Session S23.4

Integration of MRI in Evaluation and Ablation of Atrial Fibrillation

RS MacLeod*, NF Marrouche, E Kholmoyski, EVR DiBella, RS Oakes,
JE Blauer, E Fish, M Daccarett1, NM Segerson

University of Utah
Salt Lake City, UT, USA

The focus of our group is to integrate Magnetic Resonance Imaging (MRI) in all phases of evaluation, treatment, and monitoring of atrial fibrillation (AF). The rationale for the emphasis on MRI is that it is the only single noninvasive modality that could support all phases of AF management, especially the use of radio frequency ablation and pulmonary vein isolation. The main contemporary use of MRI in AF management is to provide the image data for a geometric model of the left atrium for use in subsequent electroanatomical mapping. However, the potential for utility for MRI is much greater than pre-operative imaging and we have begun to explore some of this potential. Before any intervention, MRI can reveal fibrosis, the appearance and extent of which appear to have predictive value in the suitability of a patient for ablation. With adequate progress in device technology, MRI can also provide real time navigation for placement of radiofrequency (RF) ablation catheters. Post-procedure, MRI can document the extent and progression from acute lesion to scar formation and may have potential in early differentiation of successful and unsuccessful ablation. The aspect of MRI that has the largest potential for breakthrough utility is its potential for imaging lesion formation in real time and thus providing a means to avoid the most vexing risk of atrial ablation, the formation of esophageal fistula.
We have begun to develop these new applications of MRI in atrial ablation through a combination of engineering developments and clinical and experimental studies, all of which depend heavily on computing. In clinical applications, we routinely acquire delayed enhancement MRI in all atrial ablation patients and have developed image processing techniques with which to identify and quantify the extent of fibrosis before the procedure. Results from these studies indicate that one can not only correlate fibrosis and pre-existing regions of low amplitude electrical activity in the left atrium, but also predict the likelihood of recurrence of AF following ablation based on the extent of the fibrosis. MRI performed after the procedure in these patients documents the extent of lesion formation, which we then correlate with electroanatomical mapping results from the procedure and use to predict subsequent recurrence. Results from this study suggest that scar formation is stable after about 3 months post ablation. Finally, in animal experiments, we are able to carry out RF lesions with real time MRI tracking and placement of the ablation catheter. We are then able to visualize RF lesions within minutes of creating them, then compare the imaging results with histology of the lesions. Integration of MRI in management of AF is feasible today and has enormous potential for future development.

(Abstract Control Number: 95)