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.