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.