Non-valvular Atrial Fibrillation

Inclusion Criteria

Registry cohort (Cohort 1)
Cohort 1a:
- Age ≥18 at the date of first OAC (Oral Anti-Coagulants) dispensation (index date)
- Diagnosed with atrial fibrillation or flutter in the period 5-year pre-index period. Defined as ICD10 codes; I480 (paroxysmal AF), I481 (persisting AF), I482 (chronic AF), I483 (typical AF), I484 (atypical AF) or I489 (unspecified atrial fibrillation or flutter) as given by either NPR (Norwegian Patient Register) or as a OAC (warfarin, dabigatran, rivaroxaban or apixaban) dispensed on the reimbursement code for AF in NorPD (Norwegian Prescription Database) (ICD10 I48 or ICPC-2 K78)
- Dispensation of a first-time prescription for an OAC during the study period 1 January 2014 to 31 May 2018. This initiation of an OAC is the index event and requires that there is no previous prescription for any  OAC in the preceding 365 days (counted from the date of the first dispensation backward to the end of OAC supply).
Cohort 1b:
- Age ≥18 at the beginning of the study period (1 January 2014).
- Diagnosed with atrial fibrillation or flutter prior or during the study period. Defined as ICD10 codes; I480 (paroxysmal AF), I481 (persisting AF), I482 (chronic AF), I483 (typical AF), I484 (atypical AF) or I489 (unspecified atrial fibrillation or flutter) as given by NPR.
- No dispensation of a prescription for an OAC (warfarin, dabigatran, rivaroxaban or apixaban) during the study period 1 January 2014 to 30 June 2018. The index event will be the beginning of the study period (1 January 2014) and requires that there is no previous prescription for an OAC in the preceding 365 days.
EMR cohort (Cohort 2):
- Age ≥18 at the date of first OAC dispensation (index date).
- Diagnosed with atrial fibrillation or flutter in the 5-year pre-index period defined as one of the following ICD10 codes in the EMRs obtained from the hospitals in the South-Eastern Health Region; I480 (paroxysmal AF), I481 (persisting AF), I482 (chronic AF), I483 (typical AF), I484 (atypical AF) or I489 (unspecified atrial fibrillation or flutter). 
- Dispensation of a first-time prescription for an OAC (warfarin, dabigatran, rivaroxaban or apixaban) during the study period 1 January 2014 to 31 May 2018. This initiation of an OAC is the index event and requires that there is no previous prescription of any OAC in the preceding 365 days (counted from the date of the first dispensation backward to the end of OAC supply).

Exclusion Criteria

- Valvular atrial fibrillation defined as presence of ICD10 codes in NPR; I05.2 mitral stenosis with insufficiency, I05.8 other mitral valve diseases (mitral (valve) failure), I342 (non-rheumatic mitral valve stenosis), Z952 (presence of prosthetic heart valve) and procedure codes FKD (prosthetic replacement of mitral valve), FKA (Repair of mitral valve for stenosis), FKB (Annuloplasty of mitral valve for insufficiency), FKC (Repair of mitral valve for insufficiency), FKW (Other operations on mitral valve)  and FMD (replacement of aortic valve).
- Deep Venous Thrombosis (DVT) as defined by ICD10 codes I80 (Phlebitis and thrombophlebitis), Pulmonary Embolism (PE) as defined by ICD10 code I26 or I82 (other venous embolism and thrombosis), Other venous embolism and thrombosis within last 6 months before index date.
- Knee and/or hip replacement surgery (NCSP (Nordic Classification of Surgical Procedures) procedure codes; NGB, NGC, NFB or NFC) 5 weeks before index date.