o_1977r8vv9vk1ts2ms0kd8pksa.pdf

500 D. Maulik
Fig. 33.20. Echocardiogram shows simultaneous
interrogation of the mitral
flow (MF) and aortic outflow (AO). Top:
Placement of the Doppler sample in
the left ventricular chamber just distal
to the tricuspid orifice encompassing
the mitral flow and aortic outflow. LA
left atrium, LV left ventricle
veform from any fetal artery reflects the ventricular
rhythm. On the other hand, insonation of the inferior
vena cava or pulmonary vein and of the tricuspid or
mitral flow tracts will yield the atrial rhythm. The
use of Doppler velocimetry of the inferior vena cava
for assessing fetal arrhythmia is discussed in Chap. 27.
To assess the synchronicity of the atrial and ventricular
rhythms, Doppler sample volume can be
placed and extended to encompass both atrial and
ventricular flows. It is accomplished by placing the
sample volume appropriately in the ventricular chamber
and extending it to include the atrial flow into
the ventricle and the ventricular outflow. The tricuspid
or mitral waveform reveals the atrial rhythm, and
the pulmonary or aortic outflow indicates the ventricular
rhythm (Fig. 33.20). An alternative approach,
described by Chan and colleagues [45], involves placing
the Doppler sample volume in the lower abdomen
to encompass the aorta and the inferior vena cava,
generating the ventricular and atrial rates, respectively.
In this location the two vessels lie in close
proximity and therefore are accessible to interrogation
by an extended sample volume.
In addition to rhythm determination, Doppler echocardiographic
modalities allow assessment of hemodynamic
changes associated with an abnormal rhythm.
Moreover, color Doppler echocardiography is supplemental
to 2D imaging for identifying any associated cardiac
structural malformations. This point is clinically
important, as the presence of malformations in conjunction
with arrhythmia signifies a worse prognosis.
Spectral Doppler may be particularly helpful for elucidating
the hemodynamic pathophysiology of fetal
cardiac arrhythmias. In our initial report [46] we noted
that during an ectopic beat the right ventricular stroke
volume may be reduced by 60%. Subsequent investigations
have substantially expanded the application of
Doppler sonography for studying the hemodynamic effects
of fetal cardiac arrhythmia. Lingman and MarsÆ—l
[47] observed that the systolic rising slope and peak
value of the maximum aortic velocity were significantly
increased during the first beat after the compensatory
pause in fetuses with supraventricular extrasystole; this
observation confirmed the Frank-Starling phenomenon
in the fetus and was corroborated by Reed and coworkers
[48], who reported cardiac Doppler flow
changes during fetal arrhythmias in 54 fetuses with gestational
ages of 21±41 weeks. During the postextrasystolic
beats, time velocity integrals rose by 43% across
the tricuspid orifice and 41% across the mitral orifice.
Kanzaki and associates [49] investigated fetal cardiac
arrhythmia with pulsed-wave Doppler sonography
and observed characteristic inferior vena caval flow
patterns with each arrhythmic condition. These patterns
could be explained by the atrial and ventricular
contraction characteristics. Furthermore, inferior vena
caval flow components during sinus rhythm could be
explained by the events of the cardiac cycle. Distinctive
flow velocity patterns were observed for each arrhythmic
condition. The most remarkable finding with all
the arrhythmic conditions was the high-velocity reverse
flow caused by atrial systole with closed tricuspid
valve or tricuspid regurgitation. This subject is discussed
in depth in Chap. 27.
Premature Atrial Contractions
As indicated in Table 33.9, premature atrial contractions
(PACs) are the most common form of fetal cardiac
arrhythmia. The condition is also known as at-