Echocardiography
LA size and left ventricular ejection fraction (LVEF) were assessed by transthoracic echocardiography (TTE) when available prior to the ablation. All TEEs were performed immediately before the planned ablation procedure. LA size and LAA velocities were assessed, and the LA and LAA were examined for the presence of thrombus or spontaneous echo contrast (SEC). In addition, the presence of patent foramen ovale (PFO) or atrial septal defect was assessed with color Doppler and/or injection of agitated saline. TEEs were interpreted independently by experienced cardiologists specializing in echocardiography.
Cardiac Computed Tomography
CT images were obtained on the day of ablation using a 320-detector scanner (Aquilion ONE, Canon Medical Systems) and prospective scan acquisition targeted at 40% of the R-R cycle (end-systole) without padding. Computed tomographic angiography (CTA) of the heart and great vessels was performed with intravenous iodinated contrast, including 3D iterative reconstruction of the cardiac chambers at 40% of the R-R interval.  Prospective ECG-gating was performed to reduce the effective radiation dose.   CTA was optimized for imaging the cardiac chambers and great vessels but not to visualize the complete course of the coronary arteries. A second acquisition was performed 30 seconds after the primary acquisition to assess for adequate filling of the left atrial appendage. A LA/LAA thrombus was defined as an intracavitary contrast filling defect with attenuation values similar to non-enhanced tissue. Intracavitary thrombi were differentiated from normal pectinate muscles and from filling, motion, and acquisition artifacts.