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Myxomatous degeneration of the mitral valve is the most common acquired cardiac disease in the dog. Degenerative mitral valve disease (DMVD) is a progressive disease and subtle changes in valve structure precede the development of clinically significant disease.  

Myxomatous degeneration of the mitral valve is the most common acquired cardiac disease in the dog. Degenerative mitral valve disease (DMVD) is a progressive disease and subtle changes in valve structure precede the development of clinically significant disease.  

The aetiology of DMVD is unknown. Genetic predisposition for development of the disease is likely, however the inheritance is complex.  

The mitral apparatus consists of the mitral valve leaflets, valve annulus, chordae tendinae and papillary muscles. The mitral valve leaflets are known as anterior and posterior leaflets. In the normal dog, these are thin, translucent structures that are anchored to the papillary muscles by chordae tendinae. Both papillary muscles (anterior and posterior) arise from the left ventricular free wall. The mitral valve prevents the backflow of blood from the left ventricle to the left atrium during systole. In early systole, when left ventricular pressure exceeds left atrial pressure, the mitral valve leaflets close. In normal dogs, the chordae tendinae tether the leaflets to prevent them prolapsing into the left atrium. When the mitral valve is incompetent, there is regurgitation of blood from the left ventricle to the left atrium. Mitral regurgitation may be mild, with no clinical consequence, or may be severe. The severity of mitral regurgitation is determined primarily by the size of the orifice, that results from incomplete apposition of the mitral valve leaflets, and the relationship between left ventricular and left atrial systolic pressures. Mitral regurgitation causes an increase in left atrial pressure, which over time can lead to left atrial dilation. In diastole, the left ventricle is filled by both pulmonary venous return and blood that has been regurgitated into the left atrium. Therefore, both the left atrium and left ventricle become volume overloaded. This may result in ventricular dilation and eccentric hypertrophy. In severe cases, increased left ventricular and left atrial filling pressures may result. This leads to an increase in pulmonary venous pressure and may result in [[Heart Failure, Lef-Sided|left-sided congestive heart failure]].  

Blood passes back into the left atrium, compromising the filling from the pulmonary vein, which leads to back pressure on the pulmonary capillaries. Resultant [[Oedema|oedema]] forms in the lungs, and can be heard as moist sounds on auscultation. This reduces the oxygenation of blood leading to exercise intolerance. Failure of the left side eventually compromises the function of the right side. In [[Heart Failure, Right-Sided|right sided heart failure]] there is a pooling of blood in the venous system i.e. in the [[Liver - Anatomy & Physiology|liver]]. In some cases a jet lesion can occur, where a small stream of blood passes back into the left atrium and contacts the atrial wall.

The aetiology of DMVD is unknown. Genetic predisposition for development of the disease is likely, however the inheritance is complex.  

 

Mitral valve dysplasia is a congenital malformation or degeneration of the mitral valve leaflets and its supporting structures (''chordae tendinae'', papillary muscles, valvular leaflets, annulus) resulting in valvular regurgitation (insufficiency). It is common in dogs and cats and rare in other species.

 

Chronic mitral regurgitation leads to volume overload of the left heart, which results in dilatation (eccentric hypertrophy) of the left ventricle and atrium. When mitral regurgitation is severe, cardiac output decreases, which results in signs of [[Heart Failure, Left-Sided|left sided cardiac failure]] (LCHF) and pulmonary venous congestion. Dilatation of the left-sided chambers predisposes affected animals to [[:Category:Arrhythmia|arrhythmias]]. In some cases, malformation of the mitral valve complex causes a degree of valvular stenosis as well as insufficiency.

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