Revista Română de Anatomie funcțională și clinică, macro- și microscopică și de AntropologieVol. XV Nr. 2 2016 CLINICAL ANATOMY [625430]

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Revista Română de Anatomie funcțională și clinică, macro- și microscopică și de AntropologieVol. XV – Nr. 2 – 2016 CLINICAL ANATOMY
THE EMBRYOLOGYCAL FEATURES OF ATRIOVENTRICULAR
SEPTAL DEFECT DIAGNOSED IN THE FETAL LIFE
Raluca Tulin1, S. Oprea1, C. Pantu1, R. Stanciulescu1, B. Andrei2, R.C. Jecan3,
Cezarina V oichitoiu4, A. Tulin1, A. V oichitoiu5
“Carol Davila” University of Medicine and Pharmacy, Bucharest
Faculty of General Medicine
1. Department of Anatomy
2. Department of Orthopedics
5. Department of Obstetrics and Gynecology
3. “Prof. Dr. Agrippa Ionescu” Clinical Emergency Hospital, Bucharest
Department of Plastic and Reconstructive Surgery
4. Ambulatory and Preventive Medicine, Bucharest
Diagnostic and Treatment Medical Center
THE EMBRYOLOGYCAL FEATURES OF ATRIOVENTRICULAR SEPTAL DEFECT DIAG –
NOSED IN THE FETAL LIFE (Abstract): The term “atrioventricular septal defect” (A VSD)
covers a wide spectrum of heart abnormalities characterised by a common atrioventricular junction
coexisting with abnormal atrioventricular septation. In ostium primum atrial septal defect (ASD)
there are separate atrioventricular orifices despite a common valvar junction, while in complete
A VSD the valve itself is also common. This paper focuses on the anatomy, embryology, and imag –
ing of common atrioventricular (A V) canal using imagines from a case of complete atrioventricu –
lar canal. Common A V canal may be non-syndromic or syndromic. The syndromic including Down
syndrome and the heterotaxy syndromes associated with asplenia and polysplenia. There are sta –
tistically highly significant differences between Down and non-Down canals, and between as –
plenic and polysplenic canals. In humans, the anterior (anterior) and dorsal (inferior) endocardial
cushions of the A V canal normally fuse during 34–36 days of fetal life (5th week of fetal life). An
understanding of the fusion of endocardial cushions of the A V canal relative to the ventricular and
atrial septums helps to explain normal and abnormal development and the classification of A VSD.
This malformation is diagnosed in the fetal life but it becomes symptomatic in infancy due to
congestive heart failure and failure to develop normally. Diagnosis of A VSD can be suspected from
electrocardiographic and chest X-ray findings. Echocardiography confirms it and gives anatomical
details. Over time, pulmonary hypertension becomes irreversible, thus precluding the surgical
therapy. Medical treatment (digitalis, diuretics and dilators) plays a role only until the moment of
surgery, usually performed between the 3rd and 6th month of life. Key-words : ATRIOVENTRIC –
ULAR SEPTAL DEFECT, ATRIOVENTRICULAR CANAL, ATRIOVENTRICULAR V AL VES
INTRO DUCTION
A VSD is a complex cardiac abnormalities
characterised by a variable deficiency of the
atrioventricular area (crux cordis) in the devel –
oping heart. The malformations involve the
atrial, ventricular and atrioventricular septum
and both atrioventricular valves (mitral/bicus –
pid and tricuspid).
A VSD is an uncommon congenital heart dis –
ease, accounting for ab out only 3% of cardiac malformatio ns. It occurs in two out of every
10,000 live births. Both sexes are equally af –
fected but there is a strong association with
Down’s syndrome.
Echocardiography is the key tool for the
diagnosis and anatomic classification of this mal –
formation. It shows the ostium primum atrial
septal defect (ASD), with the underlying com –
mon atrioventricular valve, and the defect of
the ventricul ar septal inflow.

268
Raluca Tulin et al.EMBR YOLOGY
Septation of the atrioventricular junction is
brought about by downgrowth of the atrial sep –
tum primum, fusion of the endocardial cushions
and forward expansion of the vestibular spine
between atrial septum and cushions (1).
