Philip Greenland and colleagues, from Northwestern University (Chicago, Illinois), undertook a prospective cohort study of 6,814 people, aged 45 to 84 without known cardiovascular disease. The analysis was part of the Multi-Ethnic Study of Atherosclerosis (MESA), a longitudinal study initiated in 2000 to explore characteristics of sub clinical cardiovascular disease in people of White, African American, Hispanic and Chinese origin. The study set out to consider whether new measures of cardiovascular disease (CVD), including carotid ultrasound, cardiac MRI and arterial compliance benefited different racial groups.
In the current analysis coronary artery calcium was assessed by chest computed tomography (CT), with the clinical teams also collecting information on traditional cardiovascular risk factors. The five year estimated incidence of CAD was calculated for each participant using a Cox proportional hazards model, with model 1 using the standard Framingham risk factors of age, sex, smoking, systolic blood pressure, use of antihypertensive medications and HDL and total cholesterol and race/ethnicity; and model 2 used these standard risk factors plus CACS. At a median follow up of 5.8 years, the results showed that adding CACS led to significant improvements in risk prediction (with a net reclassification improvement of 0.25, 95 % confidence interval, 0.16-0.34; P<.001).
Commenting on the study, European Society of Cardiology (ESC) spokesman Prof José Gonzalez Juanatey, said: “Although this study clearly shows that adding coronary artery calcium scores to traditional risk factors improves classification, the conclusions need to be considered in the real world where both costs and increased cancer risks need to be taken into account.”
Indeed, an accompanying editorial by John Ioannidis from the University of Ioannina School of Medicine (Greece) and Ioanna Tzoulaki, from Tufts University School of Medicine (Boston, Massachusetts), raised the same issues (2). In the editorial the authors state that CT (the technology used to measure calcium scores) costs between $200 and $600, and that the lifetime excess cancer risk due to radiation exposure from a single examination at age 40 years was 9 cancers per 100,000 men and 28 cancers per 100, 000 women.
Unlike traditional risk factor measurements, such as lipid and blood pressure, Gonzalez Juanatey added, scores of arterial calcium deliver no additional benefit in terms of increasing treatment options open to the patient. “No treatments are available to lower calcium scores, making the justification of screening for calcium harder to make,” he said.
The ESC’s European Prevention Guidelines, published in 2007, currently make no mention of the use of calcium scores. “Before guidelines should be changed randomised studies are needed to show whether undertaking arterial calcium scores actually results in patients living longer and suffering less cardiovascular complications,” said Gonzalez Juanatey, from The University Clinical Hospital of Santiago de Compostela, Spain.