What is Pulmonic Stenosis?
Pulmonic stenosis is an anatomic obstruction to flow from the right ventricle to the pulmonary arterial vasculature. This obstruction most commonly occurs as a congenital defect below the valve (subvavlular), at the level of the valve (valvular) or above the valve (supravalvular).
In rare cases pulmonic stenosis can occur secondary to neoplasia or endocarditis. The most common form of the disease is valvular pulmonic stenosis characterized by abnormally formed valve leaflets. The second most common form of the disease is subvalvular pulmonic stenosis occuring as a narrowing of the infundibular or subinfundibular region of the right ventricle or directly below the valve, often with a normal pulmonic valve. Supravalvular pulmonic stenosis is rare.
This disease is most commonly seen in small to medium breed dogs with English bulldogs, Mastiffs, boxers, cocker spaniels and West highland terriers being overrepresented breeds. Some brachycephalic breeds (bulldogs, boxers) will have a coronary vascular anomaly (R2A anomaly). In this situation, the left coronary artery arises from the right coronary sinus and crosses the top of the right ventricular outflow tract to the left ventricle. This coronary artery compresses the right ventricular outflow tract, creating a stenosis that is located just below the pulmonary valve. No matter what the obstruction, the end result if an increase in right ventricular pressure in order to overcome the resistance caused by the obstruction. The right ventricle will hypertrophy (concentric) over time as a result of the elevated pressures. The stenosis is generally classified as mild, moderate or severe. Physical examination will reveal a systolic ejection murmur of the heart base with a crescendo or crescendo-decrescendo quality.
Clinical signs are rare and often only seen with a severe stenosis and are most commonly exercise intolerance or syncope. Other signs include in sudden death related to myocardial ischemia or right heart failure secondary to pressure overload. Signs of right-sided heart failure include ascites, abdominal distension, difficulty breathing, inappetance, lethargy or exercise intolerance. Right-sided heart failure is rare and is most commonly seen if there is problems with the tricuspid valve such as concurrent tricuspid valve dysplasia or degeneration.
Mild and moderate pulmonic stenoses often do not require treatment. Balloon vavluloplasty is recommended for severe pulmonic stenosis in order to open the narrowing. Medical treatment for right-sided heart failure may also be indicated. Beta blockers are used to try to prevent sudden death. The prognosis for mild and moderate pulmonic stenosis is good.
It is also good for severe stenosis if balloon vavluloplasty is performed in young animals with congenital disease.
In mild-to-moderate pulmonic stenosis, the ECG is commonly normal. In dogs with severe pulmonic stenosis with secondary right ventricular hypertrophy, one may see deep S waves, right axis deviation or right bundle branch block.