Heart Risk Prediction Improves With Calcium Scan
A review of six screening tools for identifying people at high risk for heart disease who are misclassified as intermediate risk using the current standard, suggests the best one is a CT scan that looks for calcium build-up in the arteries around the heart.The review is published this week in the Journal of the American Medical Association, JAMA. The lead author is Joseph Yeboah, assistant professor of cardiology at Wake Forest Baptist Medical Center in Winston-Salem, North Carolina.
Current Method Isn't Perfect
Following current medical guidelines that recommend using the Framingham Risk Score (FRS), US doctors classify individuals as either low, intermediate or high risk of cardiovascular disease. But the FRS isn't perfect, and places a lot of people in the intermediate risk category, including a proportion who should probably be classed as high risk.
Yeboah explains to the press:
"We know how to treat patients at low and high risk for heart disease, but for the estimated 28 million Americans who are at intermediate risk, we still are not certain about the best way to proceed." For instance, it is not clear which people in the intermediate risk category could benefit from more aggressive drug therapy such as aspirin or lower targets for drug treatment of LDL cholesterol and blood pressure, and which could be managed just by changing diet and lifestyle.
The "Top Six" Risk Markers
Studies have suggested a number of ways to improve the FRS score for coronary heart disease (CHD) risk. The six regarded as the best look for the following risk markers:
1. Coronary artery calcium (CAC),
2. Carotid intima-media thickness (a measure of the thickness of the lining of the carotid artery),
3. Ankle-brachial index (ratio of blood pressure in lower legs to blood pressure in arms),
4. Brachial flow-mediated dilation (measure of health of the lining of blood vessel walls),
5. High-sensitivity C-reactive protein (CRP, a measure of inflammation), and
6. Family history of CHD.
But, as the authors note in their background information, no direct comparison of these tools has yet been done in a single group of people.
For the study, Yeboah and colleagues used data from the National Heart Lung and Blood Institute (NHLBI) Multi-Ethnic Study of Atherosclerosis (MESA), which had recruited 6,814 participants from six US field centers.
Of the MESA participants, 1,330 were classed as intermediate (FRS score greater than 5% and under 20%), and were included in the study. None had diabetes type 2, and they all had complete data on the "top six" risk markers. This complete data set allowed the researchers to do head-to-head comparisons of the six risk tools. They found the CAC score was the best at predicting which of the intermediate risk group would go on to develop CHD over an average follow-up of 7.5 years.'
Yeboah said: "If we want to concentrate our attention on the subset of intermediate-risk patients who are at the highest risk for cardiovascular disease, CAC is clearly the best tool we have in our arsenal to identify them." "However," he cautioned, "we have to look at other factors such as costs and risks associated with radiation exposure from a CT scan before deciding if everyone in the intermediate group should be screened." He called for further studies to look at costs, benefits and risks of widespread CAC screening to assess risk of heart disease. The study was funded by the National Heart Lung and Blood Institute (NHLBI) of the National Institutes of Health.