SMAD2 and atrial fibrillation: Gramley et al.found that, with chronic AF prolonged from paroxysmal AF < 6 months to permanent AF > 5 years, the extent of atrial fibrosis nearly doubles compared to baseline, and there is an increase in levels of atrial TGF-β1 and Smad2/4 activation with increased duration of chronic AF in the early phase of AF.