symptomatic Patients: While valuable for risk assessment in asymptomatic individuals, coronary calcium scoring is not routinely recommended for symptomatic patients as it may miss non-calcified plaques 1
Not Equivalent to Stenosis: A high calcium score indicates atherosclerosis but doesn't necessarily indicate significant stenosis - its specificity for ≥50% stenosis is only about 50% 1
Not an Indicator of Plaque Stability: Coronary calcification indicates neither stability nor instability of an atherosclerotic plaque 1
Limitations in Younger Patients: Younger patients may have significant non-calcified plaque burden without detectable calcium
Summary
The coronary calcium score is a powerful, non-invasive tool for quantifying coronary atherosclerosis burden and predicting cardiovascular risk. It provides valuable information beyond traditional risk factors and can guide preventive strategies, particularly in asymptomatic individuals with intermediate cardiovascular risk.