Using Coronary Artery Calcium as a Tie-Breaker in Prevention

By Parag H. Joshi, M.D., M.H.S., FACC
Assistant Professor of Internal Medicine

The new cholesterol guidelines, released at the AHA 2018 Scientific Sessions, provided several updates to the 2013 guidelines. One of the major points of emphasis in the 2013 guidelines was the use of the pooled cohorts equation risk calculator followed by a clinician-patient risk discussion prior to starting statin therapy in primary prevention. If the patient was still uncertain about starting a statin, then several other tests could be considered to help with the decision, including coronary artery calcium (CAC) scoring, high-sensitivity CRP, ankle-brachial index, or the presence of a family history of premature coronary artery disease events. 

However, a wealth of observational evidence over the interim five years between the guideline updates suggests that CAC scoring is the best decision aid for patients who are uncertain about their risk. At the AHA guidelines release session, the presenters noted that the pooled cohort equations risk calculator can overestimate risk in some and can underestimate risk in others. As a result, many providers and patients are sometimes left with uncertainty over their true risk. This is where data for CAC scoring shows its greatest benefit, which is why the recent guidelines elevated CAC scoring above the other tests as the next step to consider when patients are uncertain about this risk.

As coronary plaques mature, calcification develops. CAC is a highly specific, nearly pathognomonic, marker for coronary atherosclerosis and is directly proportional to the burden of plaque. Several cohorts representing a large proportion of men and women of various ethnicities and nationalities and of varying ages have shown the consistent ability of CAC to predict risk above and beyond risk scores. When CAC scores are greater than 100 or present in any detectable amount at younger ages, there is higher risk for heart attacks, strokes, and coronary death. Perhaps more importantly, when CAC is absent, the risk for events is much lower than estimated by risk estimators. It is this “Power of Zero” that can reassure our patients who are hesitant about starting statin therapy or even blood pressure therapy and to instead focus on lifestyle modifications when there is no CAC. 

There are a few critical points when incorporating CAC scoring into practice. First, it is currently most useful in asymptomatic primary prevention patients who have not had prior cardiovascular events. Other cardiac tests such as stress tests and coronary catheterization should be considered only for symptomatic patients and should not be triggered by high CAC results if the patient is asymptomatic. Secondly, it is useful to have a discussion about the potential risks prior to obtaining a CAC scan, including small amounts of radiation exposure (roughly similar to two mammograms), the out-of-pocket cost (about $100 in large cities), and incidental findings such as pulmonary or thyroid nodules that might trigger follow-up testing. Finally, as with all testing, it is important to anticipate results and how they will impact disease management. Thus, prior to obtaining the CAC scan, we tell the patient: If the score is 0, then we’ll focus on lifestyle modifications and consider repeating CAC scanning in about 5 years; if the score is elevated, then we’ll ensure you’re willing to start more aggressive therapy and, if so, make changes to your treatment.