Coronary artery calcium scoring in cardiovascular risk assessment of people with family histories of early onset coronary artery disease

To the Editor: Improving our understanding of the place of computed tomography (CT) coronary calcium scoring in the assessment of cardiovascular disease risk is critical. However, we disagree with the conclusions in the article by Venkataraman and colleagues1 that the results of their study support the use of CT coronary calcium scoring in individuals with intermediate risk using the Australian cardiovascular disease risk (ACVDR) calculator. Unfortunately, the study has significant flaws in its outcome measures — CT coronary artery calcium scoring and Multi‐Ethnic Study of Atherosclerosis (MESA) — which result in misleading conclusions.

The authors examined the predictive power of the ACVDR to detect individuals having a calcium score greater than zero or greater than 100. However, since CT coronary calcium scoring is not a reference standard for cardiovascular disease, this is an invalid outcome for estimating the comparative accuracy of the various cardiovascular disease risk scores.

This study also used the MESA risk score as an outcome measure, although this is a risk calculator that has not been validated in the Australian population. As the MESA score was developed to include CT coronary calcium scoring, any risk calculator that also includes this score is likely to appear to perform better than risk calculators that do not.

The authors state that their “findings suggest that Australian patients are undertreated by international standards”. The threshold recommended by the current guidelines for cholesterol‐lowering medication in the United States — used by the authors as the international standard — would more than triple the proportion of the Australian population recommended to take medication.2

Primary prevention of cardiovascular disease involves individuals who have not yet had a cardiovascular event, making it particularly incumbent on medical professionals that recommendations consider benefits and harms. The information gained from CT coronary calcium scoring needs to demonstrate that benefits outweigh risks, such as radiation exposure, costs, and incidental findings. Trials to date have shown no improvements in health outcomes. Overall, patients are more likely to be reclassified in a higher risk category, some correctly, but higher absolute numbers may be incorrectly reclassified as high risk.3 Individuals with a calcium score of zero are still at risk of cardiovascular disease, about 0.5% per year. The notion that images seen on CT coronary calcium scoring demonstrate the presence or absence of disease is appealing, but it is a gross simplification.4 While CT coronary calcium scoring may have a place in risk assessment, the findings from this study do not support its use.