Studies Examine Use of CAC Testing

In light of the new ACC/ American Heart Association cholesterol guidelines, a lack of coronary artery calcium (CAC) reclassifies approximately half of statins candidates as not eligible, according to a study published Oct. 5 in the Journal of the American College of Cardiology (JACC).

The study, led by Khurram Nasir, MD, MPH, used data from the Multi-Ethnic Study of Atherosclerosis (MESA) study – which includes 6,814 men and women aged 45 to 84 without known cardiovascular disease – and evaluated the implications of the absence of CAC in reclassifying atherosclerotic cardiovascular disease (ASCVD) risk when patients are reclassified from being eligible to ineligible for statin therapy.

Researchers found that 50 percent of the cohort was eligible for moderate- to high-intensity statins. Among those recommended for statins, 41 percent had CAC=0 and had 5.2 ASCVD events/1,000 person-years. Among 589 participants (12 percent) considered for moderate-intensity statin, 338 had a CAC=0, with an ASCVD event rate of 1.5 per 1,000 person-years. Of participants eligible for statins, 44 percent had CAC=0 at baseline and a 10-year ASCVD event rate of 4.2 per 1,000 person-years.

According to the authors, these results suggest that the absence of CAC is associated with a lower ASCVD risk among those eligible for statins and that CAC testing may have limited impact on decisions regarding statin use. 

In an editorial comment, Javier Sanz, MD, writes that “this important study confirms that, in the current era of updated and presumably improved predictive scores, CAC retains a strong ability to reclassify cardiovascular risk,” and adds that “efforts should be made to identify not only newer indications for therapy but also those who may not significantly benefit from it.”

Meanwhile, according to results of a separate study also published Oct. 5 in JACC using a cohort of 6,726 patients participating in the MESA study, an accurate estimate of 10-year coronary heart disease (CHD) risk may be obtained through tradition risk factors and CAC scores.

Researchers led by Robyn L. McClelland, PhD, found that including CAC in the MESA risk score may lead to significant improvements in risk prediction. External validation from Heinz Nixdorf Recall (HNR) and the Dallas Heart Study (DHS) provided evidence for very good to excellent discrimination and calibration. Mean calibration was excellent for both studies (-0.50 percent for HNR and -0.46 percent for DHS), indicating that on average, predicted risk was within one-half of a percent of the observed event rate.

According to the authors, “one commonly stated limitation for clinical CAC scoring is the absence of a risk calculator for integrating this information into global cardiovascular risk assessment.”

In an accompanying editorial, Donald M. Lloyd-Jones, MD, SCM, FACC, comments on both studies, noting that “the optimal approach at present appears to be a sequential screening approach, with quantitative risk assessment followed by selective CAC screening, rather than universal screening.” 

Clinical Topics: Dyslipidemia, Lipid Metabolism, Nonstatins, Novel Agents, Statins

Keywords: Atherosclerosis, Calcium, Calcium, Dietary, Calibration, Cardiovascular Diseases, Cholesterol, Coronary Disease, Coronary Vessels, Hydroxymethylglutaryl-CoA Reductase Inhibitors, Risk Assessment, Risk Factors, Risk

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