The purpose of this study is to understand temporal changes in clinical features and functions, and the relationship with outcomes of atrial fibrillation (AF). AF is a problem with speed or pattern that the heart beats. It is the most common type of arrythmia. The study will use data linkage of a single center patient data and national claims database in Korea. This study does not include an actual patient enrollment process.

Inclusion Criteria:

• Patients had incident AF diagnosis (International Classification of Diseases 10th Revision [ICD-10]; I48) in an inpatient or outpatient setting at SNUH between 1 Jan 2010 and 31 Dec 2020
• Patients aged 18 years or older on the index date

Exclusion Criteria:

• Medical claims indicating a diagnosis code indicative of rheumatic mitral valvular heart disease, mitral valve stenosis, or prosthetic heart valve during 12 months period prior to first AF diagnosis

This study will include adult patients with Atrial Fibrillation diagnosis code at Seould National Universit Hospital(SNUH) from Jan 2010 to Dec 2020.

Pfizer will provide access to individual de-identified participant data and related study documents (e.g. protocol, Statistical Analysis Plan (SAP), Clinical Study Report (CSR)) upon request from qualified researchers, and subject to certain criteria, conditions, and exceptions. Further details on Pfizer's data sharing criteria and process for requesting access can be found at: https://www.pfizer.com/science/clinical\_trials/trial\_data\_and\_results/data\_requests.