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.