2.1 Study Population
The design and methods of the KURAMA cohort study have been described previously10. Briefly, consecutive patients with RA were recruited from April 1, 2011, and the diagnosis was confirmed using the revised 1987 American College of Rheumatology (ACR) criteria for RA or the 2010 ACR/European League Against Rheumatism classification criteria for RA at the Center for Rheumatic Diseases in Kyoto University Hospital. Among the 545 RA patients included in the KURAMA study from June 2016 to December 2016, 340 consecutive patients who had records of 12-lead ECG were included in the present study. All patients provided informed consent, and procedures were conducted in accordance with the principles of the Declaration of Helsinki. The study protocol was approved by the Kyoto University Graduate School and the Faculty of Medicine Ethics Committee (R0357).