Pulmoner Darlık

The pulmonary valve lies at the origin of the pulmonary artery, the great vessel that arises from the right ventricle and carries deoxygenated blood to the lungs. Deoxygenated blood returning from the body reaches the right atrium and passes into the right ventricle, which then pumps it through the pulmonary artery to the lungs to be oxygenated. When the pulmonary valve becomes stenotic, right ventricular afterload rises and the right ventricle has to work at a higher pressure and with greater force in order to eject blood across the narrowed valve. Over time this leads to marked hypertrophy and strain of the right ventricular myocardium and, ultimately, to right heart failure.

Isolated pulmonary stenosis is almost always a congenital heart disease and accounts for 7-10% of all congenital heart disease. In adults, although very rarely, carcinoid plaques, cardiac tumours and a large sinus of Valsalva aneurysm may produce pulmonary stenosis by extrinsic compression.

In adults, pulmonary stenosis is classified into three main types:

• Stenosis of the valve itself (valvular pulmonary stenosis)
• Stenosis below the valve (subvalvular, infundibular pulmonary stenosis)
• Stenosis above the valve (supravalvular pulmonary stenosis)

In some cases, pulmonary stenosis may also be seen together with intracardiac shunt defects such as atrial septal defect (ASD) or ventricular septal defect (VSD), or with other congenital cardiac anomalies such as tetralogy of Fallot, transposition of the great arteries and double outlet right ventricle.

The most common form of the disease is valvular pulmonary stenosis, in which the obstruction lies within the valve itself. Here the leaflets are thickened and rigid and are deformed and fused to one another, giving the valve a domed appearance. As a result, the valve cannot open completely during right ventricular systole, and the right ventricle has to work at a higher pressure and with greater force.

Beyond the neonatal period, valvular pulmonary stenosis frequently remains asymptomatic in children unless it is severe. By adulthood, the increase in right ventricular muscle mass and dysfunction of the right ventricular myocardium may give rise to dyspnoea, dizziness and syncopal episodes. In milder stenosis, the only finding may be a murmur heard on auscultation over the pulmonic area. In adults, conditions that increase volume overload, pregnancy in particular, may unmask or aggravate signs and symptoms. In some patients with valvular pulmonary stenosis the valve is dysplastic, a form encountered particularly in Noonan syndrome.

In the less common subvalvular form of pulmonary stenosis, a tube-like narrowing lies beneath the valve, in the region known as the infundibulum, due to an increase in muscle mass. In the supravalvular form, the narrowing may lie in the mid-portion of the pulmonary artery, at the bifurcation or in the distal branches. The supravalvular form may occur in certain specific syndromes (Alagille syndrome, Williams syndrome) and as a consequence of congenital rubella infection.

The severity of pulmonary stenosis is graded from the pressure difference (gradient) between the right ventricle and the pulmonary artery. In mild to moderate pulmonary stenosis the right ventricular pressure remains lower than the left ventricular pressure, whereas in severe pulmonary stenosis it rises considerably and may exceed the left ventricular pressure. When a septal defect such as an atrial septal defect is present in a patient with severe pulmonary stenosis, cyanosis may develop as deoxygenated blood mixes with oxygenated blood.

Treatment of pulmonary stenosis is determined by the level and the severity of the obstruction and by the presence or absence of other associated congenital anomalies. In valvular pulmonary stenosis, where the obstruction lies within the valve itself, the recommended first-line treatment is percutaneous balloon pulmonary valvuloplasty, that is, dilatation of the pulmonary valve with a balloon without open surgery; in the other forms, open surgical techniques may be used according to the severity of the disease.

How is pulmonary valve stenosis diagnosed?

Pulmonary valve stenosis is readily diagnosed today with the advanced ultrasound systems used in echocardiography. Transthoracic echocardiography (TTE), performed simply by placing an ultrasound probe on the anterior chest wall, demonstrates the structure of the pulmonary valve and shows whether the valve is domed or dysplastic. The severity of the obstruction is then graded by calculating the pressure gradient with Doppler, and the diagnosis is usually established by measuring the gradient across the valve with continuous-wave Doppler echocardiography.

Once pulmonary stenosis has been diagnosed, transoesophageal echocardiography (TEE) is performed: the patient swallows a probe, which is then positioned in the oesophagus. TEE readily defines the severity of the stenosis, shows whether accompanying regurgitation is present, and confirms whether the valve is domed or dysplastic. If balloon treatment is planned, TEE also allows the diameter of the pulmonary annulus to be measured precisely. In addition to two-dimensional TEE, three-dimensional echocardiography, which displays valve structure particularly clearly, allows the presence and the severity of the stenosis to be assessed with ease. Echocardiography is therefore a highly useful tool both in diagnosing pulmonary stenosis and in planning its treatment. In our clinic, TTE together with two-dimensional and three-dimensional TEE is performed in all patients with suspected pulmonary stenosis.