Myxomatous mitral valve chordae. I: Mechanical properties

Background and aim of the study: Chordal rupture is the most common reason for severe mitral regurgitation requiring surgery. The features that predis pose myxomatous chordae to rupture, however, have not been studied. Thus, t he physical and mechanical properties of normal and myxomatous mitral valve chordae were measured. Methods: Chordae from 24 normal and 59 myxomatous mitral valves were cut in to 10 mm-long segments and mechanically tested to measure extensibility, mo dulus, failure stress, failure strain, and failure load. After testing, the specimens were weighed and their cross-sectional area and volume measured. Results: Chordae from myxoid mitral valves were larger (1.9 +/- 0.1 mm(2) v ersus 0.8 +/- 0.1 mm(2), p less than or equal to 0.001) and heavier (16.6 /- 1.0 mg versus 6.5 +/- 0.4 mg, p less than or equal to 0.001) than normal chordae. Myxoid chordae had significantly lower moduli (40.4 +/- 10.2 MPa versus 132 +/- 15 MPa, p less than or equal to 0.001) and failed at signifi cantly lower tensile stress (6.0 +/- 0.6 MPa versus 25.7 +/- 1-8 MPa, p les s than or equal to 0.001) and absolute load (728 +/- 50 g versus 1,450 +/- 135 g, p less than or equal to 0.001) than normal chordae. Normal and myxoi d chordae had similar measurements of extensibility and failure strain. Conclusion: Myxomatous degeneration severely affects the mechanical propert ies of mitral valve chordae. Most notably, myxoid chordae failed at loads o ne-half of those of normal chordae. This may explain why chordal rupture is the main indication for repair of myxoid mitral valves. These findings als o suggest that chordal preservation should be carried out with caution, as myxoid chordae are clearly abnormal with compromised mechanical strength.