Caught in the flow: a case report of large left atrial thrombus obstructing the mitral valve in atrial fibrillation

Background: Large, mobile left atrial thrombi can intermittently occlude the mitral orifice and precipitate rapid hemodynamic compromise in atrial fibrillation. Timely echocardiography is pivotal to diagnosis and management. Case presentation: A 71-year-old woman with previously undocumented atrial fibrillation presented with dyspnea and hypotension. Transthoracic echocardiography showed a large, mobile left atrial mass prolapsing through the mitral valve; transesophageal echocardiography confirmed a 3.3 × 2.8 cm thrombus with spontaneous echo contrast and 2 smaller septal thrombi. Mitral leaflets were thickened and calcified with commissural fusion, consistent with rheumatic disease; the transmitral gradient was mild, but biatrial enlargement suggested chronic pathology. Given thrombus size and mobility, anticoagulation and thrombolysis were deferred. The patient underwent emergency surgical thrombectomy, bioprosthetic mitral valve replacement, and left atrial appendage exclusion. Recovery was uneventful, with normal prosthetic function and no residual thrombus on follow-up imaging. Conclusion: In atrial fibrillation with suspected mechanical obstruction, bedside transthoracic echocardiography followed by transesophageal echocardiography enables rapid confirmation of a ball-valve left atrial thrombus. When the thrombus is large and highly mobile, urgent surgery is preferable to anticoagulation or thrombolysis and can be lifesaving.