LA Fibrosis Assessment
Quantification of LA fibrosis was obtained using methods previously described(19). The LA wall was segmented manually and regions of fibrosis in LGE-MRI images were defined by an intensity threshold determined by expert inspection. Fibrotic tissue is detected when its intensity is two to three standard deviations above the mean of the normal tissue intensity. A 3D LA fibrosis map was created using volume rendering module in Corview software (Marrek Inc., Salt Lake City, UT). Inter-observer and intra-observer reproducibility for this technique was previously reported (17). Fibrosis was represented as the volumetric percentage of left atrial wall enhancement.