Background: In patients with cardiac resynchronization therapy (CRT), atrial fibrillation (AF) is associated with an\nunfavorable outcome and may cause loss of biventricular pacing (BivP). An effective delivery of BivP of more than\n98% of all ventricular beats has been shown to be a major determinant of CRT-success.\nMethods: At a Swedish tertiary referral center, data was retrospectively obtained from patient registers, medical\nrecords and preoperative electrocardiograms. Data regarding AF and BivP during the first year of follow-up was\nassessed from CRT-device interrogations. No intra-cardiac electrograms were studied. Kaplan-Meier curves and Coxregression\nanalyses adjusted for age, etiology of heart failure, left ventricular ejection fraction, left bundle branch\nblock and NYHA class were performed to assess the impact of AF and BivP on the risk of death or heart\ntransplantation (HTx) at 10-years of follow-up.\nResults: Preoperative AF-history was found in 54% of the 379 included patients and was associated with, but did\nnot independently predict death or HTx. The one-year incidence of new device-detected AF was 22% but not\nassociated with poorer prognosis. At one-year, AF-history and BivP less than equal to 98%, was associated with a higher risk of death\nor HTx compared to patients without AF (HR 1.9, 95%CI 1.2-3.0, p = 0.005) whereas AF and BivP> 98% was not (HR\n1.4, 95%CI 0.9-2.3, p = 0.14).\nConclusions: In CRT-recipients, AF-history is common and associated with poor outcome. AF-history does not\nindependently predict mortality and is probably only a marker of a more severe underlying disease. BivP less than equal to 98%\nduring first-year of CRT-treatment independently predicts poor outcome thus further supporting the use of 98%\nthreshold of BivP, which should be attained to maximize the benefits of CRT.
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