“Myxomatous” Mitral Valves

Collagen Dissolution as the Primary Defect

KING, BERNARD D. M.D.
CLARK, MICHAEL A. PH.D.
BABA, NOBUHISA M.D. PH.D.
KILMAN, JAMES W. M.D.
WOOLEY, CHARLES F. M.D.

From Ohio State University College of Medicine. Columbus, Ohio.

Address for correspondence: C.F. Wooley, M.D. Division of Cardiology, Room 206. University Hospital. 410 West 10th Avenue, Columbus, Ohio 43210.

Supported in part by grants from the Central Ohio Heart Chapter of the American Heart Association.

Dr. King's present address: Mt. Sinai Hospital and Medical Center. I Gustave Levy Place, New York, New York 10029.

Dr. Clark's present address: Armed Forces Institute ot Pathology, Department of Forensic Pathology. Washington. D.C. 20306.

Received February 23, 1981: revision accepted December 16. 1982.

Circulation 66(2):p 288-296, August 1982.

SUMMARY

We studied the morphologic and histologic characteristics of redundant prolapsing (“myxomatous”) mitral valves from 12 symptomatic patients with severe mitral regurgitation who required mitral valve replacement and compared our findings with those in 13 control valves.

The mean surface area of the “myxomatous” mitral valves (MMVs) was 1990 mm and of the control mitral valves (CMVs) was 760 mm² (p < 0.001). The mean longest diameter of MMVs was 56.4 mm and of the CMVs was 36.8 mm (p < 0.001); the mean shortest diameter of MMVs was 44.8 mm and of CMVs was 22.7 mm (p < 0.001). The mean commissural diameter for MMVs was 50.4 mm and for CMVs was 30.0 mm (p < 0.001). The mean coapting line distance of MMVs was 34.1 mm and of CMVs 22.5 mm (p < 0.001). The mean surface area of the anterior cusp of MMVs was 910 mm² and of CMVs was 560 mm² (p < 0.01). The mean surface area of posterior leaflet was 927 mm² in MMVs and 534 mm² in CMVs (p < 0.02). CMV densities were nearly uniform (1.07 g/cm³), while the mean density of MMVs was 0.687 g/cm³ (p < 0.01). Dissolution of elastin was only slightly more frequent in MMVs than in CMVs. Myxomatous degeneration, noted in one-half of CMVs, was found in chordae and pars fibrosa only in MMVs (p < 0.05). Mucopolysaccharide infiltration was more severe in all sites except the annulus in MMVs than in CMVs (p < 0.05). Fragmentation of collagen was severe in either the pars fibrosa or chorda of all MMVs, but was not seen in any CMV in these areas (p < 0.05).

Gross morphology (increased surface area, increased diameter and decreased density) and histologic characteristics (collagen dissolution with myxomatous degeneration) allowed clear separation between CMVs and MMVs that produced severe mitral regurgitation. Collagen dissolution in the pars fibrosa and chordae was present only in MMVs, which suggests the primacy of collagen dissolution in mitral valves of patients with severe mitral regurgitation complicating the mitral valve prolapse syndrome. We therefore consider this process to be a disorder of collagen synthesis, content or organization (i.e., a dyscollagenosis).