Congenital malformations - Edocr

Chapter 30
Left Ventricular Outflow Tract
Obstructive Defects
BARBARA K. BURTON
INTRODUCTION
Left ventricular outflow tract obstructive (LVOTO)
defects are congenital defects of the heart and
aorta that reduce outflow into the systemic circulation.
They include mitral stenosis or atresia,
subaortic stenosis, bicuspid aortic valve, aortic
valve stenosis, supravalvular aortic stenosis, coarctation
of the aorta, interrupted aortic arch, and hypoplastic
left heart syndrome.
DESCRIPTION AND CLINICAL
PRESENTATION
Infants with mitral stenosis typically present with
tachypnea, diaphoresis, respiratory distress, and
failure to thrive—a common array of symptoms
seen in most forms of LVOTO defects. Chest radiographs
reveal pulmonary venous congestion
and cardiomegaly with enlargement of the right
ventricle. The left atrium may be enlarged. Electrocardiogram
(ECG) findings are variable but
usually include right ventricular hypertrophy.
The diagnosis can be established by echocardiography
while cardiac catheterization may be
necessary for assessment of pressure gradients.
The aortic valve is normally composed of
three leaflets. Fusion of two of these leaflets
gives rise to a bicuspid aortic valve in which the
leaflets have straight rather than semicircular
free margins. Although this results in some limitation
in the size of the valve orifice and some
decrease in mobility, it is usually a benign anomaly
in childhood. In adult life, it is associated
with an increased risk of calcific aortic stenosis
and of aortic aneurysms. 1
A large majority of patients with aortic stenosis
have aortic valvar stenosis. Approximately 10%
have supravalvular stenosis and a slightly greater
number have subaortic stenosis. The clinical findings
are variable depending on the severity of the
lesion. Patients with mild defects may be asymptomatic
while infants with severe defects may present
in shock. Physical examination reveals a systolic murmur
of variable intensity and may reveal reduced
pulses, a systolic click and gallop. A minority of patients
will exhibit an early diastolic murmur of
aortic insufficiency. Chest radiographs reveal dilatation
of the ascending aorta with eventual left
ventricular enlargement. ECG can be normal or
can show left ventricular hypertrophy with strain,
depending on the severity of the obstruction. The
diagnosis can be established and the pressure
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