Absent pulmonary valve syndrome
Absent pulmonary valve syndrome (APVS) is characterized by the
combination of an absent or hypoplastic pulmonary valve, stenosis of the
pulmonary valve annulus, and aneurysmal dilatation of the pulmonary
trunk and its branches. APVS accounts for 10-20 % of all ToF cases
prenatally, whereas the incidence in postnatal series is estimated to be
significantly lower, ranging between 3 to 6 % of all ToF cases and 0.2
to 0.4 % of all CHDs. It was first described by J. Crampton during an
autopsy of a 10-year-old boy who died from a severe heart failure in
183092. This case was further delineated by N. Chevers
in 184693,94.
According to current literature, this lesion is categorized into three
subtypes: (I) the predominant type with an absent pulmonary valve, a
ventricular septal defect and an overriding ascending aorta. It is
considered an extreme variant of tetralogy of Fallot (Fallot type APVS;
ToFAPV), also referred to as Miller-Lev-Paul syndrome in postnatal
series95. In the vast majority of cases, the ductus
arteriosus (DA) is absent. In addition, two very rare variants including
(II) APVS with an intact ventricular septum (IVS) and a patent DA
(non-Fallot type APVS) and (III) APVS with an intact ventricular septum
and concomitant tricuspid atresia have been described to date. There is
a reported association of ToFAPV with a microdeletion of 22q11.2 (21-25
%) and trisomy 13 and 1896,97. In two recent larger
prenatal series that both included first trimester cases, the incidence
of ToFAPV was up to 6 times higher than that of APV and IVS (83.1-92.5
% vs. 7.5-16.9 %)98,99. Notably, all fetuses
diagnosed in early pregnancy had a patent DA, and none of them survived
beyond 24 gestational weeks due to progressive hydrops or other lethal
conditions, which is in line with prior reports. Berg et al.
hypothesized that agenesis of the ductus arteriosus is essential for
primary fetal survival in fetuses with TOF and APVS; otherwise, the
enormous diastolic volume overload caused by the regurgitant flow from
the aorta through the patent arterial duct will subsequently lead to
early intrauterine demise100. Dilated main and branch
pulmonary arteries might result from elevated pressure and volume
loading rather than from connective tissue defects and can exert
pressure on the surrounding respiratory system (potentially causing
obstructive emphysema, atelectasis and
tracheobronchomalacia101). However, the real clinical
impact of these findings is not fully understood nor are there
significant predictors of neonatal respiratory distress as
quantification of echocardiographic variables, including the pulmonary
valve annulus, right pulmonary artery diameter and cardiomegaly, were
not linked with an unfavorable outcome99.
Figure 8 shows the above discussed hallmarks of APVS in a fetus at 27
weeks as a marked leftward rotation of the cardiac axis, as recently
reported in the study by Axt-Fliedner et al. (88 % abnormal cardiac
axis)98. The DA is apparently absent, but, most
obviously, there is huge bulging of the main and branching pulmonary
arteries. The proximity to vascular and tracheal structures is clearly
depicted. The value of conventional 3D reconstruction with color doppler
interrogation has previously been shown102. However,
to capture the entire pathology of APVS, a detailed reconstruction of
all 9 planes using FINE technology that gives an excellent overview of
the malformed anatomy is helpful.