Coronary Artery Calcium Scoring Can Help Guide Statin Therapy
Matthew J. Budoff, MD
Disclosures | January 14, 2016
RELATED DRUGS & DISEASES
Several cardiologists have questioned whether assessment of coronary artery calcium (CAC) should be used to evaluate patients for statin therapy, as currently recommended in guidelines since the National Cholesterol Education Program (NCEP) Adult Treatment Panel III update was published in 2004. Serum biomarkers and imaging tests are used to target higher- and lower-risk patients in whom statins might produce a larger or smaller absolute event reduction.
CAC Is Guideline Recommended
Risk stratification with CAC is more robust than previously published data with C-reactive protein (CRP) or other biomarkers, and is a class IIa recommendation in the 2010 American College of Cardiology Foundation/American Heart Association (ACCF/AHA) Task Force Guideline for Assessment of Cardiovascular Risk in Asymptomatic Adults. These guidelines refer to a noncontrast, limited chest CT scan acquired with an approximate 3- to 5-second breath hold. The 2013 ACC/AHA Guideline on the Assessment of Cardiovascular Risk states that “assessing CAC is likely to be the most useful of the current approaches to improving risk assessment among individuals found to be at intermediate risk after formal risk assessment.”
Disease Burden vs Risk Factor
Because CAC measurement allows for integration of the exposure to risk factors over a lifetime, CAC is best considered a measure of disease burden rather than a risk factor. This explains why it is such a powerful predictor of risk and is such a valuable negative predictor when the CAC score is 0. Influential cardiovascular epidemiologist Sir Geoffrey Rose (1926-1993) stated, “The best predictor of a life-threatening illness is the early manifestation of a life-threatening illness.” Clearly this applies to CAC scanning, where finding atherosclerosis represents an opportune time to intervene with lifestyle changes, statins, aspirin, and potentially even angiotensin-converting enzyme (ACE) inhibitors. CAC testing has been validated in multiple studies, including Dallas Heart, Rotterdam, St Francis Heart, Multi-Ethnic Study of Atherosclerosis (MESA), and others. CAC has been shown to be the best predictor of future events, in the general population, the elderly, and in persons with diabetes. It provides more robust risk prediction than carotid intima media thickness, CRP, ankle-brachial index, and family history of premature heart disease.
CAC has been shown to better stratify those patients in MESA who would benefit from statins, aspirin, ACE inhibitors, and the polypill versus other biomarkers. All of these studies demonstrate that CAC is the most useful test we have for identifying those with early atherosclerosis, but more important, it may be an even more powerful determinant that patients don’t need therapy (Power of Zero). The absence of atherosclerosis in a given patient would potentially obviate the need for anti-atherosclerotic therapies (such as aspirin, statin, and ACE inhibitors). A recent study demonstrated that a CAC score of 0 confers a 15-year warranty period against mortality in individuals at low to intermediate risk, unaffected by age or sex.
Is CAC Cost-Effective?
Many preventive physicians find direct measurement of the disease and integration of cumulative risk factor exposure very appealing. Imagine the cost savings if we were to apply CAC scoring to a study like the JUPITER trial, where statins prevented events but required a high number needed to treat (NNT). Blaha and colleagues observed a population in MESA that met inclusion criteria for JUPITER for a median follow-up of 5.8 years (IQR 5.7–5.9). Almost half of the patients in the MESA JUPITER population had CAC scores of 0, and in this group, rates of coronary heart disease (CHD) events were 0.8 per 1000 person-years (ie, [ 0.1%). Nearly three quarters of all coronary events were in the 25% of participants with CAC scores higher than 100 (20.2 per 1000 person-years or 2% per year).