DECAAF: DE-MRI Determinant of Successful Radiofrequency Catheter Ablation of Atrial Fibrillation

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).