What is cardiac calcium imaging?

What is Cardiac Calcium Imaging

Cardiac calcium imaging, also known as coronary artery calcium (CAC) scoring, is a non-invasive CT scan that detects and quantifies calcium deposits in the coronary arteries as a marker of atherosclerotic disease burden. 1, 2

Technical Overview

• CAC imaging uses either electron beam tomography (EBT) or multidetector CT (MDCT) to detect coronary calcification without contrast administration. 1

• The scan is performed using ECG-gated multidetector computed tomography with relatively low radiation exposure (0.9-1.5 mSv), comparable to 1-2 mammograms. 2, 3

• The Agatston score is the most widely used scoring system, defining calcific lesions as having CT density >130 Hounsfield units and area >1 mm². 3, 4

• Alternative scoring methods include Volume score and Mass score, though the Agatston score remains the most extensively studied and widely accepted technique in both clinical and research settings. 4

What CAC Imaging Measures

• Calcification does not occur in a normal vessel wall, thus signifying the presence of atherosclerosis; however, it is not specific for luminal obstruction. 1

• CAC scores approximate the total atherosclerotic plaque burden, with the degree of coronary calcification correlated with the extent of total atherosclerotic burden. 1, 3

• Coronary calcifications are exclusively present in atherosclerotic lesions of the intimal layer, representing definitive evidence of atherosclerosis. 3, 5

• Cardiovascular risk increases proportionally to the calcium score, with adjusted relative risks escalating at thresholds of 11-100,101-400,401-1,000, and >1,000. 3, 5

Clinical Applications and Appropriate Use

Primary Indications

• CAC scoring is most appropriate for asymptomatic adults aged 40-75 years at intermediate risk (7.5-20% 10-year ASCVD risk) or borderline risk (5-7.5% 10-year ASCVD risk) when decisions about preventive interventions, particularly statin therapy, remain uncertain. 2, 3

• The American Heart Association gives CAC scoring a Class IIa recommendation (Level of Evidence: B-NR) for these intermediate-risk patients to guide shared decision-making. 2

• Selected low-risk adults with family history of premature coronary heart disease may be considered for CAC scoring. 2, 3

Risk Stratification Value

• A calcium score of zero indicates excellent prognosis with very low risk (<1% annually) for cardiac death or myocardial infarction. 3, 5

• Among 220 symptomatic women with normal coronary arteriograms, none had detectable CAC, yielding a negative predictive value of 100%. 1

• For women, risk-adjusted relative risk ratios for all-cause mortality were elevated 2.5-, 3.7-, 6.3-, and 12.3-fold for calcium scores of 11 to 100,101 to 400,401 to 1000, and >1000, respectively. 1

• CAC scoring provides incremental prognostic value beyond traditional risk factors, particularly in the intermediate-risk population where reclassification of risk can significantly impact treatment decisions. 2, 6

Important Limitations and Caveats

• CAC testing is not appropriate as a surrogate for angiographic disease detection because of the modest relationship between CAC and obstructive coronary artery disease. 1

• Calcium testing was not recommended in the 2000 ACC/AHA expert consensus document to diagnose obstructive CAD because of its low specificity. 1

• In symptomatic patients with zero calcium score, 7-38% still have obstructive disease, as CAC=0 does not exclude non-calcified plaque or obstructive coronary disease. 2, 3

• CAC scoring should be seen primarily as a marker of atherosclerosis and not of degree of stenosis. 3, 5

• Coronary calcifications are not an indicator of stability or instability of an atherosclerotic plaque. 5

Inappropriate Uses

• Screening asymptomatic patients using coronary CT angiography (as opposed to calcium scoring alone) is considered inappropriate. 2

• Repeat coronary calcium testing is considered inappropriate. 2

• CAC scoring is generally not recommended for men <40 years or women <50 years due to low prevalence of detectable calcium and radiation exposure concerns. 2

• Low-risk patients (<6% 10-year risk) without a family history of premature coronary heart disease should not undergo CAC measurement. 2

Age and Sex Considerations

• The prevalence and severity of CAC is strongly related to increasing age and sex, with women having less prevalent and less severe CAC than men. 1

• For women, the prevalence of CAC is low premenopausally, and across age deciles, prevalence lags by 10 years when compared with male counterparts. 1

• These distributions have been developed largely in white women and should not be applied to nonwhite women until ethnicity-specific data are developed. 1

Emerging Applications

• Opportunistic detection of CAC on non-ECG-gated chest CT scans performed for noncardiac indications can enhance atherosclerotic cardiovascular disease risk stratification without additional radiation exposure, cost, or burden. 7

• Approximately 19 million non-ECG-gated chest CT scans are performed per year, and reporting opportunistic CAC from these scans has potential to alert physicians of risk independent of guideline-recommended risk calculator use. 7

• Advancements in artificial intelligence allow integration of automated CAC quantification into clinical practice to improve reporting and appropriate allocation of preventive therapies. 7