CVD risk estimation: Should you get a coronary artery calcium score (CACS)?
More than a decade doctors have been using CVD risk predication tools to lower cardiovascular diseases. The tools use traditional risk factors such as age, blood pressure, diabetes, smoking status, and cholesterol levels. The Framingham Score or the WHO/ISH risk prediction charts are popular tools used to predict CVD risk.
Because inherent uncertainty in CVD prediction persists, even in these well-established models, there have been interest in improving existing risk models by incorporating non-traditional risk factors and, ultimately, reducing CVD events and mortality.
A coronary artery calcium score (CACS) is a radiologic marker of the) degree of calcification in the coronary arteries; it has been proposed to improve current risk prediction.
US Preventive Services Task Force (USPSTF) in their 2018 guideline concluded that there was insufficient evidence to recommend adding CACS to traditional risk models.
In 2022 meta-analysis in JAMA stated that addition of CACS to traditional CVD risk models was associated with improvement in model discrimination, with a pooled gain in C statistic of 0.036 (95% CI, 0.020-0.052)—a small but statistically significant finding of unknown clinical significance.
However, a commentary in JAMA by different authors state that ‘the addition of CACS to traditional models has never, to our knowledge, been associated with reductions in coronary or CVD events. Trials to investigate this hypothesis are underway’.
According to the commentary, “CACS has other potentially harmful shortcomings compared with traditional risk factor measurement. Quantifying a CACS requires a cardiac computed tomography (CT) scan of the chest and involves the associated exposure to radiation. The effective radiation dose for a single CACS CT scan ranges from 1 to 3 mSv. It has been estimated that the life-time excess cancer risk from a single CACS CT at age 40 years, with a radiation dose of 2.3 mSv, would be 9 (3-42) cases per 100 000 men and 28 (9-130) cases per 100 000 women.
Moreover, determination of a CACS adds financial costs to risk estimation models that would otherwise include only routinely collected patient data. Despite the cost and radiation exposure for an individual being small, these could prove to be substantial when applied to a large primary prevention screening population.
Furthermore, abnormal CACS may lead to cascades of downstream testing and revascularization procedures (and more radiation) of questionable appropriateness and no benefit for individuals who are asymptomatic.
In the only randomized clinical trial of CACS scanning compared with no scanning in asymptomatic individuals with risk factors for coronary artery disease, 64% of those with a CACS greater than 400 underwent stress testing and 15% underwent coronary angiography and revascularization, adding medical costs that rose as CACS increased. Although, that study was not powered for clinical outcomes, it is notable that the rates of death or myocardial infarction were numerically higher in the CACS scan group (2.1%) compared with the no CT scan group (1.0%; P = .08).
Some proponents point to the potential of CACS to derisk patients as evidence of its usefulness. Despite proclamations regarding the “power of [a CACS of] 0” and claims of an event-free warranty period after such a score, one-fourth to one-third of total incident CVD events occur in individuals with a CACS of 0, and a significant proportion of patients with a CACS of 0 have coronary artery disease.
Bottom line
Until ongoing outcomes studies indicate a clinical benefit of CACS screening to counterbalance its potential harms, the authors writing this commentary agree with the US Preventive Services Task Force and believe that adherence to the ancient medical dictum, primum non nocere, should dictate a pause in adding CACS screening to standard clinical risk models for primary prevention of CVD.
