NEW ORLEANS — Eight easily obtained clinical variables together formed a risk score that could predict a person's risk for developing atrial fibrillation with reasonable reliability, on the basis of an analysis using data from the Framingham Heart Study.
“The next step is to show the transportability [of this risk score] to other cohorts,” Dr. Renate B. Schnabel said at the annual scientific sessions of the American Heart Association.
This is the first reported tool for assessing atrial fibrillation risk, and it is simple enough to be “easily applicable for clinical assessment,” said Dr. Schnabel, a researcher at Boston University and with the Framingham Heart Study. The risk formula has the potential to identify high-risk patients and to help in communicating risk information to patients. Further study is needed to determine whether modifying some of the component risk factors can result in a reduced incidence of atrial fibrillation, she said.
The formula was derived from data on 4,764 women and men enrolled in either the original Framingham Heart Study, which began in 1948, or in the Framingham Offspring Study, begun in 1971. The participants were aged 46–95 years at enrollment, with an average age of 61. Records from more than 8,000 clinical examinations were reviewed. Incident atrial fibrillation was identified on the basis of records in participants' charts, including ECG data.
The eight factors identified as significant determinants of risk for developing atrial fibrillation were age, gender, body mass index, systolic blood pressure, treatment for hypertension, PR interval, significant heart murmur, and heart failure. Together, these eight factors could account for 78% of incident atrial fibrillation cases.
The risk for atrial fibrillation was higher in men than in women, Dr. Schnabel said. Risk was also elevated with increases in age, body mass index, systolic blood pressure, and the duration of the PR interval. And risk was higher in people being treated for hypertension, those who had a significant heart murmur, and those with heart failure.
An example of a low-risk person is a woman aged 60 with a body mass index of 20 kg/m
In contrast, a high-risk woman would be 70 years old with a body mass index of 35, a systolic pressure of 150 mm Hg, and a PR interval of 210 msec who was also on an antihypertensive regimen and had either a heart murmur or heart failure. This woman would have a 10-year risk for developing atrial fibrillation of about 28%. A man with a similar clinical profile would have about a 29% 10-year risk.
The analysis also examined whether adding three variables obtained from an echocardiographic examination could further improve the risk score. The echo variables tested were left atrial size, left ventricular wall thickness, and fractional shortening. But even using all three of these variables together led to only a slight improvement in predictive accuracy, and they were judged to not be worth including in the risk formula, Dr. Schnabel said. Future studies will look at whether other ECG findings can make a more substantial difference.
Dr. Schnabel and her associates plan to post a calculator on the Framingham Heart Study's Web site (www.framinghamheartstudy.org/risk/index.html
This tool for predicting atrial fibrillation is 'easily applicable for clinical assessment.' DR. SCHNABEL