The Pathogenesis of the tricuspid regurgitation (TR) accompanying the rheumatic mitral valvular disease was examined. In 42 patients (29 were rheumatic, 13 were non-rheumatic), the right ventricular myocardial biopsy specimens were obtained during surgery, with which the fraction of interstitial fibrosis (% Fib.) was calculated by light microscopy and myofibrillar degeneration was evalated and scored by electron microscopy (EM-score). The relationship between the right ventricular morphology (% Fib. and EM-score) and the grade of TR was examined.
1) % Fib. was significantly higher in the rheumatic group than in the non-rheumatic group. 2) In the rheumatic group, % Fib. and EM-score were higher in proportion to the preoperative severity of TR. 3) After the change of the grade of TR was estimated in the early and distant postoperative periods in the rheumatic group, the patients were diveded into two subgroups, one with worsened TR and on without worsened TR. Both % Fib. and EM-score were significantly higher in the worsened group. These finding show that the right ventricular myocardial ultrastructural changes correlate significantly with the preoperative grade of TR and the postoperative change of TR. TR accompanying rheumatic mitral valvular disease may be caused not only by the secondary effect of back-pressure overloading to the right ventricle, but by the right ventricular myocardial ultrastructural changes due to the rheumatic disease itself and furthermore pressure and volume overloading to the right ventricular myocardium.