Multidetector computed tomography and EAT measurements
Multislice computed tomography images were acquired from contrast-enhanced electrocardiogram-gated, 80-slice multidetector cardiac computed tomography (AquillionPRIME 80; Canon Medical Systems, Tochigi, Japan), before the ablation. For the contrast-enhanced scans, 80 mL of nonionic contrast media (Omnipaque, Daiichi Sankyo Co., Tokyo, Japan) was injected intravenously at a flow rate of 5 mL/s, followed by 30 mL of saline. To obtain adequate gating, patients with a heart rate >80/min received short-acting beta blockers. The scanning parameters were 80 mm × 0.5 mm detector collimation, tube voltage of 120 kV, gantry rotation time of 350 ms, and 600–800 mA tube current. Adipose tissue was semi-automatically identified using the threshold attenuation values of -190 to -40 HU on a Workstation (Ziostation2, Amin, Tokyo, Japan). EAT was defined as the adipose tissue located within the pericardial sac. Periatrial EAT volume was calculated by manual tracing of the sum of the EAT volume of each 0.5-mm-thick axial slice. We set the bifurcation of the pulmonary artery as the top boundary and the ostium of the coronary sinus as the lower boundary (Figure 1A, B). Furthermore, the EAT of the intercaval area, which indicates the space between the right antero-inferior LA and the posterior RA, was also quantified using the axial slices. The cranial and caudal limits of the intercaval area were between the level of the superior vena cava–RA junction and the bottom of the right inferior PV. The periatrial EAT and intercaval EAT measurements were performed by two independent skilled operators. The inter- and intra-observer correlations for variables measured on computed tomography were 0.982 and 0.996 for periatrial EAT (P<0.001), and 0.925 and 0.997 for intercaval EAT (P< 0.001), respectively. Periatrial and intercaval EAT volumes were indexed for the body surface area.