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.

Atrial fibrillation (AF) is an electrophysiological condition characterized by a disorganized electrical activity in the atria of the heart. AF is associated with structural heart disease including hypertension, systolic and diastolic ventricular dysfunction and valvular heart disease. It represents a significant public health problem with the increasing longevity of the general population. A major determinant of the progression of AF is structural remodeling or fibrosis that occurs in the left atrium. A more extensively remodeled atrium represents the substrate needed for the arrhythmia to persist. Structural remodeling is also a major determinant for success of rhythm control strategies in AF. While catheter ablation has been reproducibly shown to be superior to anti-arrhythmic drug therapy for rhythm control in AF, the success of this procedure is significantly affected by the extent of structural remodeling present at the time of catheter ablation.

Delayed-Enhancement Magnetic Resonance Imaging (DE-MRI) has been demonstrated to be a very effective modality in identifying fibrotic and scarred cardiac tissue with excellent correlation with autopsy findings. This is related to the characteristics of Gadolinium, an extracellular contrast agent that is very effective in identifying regions of fibrotic non-viable myocardium. DE-MRI technology can be a very powerful, non-invasive method, of identifying the extent and the distribution of structural remodeling or fibrosis associated with AF.

Applying DE-MRI technology to the atrium causes significant technical challenges. The atrial wall is often a few millimeters thick which requires high spatial resolution to obtain adequate and useful images. In addition, image acquisition has to be gated to the diastolic phase of the atrial contraction cycle, which may be difficult to do when the patient is in AF. The ongoing research at the University of Utah has shown significant progress and very promising results overcoming the challenges mentioned. Specific image acquisition sequences have allowed for reproducible identification of high pixel intensity regions within the 2-dimensional images of the atrial wall. Three-dimensional reconstruction of the entire left atrium then provides a quantification of the overall volume occupied by these hyper-enhanced regions relative to the entire left atrial wall volume. Used prior to catheter ablation, DE-MRI can therefore identify regions of significant structural remodeling or fibrosis. The same technology has also been shown to be very useful in examining the amount and distribution of ablation related scarring.

Clinical patient characteristics will be collected for this study from clinic visits and chart reviews.

Imaging Protocol: All patients will undergo a DE-MRI within 30 days prior to the AF ablation procedure using a DE-MRI protocol. 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 (Figs. 4-5).

Clinical Follow-up: The institution where the ablation was performed will continue post-procedural care following standard of care procedures. Monitoring and definition of atrial arrhythmia AF recurrences will be guided by the HRS consensus document on ablation of atrial fibrillation.

Clinical and MRI data will be stored using the IRB-approved University of Utah database. De-identified clinical data and MRI images from participating institutions will also be submitted to the database, and will be processed at the University of Utah for pre- and post-ablation fibrosis and scar quantification. The ablation strategy utilized and procedural endpoint will be left to the discretion of the operators at the participating sites. This data will also be collected and included in the final analysis. MRI image processors at the University of Utah will be blinded to the ablation technique and mother institution using a unique de-identified study participant ID number.

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

Inclusion Criteria:

• Patients who underwent an AF ablation as per recent Heart Rhythm Society (HRS) consensus document, as per the University of Utah AFIB Database (IRB_00020347)
• Patients who have had an MRI post-ablation.
• Age ≥18 years.

Exclusion Criteria:

• Contraindication for DE-MRI with a full dose of Gadolinium-based contrast agent.
• Previous left atrial ablation or surgical procedure
• Renal failure with CrCl <60 ml/min
• Women currently pregnant, breastfeeding, or of childbearing age not currently taking or not willing to use a reliable form of contraception
• Mental or physical inability to take part in the study
• Uncontrolled hypertension
• Morbid obesity (BMI > 35), or inability to be placed in MRI due to body mass.
• Patients who have not had a DE-MRI post-ablation.

The study population will consist of those patients who have undergone catheter ablation for atrial fibrillation.