Atrial fibrillation (AF) is the most common cardiac arrhythmia in the general population. Due to the demographic change with increasing life expectancy, the incidence of AF is expected to further increase in the near future. Patients suffering from AF have an increased risk of serious complications, including stroke and heart failure. Recent studies found that patients with AF have an increased risk of cognitive decline and dementia over time. However, the magnitude of the problem, associated risk factors and underlying mechanisms remain unclear. Specific aims:1.To assess cognitive functions in patients with AF in the long-term2.To correlate structural brain damage and their short-term changes with long-term cognitive decline3.To quantify health care cost among patients with AF in SwitzerlandStatus of study: Enrollment of 2415 AF patients was completed in August 2017. Follow-up investigations are ongoing. Procedures: Study questionnaires, clinical examinations, blood samples (incl. genetics) for bio-banking, advanced 12-lead ECG, bMRI, cognitive assessments, disability, quality of life, and financial costs. Follow-up: Yearly clinical follow-up, covariate update, 12-lead ECG, cognitive assessments, and outcome evaluations. bMRI and blood sampling will be repeated after 2 years in all patients.Main clinical outcome measures: Death, stroke, systemic embolism, hospitalization for heart failure, myocardial infarction, any unplanned hospitalization, major bleeding and clinically relevant non-major bleedingPreliminary results: Overall, 2415 patients were enrolled in Swiss-AF. The mean age (± standard deviation) of the population was 73 ± 8.5 years; 27.1% were female. 45% of the patients had paroxysmal AF, whereas 29% and 26% had persistent and permanent AF, respectively. A history of stroke, bleeding, heart failure and hypertension was present in 13%, 26%, 15% and 69%, respectively. Median (interquartile range) CHA2DS2-VASc score was 3 (2-5). Of 2173 patients (90%) with oral anticoagulation, 56.2% were on non-vitamin-K antagonist oral anticoagulants.Impact: By establishing a national, comprehensive and interdisciplinary AF network, this cohort study is highly responsive to the current SNSF call for longitudinal studies and has the unique potential to provide important novel insights on long-term disease progression and clinical outcomes in patients with AF. The main focus on cognitive functioning and neurological complications is of major public health importance. Several major unmet clinical needs that will provide clinicians with better tools to take care of this growing patient population will be addressed. The current project also has a great potential to identify novel treatment targets for several important and currently unresolved public health problems, including AF, cognitive dysfunction or stroke. Detailed cost assessments will help to define more efficient patient care that will lead to less disability and reduced costs for the society as a whole.