Applied Evidence

Translating AHA/ACC cholesterol guidelines into meaningful risk reduction

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When and why to measure CAC

If the decision to initiate statin therapy is still uncertain after risk estimation and personalization, or when a patient is undecided about committing to lifelong lipid-lowering therapy, the new guideline recommends obtaining a CAC score to inform the shared decision-making process.1,18 Measurement of CAC is obtained by noncontrast, electrocardiographic-gated CT that can be performed in 10 to 15 minutes, requiring approximately 1 millisievert of radiation (equivalent of the approximate dose absorbed during 2 mammograms). Although measurement of the CAC score is generally not covered by insurance, its cost ($50-$450) nationwide makes it accessible.19

The guideline endorses reverse cascade screening for detection of familial hypercholesterolemia in family members of children and adolescents who have severe hypercholesterolemia.

CAC measures the presence (or absence) of subclinical atherosclerosis by detecting calcified plaque in coronary arteries. The absolute CAC score is expressed in Agatston units; an age–gender population percentile is also provided. Keep in mind that the presence of any CAC (ie, a score > 0) is abnormal and demonstrates the presence of subclinical coronary artery disease. The prevalence of CAC > 0 increases with age, but a significant percentage of older people have a CAC score = 0. When CAC > 0, additional information is provided by the distribution of plaque burden among the different coronary arteries.20

Among intermediate-risk patients, 50% have CAC = 0 and, therefore, a very low event rate over the ensuing 10 years, which allows statin therapy to be safely deferred unless certain risk factors are present (eg, family history, smoking, DM).1,18 It is reasonable to repeat CAC testing in 5 to 10 years to assess whether subclinical atherosclerosis has developed. The 2018 guideline emphasizes that, when the CAC score is > 0 but < 100 Agatston units, statin therapy is favored, especially in patients > 55 years of age; when the CAC score is ≥ 100 Agatston units or at the ≥ 75th percentile, statin therapy is indicated regardless of age.1

Patients who might benefit from knowing their CAC score include those who are:

  • reluctant to initiate statin therapy but who want to understand their risk and potential for benefit more precisely
  • concerned about the need to reinstitute statin therapy after discontinuing it because of statin-associated adverse effects
  • older (men, 55-80 years; women, 60-80 years) who have a low burden of risk factors and who question whether they would benefit from statin therapy
  • middle-aged (40-55 years) and who have a PCE-calculated risk of 5% to < 7.5% for ASCVD and factors that increase their risk for ASCVD, even though they are in a borderline-risk group.1

Primary prevention in special populations

Older patients. In adults ≥ 75 years who have an LDL-C level 70 to 189 mg/dL, initiating a moderate-intensity statin might be reasonable; however, it might also be reasonable to stop treatment in this population when physical or cognitive decline, multiple morbidities, frailty, or reduced life expectancy limits the potential benefit of statin therapy. It might be reasonable to use the CAC score in adults 76 to 80 years of age who have an LDL-C level of 70 to 189 mg/dL to reclassify those whose CAC score = 0, so that they can avoid statin therapy.1

Continue to: Children and adolescents

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