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a Chapter 32 Introduction to Fetal Doppler Echocardiography 479
Pulmonary and Aortic Outflows
The right and left ventricular outflow can be imaged in
the ventricular long-axis plane (Fig. 32.25). This plane
allows clear assessment of the aortic-pulmonary crossover
relation (Fig. 32.26). Color flow imaging facilitates
recognition of this important normal characteristic of
the heart. The main pulmonary arterial flow can be
conveniently seen in the parasternal short-axis plane
at the base of the heart, which demonstrates the aortic
cross section surrounded by the right atrium, right
ventricle and pulmonary trunk, and right pulmonary
Fig. 32.28. Color Doppler echocardiogram of the ductal
arch. Note the wider curve of the arch and color aliasing at
the ductal level. DA ductus arteriosus, PA pulmonary artery,
RV right ventricle, S fetal spine
Fig. 32.26. Color Doppler imaging of the cross over relation
between the origins of the great arteries. SP fetal
spine, LV left ventricle, RV right ventricle, IVS interventricular
septum, RVOT right ventricular outflow, LVOT left ventricular
outflow
Fig. 32.27. Color Doppler echocardiogram of the aortic
arch. Note the tighter curve of the arch and the change in
the color depiction of flow, reflecting the changes in the
flow direction in relation to the transducer. The curved arrow
indicates flow direction at the root of the aorta. Vertical
arrow indicates root of aorta. AA aortic arch, LV left ventricle,
DTA descending thoracic aorta
artery. The orientation of the main pulmonary artery
in this plane often facilitates alignment of the Doppler
beam along the pulmonary blood flow axis, ensuring an
optimal angle of insonation. Aortic and pulmonary arterial
hemodynamics can also be readily investigated in
the aortic arch (Fig. 32.27) and ductal arch (Fig. 32.28)
planes, respectively. Doppler frequency shift waveforms
from the main pulmonary artery are characterized by
rapidly accelerating and decelerating slopes, with sharp
peaks during right ventricular systole (Fig. 32.29). In
comparison with the maximal aortic velocity wave,
however, the immediate postpeak deceleration slope
is less acute in the pulmonary waveform. The peak velocity
values from the pulmonary artery and the aorta,
measured longitudinally in 27 normal pregnancies
from 18 weeks to term, are presented in Table 32.4
(D. Maulik and P. Ciston, unpublished data).
In a longitudinal study, Rizzo et al. [31] showed
significant increases in the pulmonic peak velocity
(p£0.001) and in the aortic peak velocity (p£0.05)
during early pregnancy between the end of the first
trimester (11±13 weeks) and midgestation (20 weeks).
Hata et al. [32] performed a cross-sectional investigation
of 54 normal fetuses at 16±40 weeks of pregnancy
and noted increases in transpulmonic peak
velocity (r = 0.39, p