Pulmonic stenosis (PS) is considered the third most common congenital heart defect in dogs. It typically affects small- to medium-breed dogs, although large-breed dogs can also be affected. To understand the problems associated with this malformation, it is necessary to understand the normal heart.
The pulmonary artery delivers blood from the right side of the heart to the lungs. In some dogs, the pulmonary valve forms incorrectly and is too narrow (see diagram). This narrowing is called stenosis. The blood flow from the right ventricle is through an opening that is smaller than normal. Just as when a river suddenly narrows, the blood flow in the pulmonary artery becomes more forceful and more turbulent in patients with pulmonic stenosis, leading to the onset of a heart murmur. Furthermore the right ventricle must create additional pressure to overcome the obstruction and this creates more work for the right side of the heart. Over time, the right side of the heart can begin to enlarge because of this extra workload.
The severity of this disease depends on how narrow the stenotic portion is and consequently how much additional pressure must be generated by the right ventricle to allow the blood to flow through this narrow opening. In severe cases, patients may eventually develop congestive heart failure.
Treatment and Prognosis
As with many congenital defects, the key to a good prognosis is early and accurate diagnosis. It is important to evaluate the severity of a patient’s disease as soon as pulmonic stenosis is suspected. Patients with mild disease may not need treatment and can expect a good quality of life if adequately followed up. Up to 70% of patients with moderate to severe disease benefit from a minimally invasive procedure called balloon valvuloplasty. In these patients, a cardiologist inserts a catheter with an inflatable balloon across the pulmonary valve. The balloon is then inflated to stretch the stenotic pulmonary valve to as normal a diameter as possible (link to the video). In selected cases of pulmonic stenosis, heart surgery can be performed.
Balloon valvuloplasty and surgery can be less rewarding or even totally contraindicated once the disease has caused permanent changes to the heart muscle. Therefore, it is critical that these options are considered as early as possible.
For patients who develop heart failure, medical therapy is necessary to control symptoms.