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Anticoagulation & Risk Factors IAtrial Fibrillation (ATRIA) Study
Atria Project


Alan S. Go, MD, Principal Investigator 
Kaiser Permanente Northern California
Daniel E. Singer, MD, Principal Investigator 
Massachusetts General Hospital
Kristi Reynolds, PhD, MPH, Co-Principal Investigator 
Kaiser Permanente Southern California

Study Summary

The ATRIA study dataset was composed to establish and characterize a contemporary registry of incident atrial fibrillation (AF) within large, diverse, community-based populations in order to provide critical insight into outcome event rates, practice patterns, and potential health disparities. The ATRIA dataset consists of patients with incident AF and has been used to address research questions related to epidemiology, management and outcomes of AF. The two participating sites (Kaiser Permanente Northern California and Kaiser Permanente Southern California) followed the same data collection steps. The final dataset was compiled at KPNC to produce an analytic dataset with a single, common structure. 


The ATRIA cohort consists of adults, aged 21 years or older at time of atrial fibrillation or atrial flutter diagnosis, who received their diagnosis between January 1, 2006 and June 30, 2009. AF was determined though patient`s electronic health record using ICD-9 Codes (ICD-10 went into effect 10/1/2015). AF was defined as follows:

  • ≥1 primary hospital discharge diagnosis of AF
  • ≥2 outpatient, non-emergency department diagnoses of AF

Table 1. ATRIA-CVRN Dataset Member Counts by Site

​Number of Members
​Percent of Dataset
Kaiser Permanente Northern California​16,817​44.9%​
Kaiser Permanente Southern California​20,675​55.1%​

A survey was conducted in a subset of patients. The survey domains included: lifestyle factors, medication adherence, history/frequency of mechanical falls, awareness of AF diagnosis and willingness to participate in future research. Patients were contacted to participate in the survey if they had a valid address, were alive, and had a warfarin prescription ≥90 days prior to AF diagnosis. A total of 15,184 patients completed the survey with an overall response rate of 60.6%.

Cohort Characteristics 

Figure 1. Distribution of Age and Gender by Site 

Data Source

All member data was extracted using the Virtual Data Warehouse (VDW). The VDW is a standardized resource comprised of: (1) computerized datasets stored behind separate security firewalls, including variables with identical names, formats, and specifications; (2) informatics tools that facilitate storage, retrieval, processing, and managing the datasets; and (3) detailed data documentation. All data are linked by a unique identifier so that data elements can be rolled up to the individual person-level. Currently, the Kaiser Permanente Northern California and Kaiser Permanente Southern California VDW`s are updated at least quarterly for relevant variables and can be updated ad hoc for specific purposes. We used the VDW to characterize each sites cohort of patients with regard to relevant exposure and outcome variables.

Key Publications

Fang MC, Go AS, Chang Y, Borowsky LH, Pomernacki NK, Udaltsova N, Singer DE. Warfarin discontinuation after starting warfarin for atrial fibrillation. Circ Cardiovasc Qual Outcomes 2010;3:624-31.

Fang MC, Go AS, Chang Y, Borowsky LH, Pomernacki NK, Udaltsova N, Singer DE. A new risk scheme to predict warfarin-associated hemorrhage: The ATRIA (Anticoagulation and Risk Factors in Atrial Fibrillation) Study. J Am Coll Cardiol 2011;58:395-401.

Singer DE, Chang Y, Fang MC, Borowsky LH, Pomernacki NK, Udaltsova N, Go AS. Should patient characteristics influence target anticoagulation intensity for stroke prevention in nonvalvular atrial fibrillation: the ATRIA study. Circ Cardiovasc Qual Outcomes 2009;2:297-304.

Piccini JP, Stevens SR, Chang Y, Singer DE, Lokhnygina Y, Go AS, Patel MR, Mahaffey KW, Halperin JL, Breithardt G, Hankey GJ, Hacke W, Becker RC, Nessel CC, Fox KA, Califf RM. Renal Dysfunction as a Predictor of Stroke and Systemic Embolism in Patients with Nonvalvular Atrial Fibrillation: Validation of the R2CHADS2 Index in the ROCKET AF and ATRIA Study Cohorts. Circulation 2012.