CHICAGO — The Framingham Risk Score failed to identify a substantial number of people who were at risk for cardiovascular disease events on the basis of their ankle-brachial index, in a review of more than 1,700 asymptomatic people.
An ankle-brachial index (ABI) of less than 0.9, a marker of peripheral artery disease, was found in 8.9% of randomly selected people who had low or moderate Framingham Risk Scores (FRSs) and were aged 50–69 years and smoked or who were 70 years or older.
“The [ABI] can identify people at risk of cardiovascular disease events beyond those identified by their Framingham Risk Score,” Dr. Andrew D. Sumner said during a poster presentation at the annual meeting of the American College of Cardiology.
“If the ABIs hadn't been measured, we'd never know [they] were at high risk,” he said in an interview.
Identifying people at high risk for cardiovascular events based on a low ABI determines their target serum cholesterol levels and other important elements of their preventive care. Existing guidelines from the American Heart Association and American College of Cardiology recommend screening asymptomatic people by measuring their ankle-brachial index, but guidelines from the U.S. Preventive Services Task Force have not endorsed ABI screening for determining risk for cardiovascular events, he noted.
“The [FRS] underestimates cardiovascular risk. Adding the ABI is useful for identifying patients who would otherwise be classified as low risk,” said Dr. Sumner, medical director of the heart station and cardiac prevention at Lehigh Valley Hospital in Allentown, Pa.
He used data collected on 1,720 randomly chosen asymptomatic Americans in the National Health and Nutrition Examination Survey (NHANES) in 1999–2004. This subgroup of the survey population was restricted to people who were 50–69 years of age and who smoked and those aged 70 years or older, regardless of their tobacco use.
Dr. Sumner and his associates calculated an FRS for each person, which categorized them into three risk strata: 30% were low risk, with an FRS that projected a less than 10% risk of a cardiovascular event over the next 10 years; 53% were moderate risk, with an FRS that projected a 10%–20% risk of an event over the same period; and 17% were high risk, with an FRS that projected a greater than 20% risk of having a cardiovascular in that period.
Using blood pressure readings, the researchers also calculated an ABI for each person. A low ABI (less than 0.9) was found in 10% of those in the low-FRS group (3.0% of the total group), 11% of those with a moderate FRS (5.9% of the total group), and in 15% of the high-FRS group (2.6% of the total group).
The prevalence of peripheral artery disease in people with low or moderate FRS was highest in women, 11.0% of whom had a low ABI. The prevalence of a low ABI in men with a low or moderate FRS was 6.3%, they reported.
'Adding the ABI is useful for identifying patients who would otherwise be classified as low risk.' DR. SUMNER