Thus, atrioventricular canal can result from
arrest or interruption of the normal endocar –
dial cushion development (2, 3).
The experimental studies showed that tera –
togenic factors or even endogenous metabolic
factors can result in abnormal development of
the atrioventricular region, which may be due
to altered apoptosis (4, 5, 6).
The previous studies showed that A VSD tends
to be associated with chromosomal abnormali –
ties, mainly Down syndrome, del (8p) syndrome,
trisomy 9, trisomy 18 (Edwards syndrome) (7, 8).
A VSD with Down syndrome has been less
frequently associated with left cardiac anoma –
lies than the isolated form (9, 10).
In isolated form the analysis of potential risk
factors showed a strong association with mater –
nal diabetes and antitussive drugs (1 1).
In patients with Down syndrome and A VSD
there is a strong association with maternal age.
In the asplenia syndrome, the A VSD is always
present, while it occurs in about 25% of pa –
tients with polisplenia (12).
Defects of A VSD can be either complete or
partial (fig. 1).
1. A Complete Atrio V entricular Canal (CA VC)
consists of a ventricular septal defect (VSD),
an ostium primum atrial septal defect (ASD),
and a single A V valve (A VV).
2. Partial Atrio V entricular Canal (P A VC) has
an ostium primum ASD, two separate A VV
orifices, and cleft present in the anterior
left-sided A VV .
The complete form is sub classified as Ras –
telli types A, B, and C.
Rastelli anatomical classification was based
on the relationships of the anterior bridging
leaflets to the crest of the ventricular septum
or right ventricle (RV) papillary muscles.
Type A : the superior bridging leaflet is
almost completely adherent to the left ventricle
and is firmly attached on the ventricular septum
by multiple chordal insertions
Type B : the superior bridging leaflet is at –
tached over the ventricular septum by an anom –
alous papillary muscle of the right ventricle
Type C: the superior bridging leaflet is not attached to the ventricular septum (free-floating
leaflet)
An echocardiographic examination shows the
degree of dysfunction of the common atrioven –
tricular valve, as well as the presence of associ –
ated cardiac malformations. To date, cardiac
catheterisation is not considered as mandatory
for the diagnosis, but can be indicated in pa –
tients older than 6 months (postnatal) with sus –
pected irreversible pulmonary hypertension.
Cardiac catheterisation allows accurate quanti –
fication of the left-to-right shunt as well as
assessment of the degree of pulmonary hyper –
tension and the reversibility of the pulmonary
artery resistances.
The main characteristic of an A VSD is the
presence of a common atrioventricular junc –
tion as compared to the separate right and left
atrioventricular junction in the normal heart.
Other morphological features include:
1. Defects of the muscular and membranous
atrioventricular septum and
2. An ovoid shape of the common atrioven –
tricular junction with moving of the left ven –
tricular outflow tract from the place between
the tricuspid and bicuspid valve.
There is disproportion of outlet and inlet
dimensions of the left ventricle, with the outlet
greater than the inlet as compared to the normal
heart where both dimensions are similar.
The valve leaflet morphology in A VSD bears
little resemblance to the arrangement of the
leaflets of normal mitral and tricuspid valves.
There are essentially five leaflets, two of which
are bridging across the crest of the interven –
tricular septum. In complete A VSD there is a
space between the bridging leaflets and the
atrioventricular valvar orifice is common.
Over the past fifty years the management of
the complete form has evolved to primary re –
pair in early infancy to prevent the development
of pulmonary hypertension. The improved prog –
nosis for patients with Down’s syndrome and
A VSD has implications for the management of
patients diagnosed in the fetal life. The postna –
tal and long term outcomes are influenced by
the presence of associated defects (usually ven –
tricular hypoplasia).
