Atrial fibrillation in mitral stenosis: histologic, hemodynamic and metabolic factors.

We examined the histologic, hemodynamic and metabolic factors associated with rheumatic mitral stenosis. Eighteen patients comprised three groups: Group I - 7 patients in sinus rhythm; Group II - 5 patients in intermittent atrial fibrillation; Group III - 6 patients in chronic atrial fibrillation. The left atrial dimension was determined by echocardiography. Left atrial pressure, mitral valve gradient, mitral valve area and the presence or absence of calcium in the mitral valve were determined at catheterization. The left atrial appendage was removed during open heart surgery and the tissue was analyzed for cell size, percent fibrosis and content of cyclic AMP and GMP. There was no difference between the groups in pulmonary capillary wedge pressure, mitral valve gradient, mitral valve area or the presence of calcium. The Group I left atrial dimension (51 +/- 2 mm, means +/- SE) was significantly smaller than that of Group III (56 +/- 2 mm, P less than 0.05). Group II was not different from Groups I or III. Although the concentration of cyclic AMP did not differ among the groups, the cyclic GMP was significantly depressed in Group III (0.15 +/- 0.02 fmol/microgram protein) when compared to Group I (0.24 +/- 0.05 fmol/microgram protein, P less than 0.01). Group II had intermediate values which did not differ from Groups I or III. The percent fibrosis was greatest in Group III (34.8 +/- 1.8%) and least in Group I (27.2 +/- 2.8%, P less than 0.05). There was no difference in cell size among the groups. Although atrial fibrillation may lead to some of these irregularities, a depressed cyclic GMP, increased fibrosis and increased left atrial dimension may play a role in the pathogenesis of irreversible atrial fibrillation.