JACC: New MRI method may assist in predicting success of treatment for a-fib

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Noninvasive imaging of the left atrial (LA) wall with MRI is a recent advancement and a powerful tool to evaluate injury related to radiofrequency (RF) energy delivery during atrial fibrillation (AF) ablation, according to a study in the Oct. 7 issue of the Journal of the American College of Cardiology.

The researchers evaluated a noninvasive method of detecting and quantifying LA wall injury after pulmonary vein antrum isolation (PVAI) in patients with AF. Using a 3D delayed-enhancement MRI sequence and novel processing methods, LA wall scarring is visualized at high resolution after RF ablation.

Christopher J. McGann, MD, from the radiology department at the University of Utah School of Medicine in Salt Lake City, and colleagues said that RF 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 currently limited to invasive methods.

The investigators preformed imaging of the LA wall with a 3D delayed-enhanced cardiac MRI sequence before and three months after ablation in 46 patients undergoing PVAI for AF. They said their 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 from eight to 12 minutes.

McGann and colleagues found that RF ablation “resulted in hyper-enhancement 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.

They also found that arrhythmia recurrence at three months correlated with the degree of wall enhancement with greater than 13 percent injury predicting freedom from AF.

In acknowledging the study’s limitations, the researchers said that although the outcomes data in the study were statistically significant, the sample size was relatively small. In addition, 3D MRI in the study was performed on a 1.5T scanner. They wrote that “significant improvements in LA wall imaging with greater spatial resolution, signal-to-noise ratio and contrast-to-noise ratio is expected at higher magnetic field (3T).”