Public health

Coronary artery calcium fails to gain USPSTF backing for CV risk prediction

The US Preventive Services Task Force (USPSTF) has determined there is insufficient evidence for nontraditional risk factors such as coronary artery calcium (CAC) scores to improve estimation of cardiovascular disease risk.

An updated evidence review found 43 studies that could help answer questions about the incremental value of coronary artery calcium (CAC) scores, ankle-brachial index (ABI) or high-sensitivity C-reactive protein (hsCRP) .

Only one study addressed whether risk assessment of asymptomatic adults using the tests could reduce the incidence of cardiovascular events and/or mortality.

It found no difference at four years between groups randomised to assessment with the Framingham Risk Score plus CAC scoring compared to the Framingham Risk Score alone.

The review found 10 studies comprising almost 80,000 patients consistently showed that the addition of the ABI to risk prediction models such as Framingham and Pooled Cohort Equations made little to no improvement in prediction of cardiovascular events.

There was more evidence – 25 studies – but inconsistent findings for hsCRP’s ability to improve discrimination over other risk prediction models.

The CAC score was rated highest of the three variables in terms of helping improve classification of individuals into meaningful risk strata. However when applied clinically, the net effect was a sizeable increase in the number of people who were not having CV events but would be considered for treatment.

The review found no evidence for harms from the testing with low radiation exposure for CT associated with the CAC score. However there was some inconsistent evidence for subsequent healthcare utilisation.

There was also some evidence of harm from treatment guided by the nontraditional risk factors, for example, an increased risk of diabetes in adults treated with high intensity statins due to elevated hsCRP levels.

An accompanying editorial in JAMA acknowledge current risk scores for atherosclerotic cardiovascular disease (ASCVD) were imperfect.

“A large proportion of ASCVD events occur among adults who are below the cutoffs used to initiate medical therapy, and many patients who do cross the threshold used to justify lifelong preventive medications are not destined to experience an ASCVD event.”

The authors agreed with the finding that CAC testing should not be a routine screening test for asymptomatic individuals because it only provides modest improvement in risk prediction.

However they felt it was most valuable for the many adults at the borders of current treatment thresholds.

“Coronary artery calcium testing is most helpful when used selectively for patients in whom treatment decisions are unclear.”

“In conclusion, in our view, there is more than sufficient evidence to support selective use of CAA testing as a tool to inform risk assessment and support the less tangible aspects of clinical decision making.”

The editorial’s view is consistent with the Cardiology Society of Australia and New Zealand’s (CSANZ) 2017 position statement on CAC scoring.

It said CAC was of most value in intermediate risk patients who are asymptomatic, do not have known coronary artery disease and aged 45 – 75 years, where it has the ability to reclassify patients into lower or higher risk groups.

“It may also be considered for lower risk patients (absolute 10-year cardiovascular risk 6-10%) particularly in those where traditionally risk scores under estimate risk e.g. especially in context of family history of premature CVD and possibly in patients with diabetes aged 40 to 60 years old.”

CSANZ said there was currently no data that CAC was cost-effective in informing primary prevention decisions.

“Given the cost of testing is currently borne entirely by the patient, discussion regarding the implications of CAC results should occur before CAC is recommended and undertaken.”

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