The tricuspid valve lies on the right side of the heart and separates the right atrium and right ventricle. The valve is open during heart relaxation (diastole) allowing de-oxygenated blood to enter the atrium and ventricle from the great veins. The valve closes during ventricular contraction (systole) preventing blood from returning to the right atrium and thereby facilitating blood flow from the right ventricle to the lungs through the pulmonic valve and pulmonary arteries. If the valve is damaged then blood will leak into the atrium during heart contraction, creating turbulence which may be heard as a cardiac murmur.
A small amount of leakage (regurgitation) is normal in healthy horses. This is reflected by a cardiac murmur that is typically holosystolic (between the first and second heart sounds), plateau-shaped (even loudness throughout systole), and typically grade III or less. This murmur is relatively common in Standardbreds and is rarely related to clinical signs or reduced athletic performance.
Moderate to severe regurgitation can be due to bacterial infection of the valve (bacterial endocarditis), rupture of the chords that prevent the valve prolapsing into the atrium, or significant degeneration of the valve. In severe cases of mitral valve disease it is possible to good a backflow build-up of pressure in the lungs (pulmonary hypertension) and secondary tricuspid valve leakage.
The diagnosis of tricuspid valve regurgitation is through auscultation and echocardiography, with Doppler capabilities.
Tags: Cardiology