Diversity of structural mitral valve alterations in hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is characterized by an asymmetrically hypertrophied left ventricle and is regarded as a disease of cardiac muscle. 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). 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.