Even though the “power of zero” in coronary artery calcium (CAC) scoring was formally included in the 2018 update to the American cholesterol guidelines, clinicians are still left with the challenge of appropriately and selectively using this tool to guide preventive care decisions.
A group of researchers from Johns Hopkins Medical Institutions in Baltimore published an editorial on this topic in the Annals of Internal Medicine, stressing that expanded use of CAC testing shouldn’t turn into widespread screening and that insurance coverage and low cost are key to providing equal access to this imaging technique. Just as CAC has been shown to be a good marker of atherosclerosis and predictive of future cardiovascular events, the “power of zero” refers to the relatively low risk that’s been observed in individuals without any CAC.
“It is critical that the main stakeholders, especially primary care physicians, understand the newly proposed role for CAC testing and do not equate it with screening,” wrote Rhanderson Cardoso, MD, and colleagues with the Johns Hopkins Ciccarone Center for the Prevention of Cardiovascular Disease. “Rather than bringing in many additional statin candidates, this testing should serve as a decision aid to ‘de-risk’ certain patients and distinguish those who may benefit from preventive pharmacologic therapies.”
Specifically, the updated guidelines recommend using CAC scoring when the benefit-risk balance is uncertain, such as borderline- or intermediate-risk patients with a projected 10-year risk of atherosclerotic cardiovascular disease (ASCVD) between 5 and 20 percent. But clinical judgment and patient preferences should play a role into whether to prescribe statins, regardless of CAC values, according to the guidelines.
Despite a guideline which “strongly endorses selective CAC testing,” Cardoso et al. said there are several factors to consider with patients, including the cost of the scan, the “modest” radiation exposure and the possibility of additional follow-up imaging for noncardiac findings unveiled during CAC scanning.
“The next step for CAC testing in primary prevention is clearly universal coverage for appropriate candidates to ensure equal access,” the authors wrote. “We must advocate for reasonable pricing (<$150). We also must reinforce that CAC testing is a decision aid and should almost never be followed by downstream cardiovascular testing, such as stress testing or cardiac catheterization.”
Even with these caveats, the authors agreed selective CAC scoring—when employed properly— has the potential to distinguish patients most likely to benefit from therapies for primary prevention.