Epicardial fat pad within the transverse sinus mimicking a left atrial appendage thrombus

Area of Science:

• Cardiology
• Medical Imaging
• Electrophysiology

Background:

• Left atrial thrombus formation in atrial fibrillation (AF) necessitates anticoagulation and contraindicates cardioversion or ablation due to thromboembolic risk.
• Accurate diagnosis of left atrial appendage (LAA) thrombus is crucial for patient management but can be diagnostically challenging.
• Anatomical variations of the LAA and surrounding structures can complicate imaging interpretation.

Observation:

• A transthoracic echocardiogram revealed a mobile, echodense structure near the LAA in a patient with atypical atrial flutter.
• The echocardiographic findings were initially suggestive of a left atrial appendage thrombus.
• The patient was being evaluated for catheter ablation for atypical atrial flutter.

Findings:

• Cardiac computed tomography (CT) was performed for further characterization of the observed structure.
• Cardiac CT imaging demonstrated that the echodense structure was an epicardial fat pad located within the transverse sinus.
• This finding excluded the presence of a left atrial appendage thrombus.

Implications:

• This case highlights the importance of multi-modality imaging in differentiating LAA thrombus from other cardiac structures.
• Accurate differentiation is essential to avoid unnecessary anticoagulation and delays in planned procedures like catheter ablation.
• Understanding anatomical variations and potential mimics is critical for correct diagnosis in complex cardiac imaging scenarios.