BACKGROUND Atrial fibrillation (AF) is associated with loss of cognition and dementia. Cardiac autonomic dysfunction has been linked to cognitive decline. We aimed to investigate if reduced cardiac autonomic function (CAF) is associated with cognitive impairment in AF patients. METHODS Patients with paroxysmal, persistent and permanent AF were enrolled from a multicenter cohort study if they had AF ("AF group") or sinus rhythm ("SR group") on a baseline 5 min ECG recording. Parameters

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... g CAF (heart rate variability triangular index (HRVI), mean heart rate (MHR), RMSSD, SDNN, total power and power in the VLF, LF, HF ranges) were calculated. We used the Montreal Cognitive Assessment (MoCA) to assess global cognitive function. RESULTS 1685 AF patients with a mean age of 73 ± 8 years, 29% females, were included. MoCA score was 24.5 ± 3.2 in the AF group (N = 710 patients) and 25.4 ± 3.2 in the SR group (N = 975 patients). After adjusting for multiple confounders, lower HRVI was associated with lower MoCA scores, both in the SR group [β = 0.049; 95% confidence interval (CI) 0.016-0.081; p = 0.003] and in the AF group (β = 0.068; 95% CI 0.020-0.116; p = 0.006). In the AF group, higher MHR was associated with a poorer performance in the MoCA (β = - 0.008; 95% CI - 0.014 to - 0.002; p = 0.014). We found no convincing evidence of association for other CAF parameters with cognition. CONCLUSION Our data suggest that impaired CAF is associated with worse cognitive performance in patients with AF. Among standard HRV parameters, HRVI might be the most promising ECG index. TRIAL REGISTRATION ClinicalTrials.gov Identifier: NCT02105844.