Computed Tomography for Coronary Artery Calcification Scoring: Mammogram for the Heart

https://doi.org/10.1016/j.pcad.2016.01.007Get rights and content

Abstract

Coronary artery calcium (CAC), identified via low-radiation, non-contrast computed tomography of the heart, quantifies the burden of calcified coronary atherosclerosis. This modality is highly useful for cardiovascular (CV) risk stratification among individuals without known coronary heart disease (CHD), especially for those at intermediate risk. The presence of CAC is associated with up to a 10-fold higher risk of adverse CV events, even after fully adjusting for the standard CV risk factors. In fact, the CAC score is among the strongest clinically available predictors of future risk of adverse CV events among primary prevention patients. Additionally, the absence of CAC in asymptomatic individuals confers a very low risk of CV events. Even in the presence of a benign CV risk factor profile and normal cardiac stress test, a very high CAC score portends a high risk of adverse CV events. On the other hand, a CAC score of zero is associated with a low CHD risk despite significant CV risk factor profiles. CAC scoring is a quick, low-cost screening tool to help risk-stratify patients and identify those likely to benefit from aggressive preventive treatments (such as high-intensity statin therapy, ezetimibe, PCSK9 inhibitors, and aspirin) and to identify those likely who warrant close monitoring. Moreover, individuals with a zero CAC score may be at low enough risk to avoid or defer daily aspirin therapy and pharmacological therapy for cholesterol management, and instead work on therapeutic lifestyle changes. An abnormal CAC score may also lead to better adherence to pharmacological regimens and suggested lifestyle changes.

Section snippets

CAC screening for predicting CHD risk

The CACS is directly and linearly associated with increased CHD risk in asymptomatic patients (Fig 1).4 The large cumulative experience with CT for detecting preclinical coronary atherosclerosis shows that CAC screening provides powerful prognostic information that is much more accurate than algorithms for predicting CV events based upon standard CV risk factors.1 In the Multi-Ethnic Study of Atherosclerosis (MESA), 6722 men and women from various ancestral backgrounds were followed for a

CAC screening for reclassification of intermediate risk individuals

Yeboah et al. compared several novel risk factors for improvement in CV risk assessment in intermediate risk individuals.13 Using data from the MESA Study, they compared six CV risk markers including: CAC screening, carotid intima-media thickness, brachial flow-mediated dilation, ankle-brachial index, C-reactive protein, and family history of CHD. Using net reclassification improvement (NRI), which is a measure of relative improvement in classification of risk with addition of other variables,

The power of zero

The latest atherosclerotic CV disease (ASCVD) guidelines on cholesterol management from the American College of Cardiology (ACC) and the American Heart Association (AHA) integrate key CV risk factors into an algorithm to help identify and aggressively treat higher risk patients.16 However, as compared to prior ATP-III guidelines, the new ASCVD guidelines increased the number of US adults eligible for statin therapy from 43 million to 56 million.17 About 80% of these newly eligible statin

Does knowledge of CACS alter patient and/or physician behavior?

Concerns have been raised about whether people who learn that their CT scan shows no CAC might become complacent about following a heart-healthy lifestyle and diet. O’Malley and colleagues studied 459 young men who discovered that they had no CAC detectable by CT. During the 1-year period following the normal scan, they noted no change in study participants' health behaviors. Thus, the authors of this study concluded that reassurance about their coronaries being free of detectable

Follow up CT CACS

A key question regarding CT CAC screening pertains to how often one should follow up with repeat imaging. A study examining 710 patients a baseline CAC = 0 reported that 62% of the patients did not develop any evidence of CAC on follow up scans within the first 5 years. They concluded that after an initial negative scan, it was safe to defer a follow up scan until at least 5 years later. Similarly, Kronmal et al. analyzed the MESA study data and noted that only 16% of the participants in the study

Recommendations for CT CAC screening

The ACC/AHA guidelines for Assessment of Cardiovascular Risk in Asymptomatic Adults made a Class IIa recommendation that measurement of CAC was an appropriate tool for CVD risk assessment in asymptomatic individuals at intermediate risk (10–20% 10-year risk of MACE). They also made a class IIb recommendation for it to be used in low-to-intermediate risk individuals (6–10% 10-year risk) as well.

The ACC/AHA 2013 Cholesterol Guidelines mention four groups that would benefit from statin therapy

CACS for triaging patients to secondary prevention

About 50% of all CV disease events occur in asymptomatic individuals with normal or low levels of LDL-C.38 Thus, it important to find better screening methods that allow us to detect high-risk individuals before they have symptomatic CHD or adverse events. It is also important to warn patients who have increased risk so that they can make properly informed choices regarding their health. CAC screening allows identification of preclinical coronary atherosclerosis in those who might benefit from

Conclusion

The CACS is among the strongest clinically available predictors of future risk of adverse CV events among primary prevention patients. The absence of CAC in asymptomatic individuals confers a very low risk of CV events in the intermediate term, and a high score identifies subjects who have increased risk and are thus candidates for aggressive prevention strategies and more frequent follow up. The individualized score allows improved shared decision making between physician and patients for

Statement of conflict of interest

All authors declare that there are no conflicts of interest.

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