The Anticoagulation and Risk Factors In Atrial Fibrillation Study - ATRIA


This study sought to determine the prevalence of atrial fibrillation in the US.


The prevalence of atrial fibrillation in the US could be projected for the years 1995-2050 age- and sex-specific prevalence calculations and United States census data.

Study Design

Study Design:

Patients Screened: approx 3 million
Patients Enrolled: 17,974
Mean Follow Up: none
Mean Patient Age: >=20 years
Female: 43

Patient Populations:

Ambulatory visit with a diagnosis of atrial fibrillation (ICD 9 code 427.31); physician-confirmed diagnoses of atrial fibrillation in electrocardiographic database; or principal hospital discharge diagnoses of atrial fibrillation (ICD-9 code 427.31).


Presumed transient atrial fibrillation identified only by an electrocardiogram performed during a hospitalization without a principal discharge diagnosis of atrial fibrillation; transient atrial fibrillation after recent cardiac surgery; no evidence of health plan membership surrounding the atrial fibrillation diagnosis; age younger than 20 years on the index date; hyperthyroidism during the 12 months before the index atrial fibrillation diagnosis.

Primary Endpoints:

Prevalence of atrial fibrillation in study population. Projected number of persons in the United States with atrial fibrillation between 1995-2050.

Drug/Procedures Used:

A cross-sectional study of adults aged >=20 years who were enrolled in a large HMO in California was performed to identify all cases of atrial fibrillation. The age- and sex-specific prevalence calculations of atrial fibrillation in the study population was applied to 1995 United States census data to estimate the number of US adults with this condition in 1995. Based on the anticipated growth of the population in the United States, the number of adults who will have diagnosed atrial fibrillation was projected by directly applying age- and sex-specific prevalence estimates from the study to US Census projections for each adult age and sex category through the year 2050.

Principal Findings:

Among nearly 3 million members enrolled in the HMO during the study period, 17,974 were identified as diagnosed with atrial fibrillation (prevalence 0.95%). Atrial fibrillation was more common in men than in women (1.1% vs 0.8%, p<0.001). Prevalence increased from 0.1% among those <55 years to 9.0% in persons aged >=80 years. Among persons aged >=50 years, prevalence of atrial fibrillation was higher in whites than in blacks (2.2% vs 1.5%, p<0.001). Based on these results, the study estimates approximately 2.3 million US adults currently have atrial fibrillation and that this will increase to more than 5.6 million by the year 2050, with more than 50% of affected individuals aged >=80 years.

An analysis was conducted using the ATRIA data to evaluate the effect of warfarin on risk of thromboembolism, hemorrhage, and death in atrial fibrillation in the usual clinical setting rather the setting of a randomized trial. Warfarin therapy was associated with a lower risk of thromboembolism compared with no warfarin therapy (either no antithrombotic therapy or aspirin) (HR 0.49, 95% CI 0.40-0.61) in a multivariate analysis. All-cause mortality was also lower in the warfarin therapy group (adjusted HR 0.69, 95% CI 0.61-0.77) but ICH was higher (adjusted HR 1.97, 95% CI 1.24-3.13).


This study demonstrates that atrial fibrillation is common among older adults. The number of patients with atrial fibrillation is likely to more than double during the next 50 years, due in large part to the growing proportion of elderly individuals. Since atrial fibrillation is a significant risk factor for stroke, greater attention needs to be focused on stroke prevention and rhythm management in patients with atrial fibrillation.

In the warfarin analysis, treatment with warfarin therapy was associated with a reduction in thromboembolic events and all-cause mortality, similar to results with warfarin therapy reported in randomized clinical trials.



Go AS, et al. Anticoagulation Therapy for Stroke Prevention in Atrial Fibrillation. JAMA. 2003;290:2685-2692.

Clinical Topics: Anticoagulation Management, Arrhythmias and Clinical EP, Anticoagulation Management and Atrial Fibrillation, Atrial Fibrillation/Supraventricular Arrhythmias

Keywords: Stroke, Multivariate Analysis, Cross-Sectional Studies, Warfarin, Risk Factors, Fibrinolytic Agents, Prevalence, Thromboembolism, Censuses, International Classification of Diseases, Atrial Fibrillation, Health Maintenance Organizations, United States, Hemorrhage

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