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Chapter 35
Doppler Echocardiographic Assessment
of Fetal Cardiac Failure
William J. Ott
Introduction
In the fetus heart failure is the end stage of many
pathological events that may lead to significant neonatal
morbidity or mortality. In the adult heart failure
is defined as ªthe pathophysiological state in which an
abnormality of cardiac function is responsible for the
failure of the heart to pump blood at a rate commensurate
with the requirements of the metabolizing tissues
and/or to be able to do so only from an elevated
filling pressureº [1, 2]. In many instances this definition
also applies to the fetus, but differences in the
anatomy and physiology of the fetal heart, when compared
with the adult or neonatal heart, may not allow
this definition to be fully applicable to the fetus.
Fetal Cardiac Anatomy
and Physiology
Anatomical and physiological differences between the
fetal and neonatal or adult heart call into question
the ability to translate the knowledge of the pathophysiological
events occurring during heart failure in
the adult or neonate to the fetus. In the adult the two
ventricular chambers of the heart work in series, with
the right ventricle pumping deoxygenated venous
blood into the pulmonary circuit and the left ventricle
supplying oxygenated blood to the systemic circulation.
The fetal heart, however, works in parallel
with little of the right ventricular output going to the
pulmonary circuit. Figures 35.1±35.3 review the normal
fetal intra-cardiac circulation.
Although there is some venous return to the fetal left
atria via the pulmonary veins, the majority of venous
return to the heart is through the superior and inferior
vena cava and associated vessels [3±8]. Deoxygenated
blood from the fetal head returns to the right atria
from the superior vena cava and directly passes
through the tricuspid valve into the right ventricle.
Studies in the fetal lamband other animal models have
shown that oxygenated venous blood from the umbilical
vein passes through the ductus venosus and preferentially
enters the left heart via the foramen ovale [3±
8]. Studies on chronically instrumented fetal lambs
have shown that, in physiological conditions, 50%±
60% of the umbilical venous blood bypasses the hepatic
circulation and enters directly into the inferior vena
cava via the ductus venosus [8]. From the inferior vena
cava, this highly oxygenated blood preferentially
streams through the foramen ovale to the left atrium,
left ventricle, and ascending aorta. Figure 35.4 shows
venous return in a 22-week fetus. Doppler flow (Fig.
35.4 b) shows that, under normal conditions, there is
always forward flow throughout the cardiac cycle in
the ductus venosus.
Although there may be many anatomical variations
in the venous return to the fetal heart, the following
general anatomical relationships are noted [9]:
1. The inferior vena cava widens in the proximal portion
and enters the atria in a slightly anterior
direction. An extension of the inferior vena cava
continues into the atria itself as a short tube-like
Fig. 35.1. Deoxygenated blood (1) enters the right atrium
from the superior and inferior vena cava. Oxygenated
blood (2) enters the right atrium primarily from the ductus
venosus