Pulmonic stenosis (PS) is a common congenital heart defect in dogs but only occasionally recognized in cats.  It involves a narrowing or stenosis in the pulmonary artery region restricting normal blood flow.  The pulmonary outflow area of the heart includes the right ventricular outflow tract (the area of the right ventricle that exits the heart), the pulmonic valve, and the pulmonary artery.  Although defects may occur in any of these areas, a dysplasia, or abnormal formation, of the pulmonic valve itself is the most common site of obstruction.  In some dogs, the lesion is associated with an abnormal formation or orientation of the coronary arteries.  The disease demonstrates a genetic basis in certain breeds.  For example, in Beagle dogs, a polygenic mode of transmission has been determined.  Obstruction to right ventricular outflow causes an increase in the pressure inside the right ventricle, which in turn leads to right ventricular hypertrophy or enlargement (RVH).  The high velocity, turbulent blood flow across the stenotic (narrowed) area is responsible for the generation of the murmur.  Marked stenosis will lead to a diminished ability of the heart to eject blood (low cardiac output) and right sided congestive heart failure.

Breeds most commonly reported to have pulmonic stenosis include the Beagle, Samoyed, Chihuahua, English bulldog, miniature schnauzer, Labrador retriever, Mastiff, Chow-Chow, Newfoundland, Basset hound, and other terrier breeds.  Clinical signs may vary from an animal being asymptomatic to developing signs of low cardiac output such as fainting (syncope) and tiring easily to overt congestive heart failure (fluid retention, abdominal enlargement, and difficulty breathing).  Clinical signs are more common in dogs over one year old, as the disease may “progress” as the animal matures and grows.

Diagnosis and staging of the disease and severity is based on a number of tests.  These include a complete physical exam and review of the history, thoracic radiographs (X-Rays), electrocardiography (ECG), and echocardiography (ECHO or ultrasound) with doppler (blood flow) studies.  Additional testing including a complete blood count (CBC) and biochemical profile may be recommended.  Occasionally, invasive techniques such as cardiac catheterization are needed for more accurate diagnosis and staging.  Grading of the severity of the obstruction is commonly done during an echocardiographic doppler study.  The degree of stenosis has been arbitrarily graded as follows:

Mild stenosis:               Doppler pressure gradients up to 49 mm Hg

Moderate stenosis:        Doppler pressure gradients of 50 to 80 or 100 mm Hg

Severe stenosis:           Doppler pressure gradients over 80 or 100 mm Hg

The natural history is dependent on the graded severity of the lesion.  Animals with mild to moderate stenosis may live normal lives with no signs or complications.  Animals with moderate to severe stenosis are more likely to develop clinical signs including exercise induced syncope (fainting), arrhythmias (abnormal heart beats or rhythms), congestive heart failure, and possibly sudden death.  Affected animals, regardless of severity, should not  be bred.

Clinical management or treatment depends on the severity of the lesion as well.  Animals with significant radiographic (X-Ray), electrocardiographic (ECG), or ultrasound changes, and animals with clinical signs should have the severity evaluated with either Doppler interrogation of the pulmonic valve or with cardiac catheterization studies.  There is no absolute cut off value, but animals with a pressure gradient of over 80 to 100 mm Hg should be considered candidates for invasive interventional procedures such as a balloon valvuloplasty (trying to open the valve with a balloon tipped catheter) or surgery.  Progressive hypertrophy and worsening of the lesion may occur.  Medical therapy for pulmonic stenosis is needed when congestive heart failure or arrhythmia complications occur.  There are also some instances where medications may prove beneficial to reduce clinical signs such as fainting.  There are no medical therapies available to treat the narrowed or stenotic lesion directly.