Background/Purpose:  It is well-known that rheumatoid arthritis (RA) is associated with cardiovascular disease such as myocardial infarction. However, little evidence exists on the risk of atrial fibrillation (AF) in patients with RA. The objective of this study was to estimate the incidence rates (IR) and rate ratios (RR) of AF among patients with RA compared to those without RA.

Methods: We conducted a large population-based cohort study using the US commercial insurance claims data. The RA cohort included adults with at least two diagnoses of RA and at least one prescription for a disease-modifying anti-rheumatic drug (DMARD). Subjects who never had a diagnosis of RA matched on age, sex, and index date with a 5:1 ratio were selected as a comparison cohort. Follow-up began with the first prescription for a DMARD for RA patients and the 2^nd physician visit date for non-RA patients after a 12-month baseline period. Patients with history of any cardiac arrhythmia, cardiovascular surgery and anticoagulant users during the baseline period were excluded.  Primary outcome was an inpatient diagnosis of AF and secondary outcome was an outpatient or inpatient diagnosis combined with a dispensing of anticoagulant within 10 days after the first diagnosis of AF. We calculated IRs and RRs of AF with 95% confidence intervals (CI). Multivariable Cox proportional hazards models compared the risk of AF between RA and non-RA patients.

Results: The study population included 20,891 RA and 104,455 non-RA patients. Mean (SD) age was 52 (12) years and 74% were women. During a mean follow-up of 2 years, 0.8% of RA patients and 0.6% non-RA patients developed AF as inpatient. Table shows the IRs for primary outcome and secondary outcome.  The RR was 1.4 (95% CI, 1.2-1.7) for primary and 1.3 (95% CI, 1.0-1.6) for secondary outcome in RA patients, compared to age- and sex- matched subjects without RA.  After adjusting for comorbidities such as cardiovascular disease and thyroid disease, various medications and health care utilization characteristics, the risk of AF was not increased in RA (hazard ratio 1.0, 95% CI: 0.8-1.3) compared to non-RA patients.

Conclusion: Our results showed that the incidence of AF was similar in both RA and non-RA patients. The risk of AF was not increased in patients with RA compared to non-RA patients after adjusting for various comorbid conditions and medications.

Table. Incidence rates per 1,000 person-years (95% confidence interval) and rate ratios (95% confidence interval) of atrial fibrillation (AF) in patients with and without rheumatoid arthritis (RA).