Coronary Artery Calcium Testing From Different Perspectives
- Polonsky TS, Greenland P.
- Viewing the Value of Coronary Artery Calcium Testing From Different Perspectives. JAMA Cardiol 2018;Jul 10:[Epub ahead of print].
The following are key points to remember from this editorial on viewing the value of coronary artery calcium (CAC) testing from different perspectives:
- Recent guidelines strongly encourage that treatment decisions for statins, antihypertensive medication, and aspirin be based on 10-year estimated risk using risk factor equations that all agree are imperfect. A large proportion of atherosclerotic cardiovascular disease (ASCVD) events occur among adults who are below the cutoffs used to initiate therapy, and many patients who do cross the threshold used to justify lifelong preventive medications will not experience an ASCVD event.
- In a recent issue of JAMA, the US Preventive Services Task Force (USPSTF) provided evidence-based recommendations on the potential use of three markers of subclinical CVD to enhance CV assessment in asymptomatic adults: the ankle-brachial index (ABI), high-sensitivity C-reactive protein (hs-CRP) level, and CAC score.
- The USPSTF stated that there was inadequate evidence to recommend for or against routine clinical use of any of the markers because of insufficient evidence that treatment decisions based on the markers alone or in combination with Pooled Cohort Equations (PCEs) have additive value. The USPSTF acknowledged that risk assessment with CAC was strong, but refused to recommend it because the clinical meaning of an improvement in risk assessment was unknown.
- This editorial presents a very strong argument that the CAC testing is unique with good evidence of value. The authors noted that studies directly comparing the three markers support the CAC as being more likely than ABI or hs-CRP to provide meaningful changes in “estimated risk.”
- One fault of the USPSTF analysis is the assumption of “routine” widespread, rather than selected use of CAC scoring. In fact, there is evidence from the MESA (Multi-Ethnic Study of Atherosclerosis) study, which evaluated the predictive value of CAC scoring in a predominantly middle-aged ethnically diverse US cohort, that adding CAC to the PCE 10-year ASCVD risk was of very little value if the goal was to stratify less than or at least 7.5% 10-year risk as in guidelines for statin therapy.
- The MESA data suggest that the CAC score is much less valuable when used in low or high risk by the PCE or Framingham Risk Score. It is most helpful when treatment decisions are unclear. Studies show that CAC testing could provide meaningful prognostic information in adults whose levels were 7.5-9.5%. In MESA, 41% of adults who would have been recommended statins based on a 10-year ASCVD risk of ≥7.5% had a CAC score of 0. More specifically, in the 7.5-9.5% group (about one-quarter of statin-recommended MESA participants), the prevalence of a CAC score of 0 was even higher at 55%, and the event rate was only 2.7 per 1,000 person-years.
- Further, 17% of the adults with an estimated 10-year risk of 7.5-9.5% and 24% of the adults with a 10-year estimated risk of 10-14.9% had CAC scores >100. The 10-year event rates for those with CAC scores >100 were >7.5%, regardless of sex or race/ethnicity, suggesting they are more likely to benefit from medical therapy.
- The USPSTF suggestion that a clinical trial using the CAC score to decide therapy would need to be very large with long-term follow-up, and would not likely be funded.
Keywords: Ankle Brachial Index, Antihypertensive Agents, Aspirin, Atherosclerosis, C-Reactive Protein, Diagnostic Imaging, Dyslipidemias, Hydroxymethylglutaryl-CoA Reductase Inhibitors, Plaque, Atherosclerotic, Primary Prevention, Risk Assessment, Risk Factors
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