Pulmonary Stensois

Pulmonary Stenosis

This one of the most common congenital defects and is characterized by obstruction of the outflow portion of the right ventricle.

Pulmonary stenosis may be classified as subvalvular, valvular or supravalvular. All types may vary in terms of severity from mild, moderate and severe.

The incidence of pulmonary stenosis in the general population is approximately 0.4% to 0.6% (or about 6 of every 1000 births) and comprises about 10% of all congenital heart defects.

This defect may occur in isolation, or in conjunction with other complex defects. It is the second most common defect (with PDA or patent ductus arteriosus, ASD or atrial septal defect and VSD or ventricular septal defect being the most common). This blog post will concentrate on isolated pulmonary stenosis.

Valvular Stenosis
Valvular stenosis is the fusion of the three leaflets of the pulmonic valve and may be mild, moderate or severe. This fusion tends to be uniform across the three leaflets, and in its severe form the narrowing may leave only a pinhole opening at the center.

The stenosed valve may have up to 4 leaflets but it is typically bicuspid or tricuspid. A “tethered” valve refers to a stenotic valve that during systole takes on a dome like appearance. A “dysplastic” valve means that the leaflets are thickened.

When the valve is moderately or severely stenotic there is often right ventricular hypertrophy and an ASD is common. Pulmonary stenosis and right ventricular hypertrophy are hallmarks of tetralogy of fallot, therefore this defect should always be ruled out when attempting to identify isolated pulmonary stenosis.

Subvalvular Stenosis
The infundibulum is the conically shaped muscular part of the RVOT (right ventricular outflow tract) that lies just inferior to the pulmonic valve. Subvalvular stenosis is rare and usually occurs in conjunction with right ventricular hypertrophy and a VSD (ventricular septal defect). As the right ventricle hypertrophies, so does the infundibulum. Subvalvular stenosis means that the diameter of the RVOT is reduced and may be described as mild, moderate or severe.

Supravalvular Stenosis
Stenosis of the pulmonary arterial tree is common, and complicates other defects such as tetralogy of fallot or transpositions, or may coexist with stenosis of the pulmonic valve and a VSD. Branch stenosis (or stenosis of one or both pulmonary arteries) is very common.

Congenital stenosis of the pulmonary trunk involves thickening of the musculature therein, whereas branch stenosis tends to be a temporary situation in which the pulmonary branches ( left and/or right pulmonary arteries) constrict as a natural way to prevent volume overload of the lungs in the presence of left-to-right shunts, such as a VSD, ASD or especially a large PDA.

Critical pulmonary stenosis is a cyanotic event and is life-threatening; the shunts (PDA, ASD) will right-to-left whereas the PDA will be left-to-right in an effort by the body to saturate the lungs.

Echocardiography
The gold standard for evaluation of pulmonic stenosis at all levels is echocardiography. The sonographer should determine whether the stenosis is subvalvular, valvular or supravalvular. Is there a VSD, ASD or PDA? Branch stenosis is the most commonly found lesion in the presence of a shunt.

Try to determine the severity of the lesion by using color, pulsed and continuous doppler. Evaluate the gradient across the lesion. Any gradient greater than 16 mmHg is considered abnormal and a gradient of 64 mmHg is considered severe. If the defect is surgically repaired, follow-up echos are usually done.

In the case of branch stenosis, if the underlying shunt (ASD, VSD or especially PDA) is repaired, then the pulmonary artery/arteries will eventually dilate and return to normal as pulmonary flow is normalized.

Be careful to rule out additional abnormalities such as tetralogy of fallot, and transpositions.