MMP1 and atrial fibrillation: In the current study, we observed in human atrial appendage tissue samples that histological fibrosis markers including cardiomyocyte size, total, but also endo and perimysial fibrosis, the tissue fibrosis markers αSMA, TIMP, NCAM, and LOX, and the serum fibrosis marker CITP/MMP1 ratio are comparable between various stages of AF and the control group.