Aetiology
The majority of cases are congenital. Possible embryological explanations for pulmonary stenosis (PS) vary from a malformation of the bulbus cordis to fetal endocarditis.[4][5] Most often, there is a typical dome-shaped pulmonary valve with a narrow central opening but a preserved mobile valve base. A dysplastic pulmonary valve, with poorly mobile cusps and myxomatous thickening, is less common (15% to 20%; even less in untreated adults) and frequently part of Noonan syndrome. In adults, a stenotic pulmonary valve may calcify late in life.
A genetic abnormality is another possible aetiology, as PS is frequently associated with genetic conditions such as Noonan syndrome, Noonan syndrome with multiple lentigines (previously known as LEOPARD syndrome), Williams syndrome, or Alagille's syndrome.[6][7]
Acquired PS is a rare condition associated with carcinoid syndrome, infectious endocarditis, myocardial tumours, and external compression. Carcinoid heart disease is caused by plaque formation on the endocardial surfaces of the right atrium and of the right valves, resulting in thickened and immobile valve leaflets.
Pathophysiology
The main pathophysiological consequence of PS is RV strain and an increase in RV pressure. The cellular effect on the RV depends on the timing of obstruction.[8] If the obstruction is present in a fetus or neonate, the myocardial response is hyperplasia of myocytes and an increase in vascularity. However, if the obstruction develops within mature myocardium, there is an increase in myocyte size (hypertrophy) without an increase in capillary network.
Mild to moderate obstruction will in general be haemodynamically well tolerated and is not associated with cyanosis or cardiac symptoms. In the severe form of PS, clinical symptoms such as dyspnoea, exercise intolerance, cyanosis, and syncope may occur. The right ventricular will eventually fail as the myocardium becomes unable to support the enhanced work load imposed by the stenosis, and patients develop jugular venous distension, peripheral oedema, pleural effusion, ascites, and hepatomegaly.
Critical PS may occur in neonates if the right ventricular outflow tract obstruction caused by the stenotic valve is so severe that it leads to cyanosis. The major source of pulmonary blood flow in severely obstructed patients is through the ductus arteriosus. Once the ductus arteriosus begins to close, blood flow will be insufficient and the neonate will become hypoxaemic.[9]
If there is no atrial or ventricular level shunt, sudden death may ensue due to compromised cardiac output.[2] Fetal and perinatal factors, including the specific physiology of PS that leads to decreased oxygen and nutrient delivery to the brain, can critically impact neurodevelopmental, warranting early and targeted interventions.[7]
Classification
Clinical classifications
Anatomical location of obstruction:
Valvular
Subvalvular (intracavitary/infundibular)
Supravalvular
Peripheral (branch).
Aetiology
Congenital
Acquired.
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