Myxomatous mitral valve chordae. I: Mechanical properties

Chordal rupture is the most common reason for severe mitral regurgitation requiring surgery. The features that predispose myxomatous chordae to rupture, however, have not been studied. Thus, the physical and mechanical properties of normal and myxomatous mitral valve chordae were measured.

Chordae from 24 normal and 59 myxomatous mitral valves were cut into 10 mm-long segments and mechanically tested to measure extensibility, modulus, failure stress, failure strain, and failure load. After testing, the specimens were weighed and their cross-sectional area and volume measured.

Chordae from myxoid mitral valves were larger (1.9 +/- 0.1 mm2 versus 0.8 +/- 0.1 mm2, p < or = 0.001) and heavier (16.6 +/- 1.0 mg versus 6.5 +/- 0.4 mg, p < or = 0.001) than normal chordae. Myxoid chordae had significantly lower moduli (40.4 +/- 10.2 MPa versus 132 +/- 15 MPa, p < or = 0.001) and failed at significantly lower tensile stress (6.0 +/- 0.6 MPa versus 25.7 +/- 1.8 MPa, p < or = 0.001) and absolute load (728 +/- 50 g versus 1,450 +/- 135 g, p < or = 0.001) than normal chordae. Normal and myxoid chordae had similar measurements of extensibility and failure strain.

Myxomatous degeneration severely affects the mechanical properties of mitral valve chordae. Most notably, myxoid chordae failed at loads one-half of those of normal chordae. This may explain why chordal rupture is the main indication for repair of myxoid mitral valves. These findings also suggest that chordal preservation should be carried out with caution, as myxoid chordae are clearly abnormal with compromised mechanical strength.