An intriguing intracardiac mass in a woman with atrial fibrillation. Left atrial appendage (LAA) thrombus.

CLINICAL INTRODUCTION: A 74-year-old hypertensive woman presented with shortness of breath. There was no associated coughing, chest pain or fever. ECG identified atrial fibrillation with rapid ventricular response. A transoesophageal echocardiogram was scheduled to exclude thrombus before cardioversion (Figure 1A); however, an echogenic structure was seen (Figure 1B arrow, see online supplementary video 1) between the left atrium, the pulmonary artery and the aortic root.

QUESTION: Which of the following is the most likely diagnosis? A. Aortic valve endocarditis with annular abscess. B. Left atrial appendage thrombus. C. Left atrial myxoma. D. Pulmonary embolism.