Pulmonary stenosis is a condition characterized by obstruction to blood flow from the right ventricle to the pulmonary artery.
This obstruction is caused by narrowing (stenosis) at one or more points from the right ventricle to the pulmonary artery. It includes obstruction from thickened muscle below the pulmonary valve, narrowing of the valve itself, or narrowing of the pulmonary artery above the valve. The most common form of pulmonary stenosis is obstruction at the valve itself, referred to as pulmonary valvar stenosis.
The normal pulmonary valve consists of three thin and pliable valve leaflets. When the right ventricle ejects blood into the pulmonary artery, the normal pulmonary valve leaflets spread apart easily and cause no obstruction (blockage) to outflow of blood from the heart. Most commonly with pulmonary valvar stenosis, the pulmonary valve leaflets are thickened and fused together along their separation lines (commissures). When the tissue is thickened, the leaflets become less pliable than normal, which contributes to the obstruction. At times, the diameter of the pulmonary valve itself is small or hypoplastic.
When the pulmonary valve is obstructed, the right ventricle must work harder to eject blood into the pulmonary artery. To compensate for this additional workload, the muscle of the right ventricle (the myocardium) gradually thickens to provide additional strength to right ventricular ejection. The increased right ventricular muscle, known as hypertrophy, is rarely a problem in itself, but instead is an indication that significant valve obstruction exists.
When the pulmonary valve is severely obstructed, especially in newborns with critical degrees of pulmonary stenosis, the right ventricle cannot eject sufficient volume of blood flow into the pulmonary artery. In these instances, blue blood bypasses the right ventricle flowing from the right atrium to left atrium, through the foramen ovale, a communication or “hole” between these two chambers that is normally present in newborns. Newborns with critical pulmonary stenosis therefore will have cyanosis (blue discoloration of the lips and nailbeds) due to lower oxygen levels in their blood.
Right ventricular failure rarely occurs with pulmonary valve stenosis.
Children with pulmonary valvar stenosis are usually asymptomatic and in normal health. A heart murmur is the most common sign detected by a physician indicating that a valve problem may be present. Children with mild-to-moderate degrees of pulmonary valve stenosis have easily detectable heart murmurs, but typically do not have any symptoms. Symptoms occur only with severe pulmonary valve stenosis.
A newborn with critical pulmonary valve stenosis develops cyanosis in the first few days of life. This is due to diminished volume of blood flow into the lungs, together with a shunt of blue blood from right to left atrium. This an emergency situation that requires immediate treatment, either balloon dilation of the valve or surgery.
In an older child, severe pulmonary valve stenosis may cause easy fatigue or shortness of breath with physical exertion. Severe pulmonary valve stenosis rarely results in right ventricular failure or sudden death.
Children with mild pulmonary valve stenosis rarely require treatment. Patients with mild pulmonary valve stenosis are healthy, can participate in all types of physical activities and sporting events, and lead normal lives. Mild pulmonary valve stenosis in childhood rarely progresses after the first year of life. However, mild pulmonary stenosis in a young infant may progress to more severe degrees and requires careful follow-up.
Children with moderate-to-severe degrees of pulmonary stenosis require treatment, the timing of which is often elective. The type of treatment required depends on the type of valve abnormality present. Most commonly, the stenotic pulmonary valve is of normal size, and the obstruction is due to fusion along the commissures or lines of valve leaflet opening. This “typical” form of pulmonary valve stenosis responds very nicely to balloon dilation. Balloon dilation valvuloplasty is performed at the time of cardiac catheterization and does not require open-heart surgery. In the newborn, balloon dilation for critical pulmonary valve stenosis can be a technically challenging procedure as these newborns are often critically ill and unstable. More typically, in older children the procedure is performed electively on an outpatient basis.
Results of balloon dilation valvuloplasty for pulmonary stenosis have been excellent. Importantly, balloon dilation cannot make an abnormal valve “normal”. Instead, the procedure decreases the degree of pulmonary valve obstruction from severe to mild in the large majority of patients. For children and adolescents with “typical” pulmonary valve stenosis, a single balloon dilation procedure is usually the only therapy ever needed. It is rare that an older child will have return of significant pulmonary valve obstruction following a successful balloon dilation procedure.
Newborns and young infants with very severe pulmonary valvar obstruction will also have an excellent response to balloon dilation, unless the valve is underdeveloped in size. However, recurrence of significant pulmonary stenosis does occur in approximately 20 percent of newborns and young infants even though the initial response to balloon dilation has been excellent. These patients may require a second balloon dilation, or an open-heart surgical procedure if the valve is small.
Open-heart surgical procedures are required for more complex valves, where balloon dilation is not sufficient therapy. These valves may be obstructed by thick and dysplastic leaflet tissue (such as in patients with Noonan Syndrome), and the diameter of the valve itself may be small in some cases. For these conditions surgical pulmonary valvotomy (opening of the valve), partial valvectomy (removal of a portion of the leaflet), and possibly a transannular patch (patch from the right ventricle to pulmonary artery) may be required during the open-heart surgery repair.
The long-term outcomes for open-heart surgery in patients with severe pulmonary valvar stenosis are also excellent. Because balloon dilation is usually the only treatment necessary for most patients, open-heart surgery is generally only performed in patients with more complex forms of pulmonary valve obstruction. However, patients with very thick valve leaflets or underdeveloped pulmonary valve sizes also have an outstanding long-term outcome following open-heart surgical repair. If there is no other associated heart disease, these children are expected to lead normal, active lives.
It is important that all children with pulmonary valve stenosis, even after very successful balloon dilation or open-heart surgery, be re-evaluated at regular intervals. Long-term follow-up with evaluation by a qualified cardiologist is essential to helping provide the highest quality outcome for patients with pulmonary valve stenosis.