LA Image Segmentation:
Left atrial wall was manually segmented by expert observers from the
LGE‐MRI images using the Corview image processing software (MARREK, Salt
Lake City, UT). Briefly, the protocol for segmentation proceeded as
follows: first, the endocardial border of the left atrium was defined,
including the PV extensions, by manually tracing the left atrium‐PV
blood pool in each slice of the LGE‐MRI volume. Next, the endocardial
segmentation was morphologically dilated and then manually adjusted to
create an assessment of the boundary of the epicardial left atrium
surface. Finally, the endocardial segmentation was subtracted from the
epicardial segmentation to define a wall segmentation, which was
manually edited to exclude the mitral valve and PVs. The resulting left
atrial wall segmentation included the 3D extent of both the left atrial
wall and the antral regions of the PVs. Images that could not be
segmented or quantified due to poor contrast, blurred left atrial
boundaries, and presence of artifacts in left atrial region were defined
as poor quality.