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.