Blood flows from the body to the right heart, the lungs,
the left heart then out to the body (see ‘Normal Cardiac Circulation’). Blood is carried from the right ventricle to
the lungs via the pulmonary artery.
What is Pulmonic Stenosis?
Pulmonic stenosis is an obstruction to blood from the right ventricle out to the lungs. This most commonly occurs at the level of the pulmonic valve itself where the normally thin valve leaflets may be thickened or remained partially fused during embryonic development. The result is the same amount of blood needing to be pumped through a narrow area. To compensate for this extra work, the right ventricle becomes thickened. The blood squirting through the narrow region becomes faster and turbulent, creating a heart murmur.
Pulmonic stenosis is most often a congenital disease (meaning your puppy was born with it). Occasionally the stenosis can be due to a fibrous ridge occurring above or below the valve. Rarer causes of stenosis include tumours in this region, infection of the pulmonic valve, narrowing of the pulmonary artery branches or abnormal development of a coronary artery (the vessels that provide blood supply to the heart muscle).
How Do I Know My Puppy Has Pulmonic Stenosis?
The first sign of pulmonic stenosis is a heart murmur, which will be present from birth. It is not uncommon for young puppies to have ‘innocent’ murmurs, which occur with a normal heart. Innocent murmurs are soft and should disappear by 16 weeks of age. A loud murmur or one that persists past 16 weeks of age should always be investigated.
Once your regular vet detects a heart murmur, referral to a cardiologist is advised. The cardiologist will perform an echocardiogram (heart ultrasound) to look at all cardiac chambers, the blood flow and diagnose the disease. Occasionally an electrocardiogram (ECG) and chest xray may be recommended to get more information on the heart and lungs.
How is Pulmonic Stenosis Treated?
Once pulmonic stenosis is diagnosed, the cardiologist will get an estimate of speed of blood flow across the obstructed region as well as look at secondary effects from this obstruction to get an estimate of disease severity. If the disease is classified as mild or moderate, no treatment may be necessary. Severe cases will initially be prescribed a beta-blocker called atenolol. This drug decreases the workload on the right heart and reduces the frequency of arrhythmias that can occur. If the stenosis is considered severe and is at the level of the valve, an interventional procedure called balloon valvuloplasty will be recommended. In this procedure, a special balloon catheter is introduced via the jugular vein into the right heart and placed over the stenotic pulmonic valve. The balloon catheter is inflated to tear open the fused valve leaflets. If successful, this procedure can result in a normal lifespan and quality of life for a dog with previously severe pulmonic stenosis.
Breeding from a dog with pulmonic stenosis is not recommended as it is likely that the disease is inherited in predisposed breeds.