Simplified heart-risk guideline may miscalculate chance for coronary event

A method that is widely used to predict the risk of a major coronary event may over- or underestimate the risk for millions of Americans, according to a study directed by a researcher at the San Francisco VA Medical Center (SFVAMC) and the University of California, San Francisco (UCSF).

The method in question is the simplified version of the Framingham model, which is used to estimate a patient’s 10-year risk of a heart attack, stroke, or other coronary event based on risk factors such as age, cholesterol levels, blood pressure, and smoking. National guidelines recommend using the risk estimates generated by the Framingham model to classify patients as among 1 of 3 risk groups. Guidelines recommend more aggressive strategies to treat cholesterol in patients classified into higher risk groups.

The original Framingham model uses a complicated mathematical equation to calculate risk, while the simplified version is based on a point system, with a certain number of points for each risk factor.

“Our study suggests that for many patients, using the point-based Framingham model would result in different risk group classification than the original Framingham model,” principal investigator Michael Steinman, MD, a physician at SFVAMC and an assistant professor of medicine at UCSF, told

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. “Because the point-based system results in different risk group placement, many patients can potentially receive LDL treatment goals that are different than the goals they would have received from the original model.”

For the study, which appears in the Online First section of the Journal of General Internal Medicine, researchers assessed data from 2,543 subjects who participated in the CDC-sponsored National Health and Nutrition Examination Surveys from 2001 to 2006. The subjects were chosen to be representative of 39 million US adults for whom guidelines recommend using the Framingham method to predict future cardiovascular risk.

For each subject, researchers calculated risk based on the original Framingham model and on the simplified model, and compared the differences, which turned out to be substantial for many patients,” said Dr Steinman, who is senior author of the paper.

Under the point-based system, 15% of the subjects were classified as being at a different level of risk than they were under the original model. Nationwide, according to the study, 5.7 million Americans would be placed into different risk groups using the point-based model than they would be using the original model, with 3.9 million misclassified into higher risk groups and 1.8 million misclassified into lower risk groups.

“Across the group, on average, these statistical differences balance out,” Dr Steinman said. “But for individual patients, they are potentially important. A lot of individuals would be treated differently, either more or less aggressively, using the point-based model.”

While ATP III guidelines suggest that the point-based model is “accurate for clinical purposes,” Dr Steinman said that there needs to be better recognition from the guidelines that there is a difference between the 2 systems. “Computer risk prediction tools should consistently use the original model, so that physicians assessing cardiovascular risk can be informed with a consistent, transparent, and standardized approach to cardiovascular risk assessment,” he said.

The study was supported by funds from the National Institute on Aging, the American Federation for Aging Research, the Hartford Foundation, the Department of Veterans Affairs, and the National Institutes of Health. The Northern California Institute for Research and Education administered some of the funds.