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CLINICAL RESEARCH: CARDIAC IMAGING

New Magnetic Resonance Imaging-Based Method for Defining the Extent of Left Atrial Wall Injury After the Ablation of Atrial Fibrillation

Christopher J. McGann, MD^_*, Eugene G. Kholmovski, PhD^_*, Robert S. Oakes, BS^,, Joshua J.E. Blauer, BS^,, Marcos Daccarett, MD, Nathan Segerson, MD, Kelly J. Airey, MD, Nazem Akoum, MD, Eric Fish^,, Troy J. Badger, MD, Edward V.R. DiBella, PhD^_*,, Dennis Parker, PhD^_*,, Rob S. MacLeod, PhD^, and Nassir F. Marrouche, MD^,_*

^_* Radiology Department, University of Utah School of Medicine, University of Utah, Salt Lake City, Utah
Division of Cardiology, Internal Medicine, University of Utah School of Medicine, University of Utah, Salt Lake City, Utah
Bioengineering Department, University of Utah, Salt Lake City, Utah

Manuscript received February 22, 2008; revised manuscript received April 11, 2008, accepted May 5, 2008.

^_* Reprint requests and correspondence: Dr. Nassir F. Marrouche, Atrial Fibrillation Program and Electrophysiology Laboratory, Division of Cardiology, University of Utah Health Sciences Center, 30 North 1900 East, Room 4A100, Salt Lake City, Utah 84132-2400 (Email: nassir.marrouche{at}hsc.utah.edu).

Objectives: We describe a noninvasive method of detecting and quantifying left atrial (LA) wall injury after pulmonary vein antrum isolation (PVAI) in patients with atrial fibrillation (AF). Using a 3-dimensional (3D) delayed-enhancement magnetic resonance imaging (MRI) sequence and novel processing methods, LA wall scarring is visualized at high resolution after radiofrequency ablation (RFA).

Background: Radiofrequency ablation to achieve PVAI is a promising approach to curing AF. Controlled lesion delivery and scar formation within the LA are indicators of procedural success, but the assessment of these factors is limited to invasive methods. Noninvasive evaluation of LA wall injury to assess permanent tissue injury may be an important step in improving procedural success.

Methods: Imaging of the LA wall with a 3D delayed-enhanced cardiac MRI sequence was performed before and 3 months after ablation in 46 patients undergoing PVAI for AF. Our 3D respiratory-navigated MRI sequence using parallel imaging resulted in 1.25 x 1.25 x 2.5 mm (reconstructed to 0.6 x 0.6 x 1.25 mm) spatial resolution with imaging times ranging 8 to 12 min.

Results: Radiofrequency ablation resulted in hyperenhancement of the LA wall in all patients post-PVAI and may represent tissue scarring. New methods of reconstructing the LA in 3D allowed quantification of LA scarring using automated methods. Arrhythmia recurrence at 3 months correlated with the degree of wall enhancement with >13% injury predicting freedom from AF (odds ratio: 18.5, 95% confidence interval: 1.27 to 268, p = 0.032).

Conclusions: We define noninvasive MRI methods that allow for the detection and quantification of LA wall scarring after RF ablation in patients with AF. Moreover, there seems to be a correlation between the extent of LA wall injury and short-term procedural outcome.

Key Words: delayed enhancement magnetic resonance imaging • atrial fibrillation • image processing

Abbreviations and Acronyms   3D = three-dimensional   AF = atrial fibrillation   CI = confidence interval   DE-CMRI = delayed-enhancement cardiac magnetic resonance imaging   ECG = electrocardiogram   FLASH = fast low angle shot   GRAPPA = generalized autocalibrating partially parallel acquisitions   LA = left atrium/atrial   LV = left ventricle/ventricular   MRI = magnetic resonance imaging   OR = odds ratio   PVAI = pulmonary vein antrum isolation   RFA = radiofrequency ablation   RF = radiofrequency   TE = echo time   TI = inversion time   TR = repetition time

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