IHSS and the Mitral Valve

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Mechanism of mitral regurgitation in hypertrophic cardiomyopathy: mismatch of posterior to anterior leaflet length and mobility.
Schwammenthal E, Nakatani S, He S, Hopmeyer J, Sagie A, Weyman AE, Lever HM, Yoganathan AP, Thomas JD, Levine RA.
Circulation. 1998 Sep 1;98(9):856-65.

BACKGROUND: In hypertrophic cardiomyopathy, a spectrum of mitral leaflet abnormalities has been related to the mechanism of mitral systolic anterior motion (SAM), which causes both subaortic obstruction and mitral regurgitation. In the individual patient, SAM and regurgitation vary in parallel; clinically, however, great interindividual differences in mitral regurgitation can occur for comparable degrees of SAM. We hypothesized that these differences relate to variations in posterior leaflet length and mobility, restricting its ability to follow the anterior leaflet (participate in SAM) and coapt effectively. METHODS AND RESULTS: Different mitral geometries produced surgically in porcine valves were studied in vitro. Comparable degrees of SAM resulted in more severe mitral regurgitation for geometries characterized by limited posterior leaflet excursion. Mitral geometry was also analyzed in 23 patients with hypertrophic cardiomyopathy by intraoperative transesophageal echocardiography. All had typical anterior leaflet SAM with significant outflow tract gradients but considerably more variable mitral regurgitation; therefore, regurgitation did not correlate with obstruction. In contrast, mitral regurgitation correlated inversely with the length over which the leaflets coapted (r= -0.89), the most severe regurgitation occurring with a visible gap. Regurgitation increased with increasing mismatch of anterior to posterior leaflet length (r=0.77) and decreasing posterior leaflet mobility (r= -0.79). CONCLUSIONS: SAM produces greater mitral regurgitation if the posterior leaflet is limited in its ability to move anteriorly, participate in SAM, and coapt effectively. This can explain interindividual differences in regurgitation for comparable degrees of SAM. Thus, the spectrum of leaflet length and mobility that affects subaortic obstruction also influences mitral regurgitation in patients with SAM.

Diversity of structural mitral valve alterations in hypertrophic cardiomyopathy.
Klues HG, Maron BJ, Dollar AL, Roberts WC.
Circulation. 1992 May;85(5):1651-60.
Pathology Branches, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Md 20892.

BACKGROUND. Hypertrophic cardiomyopathy (HCM) is characterized by an asymmetrically hypertrophied left ventricle and is regarded as a disease of cardiac muscle. METHODS AND RESULTS. To assess the possibility that the mitral valve itself may be involved in the disease process, we studied mitral valves from 94 patients with HCM and 45 normal control subjects. The area of the mitral leaflets was increased in patients with HCM compared with control subjects (12.9 +/- 3.7 versus 8.7 +/- 2.0 cm2; p less than 0.001). For the overall group of patients, this increase was largely caused by an increase in anterior leaflet length (2.2 +/- 0.5 cm for HCM versus 1.8 +/- 0.3 cm for control subjects; p less than 0.001), because circumference did not differ between the two groups. Mitral leaflet area was increased (greater than or equal to 12.0 cm2) in 55 (58%) of the 94 valves. In 12 of these 55 valves, both the anterior and posterior leaflets were enlarged; the other 43 valves had asymmetrical or segmental enlargement of either the anterior leaflet (36 patients) or a portion of posterior leaflet (seven patients). In addition, nine patients had a congenital malformation of the mitral apparatus in which one or both papillary muscles inserted directly into anterior mitral leaflet (mitral valve area was normal in seven of the nine). CONCLUSIONS. Sixty-two (66%) of 94 mitral valves had a constellation of structural malformations, including increased leaflet area and elongation of the leaflets or anomalous papillary muscle insertion directly into anterior mitral leaflet. These findings expand the morphological definition of HCM by demonstrating that the disease process is not confined to cardiac muscle but rather many patients also have structural abnormalities of the mitral valve that are unlikely to be acquired or secondary to mechanical factors.

Echocardiographic assessment of mitral valve size in obstructive hypertrophic cardiomyopathy. Anatomic validation from mitral valve specimen.
Klues HG, Proschan MA, Dollar AL, Spirito P, Roberts WC, Maron BJ.
Circulation. 1993 Aug;88(2):548-55.
Pathology Research Branch, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Md.

BACKGROUND. In patients with hypertrophic cardiomyopathy, obstruction to left ventricular outflow is produced by systolic anterior motion of the mitral valve. In many of these patients, the mitral leaflets are elongated and increased in overall size. Mitral valve size may be responsible, in part, for the presence and magnitude of the outflow gradient and the pattern of systolic anterior motion of the leaflets. It may also influence the effectiveness of ventricular septal myotomy-myectomy in relieving subaortic obstruction. Therefore, the present study was undertaken to determine whether mitral valve dimensions could be assessed in quantitative terms from the echocardiogram in patients with hypertrophic cardiomyopathy. METHODS AND RESULTS. A group of 37 patients with hypertrophic cardiomyopathy was selected for this study by virtue of having a high-quality transthoracic or intraoperative echocardiogram suitable for certain quantitative measurements from stop-frame images as well as a morphologically intact mitral valve specimen (removed during surgery). Seven measurements of mitral valve dimensions were obtained from the two-dimensional and M-mode echocardiograms. A univariate regression analysis identified the mitral valve opening area as the best single predictor of actual mitral leaflet area measured from the specimen (r2 = .75; r = .87). The linear relation between mitral valve opening area as assessed by two-dimensional echocardiography and actual mitral leaflet area measured from the mitral valve specimen accounted for approximately 75% of the variability in mitral leaflet area. With such statistical models, it was possible to reliably identify from the echocardiogram enlarged mitral valves (> or = 12.0 cm2) in 16 of 19 patients (84%) and normal-sized valves in 15 of 18 patients (83%). CONCLUSIONS. In a selected group of patients with obstructive hypertrophic cardiomyopathy, a model derived from a regression analysis of quantitative echocardiographic measurements permitted (with good precision) estimation of actual mitral leaflet area and consequently overall mitral valve size and the discrimination of enlarged from normal-sized mitral valves.

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