The 2018 ACC/AHA Cholesterol Guideline suggests that coronary artery calcium (CAC) testing may be considered in adults 40-75 years of age without diabetes mellitus and with LDL-C levels ≥70 mg/dl-189 mg/dl at a 10-year atherosclerotic cardiovascular disease (ASCVD) risk of ≥7.5% to <20% (i.e., intermediate risk group) if a decision about statin therapy is uncertain.¹ In such patients, if CAC is zero, treatment with statin therapy may be withheld or delayed, except in cigarette smokers, those with diabetes mellitus, and those with a strong family history of premature ASCVD. According to the guideline, a CAC score of 1 to 99 favors statin therapy, especially in those ≥55 years of age. For any patient, if the CAC score is ≥100 Agatston units or ≥75th percentile, statin therapy is indicated unless otherwise deferred by the outcome of clinician-patient risk discussion.

In explaining the rationale for the inclusion of CAC, the authors of the guideline stated that "Identification of subclinical atherosclerosis rather than use of serum biomarkers is preferred, because of the extensive body of evidence demonstrating the superior utility of atherosclerosis disease assessment, particularly with CAC measurement, over any serum biomarker for the prediction of future ASCVD events, including both coronary heart disease and stroke."²

Top three take home points from the guideline:

1. When to consider CAC testing? In intermediate-risk or selected borderline-risk adults, if the decision about statin use remains uncertain, it is reasonable to use a CAC score in the decision to withhold, postpone or initiate statin therapy.
2. Emphasis on "power of zero:" use of CAC testing to identify low risk patients. As opposed to risk enhancers and screening tools that may be used to identify higher risk patients, CAC testing is now mostly used for identifying lower risk patients among those who would otherwise be candidates for statin therapy but who have a preference to avoid such therapy.
3. Not everyone benefits from CAC testing: selective use encouraged. Many individuals can be treated with statin therapy and do not require CAC testing. However, when there is uncertainly about patient risk or a desire to defer statin therapy, CAC testing may be used to enhance shared decision making.
4. CAC may also be useful in older individuals. The new guideline also supports the utility of CAC measurement in identifying the absence of atherosclerotic plaque in older adults. Specifically, the guideline states that in adults 76 to 80 years of age with an LDL-C level of 70 to 189 mg/dL, it may be reasonable to measure CAC to reclassify those with a CAC score of zero to avoid statin therapy.

Other tips for cardiologists on CAC testing:

1. Must interpret CAC test results in context of overall patient risk. A CAC score of zero can be helpful in reclassifying risk to a lower risk group;³ however, a score of zero does not imply zero risk, and the results of the test should always be incorporated with other known risk factors. It is for this reason that CAC testing is not recommended in high risk patients (i.e., 10-year ASCVD risk ≥20%), and that at times clinicians and patients may elect to initiate statin therapy despite a CAC of zero.
2. Communication of results. It is important to appropriately communicate the results of CAC testing with patients. Patients should understand that the presence of CAC implies that they have coronary plaque, and thus are at higher risk of ASCVD events. There is data that showing patients pictures of their scans may be helpful in promoting better adherence with lifestyle and medical therapies. Thus, clinicians should be encouraged to review test results with patients. This is also important as it has been shown that the identification of CAC leads to a higher rate of initiation or of lipid lowering and blood pressure lowering therapies, as well as favorable changed in diet and exercise.⁴
3. Aggressive treatment...but otherwise no further testing needed after CAC. The vast majority of asymptomatic patients with elevated CAC scores do not need any further testing. They do, however, require more aggressive medical and lifestyle therapies.⁵ For patients with severe CAC, exercise treadmill testing may be reasonable if there is uncertainty regarding the presence of anginal symptoms.
4. What about CAC testing under the age of 40? There is less data on guiding the use of CAC testing in young individuals (age 35-40); however, one study has shown that the presence of even a small amount of CAC at a young age implies a substantial increase in future risk, and thus should trigger aggressive therapies.⁶ However, a calcium score of zero may be less reassuring in very young adults. Therefore, CAC testing in those under the age of 40 is currently not supported by guidelines.

Despite the significant role of CAC testing in the 2018 cholesterol guideline, this test is still not widely covered by payors. As a result, many patients often pay out-of-pocket for this test – and fortunately in many places the cost may be as little as $100 - $200. Nevertheless, better coverage for this test, and thus more uniform access, is needed and hopefully will occur as a result of the new guideline.

References

1. Grundy SM, Stone NJ, Bailey AL, et al. 2018 AHA/ACC/AACVPR/AAPA/ABC/ACPM/ADA/AGS/APhA/ASPC/NLA guideline on the management of blood cholesterol: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines. J Am Coll Cardiol 2018. [Epub ahead of print]
2. Lloyd-Jones DM, Braun LT, Ndumele CE, et al. Use of risk assessment tools to guide decision-making in the primary prevention of atherosclerotic cardiovascular disease: a special report from the American Heart Association and American College of Cardiology. J Am Coll Cardiol 2018. [Epub ahead of print]
3. Nasir K, Bittencourt MS, Blaha MJ, et al. Implications of coronary artery calcium testing among statin candidates according to the American College of Cardiology/American Heart Association cholesterol management guidelines: MESA (Multi-Ethnic Study of Atherosclerosis). J Am Coll Cardiol 2015;66:1657-68.
4. Gupta A, Varshney R, Lau E, et al. The identification of coronary atherosclerosis is associated with initiation of pharmacologic and lifestyle preventive therapies: a systematic review and meta-analysis. J Am Coll Cardiol 2016;67:1972.
5. Hecht H, Blaha MJ, Berman DS, et al. Clinical indications for coronary artery calcium scoring in asymptomatic patients: expert consensus statement from the Society of Cardiovascular Computed Tomography. J Cardiovasc Comput Tomogr 2017;11:157-68.
6. Carr JJ, Jacobs DR Jr, Terry JG, et al. Association of coronary artery calcium in adults aged 32 to 46 years with incident coronary heart disease and death. JAMA Cardiol 2017;2:391-9.
7. Miedema MD, Duprez DA, Misialek JR, et al. Use of coronary artery calcium testing to guide aspirin utilization for primary prevention: estimates from the multi-ethnic study of atherosclerosis. Circ Cardiovasc Qual Outcomes 2014;7:453-60.

Clinical Topics: Cardiovascular Care Team, Dyslipidemia, Prevention, Lipid Metabolism, Nonstatins, Novel Agents, Statins

Keywords: Primary Prevention, Secondary Prevention, Risk Factors, Hydroxymethylglutaryl-CoA Reductase Inhibitors, Plaque, Atherosclerotic, Calcium, Coronary Vessels, Blood Pressure, Cholesterol, Coronary Disease, Atherosclerosis, Stroke, Life Style, Diabetes Mellitus, Biomarkers

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