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, asymptomatic people who had low or moderate Framingham Risk Scores (FRSs) and were either 50–69 years old and smoked or were 70 years or older.
“We showed that the ankle-brachial index can identify people at risk of cardiovascular disease events beyond those identified by their Framingham Risk Score,” Dr. Andrew D. Sumner said while presenting a poster at the annual meeting of the American College of Cardiology.
“If the ABIs had not been measured, we'd never know these people were at high risk,” Dr. Sumner 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.
He noted that although existing guidelines from the American Heart Association and American College of Cardiology recommend screening asymptomatic people by measuring their ankle-brachial index, guidelines from the U.S. Preventive Services Task Force have not endorsed ABI screening for determining a person's risk for cardiovascular events.
“The Framingham Risk Score 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.
His study 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 NHANES survey population was restricted to people 50–69 years old who smoked and those 70 years or older regardless of their tobacco use.
Dr. Sumner and his associates calculated an FRS for each of these people, 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 next 10 years; and 17% were high risk, with an FRS that projected a greater than 20% risk of having a cardiovascular event over the next 10 years.
Using blood pressure readings, the researchers also calculated an ankle- brachial index for each person.
A low ABI, less than 0.9, was found in 10% of the people in the low-FRS group (3% of the total group evaluated in this study), 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 among people with low or moderate FRS was highest among women, 11.0% of whom had a low ABI.
The prevalence of a low ABI among men with a low or moderate FRS was 6.3%.
Although it is possible to obtain an ankle blood pressure using just a pressure cuff and stethoscope, the most common method today uses Doppler echo to monitor the ankle pulse when measuring ankle pressure, Dr. Sumner said.
Primary care physicians who don't have an echo device in their office can refer patients for an ABI assessment, he noted.