o_1977r8vv9vk1ts2ms0kd8pksa.pdf

a Chapter 31 Doppler Examination of the Fetal Pulmonary Venous Circulation 455
5. Left ventricular size and performance
6. Mitral valve size and function (e.g., regurgitation).
Fig. 31.10. Reference range (individual values, mean and
95% data intervals) for velocities during atrial contraction
in the pulmonary veins plotted against gestational age.
(From [9])
Abnormal Patterns
of Flow Velocity Waveforms
If we assume that left atrial pressure is a major determinant
of the pulmonary vein velocity waveform, an
obstruction of the left atrium should lead to typical
changes in the waveform envelope. This was confirmed
for fetuses with hypoplastic left heart syndrome,
for example, where a distinct reversed flow
during atrial contraction was demonstrated (Fig.
31.12) [13±15]. When the mitral valve is closed or severely
dysplastic, left atrial blood can only escape
during atrial contraction by passing across the foramen
ovale from left to right or by returning to the
lung. The larger the interatrial communication, the
less blood will return into the lung during atrial contraction,
and vice versa. Better et al. [14] reported an
increase in systolic velocity and a reversal in A-velocity
in such fetuses that correlated with the degree of
restriction of the atrial septum after birth. This was
Fig. 31.11. Reference range (individual values, mean and
95% data intervals) for pulsatility index of the pulmonary
veins plotted against gestational age. (From [9] with permission)
peak velocities and TVI is compatible with the increase
in pulmonary blood flow during gestation.
Given that the fetal pulmonary vein waveform reflects
changes in the left atrium, studies have been
performed to analyze indirectly the impact of left atrial
pressure changes on the waveform. The pulmonary
venous velocity pattern can be influenced by following
determinants [12]:
1. Pulmonary volume flow
2. Foramen ovale size and flow
3. Left atrial compliance (size and muscle distensibility)
4. Atrial contraction, end-diastolic pressure (e.g.,
adrenergic drive, hypoxemia)
Fig. 31.12. Three types of an obstructed left atrium as reflected
in the pulmonary vein flow velocity waveforms. The
upper wave is a mild obstruction with a slight reverse A-
wave, the middle wave is a serious obstruction with a pronounced
reversed A-wave. The lower wave is severely abnormal
and indicates an obstructive left atrium, often associated
with thickened pulmonary veins and congestive
lungs