The
ductus arteriosus (see fig 23) connects the descending aorta
(distal to the left subclavcan artery takeoff from the aorta
to supply the left arm) to the left pulmonary artery. The ductus
arteriosus serves in the fetus to shunt blood from the pulmonary
artery (avoiding the unexpanded lungs) to the descending aorta
for oxygenation in the placenta of the womb. It closes normally
soon after birth. However, in some babies it does not close
spontaneously, and there is continuous flow from the aorta to
the pulmonary artery (i.e. left to right shunting) (see figure).
This abnormality accounts for 10% of congenital heart disease
cases, and is higher than average in pregnancies associated
with persistent perinatal hypoxemia (reduced oxygen levels)
or maternal rubella (German measles) and among babies born at
high altitude or prematurely. Diagnosis includes the following:
1)physical examination especially looking for a "machinery"
at the second left anterior intercostal space (between the second
and third ribs) murmur occurring throughout the cardiac cycle.
2) EKG 3) Chest X ray showing heart enlargement, dilated pulmonary
arteries, and a prominent ascending aorta. The right ventricle
may enlarge if high pressure occurs the pulmonary arteries.
4) Echocardiography with doppler may visualize the ductus and
show continuous flow in the pulmonary artery. 5) Heart catheterization
and angiography allow determination of the size of the shunt,
pulmonary vascular resistance and visualization of the ductus
arteriosus itself. A small patient ductus is usually asymptomatic
and a person with such a small defect can have a normal life
span. But the area can become infected and lead to infected
blood clots being thrown into the lungs. A moderate sized defect
may cause symptoms of fatigue, shortness of breath, and palpatations
in childhood or adulthood. In addition, the ductus may enlarge
as an aneurysm and rupture. Larger shunts may cause left heart
failure. Finally, pulmonary hypertension may occur, and cause
the shunts to reverse direction into the descending aorta. One
third of patients with a patent ductus arteriosus which is not
surgically repaired, die of heart failure, pulmonary hypertension,
or endarteritis by the age of 40 years and two thirds die by
the age of 60 years. Surgical ligation of the patent ductus
arteriosus, often done without cardiopulmonary bypass, has an
associated mortality of less than 0.5%. But if there is an aneurysm
or calcification of the ductus, resection with cardiopulmonary
bypass may be required. The risk of endarteritis (inflammation
of the arteries) associated with unrepaired patent ductus arteriosus
and the low risk associated with ligation, it is recommended
that even a small patent ductus be ligated surgically or occluded
with a percutaneously placed closure device. The onset of severe
pulmonary vascular obstructive disease is a contraindication
to surgical ligation or occlusion.