Objectives: This study aimed to clarify the clinical impact of transient atrial fibrillation (AF) attacks themselves and the efficacy of cardiac resynchronization therapy (CRT) in patients with intermittent AF. Background: The benefit of CRT in patients with intermittent AF, especially the effect of the AF attacks themselves, remains unclear. Methods: Among our cohort of 269 consecutive CRT patients, we compared the percent of biventricular pacing (BIVP%) and other clinical characteristics between patients with intermittent AF and those with sinus rhythm (SR). Results: During a median follow-up of 942 days (interquartile range: 379 to 1,464 days) a total of 22 patients, including 59% of CRT responders, developed heart failure (HF) due to a transient AF attack itself, and that accounted for 21% of all HF events. The BIVP% during the AF attacks was significantly lower than that during SR (p < 0.05). When compared to the SR groups, patients with intermittent AF had a significantly higher risk of developing HF or death (hazard ratio: 2.2; 95% confidence interval: 1.3 to 3.8). However, the patients who received a BIVP% of ≥90% during AF attacks were comparable to those with SR (hazard ratio: 1.2; 95% confidence interval: 0.4 to 3.0). Conclusions: A substantial number of patients developed HF due to transient AF attacks themselves even in the CRT responders, and the reason was mainly due to the loss of the BIVP%.
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