Mitral valve prolapse related to geometrical changes of the heart in cases of progressive muscular dystrophy.

The significance of geometrical changes of the heart for the development of mitral valve prolapse (MVP) was studied by echocardiograms and chest x-ray films in 58 cases of progressive muscular dystrophy (PMD). The incidence of MVP was significantly higher (p less than 0.001) in cases where the thoracic spine was straight or lordotic compared with cases of kyphotic thoracic spine. The flattening of the thorax associated with deformation of the thoracic spine was correlated with the left atrial dimension and left ventricular dimension (r = 0.62, r = 0.37, respectively; p less than 0.001), and MVP developed predominantly in cases with flattened thorax and small left atrial or left ventricular dimensions. The left atrial and left ventricular dimensions were significantly smaller in cases with MVP compared to cases without MVP (p less than 0.001, p less than 0.005, respectively). When both the left atrial and the left ventricular dimension shortened to certain levels, MVP was observed in almost all cases. From these results, it was suggested that the portion from the left atrium to the left ventricle was pressed by the forward bending of the thoracic spine, and the subsequent geometrical changes of the mitral ring and the left ventricle could produce redundancy of the chorda tendinea of the mitral valve, resulting in the occurrence of MVP.