2. DISCUSSION
APVS is a rare congenital heart disease (CHD) with an incidence of
0.2%–0.4% in all live birth with CHD,characterized by absent or
severe dysplasia of pulmonary valve
leaflets[1-3].
APVS is commonly classified into two types: The majority of APVS fetuses
is accompanied with TOF, so defined as TOF-type APVS; the minority is
absent from VSD, defined as non-TOF-type APVS[3,4]. TOF-type APVS usually got stenosis of
pulmonary valve annulus, post-narrow expansion of PA and absent PDA in
the previous studies. The inflation of PA trunk and RPA may compress the
airway to collapse and softening, which leads to respiratory distress
and heart failure in neonatal period. The clinical manifestations are
critical, coupled with extracardiac malformations and / or chromosomal
abnormalities, the overall prognosis is poor. Non-TOF-type APVS is
commonly associated with intact ventricular septum, tricuspid valve
atresia or hypoplasia and PDA. The PA trunk usually does not expand, but
shows hypoplasia, which proceeds to the immaturity of vessel and tissues
in lung. The total mortality of APVS was 75%, including intrauterine
death and postnatal death, only 25% were alive after postnatal surgery;
therefore, prenatal diagnosis of APVS is significant[3]. Although the postoperative survival rate has
improved in recent years, the heart surgery is still complicated.
Sometimes heart transplantation is required in emergency[5]. So early diagnosis of APVS in utero is
meaningful.
Most
TOF-type APVS fetuses are
diagnosed after 20 weeks of gestation by echocardiography. Except for
positive grayscale images, Color doppler flow imaging (CDFI) shows color
mosaic to-and-from blood flow in PA. Spectrum Doppler shows high-speed
blood flow antegrade and retrograde in PA. In this study, based on the
high resolution of ultrasound, APVS was suspected at 13 weeks of
gestation by a skilled sonographer in the first trimester screening, and
was confirmed 7 days later. Two weeks later, fetal echocardiography was
performed again. In the last two checks, PA and PDA were found with
obvious morphological change,which might be helpful in the study of
mechanism and development of TOF-type APVS in early middle pregnancy.
In the past, absence of PDA has always been considered in company with
dilation of PA in fetus with TOF-type APVS, because the insufficient
pulmonary systemic shunt aggravated volume load of RV caused by
to-and-from blood flow in PA [6,7]. However, such
claims are practically based on the discoveries of TOF-type APVS after
20 weeks of gestation. The process and pathogenesis before 20 weeks were
unclear with controversies in correlation between PA dilatation and PDA
absence. In the present case at 14 weeks of gestation, the diameter of
PDA was wide with unobstructed bidirectional shunt. PA expansion was not
distinct. At 16 weeks of gestation, there was PA expansion without PDA
absence, which was obviously inconsistent with previous study. The
restriction of PDA might be associated with the dilation of PA trunk and
PA branches, which leaded to the decrease of blood flow volume through
PDA. It advocated the controversial hypothesis that APVS with TOF leads
to depressed diastolic pressure of immature PDA and ultimately result in
the restriction or closure at an early gestational
age [8]. It
suggested the dynamic pathological change of PDA in TOF-type APVS fetus
in early middle pregnancy. If the fetus developed further in utero,
disuse atrophy or atresia of PDA might occur in the future. In addition,
it has been reported that several fetuses
with TOF-type APVS had constricted
PDA after 20 weeks of gestation. It also confirmed that the absence of
PDA is not inevitable for the existence of
TOF-type APVS. It further proves
the rationality of the inference in this study.
APVS may be associated with fetal chromosomal abnormalities, among which
22q11 microdeletions, 13 trisomy and 18 trisomy are most common[9]. It is suggested that 70% of TOF-type APVS
were associated with karyotype abnormality. In this case, 984.766kb
deletion was detected at 20p12.2 by chromosome microarray analysis
(CMA). JAG1 gene in this fragment is in autosomal dominant inheritance,
and the deletion is related to TOF and Alagille syndrome. The parents of
the fetus were in good health without genetic defects and the deletion
of JAG1 gene in fetus was thought to be caused by gene mutation and lead
to poor prognosis.
TOF-type APVS is combined with cardiac extracardiac malformations
sometimes which is independent influencing factor of prognosis. In this
case, a left renal cyst was found which might be sign of cystic
dysplasia of kidney.
In this case, the pregnancy was terminated. Fetal autopsy confirmed the
ultrasound diagnosis.