Prior to the procedure, the patient will most likely have a trans esophageal echo cardiogram (TEE), a cardiac magnetic resonance imaging (MRI) scan, or a cardiac computed tomographic (CT) scan. A TEE is performed on patients with atrial fibrillation, regardless of whether they received anti coagulation therapy, to screen for a left atrial thrombus. Routine TEE may not be performed in patients with paroxysmal atrial fibrillation who present in sinus rhythm on admission and have no structural heart disease or risk factors for stroke. A cardiac CT or MRI scan shows the pulmonary veins and left atrium—in particular the anatomic relationship between the left atrium, the esophagus, and adjacent vascular structures.