COL1A1 and atrial fibrillation: Increasing evidence shows that interstitial atrial fibrosis is increased in some forms of AF in both humans and animal models.4, 25, 26, 27 In this study, we observed the obvious increase of fibrosis in atrial appendage tissue of patients with sinus rhythm, along with the significant elevation of COL1A1, COL3A1 and ACTA2.