Abstract 274: Prevalence of undiagnosed non-valvular atrial fibrillation in the United States

Abstract

Background: Because atrial fibrillation (AF) is often asymptomatic, clinically silent and therefore undiagnosed, the prevalence of AF is difficult to estimate. In fact, ischemic stroke is often the first clinical sign of AF among previously undiagnosed patients. In this study, we estimated the prevalence of undiagnosed AF using a back-calculation approach that relies on the fact that AF causes stroke but causality generally does not run from stroke to AF. Methods: We first estimated the prevalence of diagnosed non-valvular AF in the elderly (65+) and working age (18-64) U.S. population from a 5% Medicare sample and an OptumInsight commercial claims database from 2004-2010 using validated ICD9 algorithms. To estimate the prevalence of undiagnosed non-valvular AF, our back-calculation methodology used two measured inputs: (i) the number of patients who are diagnosed with new non-valvular AF in the current or subsequent quarter after a stroke; (ii) the probability that patients with non-valvular AF have a stroke, based on CHADS2 risk scores. We confirmed calibration by comparing our prevalence estimates of diagnosed AF with prior Medicare and commercial claims analyses. Results: Between 2005 and 2009, the estimated prevalence of AF gradually increased, reaching 9.9% of the elderly U.S. population and 0.88% of the working aged population by 2009. Among the Medicare AF cases in 2009, 11% of these cases (1.1% out of 9.9%) were undiagnosed; among working aged patients with AF, 8% of cases (0.07% out of 0.88%) were undiagnosed. In addition, a large share of the undiagnosed cases was at high risk of stroke. Among the undiagnosed AF cases for elderly and working age adults, 26% and 37%, respectively have a CHADS2 score of 1, and 68% and 26% have a CHADS2 score of 2+. Conclusions: Among elderly and working adult U.S. populations, a substantial proportion of individuals with undiagnosed AF have moderate to high risk of stroke. Screening for AF could favorably impact the disease burden.