2.2 Echocardiography study
All patients underwent transthoracic echocardiography before the ablation. The left atrial diameter was measured at end-systole on the M-mode image obtained from the parasternal long-axis view. Transthoracic echocardiography was performed with a 5 MHz multiplane probe and live images were interpreted by experienced physicians who were blinded to the outcome of the ablation. Transesophageal echocardiography prior to the PVI was performed to exclude any left atrial or left atrial appendage thrombi.