ArticlesDevelopment of a risk score for atrial fibrillation (Framingham Heart Study): a community-based cohort study
Introduction
Atrial fibrillation is the most common sustained dysrhythmia and affects more than 2 million individuals in the USA.1, 2 Prevalence is expected to rise substantially over the next few decades because of the ageing population, improved cardiovascular treatments, and lengthened survival of individuals with heart disease.1, 2 Onset of the condition is associated with strikingly increased morbidity and mortality, even after adjustment for comorbid cardiovascular conditions.3, 4 The most life-threatening sequelae of atrial fibrillation are development of thromboembolic events and heart failure.5, 6 Early identification of individuals who are at risk in the community would allow prevention and targeted intervention, and could decrease health-care costs.7
The Framingham Heart Study8, 9, 10 and other investigations11, 12, 13 have shown that risk factors such as ageing, diabetes, hypertension, obesity, and cardiovascular disease, including alterations in cardiac structure and function,9, 13 consistently predispose individuals to atrial fibrillation. However, to our knowledge, an instrument that integrates multiple risk factors to establish an individual's absolute risk of the condition is unavailable.
A recent National Heart, Lung, and Blood Institute workshop14 drew attention to increasing scientific interest in developing prevention strategies for atrial fibrillation, for which a thorough understanding of the predisposing factors is essential. Establishment of a risk score that incorporates standard clinical characteristics would help to assess new technologies, biomarkers, and genetic data to improve risk prediction. Additionally, the risk score would identify individuals at highest risk, to target enrolment in future primary prevention trials. We postulated that atrial fibrillation is well predicted by a risk score and therefore we aimed to formulate a risk algorithm composed of weighted clinical factors that can be assessed in primary care.
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Participants
We retrospectively selected 4764 participants (n=8044 examinations) who did not have atrial fibrillation and were aged 45–95 years, from Framingham Heart Study original cohort15 examination cycle 11 (1968–71, n=2955) or examination cycle 17 (1981–84, n=2179), or offspring16 examination one (1971–75, n=5124) or examination three (1984–87, n=3873) (webappendix pp 1–3). Participants were monitored for the first event of atrial fibrillation for a maximum of 10 years from the beginning of each
Results
The study cohort (8044 examinations) was aged 45–95 years and more than half were women (table 1; sex-specific data webappendix p 5). Fewer than 5% of individuals had baseline left ventricular hypertrophy, significant cardiac murmur, heart failure, or myocardial infarction. During the 10-years of follow-up, 457 (10%) of the 4764 participants developed atrial fibrillation. 253 events occurred in men during 32 544 person-years of follow-up (6·3 per 1000 age-adjusted person-years), and 204 events
Discussion
We present a scoring system in a community-based cohort to predict an individual's absolute risk of developing atrial fibrillation within the next 10 years from clinical factors that can be assessed readily in primary care. The risk score is reasonably accurate for stratification of individuals into risk categories. The score incorporates risk factors that are known to be associated with atrial fibrillation; the score is slightly improved by the addition of standard echocardiographic
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