Relation of Left Atrial Pathology to Atrial Fibrillation in Mitral Valvular Disease

Biopsies of the posterior wall of the left atrium were obtained from 44 patients undergoing mitral surgery for mitral valvular disease, and the specimens were graded according to severity of morphologic change. In grade I the atrial myocardium is essentially normal; grade II patients show moderate to severe fibrosis and preservation of muscle mass and architecture; grade III patients show extensive fibrosis, a loss of muscle mass, and disruption of architecture. The pathological grading was compared with such clinical parameters as type of valvular lesion, rhythm before surgery, and degree of left atrial enlargement. Cardioversion was attempted after surgery whenever feasible. Nine patients were successfully cardioverted, and all had grade II changes. Three additional patients succeeded and then relapsed; one had grade II and two had grade III changes. In seven patients cardioversion failed, and six of these had grade III changes. The one exception was a patient in grade I who had a cardiomyopathy. We propose that fibrosis after rheumatic inflammatory insults leads to atrial fibrillation by disturbing impulse propagation in the atrium; prolonged atrial fibrillation leads to a disuse atrophy of muscle, and atrial fibrillation becomes irreversible. These pathologic changes may be used for predicting success or failure of cardioversion and probability of maintaining sinus rhythm.