Validation of an Atrial Fibrillation Risk Algorithm in Whites and African Americans

Abstract

Background We sought to validate a recently published risk algorithm for incident atrial fibrillation (AF) in independent cohorts and other racial groups. Methods We evaluated the performance of a Framingham Heart Study (FHS)-derived risk algorithm modified for 5-year incidence of AF in the FHS (n = 4764 participants) and 2 geographically and racially diverse cohorts in the age range 45 to 95 years: AGES (the Age, Gene/Environment Susceptibility-Reykjavik Study) (n = 4238) and CHS (the Cardiovascular Health Study) (n = 5410, of whom 874 [16.2%] were African Americans). The risk algorithm included age, sex, body mass index, systolic blood pressure, electrocardiographic PR interval, hypertension treatment, and heart failure. Results We found 1359 incident AF events in 100 074 person-years of follow-up. Unadjusted 5-year event rates differed by cohort (AGES, 12.8 cases/1000 person-years; CHS whites, 22.7 cases/1000 person-years; and FHS, 4.5 cases/1000 person-years) and by race (CHS African Americans, 18.4 cases/1000 person-years). The strongest risk factors in all samples were age and heart failure. The relative risks for incident AF associated with risk factors were comparable across cohorts and race groups. After recalibration for baseline incidence and risk factor distribution, the Framingham algorithm, reported in C statistic, performed reasonably well in all samples: AGES, 0.67 (95% confidence interval [CI], 0.64-0.71); CHS whites, 0.68 (95% CI, 0.66-0.70); and CHS African Americans, 0.66 (95% CI, 0.61-0.71). Risk factors combined in the algorithm explained between 47.0% (AGES) and 63.6% (FHS) of the population-attributable risk. Conclusions Risk of incident AF in community-dwelling whites and African Americans can be assessed reliably by routinely available and potentially modifiable clinical variables. Seven risk factors accounted for up to 64% of risk. The prevalence and incidence of atrial fibrillation (AF) have been increasing over the last several decades.1,2 The improved assessment of risk for incident AF was formulated as a major goal of a recently convened National Heart, Lung, and Blood Institute workshop.3 A risk algorithm based on readily available clinical variables for 10-year incidence of AF in Framingham Heart Study (FHS) participants has been pub lished (http://www.framinghamheartstudy.org/risk/index.html).4Transportability to independent cohorts and other racial groups with different incidence rates and distributions of risk factors has to be shown before general recommendations for the use of the risk algorithm can be given. In particular, in African Americans, a paradoxically low prevalence of AF has consistently been reported despite a high risk factor burden.5,6 Thus, it is important to understand how the classic risk factors for AF combined in a risk prediction algorithm are associated with risk in African Americans. We tested a risk algorithm for AF incidence developed in the Framingham Heart Study in 2 large, independent, community-based cohorts from Europe (Age, Gene/Environment Susceptibility-Reykjavik Study [AGES]7) and the United States (Cardiovascular Health Study [CHS]8). In the CHS, we had the opportunity to examine risk factor prevalence and association with incident AF in whites and African Americans. An accurate risk assessment tool is necessary to address the increasing burden of AF in the community by facilitating the identification of individuals at increased absolute risk to potentially target for intervention trials. With the current project we intended to take the second step of a risk algorithm implementation: the validation of the risk function in samples independent of the derivation cohort.