Mitral Valve Dysplasia
Congenital malformation of the mitral valve complex (mitral valve dysplasia) is a common congenital cardiac defect in cats. Canine breeds predisposed are Bull Terriers, German Shepherds, and Great Danes. Mitral valve dysplasia results in mitral insufficiency and systolic regurgitation of blood into the left atrium. Any component of the mitral valve complex (valve leaflets, chordae tendineae, papillary muscles) may be malformed, and often more than one component is defective.
Malformation of the mitral valve complex results in significant valvular insufficiency. Chronic mitral regurgitation leads to volume overload of the left heart, which results in dilatation of the left ventricle and atrium. Severe mitral regurgitation can subsequently result in pulmonary venous congestion and left-side CHF. Dilatation of the left-side chambers predisposes affected animals to arrhythmias. When mitral regurgitation is severe, cardiac output decreases and signs of poor cardiac output may occur (weakness, syncope). In some cases, malformation of the mitral valve complex causes a degree of valvular stenosis as well as insufficiency (see Mitral Valve Stenosis).
Clinical signs correlate with the severity of the defect. Affected animals may display signs of left-side CHF. A holosystolic murmur of mitral regurgitation is prominent at the left cardiac apex. A diastolic heart sound (gallop rhythm) is present in some cases. Affected animals may have a precordial thrill over the left cardiac apex. Electrocardiography may demonstrate atrial arrhythmias (atrial premature complexes, atrial fibrillation), especially in severely affected animals with left atrial dilatation. There may also be evidence of both left atrial (widened P waves) and left ventricular enlargement. Thoracic radiographs may demonstrate severe left atrial enlargement. Left ventricular enlargement and pulmonary venous congestion can also be noted. Echocardiography demonstrates malformation of the mitral valve complex (fused chordae tendineae and thickened, immobile valve leaflets, abnormal appearance to the papillary muscles) and left atrial and ventricular dilatation. Doppler echocardiography demonstrates severe mitral regurgitation. Evidence of mitral stenosis can be identified on the echocardiogram (see Mitral Valve Stenosis).
Prognosis for animals with clinical signs and severe disease is poor. Mildly affected animals may remain free of clinical signs for several years. Animals with CHF should be treated medically. For therapy of progressive left-side CHF, see Management of heart failure.