Pulmonary stenosis
The prevalence of pulmonary stenosis (PS) is estimated to be 6-8 in 10.000 live births, accounting for 8–10 % of CHDs54-56. Stenosis of the RVOT was first introduced in medical literature by Giovanni B. Morgagni in 176157,58 and represents the most common cause of congenital outflow tract obstruction and the second most common CHD postnatally. PS causes a decrease of blood flow from the right ventricle to the pulmonary arteries, subsequently resulting in elevations of right ventricular and pulmonary arterial (proximal to the stenosis) systolic pressure that depend on the severity and distribution of the stenotic part. The level of stenosis may be infravalvular (infundibular), supravalvular or, most frequently, valvular (in 80 % to 90 % of cases due to fusion of the valve commissures). In moderate forms of pulmonary stenosis, the RV morphology can be normal and might escape prenatal diagnosis. In those cases, an increase in flow velocity across the valve is usually the only diagnostic hint. Early diagnosis of PS might be cumbersome because of the diverse spectrum and different course throughout pregnancy54. In the absence of RV hypertrophy (decrease in ventricular diastolic compliance and end-diastolic volume), the peak velocity is correlated with the severity of RVOTO59. The fetus in figure 3 had moderate cardiomegaly on conventional two-dimensional ultrasound (2DUS), and Doppler interrogation showed turbulent flow across the pulmonary valve and a concomitant tricuspid insufficiency with > 3 m/s. Standardized analysis using FINE clearly demonstrated moderate cardiomegaly and a narrow RVOT with thickened doming valvular tissue.
A recent cohort study on neonatal outcomes and the need for postnatal pulmonary valvuloplasty revealed that fetuses with mild-to-moderate PS had increased right cardiac output and signs of diastolic dysfunction with a higher ductus venosus pulsatility index. Fetuses that needed cardiac intervention were found to have significantly smaller and more hypertrophic RVs and pulmonary valve diameters and reduced tricuspid annular-plane systolic excursion (TAPSE)56. Mild-to-moderate cases of PS carry a favorable prognosis. Nevertheless, the thin wall of the RV makes it sensitive to alterations in the pulmonary artery pressure. With ongoing pregnancy, PS may worsen and result in severe PS (figure 4) that may even progress to pulmonary atresia. Due to the chronic increase in afterload, the RV dilates and develops muscular hypertrophy60. The tricuspid annulus might also dilate, causing severe tricuspid regurgitation (as shown in figure 4), which may subsequently lead to severe right heart failure.