Pulmonic stenosis

© Rand, J (2006) Problem-based feline medicine. Saunders Elsevier, Sydney

With congenital valvular malformation of the pulmonic valve, there is thickening of the valve leaflets and poor motility during systole, resulting in fixed obstruction of outflow of blood. In some cases, supravalvular or subvalvular stenosis may be found.

The increased resistance to blood flow across the pulmonary valve stenosis results in elevation of right ventricular systolic pressure. Secondary right ventricular hypertrophy and dilation may develop, along with arrhythmias.

Dilation and hypertrophy of the right ventricle may result in secondary tricuspid insufficiency. Signs of right-sided congestive heart failure may develop. Pulmonic stenosis is often seen with other cardiac defects such as tetralogy of Fallot, atrial and ventricular septal defects and tricuspid dysplasia. It is a rare congenital defect in cats.

Clinical signs

Many cats are asymptomatic and present for evaluation of a heart murmur. The age of presentation varies from the first few months of life until middle age. cats with symptoms may show dyspnoea or open-mouth breathing after mild to moderate exercise. The murmur is best heard at the left heart base. It is an ejection systolic murmur, which varies in intensity during systole because of the crescendo and decrescendo character. Characterisation of the ejection murmur may be difficult in a cat because of the fast heart beat.

Diagnosis

On x-ray, there is normal cardiac size or right ventricular enlargement. Dilated main pulmonary artery (post-stenotic dilatation) may be seen as a bulge in the left cranio-lateral part of the cardiac silhouette in the ventro-dorsal view or dorso-ventral view. Under-perfused pulmonary circulation is seen as hypovascular lung fields characterised by hyperinflated lungs and a decreased peripheral pulmonary vasculature.

On ECG, there is a tachycardia frequently seen, with >220 bpm. Right axis deviation is seen between -60 and -180 degrees in the frontal plane. Deep S waves are seen on leads II, aVF and III.

Echocardiographic examination often reveals pulmonary stenosis, pulmonary artery hypoplasia and a dysplastic pulmonic valve. Doppler study across the pulmonary valve will determine the degree of stenosis. Velocities of blood flow obtained by continuous wave Doppler above 2.0 m/s are diagnostic of stenosis.

Differential diagnosis

Tetralogy of Fallot - the murmur of pulmonic stenosis may be similar to the murmur heard in Tetralogy of Fallot, but cyanosis or brick-red mucous membranes are not seen with pulmonic stenosis.

Cardiomyopathies - the murmur is usually not as loud and may vary in intensity.

Treatment

Use furosemide if congestive heart failure is present.

Surgical options are available but rarely used.

Prognosis

Most cats reach middle age and some even have a normal lifespan. Long-term prognosis depends on the severity of obstruction to blood flow.