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The VSD is the most frequently occurring congenital
cardiac lesion, accounting for about one-third of all
cardiovascular malformations [36]. An isolated VSD
carries an excellent prognosis, and most VSDs close
spontaneously within 5 years of life [37]. Prenatal diagnosis
of the defect depends on the size of the defect
and the presence of associated cardiac malformations
causing hemodynamic disturbance. However,
isolated VSDs of moderate or small size may not be
easily recognizable during Doppler echocardiographic
examination, as they are not associated with detecta
Chapter 33 Doppler Echocardiography for Managing Congenital Cardiac Disease 493
Fig. 33.9. Color Doppler depiction of an ostium secundum
atrial septal defect. It is noteworthy that the condition may
not be distinguishable from physiologic flow through the
foramen ovale
Atrial, Atrioventricular,
and Ventricular Anomalies
Atrial Septal Defects
Recognition of defects in the interatrial septum is challenging
as physiologic flow exists across the foramen
ovale, the septum is less echogenic than the interventricular
septum, and the valve of the foramen ovale is not
always recognizable. The ASD may be located (1) in the
fossa ovalis in the central septum, where it is known as
an ostium secundum defect; (2) in the upper septum,
where it is known as a sinus venosus defect, often associated
with anomalous venous return; and (3) in the
posterior septum, where it is known as an inferior vena
caval defect. Of the three, the ostium secundum defect
is the most common and the inferior vena caval defect
the least common. It is difficult to identify an ASD unless
the deficiency is a large one. Figure 33.9 shows a
large ostium secundum defect that was almost indistinguishable
from the normal foramen ovale, except the
valve of the foramen could not be seen even with careful
high-resolution imaging.
Atrioventricular Septal Defect
In contrast to the deficiencies of the ASD, defects involving
the atrioventricular septum (AVSDs) are more
easily identifiable in the fetus because of their large size
and associated structural and hemodynamic anomalies.
Variously known as A-V canal defect, endocardial
cushion defect, and ostium primum defect, the AVSD is
characterized by complete absence of the interatrial
septum and the presence of a common A-V orifice
(Fig. 33.10). The A-V flow direction is regulated by a
five-leaflet valve. Occasionally there are two A-V orifices
separated by a straddling A-V valve, known as
Fig. 33.10. Color flow depiction of atrioventricular septal
defect. The image is a two-dimensional frame from a realtime
three-dimensional duplex color flow image. Note the
flow across the ventricular septal defect (horizontal arrow).
The interatrial septum is absent and the flow in the common
atrial cavity is turbulent. External simulated fetal heart
rate gating (G) was used to combine the sub-volumes. RV
right ventricle, LV left ventricle, IVS interventricular septum,
CA common atrium, CAVV common atrioventricular valve
the double-outlet atrium. AVSD variations exist in
which the malalignment of the septum may lead to
right or left atrial outflow obstruction. Hemodynamic
abnormalities associated with AVSD may be recognizable
by prenatal Doppler echocardiographic examination.
Of specific relevance is the A-V flow regurgitation
caused by the valvular incompetence. The condition
has a high association with trisomy 21: Approximately
80% of infants with AVSD have trisomy 21 and approximately
40% of infants with Down syndrome suffer from
AVSD [35]. Therefore when fetal echocardiographic examination
leads to the prenatal diagnosis of AVSD, fetal
karyotyping should be offered.
Ventricular Septal Defect