MMP9 and atrial fibrillation: In a prospective case–cohort study evaluating the relationships between collagen turnover markers and AF incidence, the investigators demonstrated that only elevated activity of MMP-9 was independently associated with increased risk of AF [55].On the basis of various studies, a new model has been proposed, assuming that atrial fibrosis or more broadly defined atrial disease resulting from AF is a common thread connecting the arrhythmia and thromboembolic events.