Case 20 — Text

Text from “Small Animal Cardiovascular Medicine”

Mitral Valve Stenosis

Mitral valve stenosis is defined as a narrowed mitral valve orifice due to an abnormal mitral valve. The increased resistance to blood flow results in a pressure gradient across the mitral valve and an increase in left atrial pressure.

Prevalence

Mitral stenosis (MS) is a rare cardiac abnormality in dogs and cats, diagnosed in approximately 1 dog per year in a busy referral university hospital. When identified in young dogs, it is often diagnosed in conjunction with another cardiac abnormality, most commonly subaortic stenosis. MS can also be diagnosed in older dogs with no coexisting abnormalities; in older dogs it is often impossible to determine if the abnormality is congenital or acquired. Of 17 cases in the literature, five were diagnosed in Bull terriers. The authors believe that most mitral stenosis in dogs and cats is probably congenital.

Pathophysiology

Mitral stenosis produces obstruction to blood flow from the left atrium to the left ventricle in diastole. The increased resistance results in increased left atrial, pulmonary vein, and pulmonary capillary pressures. Severe mitral stenosis causes pulmonary edema. Exercise increases left atrial pressure further, potentially causing exercise-induced dyspnea or syncope. Syncope may occur when flow cannot increase appropriately during exercise, when tachyarrhythmias develop, or through a reflex mechanism involving ventricular mechanoreceptor stimulation.

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