Infection, fever or parasitic damage can lead to the fibrosis of the valve flaps causing incomplete closure of the semilunar valve. Congenital defects may also result in incomplete closure of the valve. Failure of the aortic semilunar valve to close allows blood to regurgitate back into the left ventricle after ejection into the aorta is complete, allowing the left ventricle to begin filing from the aorta before the mitral valve opens to allow normal filling from the left atrium. Blood leaving the aorta in two directions, back into the ventricle and distally towards the body, causes a decrease in aortic & subsequently arterial diastolic pressure. The increase in blood volume and pressure in the left ventricle causes this ventricle to contract more forcefully resulting in an increase in ventricular and aortic systolic pressure and an increase in the stroke volume. Chronically, aortic valve failure leads to ______________________ congestion, pulmonary edema and dilation of the left ventricle and atrium. Aortic valve insufficiency is often _________________ , and clinical signs and symptoms are general when they do present. Clinical signs and symptoms include exercise intolerance, heart murmur and lung edema.
Diagnosis of aortic valve insufficiency is made through auscultation and EKG.
Treatment of aortic valve insufficiency may not be necessary in asymptomatic individuals. If treatment is required the administration of vasodilators, anti-arrhythmia drugs, diuretics and anticoagulants may improve the horse’s condition.
Mitral Valve Insufficiency
Mitral valve insufficiency describes the dysfunction of the mitral, or bicuspid, valve. This valve lies between the left atrium and the left ventricle and is designed to prevent the backflow of blood into the atrium during ventricular contraction. Infection, fever or parasitic damage can lead to the fibrosis of the valve flaps causing incomplete closure of the mitral valve. Congenital defects may also result in incomplete closure of the valve. During ventricular systole blood is forced back into the atrium, through the faulty valve. The regurgitation of blood back into the atrium decreases the net _____________________ of the left ventricle, thereby decreasing the amount of blood delivered to the aorta. Though net stroke volume is decreased, the total stroke volume, the volume of blood forced into the aorta plus the volume of blood forced into the left atrium, is increased causing the left ventricle to contract more _______________________. This results in the left ventricle becoming __________________ . Pulmonary congestion and pulmonary edema result from mitral valve insufficiency as the left atrium is partially filled by the backflow from the ventricle, causing blood to back up in the pulmonary circulation. Chronic mitral valve insufficiency causes the dilation or
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