Coronary artery calcium scoring: Its practicality and clinical utility in primary care
ABSTRACT
Coronary artery calcium scoring is useful as a risk-stratification tool in coronary artery disease, and it outperforms other risk-assessment methods. American College of Cardiology/American Heart Association guidelines give the test a IIB recommendation in clinical scenarios in which risk stratification is uncertain. However, if the test is not used in the appropriate clinical setting, misinterpretation of the results can lead to unnecessary cardiac testing. This review provides the primary care provider with basic knowledge about the test’s clinical utility, interpretation, risks, and limitations.
KEY POINTS
- Coronary artery calcium testing is useful in diagnosing subclinical coronary artery disease and in predicting the risk of future cardiovascular events and death.
- Given the high negative predictive value of the test, it can also serve to reclassify risk in patients beyond traditional risk factors.
- Along with shared decision-making, elevated calcium scores can guide the initiation of statin or aspirin therapy.
- A high score in an asymptomatic patient should not trigger further testing without a comprehensive discussion of the risks and benefits.
Coronary artery calcium scoring vs other risk-stratification methods
Current guidelines on assessing risk still rely on the traditional 10-year risk model in clinical practice.25 Patients are thus classified as being at low, intermediate, or high risk based on their probability of developing a cardiovascular event or cardiovascular disease-related death in the subsequent 10 years.
However, the predictive value of this approach is only moderate,28 and a significant number of cardiovascular events, including sudden cardiac death, occur in people who were believed to be at low or intermediate risk according to traditional risk factor-based predictions. Because risk scores are strongly influenced by age,29 they are least reliable in young adults.30
Akosah et al31 reviewed the records of 222 young adults (women age 55 or younger, men age 65 or younger) who presented with their first myocardial infarction, and found that only 25% would have qualified for primary prevention pharmacologic treatments according to the National Cholesterol Education Program III guidelines.32,33 Similar findings have been reported regarding previous versions of the risk scores.33
Thus, risk predictions based exclusively on traditional risk factors are not sensitive for detecting young individuals at increased risk, and lead to late treatment of young adults with atherosclerosis, which may be a less effective strategy.34
The reliance on age in risk algorithms also results in low specificity in elderly adults. Using risk scores, elderly adults are systematically stratified in higher risk categories, expanding the indication for statin therapy to almost all men age 65 or older regardless of their actual vascular health, according to current clinical practice guidelines.35,36
Risk scores are based on self-reported history and single-day measurements, since this kind of information is readily available to the physician in the clinic. Moreover, our knowledge about genetic and epigenetic factors associated with the development of atherosclerosis is still in its infancy, with current guidelines not supporting genetic testing as part of cardiovascular risk assessment.37 Thus, a reliable measure of an individual’s lifelong exposure to a number of environmental and genetic factors that may affect cardiovascular health appears unfeasible.
Atherosclerosis is a process in which interactions between genetic, epigenetic, environmental, and traditional risk factors result in subclinical inflammation that could develop into clinically significant disease. Therefore, subclinical coronary atherosclerosis has been shown to be a strong predictor of future incident cardiovascular disease events and death. Thus, alternative approaches that directly measure disease, such as calcium scoring, may help further refine risk stratification of cardiovascular disease.
The MESA trial (Multi-Ethnic Study of Atherosclerosis), for instance, in 6,814 participants, found coronary calcium to provide better discrimination and risk reclassification than the ankle-brachial index, high sensitivity C-reactive protein level, and family history.38 Coronary calcium also had the highest incremental improvement of the area under the receiver operating curve when added to the Framingham Risk Score (0.623 vs 0.784).
Reclassifying cardiovascular risk also has implications regarding whether to start therapies such as statins and aspirin.
For considering statin therapy
Nasir et al39 showed that, in patients eligible for statin therapy by the pooled cohort equation, the absence of coronary artery calcium reclassified approximately one-half of candidates as not eligible for statin therapy. The number needed to treat to prevent an atherosclerotic cardiovascular event in the population who were recommended a statin was 64 with a calcium score of 0, and 24 with a calcium score greater than 100. In the population for whom a statin was considered, the number needed to treat was 223 with a calcium score of 0 and 46 for those with a score greater than 100. Moreover, 57% of intermediate-risk patients and 41% of high-risk patients based on the Framingham Risk Score were found to have a calcium score of 0, implying that these patients may actually be at a lower risk.
The Society of Cardiovascular Computed Tomography guidelines40 say that statin therapy can be considered in patients who have a calcium score greater than 0.
For considering aspirin therapy
Miedema et al41 studied the role of coronary artery calcium in guiding aspirin therapy in 4,229 participants in the MESA trial who were not taking aspirin at baseline. Those with a calcium score higher than 100 had a number needed to treat of 173 in the group with a Framingham Risk Score less than 10% and 92 with a Framingham Risk Score of 10% or higher. The estimated number needed to harm for a major bleeding event was 442. For those who had a score of 0, the estimated number needed to treat was 2,036 for a Framingham Risk Score less than 10% and 808 for a Framingham Risk Score of 10% or higher, with an estimated number needed to harm of 442 for a major bleeding event.
The Society of Cardiovascular Computed Tomography guidelines40 recommend considering aspirin therapy for patients with a coronary calcium score of more than 100.
McClelland et al42 developed a MESA risk score to predict 10-year risk of coronary heart disease using the traditional risk factors along with coronary calcium. The score was validated externally with 2 separate longitudinal studies. Thus, this may serve as another tool to help providers further risk-stratify patients.
COST-EFFECTIVENESS OF THE TEST
As coronary calcium measurement began to be widely used, concerns were raised about the lack of data on its cost-effectiveness.
Cost-effectiveness depends not only on patient selection but also on the cost of therapy. For example, if the cost of a generic statin is $85 per year, then calcium scoring would not be beneficial. However, if the cost of a statin is more than $200, then calcium scoring would be much more cost-effective, offering a way to avoid treating some patients who do not need to be treated.43
Hong et al43 showed that coronary calcium testing was cost-effective when the patient and physician share decision-making about initiating statin therapy. This is especially important if the patient has financial limitations, is concerned about side effects, or wants to avoid taking unnecessary medications.
