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a Chapter 33 Doppler Echocardiography for Managing Congenital Cardiac Disease 489
Fig. 33.2. Fetal Doppler echocardiographic examination of
tetralogy of Fallot and aneurysmal dilatation of the main
pulmonary artery. The large echo-free space present on
the left of the aorta on real-time two-dimensional examination
(left) was demonstrated by pulsed Doppler to be vascular
in nature, as pulsatile flow similar to that obtained in
the pulmonary artery could be demonstrated within it
(right). This Doppler finding helped to make a confident
diagnosis of aneruysmal dilatation of the main pulmonary
artery. Arrow indicates the location of the Doppler sample
volume. A aorta, B Doppler baseline, F Doppler waveforms,
L left branch of the pulmonary artery, RV right ventricle.
(Reprinted from [12] with permission)
of the heart. Thus the diagnosis of tricuspid atresia
may be facilitated by color Doppler insonation demonstrating
no recognizable flow across the tricuspid
orifice [13].
2. Presence of flow in unexpected locations. Visualizing
flow in an expected or an unexpected vascular location
may significantly enhance our ability to identify
and define congenital cardiac lesions. Identifying the
presence of flow in an expected location may be helpful
for establishing structural integrity when the imaging
appearance is uncertain. The color or spectral Doppler
recognition of flow in an unexpected location may, on
the other hand, assist in diagnosing a malformation.
For example, the demonstration of spectral Doppler
flow patterns in a large echo-lucent area adjacent to
the aorta helped us to make the prenatal diagnosis of
pulmonary arterial aneurysm [2] (Fig. 33.2). Similarly,
demonstration of a flow jet across the interventricular
septum indicates a septal defect. It should be noted,
however, that large defects may be recognizable by
imaging alone without the added benefit of color Doppler
flow depiction, whereas small defects may not be
recognizable even by color flow mapping unless there
is a demonstrable flow jet through the septal defect.
As the right and left ventricular intracavitary pressures
are approximately equal in the fetus, there is no flow
across the defect unless there are additional malformations,
such as outflow tract stenosis altering the interventricular
pressure equilibrium. The presence of a
flow jet across a ventricular septal defect (VSD) therefore
should alert the observer about the existence of additional
cardiac lesions. Although atrial septal defects
(ASDs) are more difficult to recognize in the fetus, large
defects are easily identifiable by the clear demonstration
of confluence of flow between the two atria without
a visible intervening septal structure (see below).
3. Abnormal flow direction. Spectral Doppler depiction
of directionality of flow offers a unique opportunity
to detect abnormal cardiac hemodynamics. Demonstration
of aberrant flow patterns, such as regurgitant
flow across a valvular orifice or abnormal flow direction
in a vessel, significantly enhances our ability to
define fetal cardiac lesions (Fig. 33.3). Atrioventricular
regurgitant flow has been identified using spectral and
color Doppler [2, 7, 27]. Isolated semilunar valve incompetence
of the pulmonary trunk or the aorta is rare
and is often difficult to detect, even when present in association
with other cardiac anomalies.
Doppler echocardiography can significantly assist
in assessing the severity of valvular incompetence.
Several approaches have been described in relation to
pediatric and adult echocardiographic applications.
They include assessment of: (1) the duration of the
regurgitant flow in relation to the cardiac cycle; (2)
the magnitude of the length of the regurgitant jet into
the atrial cavity as measured by pulsed-wave Doppler
interrogation; and (3) measurement of the regurgitant
jet as a proportion of the area of the atrial cavity.
If the regurgitant flow is minimal and occupies
only a fraction of the total duration of the cardiac cycle,
it may be considered relatively benign in the absence
of associated cardiac anomalies. Pansystolic