This is a multi-center, observational, 1-year prospective cohort study (1 year follow-up, at 3, 6 and 12 month) with approximately 675 participants. We will conduct a thorough outcomes assessment utilizing data from Magnetic Resonance Imaging (MRI) scans, as well as pre-procedure and follow-up data. Scans will be blinded to location of participating site. MRI scans will be sequenced and analyzed as they arrive from the database.

Imaging Protocol: All patients will undergo a Delayed-Enhancement MRI (DE-MRI) within 30 days prior to the atrial fibrillation (AF) ablation procedure. The purpose of the initial MRI is to quantify the degree of atrial structural remodeling or fibrosis pre-ablation. Following ablation, DE-MRI will be obtained at 3, 6, and 12 months follow-up to detect and quantify ablation-related scar formation.

Clinical Follow-up: The institution where the ablation was performed will continue post-procedural care following standard of care procedures.

Atrial arrhythmia recurrences will be catalogued up to one year post-ablation and predictors of recurrences of AF will be determined by statistical analysis. The specific mechanism and electrophysiological characteristics of atrial arrhythmia recurrence will also be analyzed.

Our hypotheses are (1) DE-MRI will reproducibly stage the progression left atrium fibrosis in AF; (2) DE-MRI will reproducibly aid in quantifying and identifying the distribution of catheter ablation-related scarring in the left atrium; and (3) the stage of left atrium fibrosis pre-ablation and the amount and location of scarring will predict success of catheter ablation therapy for AF.