2.2 CT-based measurement of LAPW thickness
Multidetector helical CT had been performed with a 320-row detector, dynamic volume CT scanner (Aquilion ONE; Toshiba Medical Systems, Tokyo, Japan) before the ablation procedure. 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). Patients’ heart rate <65 bpm was maintained by Landiolol administration, and nonionic iodinated contrast medium (Iomeron, Eisai Co, Tokyo, Japan) was injected at 0.07 mL/kg/second for 9 seconds. Timing of the image acquisition was determined by means of bolus tracking software; imaging was initiated when contrast reached the LA. During the end-expiratory phase, the volume acquisition was gated to 65%–75% of the R-R interval on the lead II electrocardiogram during sinus rhythm or AF rhythm. Thickness of the LAPW was measured as previously described.9–11 The acquired CT images were transferred to a workstation (ZIO M900 3.0; QUADRA: Amin Co., Ltd., Tokyo, Japan). Hounsfield units (HUs) of −50 to −200 were assigned to detect epicardial fat and exclude it from the LAPW.9–13 Thickness of the LAPW was measured at the roof and floor lines, with each line was divided into 3 segments: right, center, and left segments. Coronal plane images were used to measure wall thickness at the roof line and horizontal plane images to measure wall thickness at the floor line (Figure 1). Wall thickness was measured at 3 sites per segment, the average of the 3 values was calculated for each segment, and these average values were used for analysis.9–11