Diagnostic ultrasound ( PDFDrive )

CHAPTER 37 The Fetal Heart 1275
Placenta
Ductus
arteriosus
Foramen
ovale
Ductus
venosus
Umbilical
vein
Umbilical
arteries
FIG. 37.2 Diagram of Fetal Shunts. Blood from the umbilical vein
is shunted through the ductus venosus to the right atrium and then
across the foramen ovale to the left atrium. Fetal cardiac output from
the right side of the heart is shunted to the descending aorta through
the ductus arteriosus.
demonstrates four cardiac chambers. Four-chamber views
can be obtained with the angle of insonation parallel to the
interventricular septum (apical four-chamber view; Fig. 37.5A,
Video 37.1) or perpendicular to the septum (subcostal fourchamber
view; Fig. 37.5B, Video 37.2). In a four-chamber view
the echogenic foraminal lap of the foramen ovale can be observed
moving into the let atrium. he two superior pulmonary veins
may be seen entering the spherical let atrium. he atrioventricular
valves are visible in the four-chamber view. he septal
lealet of the tricuspid valve inserts slightly more apically on the
interventricular septum than the anterior lealet of the mitral
valve. he let ventricle has a relatively smooth inner wall, and
a more elongated shape than the right ventricle. In the normal
heart, the let ventricle is the apex forming ventricle. he internal
surface of the right ventricle is coarse, particularly near the apex,
where the moderator band of the trabecula septomarginalis
is frequently recognized as a small, brightly echogenic focus.
his helps identify the morphologic right ventricle.
From the subcostal four-chamber view, angling the transducer
toward the fetus’s right shoulder permits evaluation of the continuity
of the let ventricle with the ascending aorta (Fig. 37.6). Further
angulation in the same direction shows the right ventricle in
continuity with the pulmonary artery (Fig. 37.7, Videos 37.3
and 37.4). he diameter of the pulmonary artery is approximately
9% larger than that of the aorta between 14 and 42 weeks. he
measured diferences in these vessels and with M-mode versus
two-dimensional (2-D) imaging are negligible (2%-5%) for both
the pulmonary artery and the aorta. 35 Further rightward rotation
produces a sagittal view of the fetal thorax and a short-axis view
of the ventricles (Fig. 37.8, Video 37.5). Angulation toward the
let fetal shoulder from this view shows the aorta as a central
circle, with the pulmonary artery draping anteriorly and to the
let (Fig. 37.9).
he apical four-chamber view may also be used as a starting
point when evaluating normal cardiac anatomy. Yagel and colleagues
36 described a series of planes arising from the apical
four-chamber view, all accomplished by moving the transducer
in a cephalad direction. A slight cephalad advancement will show
an apical ive-chamber view, which is useful in assessing continuity
of the ascending aorta with the let ventricle (Fig. 37.10).
Continued cephalad movement should result in visualization of
the bifurcating pulmonary artery and its relationship to the right
ventricle. A three-vessel and trachea view should be visualized
next (Fig. 37.11, Video 37.6). his view allows evaluation of
the main pulmonary artery–ductus arteriosus conluence, the
transverse aortic arch, and the SVC. Comparison of vessel size,
conirmation of vessel presence, and determination of blood
low direction with color Doppler can all be accomplished at
this level. In addition, appropriate location of both great vessels
to the let of the trachea can be conirmed. 36 Returning to a
sagittal plane of the fetus, directing the transducer from the fetal
let shoulder to the right hemithorax demonstrates the distinctive
candy-cane shape of the aortic arch (Fig. 37.12, Videos 37.7 and
37.8). he three major vessels to the head and neck and the
ductus arteriosus may be seen. he aortic arch should not be
confused with the ductal arch (Fig. 37.13), which is formed by
the right ventricular outlow tract, pulmonary artery, and ductus
arteriosus. he ductal arch is broader and latter than the aortic
arch. Lastly, sliding the transducer to the right while maintaining
a sagittal plane on the fetus should allow visualization of the
IVC and SVC entering the right atrium.
M-mode echocardiography provides a 2-D image of motion
over time. It is useful in evaluating heart rate, chamber size, wall
thickness, and wall motion (Fig. 37.14). Simultaneous M-mode
imaging through an atrium and ventricle is helpful in analyzing
arrhythmias (Fig. 37.15). Chamber size and function should be
evaluated at the level of the atrioventricular (A-V) valves. 37
Spectral Doppler ultrasound evaluation of the fetal heart
can be used to determine the velocity of low through the vessels
or valves (Fig. 37.16) and to evaluate regurgitant low through
the valves of the heart (Fig. 37.17). Variation in low velocity
may relect structural or functional cardiac abnormalities. For
example, a stenotic A-V valve will be associated with an abnormal
low pattern through the afected valve. Spectral Doppler ultrasound
is useful in assessing the functional signiicance of structural
abnormalities and arrhythmias.
Color Doppler ultrasound permits a rapid interrogation of
low patterns within the heart and great vessels (Fig. 37.18),
allowing functional and structural abnormalities to be more
rapidly characterized. For example, valvular stenosis is clearly
demonstrated with color Doppler ultrasound, as is reversed low
through insuicient valves or in the great vessels. Color Doppler
ultrasound oten reduces the amount of time required for spectral