The pathology of mitral papillary muscles in mitral regurgitation associated with discrete subaortic stenosis.

Two patients needed mitral valve replacement for severe mitral regurgitation after surgical relief of subaortic stenosis. A third, much older patient (who died) also had mitral regurgitation after surgery to relieve subaortic stenosis and to close a ventricular septal defect. All the mitral valves showed both macroscopic and microscopic abnormalities, the latter being characterized by myocytolysis, vasculitis, and fibrosis. The severity of these abnormalities was inversely proportional to the age of the patient. The findings were compared with those (surgical and necropsy specimens) of five patients with congenital "left-sided" anomalies (group 1) and five with "right-sided" lesions (group 2). Coagulation necrosis and ischemic changes were observed in both of the control groups, but none demonstrated the combination of features observed in the patients with subaortic stenosis. The observation of myocytolysis, vasculitis, and fibrosis suggests that there may be a pathologic substrate for mitral valve malfunction in patients, especially very young ones, with subaortic stenosis.