4.1 Limitations
This study had several important limitations. First, we did not have data on additional medications unrelated to RA treatment in the study patients. Drugs not intended for RA, such as amiodarone, quinidine, and isoprenaline, may also influence the QTc interval1,12,26, but we failed to analyze the potential influence of these drugs. In addition, all data were only obtained at baseline; therefore, we were not able to analyze the follow-up changes of medications and treatment effects due to the cross-sectional design of this study. Second, potassium and calcium channels are associated with the action potential duration, leading to changes in the QT interval1. However, patient laboratory data on electrolytes were not investigated in this study despite the observation of treatment effects on both systemic inflammation and QT interval. Finally, we could not analyze adverse cardiac events in the study patients. As the QTc interval has been reported to be associated with cardiovascular events, future large-scale studies are necessary to examine the relationship between the QTc interval and patient prognosis.