Coronary Artery Calcium Score Can Improve Risk Prediction

Computed tomography (a CT scan) of the heart can reveal the presence of calcium in the walls of the coronary arteries.  This is a way of determining how much atherosclerotic plaque is present, with measurement of the coronary artery calcium score, or CACS.  The score has been shown to correlate with the risk of future cardiovascular events; however, there has been doubt as to what the CACS brings to the party – there are already a number of traditional risk factors that are considered reliable.  A new study, reported in the Journal of the American Medical Association, was designed to answer this question – whether adding CACS to prediction based on traditional risk factors improves the classification of risk.

Over 6,800 participants from the Multi-Ethnic Study of Atherosclerosis, who were without known cardiovascular disease, were recruited in Chicago in 2000 to 2002.  Two models were used to determine risk estimates for the occurrence of coronary heart disease.  The first used the following factors: age, gender, smoking, systolic blood pressure, high blood pressure medication use, total and high-density lipoprotein (HDL) cholesterol, and race/ethnicity.  (These factors are those mostly used in published Framingham Heart Study predictions.)  The second model used the same factors as the first plus the CACS.  The 5-year risk estimates using each model were used to categorize the participants into 3 groups: 0% to 3%, 3% to 10%, and more than 10%. 

Over an average of 5.8 years there were more than 200 coronary heart disease events.  The second model (that including the CACS) resulted in significant improvements in risk prediction, compared to the first model.  In the first model, 69% of the participants were classified in the highest or lowest risk categories, compared with 77% in the second model.  In other words, more people were placed in the most extreme risk groups; this represents a clear improvement, or, as the authors of the study state: “. . . a more refined estimation of future risk of CHD events than traditional risk factors alone.”

Some concern has been voiced about the safety and cost associated with the widespread use of CACS testing. It’s probably best, therefore, to reserve its use for symptomless patients who are at intermediate risk for a CHD event, based on their Framingham risk score.