Coronary artery calcium scan may be most valuable for a specific group of patients

It's an increasingly popular scan that measures calcium in the heart's arteries and helps predict risk of future heart disease. But according to a new Northwestern Medicine study, the quick and inexpensive test - known as a coronary artery calcium scan - may be most valuable only for a specific group of patients.

After following more than 6,000 adults for 10 years, the Northwestern scientists found that, overall, the calcium scans added relatively little to risk prediction from PREVENT, the American Heart Association's flagship risk calculator.

PREVENT relies on routine metrics (such as blood pressure, cholesterol, age and sex) to estimate a person's risk of heart disease within the next 10 or 30 years. Calcium tests are CT scans that detect calcium-containing plaque in the heart's arteries. The scans give patients a calcium score. The higher it is, the greater the risk of future heart disease.

In the study, the calcium scores were most valuable for adults whose heart disease risk was initially classified as borderline or intermediate by PREVENT. In these patients, the calcium scores offered a clearer picture of who was more likely to develop heart disease and who wasn't.

Coronary artery calcium scans are becoming more widely available and less expensive. Our findings suggest that not everyone necessarily needs or would benefit from a coronary artery calcium scan for the purpose of predicting risk of heart attack and stroke."

Dr. Nilay Shah, study senior author, assistant professor of medicine, division of cardiology, Northwestern University Feinberg School of Medicine

"Routinely using a calcium scan in people who are at low risk may result in unnecessary radiation exposure, testing and costs with unclear clinical benefits," Shah added. "Using calcium scans in people who are at high risk is likely to result in unnecessary testing because these individuals are recommended to start a statin regardless of what the calcium scan shows."

The study will publish on Aug. 26 in JAMA.

Predictions vs. reality

Shah and colleagues analyzed data from more than 6,000 adults ages 45 to 79 enrolled in the Multi-Ethnic Study of Atherosclerosis. At the start of the study, participants received a calcium score and a PREVENT estimate representing their risk of a cardiovascular event within the next 10 years.

During the following decade, 6% of participants experienced a heart attack or stroke. And when the scientists compared predictions made with and without calcium scores, they found only a modest benefit from adding the calcium scores. The prediction model's discrimination, a measure of how well it forecasted who would go on to have a heart event, improved only slightly, from 0.73 to 0.75 after calcium scores were added.

But when the scientists zoomed in on participants who PREVENT placed in borderline or intermediate risk groups (those initially deemed to have a 3% to 9% risk of heart disease within 10 years), adding the calcium scores had a more substantial impact on improving the prediction of a heart event.

"For patients at borderline risk, knowing their calcium score can help determine whether their risk is actually lower or higher than initially estimated, which can help guide treatment decisions," Shah explained.

Why it matters

About 10% of U.S. adults age 30-79 have cardiovascular disease, the leading cause of death in the nation. However, a large proportion of heart events are preventable, Shah said.

"The findings help us understand how best to use the available tools to estimate someone's risk of a heart attack or stroke. That provides more precise guidance for who is most likely to benefit from using a statin to help prevent heart disease," Shah said.

Shad added that the findings reinforce the clinical value of the relatively new PREVENT calculator, which performed well on its own in predicting cardiovascular risk.

Next steps

The utility of adding calcium scores to PREVENT estimates among high-risk groups, such as South Asian and Filipino adults, remains to be evaluated, Shah noted. The same is true for younger adults, as this study only included those ages 45 to 79 at baseline.

Other Northwestern co-authors are Xiaoning Huang, Lucia Petito, Norrina Allen, Dr. Philip Greenland and Dr. Sadiya Khan.