TGFB1 and atrial fibrillation: A detailed study conducted on fibroblasts isolated from the atrial appendage of patients with AF who underwent cardiac surgery (Altieri, 2018a) revealed that atrial fibroblasts express high levels of PAR-1; when activated in vitro by thrombin-mediated cleavage, PAR-1 elicited myofibroblast transformation; production of collagen; and synthesis of TGFβ, MCP-1, and endothelin-1.