Mural thrombosis of the left atrium following replacement of the mitral valve.

The nature and incidence of postoperative mural thrombosis of the septal and/or posterior walls of the left atrium were studied in autopsy specimens of hearts from patients in whom the mitral valve had been replaced by a prosthesis 1 day or longer before death. The cases were divided into length of postoperative period as follows; Group I, 1 to 60 days, 57 cases; Group II, 61 days or longer, 36 cases. In Group I mural thrombus of the septal and/or posterior walls of the left atrium was found in 35 of 57 patients (61%). Thrombi against the septal wall tended to be broad and flat. Thrombi involving the posterior wall tended to be multifocal. In Group II, lesions interpreted as old thrombi of the atrial septum were found in 23 of 36 subjects (64%). Grossly, the old lesions were represented by gray nodularity. Histologically such lesions were consistent with organized thrombi. Superimposed recent thrombosis occurred in some cases. Systemic embolism occurred in each group. In the cases in which left-sided thrombi were restricted to the septal and/or posterior walls of the left atrium, systemic embolism was observed in 10 of 23 cases in Group I (43%) and in two of seven cases in Group II (29%). Obstruction of the mitral prosthesis by bulky mural thrombosis originating at the septal wall of the left atrium was observed in one case. The study suggests that the process of postoperative mural thrombosis of the septal and posterior walls of the left atrium may result from trauma to these structures during the operative procedure.