Morphology
Absent pulmonary valve syndrome is often associated with tetralogy of Fallot, and is
characterized by poorly developed pulmonary valve leaflets which consist of rudimentary
nodules of gelatinous tissue. The heart is greatly enlarged and the pulmonary trunk ant
its branches are markedly dilated, often reaching aneurysmal proportions. The pulmonary
annulus is restrictive, and the infundibulum is hypoplastic and long. A large
perimembranous ventricular septal defect is present if associated with tetralogy of
Fallot. The arterial duct is usually not patent and "agenesis" of the arterial
duct has been associated with this lesion. Enlargement of the pulmonary trunk is probably
related to the high in utero pulmonary vascular resistance and the absence of the arterial
duct, a setup for a water-hammer pulse with little outflow. The massively enlarged
pulmonary arteries compress the main stem bronchi, often producing emphysema of the
affected lung. There are also cases of abnormal pulmonary arterial branching pattern, with
peripheral vessels entwining and compressing small intrapulmonary bronchi.
Embryologic derivative of tetralogy with absent pulmonary valve leaflet syndrome.
Approximately 20 - 30 percent of cases with tetralogy and pulmonary stenosis have an
absent arterial duct. The combination of an incompetent pulmonary valve, a patent arterial
duct, and a ventricular septal defect is probably incompatible with in utero life,
in that blood ejected from the left ventricle crosses the patent arterial duct, returns to
the right ventricle, and back to the left ventricle by way of the ventricular septal
defect. This diastolic runoff and steal results in a situation in which no significant
forward blood flow occurs. Cases which include tetralogy of Fallot with an incompetent
pulmonary valve, a patent arterial duct, but discontinuous pulmonary arteries, with the
left pulmonary artery arising from the aorta are compatible with in utero survival,
and such patients are identified. Furthermore, congenital absence of the pulmonary valve
but with intact ventricular septum and a patent arterial duct is compatible with life,
although these patients are often critically ill. It therefore appears that the
combination of a nonrestrictive ventricular septal defect, a normally formed arterial
duct, and absent pulmonary valve is compatible with in utero survival, and that the
20 - 30% of patients with tetralogy of Fallot with absent pulmonary valve leaflet syndrome
in whom the arterial duct does not develop are selected for survival. tetralogy of Fallot
with absent pulmonary valve leaflet syndrome may potentially be palliated in utero,
by ligation of the pulmonary artery and creation of a systemic-to-pulmonary shunt, thereby
eliminating the water-hammer effect.
Hemodynamics
The combination of rudimentary pulmonary valve cusps with a narrow annulus produces
pulmonary stenosis and insufficiency. Right ventricular pressure is equal to left
ventricular pressure. In the neonate, the predominant shunt is often right to left, but
bi-directional and ultimately left-to-right shunting occur as pulmonary resistance falls
after birth, especially if the respiratory insufficiency is not severe.
Diagnosis
2-D echocardiography is well able to demonstrate the enlarged pulmonary arteries and
the ventricular septal defect, while Doppler echocardiography confirms the presence of
pulmonic stenosis and insufficiency. Right ventriculography demonstrates the narrow
pulmonary annulus and the dilated pulmonary arteries, while pulmonary arteriography
demonstrates the pulmonary arterial dilatation and the degrees of pulmonary insufficiency.
Clinical Course & Management
The two hallmark features are the presence of a to-and-from murmur along the left
sternal border and respiratory insufficiency. May of the infants are cyanotic. The chest
film shows cardiomegaly, dilation of the pulmonary arteries, and sometimes hyperexpansion
of one or more pulmonary segments. The prognosis is largely determined by the degree of
respiratory insufficiency in early infancy. Infants with the severe form of the syndrome
frequently die from respiratory distress and hypoxemia. Bronchial compression by the
enlarged pulmonary arteries often produces a "ball-valve" effect, in which air
is trapped within the lungs but cannot exit. Medical management is directed primary at
ventilatory and pulmonary management. Prostaglandin therapy is of little benefit due to
the lack of an arterial duct. Optimal neonatal operative management entails transatrial or
trans-ventricular patch closure of the ventricular septal defect, placement of a valved
homograft between the right ventricle and pulmonary artery, and reduction pulmonary
arterioplasty. |