FNDC5 and atrial fibrillation: After adjusting for an age ≥ 64 years and a presence of atrial fibrillation, diabetes mellitus, chronic kidney disease (CKD) stages 1–3 and dilated cardiomyopathy, the multivariable Cox regression analysis showed that an irisin level of ≤7.2 ng/mL was an independent predictor of cumulative clinical endpoint.