2.3 Determination of the posterior lines and esophageal routes
The PV ostia was defined by an abrupt angular change between the LA and
PV planes. Circumferential ablation lesions were created by encircling
the ipsilateral left and right PV ostia. The roofline was made by
connecting both sides of the PV isolation ring at the top level. Then
the PV isolation ring, roofline, along with both CPL and MPL posterior
lines, were shown on the 3D CT images (Figure 1). CPL was defined as a
straight line connecting both sides of the inferior PVs at the bottom
level, as established in previous
studies.6,
8 MPL was designed as follows: (1) A
curve inferior to CPL on the endocardium of LA from posterior-anterior
view and a smile was formed, where MPL corresponded to the curve of the
lower lip, (2) the most inferior point of MPL was located at the level
of the midpoint, where a line connected the midpoint of CPL and the most
inferior point of LA, (3) MPL started from the anterior-inferior part of
the left PV isolation ring and ended at the bottom level of the right
PV, (4) the curve was bilateral symmetry. CT images in the axial,
sagittal, and coronal planes were evaluated to determine the route and
outline of the esophagus along the posterior LA
wall.12,
15 The posterior line segment that
touched by the esophagus was divided into 2 equal portions by 3 points,
respectively. According to the MPL, the esophageal route was classified
into three types (Figure 1): type A esophageal route
covered the start portion of MPL
(only descending limb of the curve), type B esophageal route covered the
middle portion of MPL (both descending and ascending limb of the curve),
and type C esophageal route covered the end portion of the MPL (only
ascending limb of the curve). Esophageal route type 1 was defined as the
esophagus closer to the left inferior PV than to the right inferior PV,
and esophageal route type 2 was defined as the esophagus closer to the
right inferior PV than to the left inferior PV, as described
previously.16 The
topological locations of the esophagus among LAPW, inferior PVs, aorta,
and spine, were determined at the left inferior PV level and MPL level.