This population-based study will identify patients with rapid and irregular heartbeat which is not due to a fault with the heart valves (non-valvular atrial fibrillation) who initiate rivaroxaban, apixaban or warfarin as treatment for Stroke Prevention in Atrial Fibrillation (SPAF). Purpose of the study is to learn more about the safety and how well the drugs rivaroxaban, apixaban and warfarin work in patients appropriately and inappropriately receiving standard and reduced doses of each drug for reducing the risk of stroke in atrial fibrillation. Real world data from routine general practice stored in the primary care database in the UK, The Health Improvement Network (THIN), will be used for investigation.

Primary objectives are to assess the safety and effectiveness of rivaroxaban, apixaban and warfarin based on the risk of intracranial hemorrhage and hemorrhagic strokes (safety) and ischemic stroke, systemic embolism and myocardial infarction (effectiveness). Secondary objectives comprise the assessment of the mentioned risks in subpopulations of patients with renal impairment or diabetes, mortality rates, and drug utilisation as well as patient characteristics before and after the first intracranial hemorrhage or ischemic stroke.

Inclusion Criteria:

• Patients with non-valvular atrial fibrillation
• New users of rivaroxaban, apixaban or warfarin
• At least one year enrollment with the general practice (GP)
• One year since first health contact recorded in THIN prior to the first prescription of a study drug

Exclusion Criteria:

• Patients with other recent indications of oral anticoagulant initiation
• Individuals on more than one oral anticoagulant on the start date
• Users of rivaroxaban apart from 15 / 20 mg daily dose
• Users of apixaban apart from 5 / 10 mg daily dose

UK population sample representative for age, sex and geographic distribution

Availability of this study's data will be determined according to Bayer's commitment to the EFPIA/PhRMA "Principles for responsible clinical trial data sharing". This pertains to scope, timepoint and process of data access.

As such, Bayer commits to sharing upon request from qualified researchers patient-level clinical trial data, study-level clinical trial data, and protocols from clinical trials in patients for medicines and indications approved in the US and EU as necessary for conducting legitimate research. This applies to data on new medicines and indications that have been approved by the EU and US regulatory agencies on or after January 01, 2014.

Interested researchers can use www.clinicalstudydatarequest.com to request access to anonymized patient-level data and supporting documents from clinical studies to conduct research. Information on the Bayer criteria for listing studies and other relevant information is provided in the Study sponsors section of the portal.