Mechanical properties of myxomatous mitral valves

Objective: We sought to characterize the mechanical properties of normal and myxomatous mitral valve tissues. Methods: We tested 113 mitral valve sections from patients undergoing mitral valve repair or replacement for myxomatous mitral valve prolapse and sections from 33 normal valves obtained at autopsy. Results: Myxomatous mitral valve leaflets were more extensible than normal leaflets when tested parallel to the free edge (41.2% +/- 18.5% vs 17.3% +/- 6.7% circumferential strain [mean SD]; P < .001), as well as perpendicular to the free edge (43.2% +/- 19.4% vs 17.3% +/- 6.7% radial strain; P < .001). Myxoid leaflets were less stiff circumferentially (4.0 +/- 1.6 vs 6.1 +/- 1.4 kN/m; P < .001) and radially (4.5 +/- 1.1 vs 6.1 1.4 kN/m; P <.001) than normal leaflets. Leaflet strength, however, was similar in both groups. Conclusions: Myxomatous mitral valve leaflets are physically and mechanically different from normal mitral valve leaflets. They are more extensible and less stiff. Compared with chordae examined previously, however, they are affected much less. Myxomatous mitral valve disease may therefore affect the collagen in the chordae more severely than that in the leaflets.