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).