Congenital malformations - Edocr

200 PART V CARDIAC MALFORMATIONS
gradient between the left ventricle and the aorta
can be assessed by two-dimensional and Doppler
echocardiography.
Coarctation of the aorta refers to narrowing
of the thoracic descending aorta caused by
thickening of the aortic media. It may be an isolated
defect but often occurs in association with
other LVOTO defects, commonly in association
with aortic stenosis. Coarctations are frequently
classified as being preductal, juxtaductal, or
postductal although most are juxtaductal.
Most patients with an isolated coarctation of
the aorta are asymptomatic. When symptoms are
noted in infancy, it is most often because of associated
cardiovascular anomalies or because
there is diffuse tubular hypoplasia of the aorta, a
defect that is histologically different than coarctation.
In tubular hypoplasia of the aorta, there is a
long narrow segment of proximal or distal aortic
arch and isthmus but the media of the aorta is
normal. When an infant with a severe coarctation
or tubular hypoplasia presents in infancy, a previously
asymptomatic infant may suffer sudden cardiovascular
collapse at the time of closure of the
ductus when there is a sudden precipitous drop in
blood being delivered to the systemic circulation.
The classical physical findings in less severely affected
patients are elevated blood pressure in the
upper extremities, decreased blood pressure in
the lower extremities, and decreased or absent
pulses in the lower extremities. The chest radiograph
and ECG are usually normal. Over time,
the typical rib notching may develop because of
the gradual dilatation of intercostal collateral arteries.
The diagnosis can be established by twodimensional
and Doppler echocardiography using
suprasternal notch views.
Interrupted aortic arch is a discontinuity in
the aorta with the blood supplied to the descending
aorta either by the ductus arteriosus or
by a proximal aortic branch vessel. It is subdivided
into three types: (1) type A, in which the
interruption is distal to the origin of the left subclavian
artery; (2) type B, in which the interruption
is proximal to the origin of the subclavian
artery and between the left common carotid
and left subclavian arteries; and (3) type C, in
which the interruption is proximal to the left common
carotid artery between the innominate and
the left common carotid arteries. Type B is the
most common, accounting for approximately
65% of all cases. In virtually every case, interrupted
aortic arch is associated with intracardiac
anomalies, the nature of which affects clinical
presentation. Most affected infants present with
respiratory distress, cyanosis, and variably decreased
peripheral pulses. Differential cyanosis
is a useful clinical sign, if present, but rarely occurs
because 85% of affected infants have an associated
ventricular septal defect. Most cases of
interrupted aortic arch can be diagnosed accurately
by echocardiography.
Hypoplastic left heart syndrome is a complex
congenital heart malformation associated
with atresia or severe hypoplasia of the aortic
and mitral valves, severe hypoplasia of the left
ventricle and hypoplasia of the ascending aorta.
Other cardiac defects may also be present including
atrioventricular septal defect, atrial septal
defect, anomalous pulmonary venous connections,
and persistent left vena cava. Infants with
this severe disorder are typically asymptomatic
at birth because the open ductus arteriosus supplies
blood to the systemic circulation. As soon
as the ductus begins to constrict, however, there
is a dramatic reduction in systemic blood flow
and the signs and symptoms of shock develop
rapidly. Most affected infants develop a significant
metabolic acidosis with elevated lactic acid
levels. The chest radiograph reveals cardiomegaly
with increased pulmonary vascularity. ECG reveals
right atrial enlargement with peaked P
waves and right ventricular hypertrophy. The
diagnosis can be confirmed by two-dimensional
and Doppler echocardiography.
ASSOCIATED SYNDROMES
The multiple malformation syndromes most
commonly associated with LVOTO defects are
listed in Table 30-1. Among the most common