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a Chapter 29 Doppler Ultrasound Examination of the Fetal Coronary Circulation 439
calcification die within the first year of life complicated
by cardiac and pulmonary failure, severe hypertension,
renal infarction, peripheral gangrene, and
bowel infarction [76].
Critical Aortic Stenosis
Critical aortic stenosis in fetal life can be associated
with a marked decrease in left ventricular output and
reversal of shunting across the foramen ovale. Under
these circumstances coronary perfusion pressure is
affected by a decrease in arterial pressure and an elevation
of right atrial pressure thereby decreasing the
driving force across the coronary vascular bed. Concurrently,
left ventricular work and therefore myocardial
oxygen demand are increased. Development of
acute heart sparing has been documented in a fetus
presenting with severe left ventricular outflow tract
obstruction and non-immune hydrops due to critical
aortic stenosis. While these findings were ameliorated
initially by transplacental digoxin therapy, visualization
of coronary blood flow became visible at 39
weeks coinciding with shunt reversal across the foramen
ovale [79].
Persistent Left Superior Vena Cava
While Doppler examination of the coronary sinus has
limited utility in the human fetus, substantial dilatation
may result from volume overload from a persistent
left superior vena cava draining into the coronary
sinus [80±82]. The frequency of a persistence of
the left vena cava is 1±2 per 1000 but may be as high
as 9% in the presence of congenital heart defects
[83]. The degree of dilatation is often marked and lies
appreciably above normal reference limits. This dilatation
appears to be predominantly related to vascular
volume changes and is independent of associated cardiac
defects [63]. Other causes of coronary sinus dilatation
in the human fetus may be a coronary arteriovenous
fistula and anomalous pulmonary vein drainage
into the coronary sinus. It is important to note
that because of its close proximity to the insertion of
the atrioventricular valve, a dilated coronary sinus
has been mistaken for an atrial septal defect of ostium
primum type and/or an atrioventricular septal
defect, respectively [84±86]. Coronary sinus dynamics
may be attenuated in fetal conditions associated with
elevated right-heart pressures, severe fetal cardiac
dysfunction, and hydrops. These alterations in dynamics
may indicate elevated coronary sinus pressures
or changes in coronary blood flow [45].
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