2.2 Cardiac imaging and image analysis
Multi-detector helical 3D-dimensional (3D) CT was performed with a 320-row detector, dynamic volume CT scanner (Aquilion ONE; Toshiba Medical Systems, Tokyo, Japan). The scanning was performed at a slice thickness of 0.5 mm, gantry rotation time of 350 ms, tube voltage of 120 kV, and tube current of 300–580 mA for optimum detection of fine structures (resolution of approximately 0.3 mm). Electrophysiologic study was performed 18 days after the CT study on average. Each patient’s heart rate was maintained at <65 bpm by administration of landiolol, and nonionic iodinated contrast (Iomeron, Eisai Co, Tokyo, Japan) was injected at 0.07 mL/kg/sec for 9 seconds. Timing of the image acquisition was determined by bolus tracking software; imaging was initiated when contrast reached the LA. End-expiratory phase images were obtained by gating the image acquisition to 65–75% of the R-R interval on the lead II electrocardiogram during sinus rhythm or AF rhythm. The acquired CT images were transferred to a workstation (ZIO M900 3.0; QUADRA: Amin Co., Ltd., Tokyo, Japan).
For the purpose of the study, we measured angles between the LA and extracardiac structures in all patients. These were the angle between the midline of the ascending aorta and the midline of the LA (aorta-LA angle), i.e., line connecting the right PV carina to the center of the mitral valve (Figure 1A), and the angle between the midline of the ascending aorta and the left ventricle, i.e., line connecting the mitral valve and LV apex (aorta-LV angle) (Figure 1B). The surface diameter of each aortic valve cusp (LCC, left coronary cusp; NCC, non-coronary cusp; RCC, right coronary cusp), and the minimum distances from the LA to the NCC and LCC were also measured (Figure 1C).