In most patients with A VSD the right and
left components of the common atrioventricular
junction are comparable and the ventricles are
similarly sized (balanced A VSD). In a mi nority

269
The Embryologycal Features of Atrioventricular Septal Defect Diagnosed in The Fetal Lifeof cases the common atrioventricular junction
is committed to the ri ght or left ventricle lead –
ing to right or left ventricular dominance and
relative hypoplasia of the opposing ventricular
chamber. The reported incidence of the combi –
nation of A VSD and Tetralogy of Fallot is 5%
of all patients with A VSD. The combination is
more common in patients with Down’s syn –
drome whereas most other associated lesions
complicating A VSD are more common in pa –
tients without Down’s syndrome. Complex
forms of A VSD are found in the majority of
hearts with right atrial isomerism and in around
half with left atrial isomerism (9).
FETAL DIAGNOSIS
The view of the heart most commonly used
in routine antenatal ultrasound scanning is the
four-chamber view. A VSD is one of the lesions
potentially detectable on this view.
The key diagnostic feature on the four-
chamber view of the heart is the presence of a
common atrioventricular valve. In a good four-
chamber view the defects in the atrial and ven –
tricular septum should also be visible (fig. 2
and 3).
In utero detection rates of A VSD remain
lower than might be expected. In one UK study
of 92 consecutive live born infants with A VSD,
only 29% were detected by routine obstetric
ultrasound (13).
The spectrum of A VSD in fetal life is dif –
ferent from that diagnosed postnatal. Up to
45% of those diagnosed in utero may have as –
sociated heterotaxy syndromes, particularly left
atrial isomerism (14).
Fetal echocardiography in cases of A VSD
therefore should include determination of atri -al sites, ventriculoatrial connections, ventricu –
lar siz e and aortic arch caliber. The detection
of these associated abnormalities is very impor –
tant so that when counseling parents an accurate
indication of outcome can be given. The mor –
tality is higher in those with other associated
cardiac abnormalities; especially in the com –
bination of left atrial isomerism has a very poor
prognosis with a frequent abortion. In utero
diagnosis of this lesion is important due to the
strong association with chromosomal abnor –
malities, especially Down syndrome (trisomy
21). Abnormal karyotype is more common in
isolated A VSD (48–58%) (15).
PROGNOSIS
Half of children with untreated A VSD die in
the first year of life (16-18).
The main cause of death in infancy is either
heart failure or pneumonia. In surviving pa –
tients with unrepaired complete atrioventricular
canal, irreversible pulmonary vascular disease
becomes increasingly common and affects all
patients older than 2 years of age. Long-term
prognosis in patients with irreversible pulmo –
nary hypertension is poor (19).
CONCLUSION
Due to the strict association with Down syn –
drome and other chromosomal anomalies, ge –
netic antenatal counseling after the fetal echo –
cardiographic diagnosis of A VSD is mandatory.
At present, prenatal diagnosis of A VSD has
been associated with a 58% risk of aneuploidy,
mainly trisomy 21. Due to the strong associa –
tion between chromosomal abnormalities and
A VSD, when this malformation seems isolated
at antenatal echocardiography, the risk of tri –
Fig. 1. AL- Anterior leaflet; PL- Posterior Leaflet; MV- Mitral V alve; TV- Tricuspid V alve;
Lt A VV – Left Atrio V entricular V alve; Rt A VV – Right Atrio V entricular V alve;
IVS- Inter V entricular Septum

270
Raluca Tulin et al.somy 21 is significantly higher than when oth –
er associated cardiac lesions are diagnosed.
A VSD is a defect with great variability in the
anatomic patterns and heterogeneity of causes
also in the subset without Down syndrome and
without heterotaxy. Early diagnosis of A VSD is
important in order to institute appropriate med -ical and supportive treatment and to plan time –
ly surgical intervention. In the current era the
operative mortality is low with a good long
term outlook for most patients, with or without
Down’s syndrome.
Fig. 2. Fetal cardiac ultrasound at 26 weeks’
gestation (four-chamber view) demonstrating
complete A VSD with a large hole in the middle
of the heart and the absence of the crux
of the heart.
Fig. 3. Fetal car diac ultrasound at 26 weeks
gestation demonstrating complete A VSD with a
common atrioventricular valve and large atrial and
ventricular septal defects. There is a not a
differential insertion of the A-V valves
(linear insertion). V entricles are similarly sized
(balanc ed A VSD).
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