Coronary artery calcium scoring: Its practicality and clinical utility in primary care

RISKS AND DOWNSIDES OF CALCIUM SCORING

According to some reports, $8.5 billion is spent annually for low-value care.⁴⁴ Many of the 80 million CT scans performed annually in the United States are believed to be unnecessary and may lead to additional testing to investigate incidental findings.⁴⁵

Growing use of coronary calcium measurement has raised similar concerns about radiation exposure, healthcare costs, and increased downstream testing triggered by the detection of incidental noncardiac findings. For instance, Onuma et al⁴⁶ reported that, in 503 patients undergoing CT to evaluate coronary artery disease, noncardiac findings were seen in 58.1% of them, but only 22.7% of the 503 had clinically significant findings.

Some of these concerns have been addressed. Modern scanners can acquire images in only a few seconds, entailing lower radiation doses than in the past.^13,14 The cost of the test is currently less than $100 in many US metropolitan areas.⁴⁷ However, further studies are needed to adequately and cost-effectively guide follow-up imaging of incidental noncardiac findings.⁴⁸

An important limitation of calcium scoring for risk assessment is that no randomized controlled trial has evaluated the impact of preventive interventions guided by calcium scores on hard event outcomes. It can be argued that there have been plenty of observational studies that have shown the benefit of coronary calcium scoring when judiciously done in the appropriate population.⁴⁹ Similarly, no randomized controlled trial has tested the pooled cohort equation and the application of statins based on its use with the current guidelines. The feasibility and cost of a large randomized controlled trial to assess outcomes after coronary artery calcium measurement must also be considered.

Another limitation of coronary calcium scoring is that it cannot rule out the presence of noncalcified atherosclerotic plaque, which often is more unstable and prone to rupture.

In addition, calcification in the coronary vascular bed (even if severe) does not necessarily mean there is clinically relevant coronary stenosis. For instance, an asymptomatic patient could have a coronary artery calcium score higher than 100 and then get a coronary angiogram that reveals only a 30% lesion in the left anterior descending coronary artery. This is because accumulation of (calcified) plaque in the vessel wall is accommodated by expansion of vessel diameter, maintaining luminal dimensions (positive remodeling). By definition, this patient does have coronary artery disease but would be best served by medical management. This could have been determined without an invasive test in an otherwise asymptomatic patient. Thus, performing coronary angiography based on a coronary artery calcium score alone would not have changed this patient’s management and may have exposed the patient to risks of procedural complications, in addition to extra healthcare costs. Therefore, the presence or absence of symptoms should guide the clinician on whether to pursue stress testing for invasive coronary angiography based on the appropriate use criteria.^50,51

WHO SHOULD BE TESTED?

In the ACC/AHA 2013 guidelines,³⁷ coronary calcium scoring has a class IIB recommendation in scenarios where it may appear that the risk-based treatment decision is uncertain after formal risk estimation has been done. As discussed above, a score higher than 100 could be a rationale for starting aspirin therapy, and a score higher than 0 for statin therapy. The current guidelines also mention that the coronary calcium score is comparable to other predictors such as the C-reactive protein level and the ankle-brachial index.

Compared with the ACC/AHA guidelines, the 2016 Society of Cardiovascular Computed Tomography guidelines and expert consensus recently have added more specifics in terms of using this test for asymptomatic patients at intermediate risk (10-year risk of atherosclerotic cardiovascular disease 5%–20%) and in selected patients with a family history of premature coronary artery disease and 10-year risk less than 5%.^40,52 The 2010 ACC/AHA guidelines were more specific, offering a class IIA recommendation for patients who were at intermediate risk (Framingham Risk Score 10%–20%).⁵³

The ACC/AHA cited cost and radiation exposure as reasons they did not give coronary calcium measurement a stronger recommendation.³⁷ However, as data continue to come in, the guidelines may change, especially since low-dose radiation tools are being used for cancer screening (lungs and breast) and since the cost has declined over the past decade.

OUR APPROACH

Given the negative predictive value of the coronary calcium score, our approach has been to use this test in asymptomatic patients who are found to be at intermediate risk of atherosclerotic cardiovascular disease based on the ACC/AHA risk calculation and are reluctant to start pharmacologic therapy, or who want a more personalized measure of coronary artery disease. This is preceded by a lengthy patient-physician discussion about the risks and benefits of the test.⁵⁴

The patient’s risk can then be further clarified and possibly reclassified as either low or high if it doesn’t remain intermediate. A discussion can then take place on potentially starting pharmacologic therapy, intensive lifestyle modifications, or both.^54,55 If an electronic medical record is available, CT results can be shown to the patient in the office to point out coronary calcifications. Seeing the lesions may serve an as additional motivating factor as patients embark on primary preventive efforts.⁵⁶

Below, we describe cases of what we would consider appropriate and inappropriate use of coronary artery calcium scoring.