Mitral Valve Stenosis
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 is rare in dogs and cats and can occur together with other congenital defects such as subaortic stenosis, mitral valve dysplasia, and pulmonic stenosis.
The disease results in increased resistance to left atrial outflow, creating a pressure gradient between the left atrium and left ventricle. This leads to left atrial enlargement and increases in pulmonary venous and capillary wedge pressures. Pulmonary edema can develop as a consequence, and syncope occurs in some cases.
Mitral stenosis can result in a diastolic heart murmur that is typically low-grade (I-II/VI). If concurrent mitral valve dysplasia is present, a systolic murmur with maximum intensity at the left cardiac apex may be heard. Radiographs demonstrate varying degrees of left atrial enlargement and pulmonary edema in animals with left-side CHF. Electrocardiography may demonstrate widened P waves (indicating left atrial enlargement) and supraventricular arrhythmias. Echocardiography provides a definitive diagnosis. Doming of the mitral valve leaflets toward the left ventricle during diastole, left atrial enlargement, and thickening of the mitral valve leaflets can be noted. Doppler echocardiography demonstrates turbulent diastolic flow across the mitral valve, beginning at the mitral valve and extending into the left ventricle. A pressure gradient is documented between the left atrium and left ventricle in early diastole.
Medical management of animals with mitral valve stenosis involves use of diuretics and dietary sodium restriction. Excessive diuresis should be avoided, because this can reduce cardiac output severely. Surgical or interventional therapy options include closed commisurotomy (disruption of the stenosis without the use of bypass), open commisurotomy, mitral valve replacement, and balloon valvuloplasty.