Pulmonary valve stenosis usually occurs when the pulmonary valve doesn't grow properly during foetal development. Babies who have the condition may have other congenital heart abnormalities, as well. It's not known what causes the valve to develop abnormally.
Normal pulmonary valve anatomy
The pulmonary valve is made up of three thin pieces of tissue called cusps that are arranged in a circle. With each heartbeat, the valve opens in the direction of blood flow — into the pulmonary artery and continuing to the lungs — then closes to prevent blood from flowing backward into the heart's right ventricle.
What happens in pulmonary valve stenosis
One or more of the cusps may be defective or too thick, or the cusps may not separate from each other properly. If this happens, the valve doesn't open correctly, restricting blood flow.
Other contributing conditions
Sometimes other medical conditions or having an artificial valve can cause the condition.
- Carcinoid syndrome. This syndrome — a combination of signs and symptoms, including flushing of the skin and diarrhoea — results from the release of a chemical, serotonin, from growths called carcinoid tumours in the digestive system.
- Rheumatic fever. This complication of an infection caused by streptococcus bacteria, such as strep throat, may injure the heart valves.
Because pulmonary valve stenosis usually develops before birth, there aren't many known risk factors. However, certain conditions and procedures can increase your risk of developing pulmonary valve stenosis later in life, including:
- Carcinoid syndrome
- Rheumatic fever
- Noonan syndrome
- Pulmonary valve replacement