C h a p t e r 1 9
Disorders of Cardiac Function
479
are largely asymptomatic and are diagnosed by the
presence of a systolic murmur. Moderate or greater ste-
nosis has been shown to progress over time, particularly
before 12 years of age, so these children require careful
follow-up. Critical pulmonary stenosis in the neonate
is evidenced by cyanosis due to right-to-left atrial-level
shunting and right ventricular hypertension. These
infants require prostaglandin E
1
to maintain circulation
to the lungs through the ductus arteriosus.
84
Pulmonary valvotomy is the treatment of choice for
all valvular defects with pressure gradients from the
right ventricle to the pulmonary circulation greater than
30 mmHg. Transcatheter balloon valvuloplasty has been
quite successful in this lesion. Stenosis in the peripheral
pulmonary arteries can also be effectively treated with
balloon angioplasty, with or without stent placement.
84
Tetralogy of Fallot.
Tetralogy of Fallot is the most
common cyanotic congenital heart defect, accounting
for approximately 5% to 7% of all congenital heart
defects.
85
As the name implies, tetralogy of Fallot consists
of four associated defects: (1) a ventricular septal defect
involving the membranous septum and the anterior por-
tion of the muscular septum; (2) dextroposition (shifting
to the right of the aorta) so that it overrides the right
ventricle and is in communication with the septal defect;
(3) obstruction or narrowing of the pulmonary outflow
channel, including pulmonic valve stenosis, a decrease in
the size of the pulmonary trunk, or both; and (4) hyper-
trophy of the right ventricle because of the increased
work required to pump blood through the obstructed
pulmonary channels
86
(see Fig. 19-21C). Variations of
the defect can include complete atresia of the pulmonary
valve or absence of pulmonary valve tissue altogether.
Most children with tetralogy of Fallot display some
degree of cyanosis that is caused by a right-to-left shunt
across the ventricular septal defect. The degree of cyano-
sis is determined by the restriction of blood flow into the
pulmonary bed. Right ventricular outflow obstruction
causes deoxygenated blood from the right ventricle to
shunt across the ventricular septal defect and be ejected
into the systemic circulation. The degree of obstruc-
tion may be dynamic and can increase during periods
of stress, causing hypercyanotic attacks (“tet spells”).
These spells typically occur in the morning during cry-
ing, feeding, or defecating. These activities increase the
infant’s oxygen requirements. Crying and defecating
may further increase pulmonary vascular resistance,
thereby increasing right-to-left shunting and decreasing
pulmonary blood flow. With the hypercyanotic spell, the
infant becomes acutely cyanotic, hyperpneic, irritable,
and diaphoretic. Later in the spell, the infant becomes
limp and may lose consciousness. Placing the infant
in the knee–chest position increases systemic vascular
resistance, which increases pulmonary blood flow and
decreases right-to-left shunting. During a hypercyanotic
spell, toddlers and older children may spontaneously
assume the squatting position, which functions like the
knee–chest position to relieve the spell.
Total surgical correction is required for all children
with tetralogy of Fallot. Early definitive repair in infancy
is currently advocated in most centers experienced in
intracardiac surgery in infants.
86
Transposition of the Great Arteries.
In complete
transposition of the great arteries, the aorta arises from
the right ventricle, and the pulmonary artery arises from
the left ventricle (see Fig. 19-21F). The defect is more
common in infants whose mothers have diabetes and is
two to three times more common in boys.
87
Cyanosis is the most common presenting symptom,
resulting from an anomaly that allows the systemic
venous return to be circulated through the right heart
and ejected into the aorta, and the pulmonary venous
return to be recirculated to the lungs through the left
ventricle and main pulmonary artery. In infants born
with this defect, survival depends on communication
between the right and left sides of the heart in the form
of a patent ductus arteriosus or septal defect. Ventricular
septal defects are present in 50% of infants with trans-
position of the great arteries at birth and may allow
effective mixing of blood. Prostaglandin E
1
should be
administered to neonates when this lesion is suspected
in an effort to maintain the patency of the ductus arteri-
osus. Balloon atrial septostomy may be done to increase
the blood flow between the two sides of the heart. In this
procedure, a balloon-tipped catheter is inserted into the
heart through the vena cava and then passed through
the foramen ovale into the left atrium. The balloon
is then inflated and pulled back through the foramen
ovale, enlarging the opening as it goes.
Corrective surgery is essential for long-term survival.
An arterial switch procedure, which corrects the relation
of the systemic and pulmonary blood flows, is the cur-
rent procedure of choice, and has survival rates greater
than 90%.
87
This procedure is preferably performed in
the first 2 to 3 weeks of life, before the postnatal reduc-
tion in pulmonary vascular resistance occurs. The cor-
onary arteries are moved to the left-sided great artery
and any ventricular septal defects are closed during the
same operation. Complications of the arterial switch
procedure may include coronary insufficiency, supra-
valvar pulmonary stenosis, neoaortic regurgitation, and
rhythm abnormalities.
87
Coarctation of the Aorta.
Coarctation of the aorta
consists of a localized narrowing of the aorta. It can
occur proximal to (preductal) (see Fig. 19-21H), distal
to (postductal), or opposite of (juxtaductal) the entry of
the ductus arteriosus. Approximately 98% of coarcta-
tions are juxtaductal. The defect is frequently associated
with other congenital cardiac lesions, most commonly
bicuspid aortic valve, and occurs in approximately 10%
of subjects with Turner syndrome, suggesting a genetic
linkage
88
(see Chapter 6).
The classic sign of coarctation of the aorta is a dis-
parity in pulsations and blood pressures in the arms and
legs. The femoral, popliteal, and dorsalis pedis pulsa-
tions are weak or delayed compared with the bound-
ing pulses of the arms and carotid vessels. Normally, the
systolic blood pressure in the legs obtained by the cuff
method is 10 to 20 mm Hg higher than in the arms.
