o_1977r8vv9vk1ts2ms0kd8pksa.pdf

522 W. J. Ott
Velocity Measurements Across
the Atrioventricular Valves
Blood flow across the atrioventricular valves can easily
be seen with Doppler sonography (Fig. 35.6) [14,
22±26]. Blood flow velocity can be studied at the level
of the mitral or tricuspid valves by placing the Doppler
sample volume immediately distal to the valve
leaflets in the right or left ventricle. In addition to
Fig. 35.6. Gray-scale image of a color Doppler axial scan
through the fetal chest at 25 weeks showing flow across
the AVvalves
obtaining diastolic velocities across the atrioventricular
valves, the presence of valvular insufficiency can
be ascertained by moving the Doppler gate retrograde
through the valve opening. Valvular stenosis has been
reported to be associated with increased velocity flow
through the affected valve. The waveforms recorded
at the level of the mitral and tricuspid valves are
characterized by two diastolic peaks: an early ventricular
filling peak (E wave) and a second filling peak
corresponding to the active ventricular filling phase
during atrial contraction (A wave; Figs. 35.7, 35.8).
These waveforms can be recorded as early as 12
weeks' gestational age [27].
The ratio between the A and E waves (A/E) is an
index of ventricular diastolic function and is related
to both cardiac compliance and preload conditions.
The A/E ratio shows a significant decrease with advancing
gestational age but remains above unity
(Figs. 35.7, 35.8). This picture is the converse of that
seen in the adult and suggests that ventricular compliance
is less in the fetus than the neonate but improves
with advancing gestational age. Reed [23] and
Reed et al. [25] have shown that in most of the fetuses
studied, tricuspid flow velocities during both
early and late diastole were greater than those across
the mitral valve. This confirms the impression of
right heart dominance in the fetus that is seen when
evaluating ventricular outflow.
Fig. 35.7. Doppler blood flow across the mitral (left) and tricuspid (right) valves of a 20-week fetus. Note that the A/E ratio
is greater than one