Mitral Valve Insufficiency

The causes of mitral valve insufficiency may largely be divided into two categories: organic or primary and functional or secondary. In the first case, the cause of insufficiency is due to a morphological change of the valve. Numerous diseases may damage the valve. Of the degenerative disease we may list myxomatous degeneration, fibroelastic deficiency or annular calcifications. Of the phlogistic diseases we may note rheumatic or bacterial endocarditis. Congenital defects include the isolated cleft of the anterior leaflet of the mitral valve (not to be confused with the cleft of the atrioventricular septal defect, which is a congenital malformation affecting the entire mitral valve apparatus), double orifice, parachute mitral valve etc. Ischemic diseases include fibrosis or rupture of the papillary muscles after acute myocardial infarction. In the so-called ‘‘functional’’ form, the valve is described as morphologically normal (below we shall see that in reality this is not so) but insufficient due to a modification in the geometry of the left ventricle with which it is intimately connected. The changes to the left ventricle that cause insufficiency may be classified as localized (the most conventional case is inferoposterior infarction with ‘‘asymmetrical’’ transmission on the medial portions of the two leaflets) or diffuse (dilated cardiomyopathy with ‘‘symmetrical’’ traction on the entire valve fissure). In this chapter we shall describe organic or primary, mitral insufficiency. In the next chapter we shall discuss functional, or secondary, mitral valve insufficiency. One classification that has been particularly successful is the one of Carpentier [1], which differentiates insufficiency into three categories: mitral valve insufficiency with ‘‘normal’’ leaflet movement (type I), due to perforation or erosion of the leaflet(s) (generally in endocarditis) or dilatation of the annulus (e.g. in atrial fibrillation); mitral valve insufficiency with ‘‘excessive’’ leaflet movement (type II), such as prolapse or rupture of the chordae tendineae; and finally mitral valve insufficiency with reduced leaflet movement (type III), which can further be subdivided into type IIIa, where reduced movement is diastolic (mitral valve stenosis) and type IIIb, where the reduced movement occurs in systole due to leaflet traction or dilatation/deformation of the left ventricle. In Western countries the most common cause of mitral valve insufficiency is due to degenerative changes, occurring in 60 % of cases, followed by ‘‘functional’’ changes (approximately 20–30 %), endocarditis (5–10 %), rheumatic (2–5 %) and a group of miscellaneous causes such as inflammation, trauma and congenital conditions (2 %) [2].