Limitations
This was a retrospective study that involved a small sample size, which might have led to a statistical bias. Controlled studies are required to confirm the effects of CRT upgrades in patients with CS. There was a possibility that the differences in the baseline characteristics in each group (gender and LA diameter) affected the incidence of composite outcomes after the CRT upgrade. In general, women tend to have a better CRT response and clinical outcome than men.17, 18Although more female patients were included in group 1, the echocardiographic response in group 1 was the worst. Therefore, we considered that the good long-term prognosis despite the lack of a high echocardiographic response in group 1 was influenced by the corticosteroid therapy. Although we could not determine the outcome of the CRT upgrade in patients with CS in this study, further studies are warranted to evaluate the outcome of a CRT upgrade.