GDF15 and atrial fibrillation: Previous studies have reported various biomarkers of AF, such as hs-CRP (19), MMP-9 (18), N-terminal pro-B type natriuretic peptide (NT-proBNP) (20), bone morphogenic protein-10 (BMP10) (14), growth differentiation factor (GDF-15) (21), and serum soluble ST2 (sST2) (22).