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.
Pathophysiology of Mitral Valve Dysplasia in Animals
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 Mitral Valve Stenosis in Animals Mitral valve stenosis is a narrowing of the mitral valve orifice caused by abnormalities of the mitral valve, resulting in obstruction to left ventricular inflow. This congenital abnormality... read more as well as insufficiency.
Clinical Findings and Treatment of Mitral Valve Dysplasia in Animals
Mitral regurgitation creates a holosystolic heart murmur heard loudest over the left apex, similar to the murmur of acquired degenerative valvular disease
Echocardiography shows malformation of various components of the mitral valve apparatus, with varying degrees of regurgitation and, less often, stenosis
Animals exhibiting clinical and radiographic evidence of left heart failure (pulmonary edema) should be treated medically
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 Mitral Valve Stenosis in Animals Mitral valve stenosis is a narrowing of the mitral valve orifice caused by abnormalities of the mitral valve, resulting in obstruction to left ventricular inflow. This congenital abnormality... read more can be identified on the echocardiogram.
Prognosis for animals with clinical signs and severe mitral valve dysplasia 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 Management of Heart Failure The three primary functions of the cardiovascular system are to maintain 1) normal blood pressure and 2) normal cardiac output, both at a 3) normal venous/capillary pressure. Heart failure is... read more .
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Also see pet health content regarding mitral valve dysplasia in dogs Mitral Valve Dysplasia Congenital abnormalities of the cardiovascular system are defects that are present at birth. They can occur as a result of genetic defects, environmental conditions, infections, poisoning, medication... read more and cats Mitral and Tricuspid Valve Dysplasia Congenital abnormalities of the cardiovascular system are defects that are present at birth. They can occur as a result of genetic defects, environmental conditions, infections, poisoning, medication... read more .