2.2 Echocardiographic image acquisition
All patients were examined with the Philips EPIQ 7C ultrasound system, and the require image were collected by S5-1 and X5-1 probes. During the examination, all patients in the control and paroxysmal AF groups had sinus rhythm and heart rate <100 beats/min, while the average ventricular rate <100 beats/min in the persistent AF group. First, after connecting the ECG, the patient was placed in the left lateral position, and the S5-1 probe was used to observe the parasternal-long axis view. Subsequently, the near-field area was enlarged and the image gain was appropriately adjusted to fully display EAT, which located in front of the right ventricular free wall and beneath the pericardium. Using the aortic annulus as a reference, the reference line was placed across the aortic annulus and the right ventricular free wall, and EAT thickness was measured vertically in front of the right ventricular free wall at end-systole. Then, the parasternal-long axis view and apical two-chamber and four-chamber views were collected, and four cardiac cycles were continuously recorded to obtain LAD and LVEF which was analyzed by the biplane Simpson’s method. Finally, the X5-1 probe was used to display the apical four-chamber view, and the “full-volume” mode was selected to record four cardiac cycles continuously to obtain the three-dimensional volume of left atrium.