The trajectory of atrial fibrillation (AF) patients within the national health system and their recent temporal trends remains to be fully elucidated. To study the AF incidence, mortality and case-fatality, the investigators implemented a longitudinal cohort study with the linked electronic health records of 5.6 million population in the UK from 1998 to 2016 (CALIBER). A matched case-control study design was used to investigate the causes of hospitalization and death comparing individuals with and without incident AF.

Inclusion Criteria:

• The investigators identify individuals aged 18 years or older and registered in the current primary care practice for at least one year.

Exclusion Criteria:

• Individuals are excluded if they had a prior history of AF before study entry.

The investigators implement two study designs, first a longitudinal cohort study to assess AF incidence and second a matched case-control study for mortality, cause of death and hospitalization.

The investigators identify individuals aged 18 years or older and registered in the current primary care practice for at least one year. Individuals are excluded if they had a prior history of AF before study entry. For the nested case-control study, controls are matched to incident AF patients according to sex and age (10-year age strata).