Mitral Annulus Disjunction

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N Engl J Med. 1986 Feb 27;314(9):535-40.
The association of floppy mitral valve with disjunction of the mitral annulus fibrosus.
Hutchins GM, Moore GW, Skoog DK.

Floppy mitral valve is usually attributed to connective-tissue degeneration. However, we have observed several instances in which both a floppy mitral valve and an abnormal mitral annulus fibrosus were present at autopsy. To study this association, we examined 900 hearts (after postmortem arteriography and fixation in distention) from autopsies of adults at The Johns Hopkins Hospital. Twenty-five (3 percent) of the hearts had a morphologically typical floppy mitral valve; in 23 of them (92 percent), the mitral annulus fibrosus showed disjunction--i.e., a separation between the atrial wall-mitral valve junction and the left ventricular attachment. In 42 other hearts (5 percent), which were from significantly younger patients (mean age [+/- SE], 60 +/- 2 years vs. 68 +/- 3; P less than 0.05), there was mitral annulus disjunction but no floppy mitral valve. Two hearts had a floppy mitral valve but no disjunction of the annulus; both of them had old infarcts of the papillary muscle. Our results show that floppy mitral valve is significantly associated with disjunction of the mitral annulus fibrosus (P less than 0.001). We suggest that floppy mitral valve develops from hypermobility of the valve apparatus, and that it is usually secondary to disjunction of the mitral annulus fibrosus, an anatomic variation in the morphology of the annulus.

Am J Anat. 1986 Aug;176(4):447-60.
Development of aortic and mitral valve continuity in the human embryonic heart.
Teal SI, Moore GW, Hutchins GM.

The anatomic relationship of the aortic and mitral valves is a useful landmark in assessing congenital heart malformations. The atrioventricular and semilunar valve regions originate in widely separated parts of the early embryonic heart tube, and the process by which the normal fibrous continuity between the aortic and mitral valves is acquired has not been clearly defined. The development of the aortic and mitral valve relationship was studied in normal human embryos in the Carnegie Embryological Collection, and specimens of Carnegie stages 13, 15, 17, 19, and 23, prepared as serial histologic sections cut in the sagittal plane, were selected for reconstruction. In stage 13, the atrioventricular valve area is separated from the semilunar valve area by the large bend between the atrioventricular and outflow-tract components of the single lumen heart tube created by the left interventricular sulcus. In stages 15 and 17, the aortic valve rotates into a position near the atrioventricular valves with development of four chambers and a double circulation. In stage 19, there is fusion of aortic and mitral endocardial cushion material along the endocardial surface of the interventricular flange, and this relationship is maintained in subsequent stages. Determination of three-dimensional Cartesian coordinates of the midpoints of valve positions shows that, while there is growth of intervalvular distances up to stage 17, the aortic to mitral distance is essentially unchanged thereafter. During the period studied, the left ventricle increases in length over threefold. The relative lack of growth in the saddle-shaped fold between the atrioventricular and outflow tract components of the heart, contrasting with the rapid growth of the outwardly convex components of most of the atrial and ventricular walls, may be attributed to the different mechanical properties of the two configurations. It is postulated that the pathogenesis of congenital heart malformations, which characteristically have failure of development of aortic and mitral valve continuity, may involve abnormalities of rotation of the aortic region or malpositioning of the fold in the heart tube.

J Cardiol Suppl. 1990;23:21-8; discussion 29-30.
Morphological observation of the mitral annulus fibrosus in patients with mitral valve prolapse [Article in Japanese]
Sugiura M, Ohkawa S, Watanabe C, Toku A, Imai T, Kuboki K, Shimada H.
Division of Clinical Pathology, Tokyo Metropolitan Institute of Gerontology.

Sixteen cases of mitral valve prolapse (MVP) with mitral regurgitation (MR) in the aged (mainly in their eighth and ninth decades) with both clinical and pathological evidences were investigated. One hundred autopsy cases served as the control. The longitudinally-sectioned mitral annulus fibrosus was pathologically studied in all with special reference to the atrium-valve disjunction reported by Hutchins. Morphologically, the mitral annulus fibrosus was classified either as type A (the mitral valve attaches to the left ventricle), type B (the mitral valve attaches to the left atrium: Hutchins' disjunction), type C (the atrialis continues to the left atrium and the fibrosa to the left ventricle), or type D (mitral annulus calcification). Type B was observed in only 31% of the MVP cases, whereas it was seen in 43% of the control cases. It was concluded that Hutchins' observation could not be regarded as the characteristic pathological finding of MVP.

J Cardiol Suppl. 1991;25:63-73; discussion 74.
Morphological observation of the mitral annulus fibrosus (II) [Article in Japanese]
Sugiura M, Watanabe C, Ohkawa S, Toku A, Imai T, Kuboki K, Shimada H.
Division of Clinical Pathology, Tokyo Metropolitan Institute of Gerontology.

In 1986, Hutchins observed a high incidence of the disjunction of the mitral annulus fibrosus in mitral valve prolapse syndrome. However, we could not prove his view in our previous study using one section in each case. In this study, the types of mitral annulus fibrosus were analyzed in plural sections. Autopsy hearts of nine aged cases were used for examination of the mitral annulus fibrosus in five to eight longitudinal sections from the posterolateral wall. The types of the mitral annulus fibrosus were classified as; Type A (the mitral valve attaches to the left ventricle), Type B (the valve attaches to the left atrium), Type C (the atrialis layer of the valve continues to the left atrium, while the fibrosa layer continues to the left ventricle), and type D (mitral annulus calcification). A1-3 and B1-3 are subtypes. In the nine cases there were no consistent patterns in type distributions. All sections showed Type A1 (Case 2), Type A1 to A3 (Case 5), and Type B1 to B3 (Case 8). In other cases, a combination of Type A and B (Case 4, 6, 7, 9), and inclusion of Type C (Case 1) and Type D (Case 3) were found. The location of the middle scallop of the posterior mitral leaflet corresponded to the section of the previous study. Among three cases of Type A in the middle scallop, two showed Type A in every section. Among five cases of Type B in the middle scallop, only one case showed Type B in every section. Other four cases showed various combinations with the other types. A case of Type D in the middle scallop showed also Type B and Type C. The conclusion of this study was that in 1/3 of the cases, the type of the mitral annulus fibrosus was consistent, but in the other 2/3 they were not consistent. In other words, one section is not necessarily representative of the morphology of the mitral annulus fibrosus in each case.

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