Which imaging modality is used to assess left atrial thrombus prior to atrial fibrillation cardioversion?

• A. Transthoracic echocardiography (TTE)
• B. Cardiac MRI
• C. Transesophageal echocardiography (TEE)
• D. CT angiography

Answer: (C)

Transesophageal echocardiography is used to assess for a left atrial thrombus before cardioversion because it provides the best, most direct view of the left atrial appendage, where clots most commonly form in atrial fibrillation. The esophagus sits right behind the left atrium, allowing high-resolution visualization that transthoracic echoes often miss. This makes TEE highly sensitive and specific for detecting thrombus, so you can proceed with cardioversion safely or decide to delay and optimize anticoagulation if a clot is present. Other modalities like MRI or CT can detect thrombus but are less practical as first-line options due to availability, time, and the need for contrast or radiation.