Left Atrial Appendage Thrombosis in Patients With Atrial Fibrillation.

BACKGROUND: In the Left Atrial Appendage Occlusion Study (LAAOS) III, the risk of ischemic stroke in patients with atrial fibrillation was lower with surgical left atrial appendage (LAA) occlusion plus anticoagulation than with anticoagulation alone. OBJECTIVES: Because of the added benefit of LAA occlusion, we hypothesized that, despite anticoagulation, the LAA can contain thrombi that act as a source of emboli. METHODS: We examined LAA specimens from 57 participants in the LAAOS III trial using histologic and immunohistochemical analysis to determine the prevalence of thrombosis and describe potential risk factors for its development. RESULTS: One LAA contained a large thrombus in its lumen. Microthrombi containing red blood cells and leukocytes, and staining for fibrin, were evident in 21 of 57 (37%) LAA specimens. The microthrombi were localized in the trabecular crypts and stained for von Willebrand factor. A layer of fibrin was observed on the endocardial wall in 58% of specimens in association with adherent leukocytes that stained for tissue factor. CONCLUSIONS: Despite only a brief interruption of anticoagulant therapy before surgery, fibrin microthrombi and endocardial fibrin deposition are common in LAA. These findings suggest a persistent local thrombogenic potential during perioperative interruption of anticoagulation.