478
U N I T 5
Circulatory Function
higher than normal, and thus the size of the left-to-right
shunt may initially be limited. As the pulmonary vascu-
lar resistance falls during the first few weeks after birth,
the size of the left-to right shunt increases. Eventually, a
large left-to-right shunt develops, and clinical symptoms
(e.g., tachypnea; diaphoresis, especially with feeding;
and failure to thrive) become apparent. In most cases
pulmonary vascular pressure is only slightly elevated
during infancy, and the major contributor to pulmonary
hypertension is an increase in pulmonary blood flow.
However, in some infants with a large septal defect,
pulmonary arteriolar thickness never decreases. With
continued exposure to high pulmonary blood flow, pul-
monary vascular disease develops. In untreated patients,
the pulmonary vascular resistance can eventually exceed
the systemic resistance. In this case, a reversal of shunt
flow occurs and the child demonstrates progressive
cyanosis as deoxygenated blood moves from the right
to the left side of the heart. These symptoms, coupled
with irreversible changes in the pulmonary vasculature,
represent an end-stage form of congenital heart disease
called
Eisenmenger syndrome
, a condition that is quite
rare today due to advances in diagnosis and treatment.
The treatment of a ventricular septal defect depends
on the size of the defect, accompanying hemodynamic
derangements, and symptomatology. Children with
small or medium-sized defects may be followed without
intervention if they remain free from signs of congestive
heart failure or pulmonary hypertension. Ventricular
defects do not increase in size, and some spontaneously
close over time.
22
Prophylactic antibiotic therapy is given
during periods of increased risk for bacteremia. The man-
agement of infants with large ventricular defects aims
to control heart failure and prevent the development of
pulmonary vascular disease. Symptomatic infants may
require feeding supplements or tube feeding to promote
growth and development. In the symptomatic infant in
whom complete repair cannot be achieved because of
size or other complicating lesions, a palliative procedure
may be performed to reduce symptoms. Placement of a
synthetic band around the main pulmonary artery (pul-
monary artery banding) can reduce pulmonary blood
flow until complete repair can be accomplished. Surgical
closure of the defect is completed by placement of a syn-
thetic or autologous patch effectively to close the shunt
across the ventricular septum. These procedures are
typically done electively in the infant or young child and
are associated with low morbidity and mortality rates.
Endocardial Cushion Defects.
The endocardial cush-
ions form the AV canals, the upper part of the ventricu-
lar septum, and the lower part of the atrial septum. The
endocardial cushions surround this canal and contribute
tissue to the lower part of the atrial septum, the upper
part of the ventricular septum, the septal leaflet of the tri-
cuspid valve, and the anterior leaflet of the mitral valve.
83
Any flaw in the development of these tissues results in an
endocardial cushion defect. Endocardial cushion defects
are responsible for approximately 2% of all congenital
heart defects. As many as 30% of children with Down
syndrome have endocardial cushion defects.
66
Because the endocardial cushions contribute to mul-
tiple aspects of heart development, several variations
of endocardial cushion defects are possible. The defect
may be described as
partial
or
complete.
The anatomy
of the AV valve determines the classification. In partial
AV canal defects, the two AV valve rings are complete
and separate. The most common type of partial AV
canal defect is an ostium primum defect, often associ-
ated with a cleft in the mitral valve. In a complete canal
defect, there is a common AV valve orifice along with
defects in both the atrial and ventricular septal tissue
(see Fig. 19-21E). Other cardiac defects may be associ-
ated with endocardial cushion defects and most com-
monly include cardiac malposition defects and tetralogy
of Fallot.
83
Physiologically, endocardial cushion defects result
in abnormalities similar to those described for atrial
or ventricular septal defects. The direction and magni-
tude of a shunt in a child with an endocardial cushion
defect are determined by the combination of defects and
the child’s pulmonary and systemic vascular resistance.
The hemodynamic effects of an isolated ostium primum
defect are those of the previously described atrial septal
defect. These children are largely asymptomatic during
childhood. With a complete AV canal defect, pulmonary
blood flow is increased after the pulmonary vascular
resistance falls because of left-to-right shunting across
both the ventricular and atrial septal defects. Children
with complete defects often have effort intolerance,
easy fatigability, failure to thrive, recurrent infections,
and other signs of congestive heart failure, particularly
when the shunt is large. Pulmonary hypertension and
increased pulmonary vascular resistance result if the
lesion is left untreated.
The timing of treatment for endocardial cushion
defects is determined by the severity of the defect and
symptoms. With an ostium primum defect, surgical
repair usually is planned on an elective basis before the
child reaches school age. Corrective surgery is required
for all complete AV canal defects. Infants with severe
symptoms may require a palliative procedure in which
the main pulmonary artery is banded to reduce pulmo-
nary blood flow. This typically improves the infant’s
ability to grow and develop until a complete repair can
be performed.
83
Pulmonary Stenosis.
Obstruction of blood flow from
the right ventricle to the pulmonary circulation is termed
pulmonary stenosis.
The obstruction can occur as an
isolated valvular lesion, within the right ventricular
chamber, in the pulmonary arteries, or as a combination
of stenoses in multiple areas. It is a relatively common
defect, estimated to account for approximately 10% of
all congenital cardiac disease, and is often associated
with other abnormalities.
84
Pulmonary valvular defect, the most common type of
disorder, usually produces some impairment of pulmo-
nary blood flow and increases the workload imposed
on the right side of the heart (see Fig. 19-21D). Most
children with pulmonic valve stenosis have mild ste-
nosis that does not increase in severity. These children
