476
U N I T 5
Circulatory Function
which have a vasodilating effect. Ductal closure also
may be delayed in infants with congenital heart defects
that produce a decrease in oxygen tension.
78
Persistent patency of the ductus arteriosus is defined
as a duct that remains open beyond 3 months in the
full-term infant. The size of the persistent ductus and
the difference between the systemic and pulmonary
vascular resistance determine its clinical manifesta-
tions. Blood typically shunts across the ductus from
the higher-pressure left side (systemic circulation) to
the lower-pressure right side (pulmonary circulation).
After the infant’s pulmonary vascular resistance falls,
the patent ductus arteriosus provides for a continuous
runoff of aortic blood into the pulmonary artery. With
a large patent ductus, the runoff is continuous, result-
ing in increased pulmonary blood flow, pulmonary
congestion, and increased resistance against which the
right side of the heart must pump. Increased pulmonary
venous return and increased work demands may lead to
left ventricular failure.
79
Spontaneous closure of the ductus seldom occurs
after infancy. In the full-term infant or older child, clo-
sure can be achieved with either surgical ligation or
device occlusion. In children with a small patent ductus,
closure is done to prevent infective endocarditis or other
complications. In children with a moderate to large pat-
ent ductus, closure is accomplished to treat heart failure,
prevent the development of pulmonary vascular disease,
or both.
78
Drugs that inhibit prostaglandin synthesis
(e.g., indomethacin) may be used to induce closure of
a patent ductus in preterm newborns. Indomethacin
works best if it is used in infants younger than 13 days
of age; it is not effective later than 4 to 6 weeks of age.
78
Although closure of a patent ductus is uniformly rec-
ommended when it is present as an isolated lesion, delib-
erate maintenance of ductal patency can be a lifesaving
therapy for children with complex forms of congenital
heart disease who have ductal-dependent pulmonary or
systemic blood flow, or those with obligatory mixing of
the arterial and venous circulations (i.e., transposition
B
Atrial septal defect
C
Ventricular septal defect
F
Tetralogy of Fallot
E
Pulmonary stenosis
D
Endocardial cushion defect
G
Transposition of the great vessels
A
Patent ductus arteriosus
H
Postductal coarctation
of the aorta
FIGURE 19-21.
Congenital heart defects.
(A)
Patent ductus arteriosus.The high-pressure blood of the
aorta is shunted back to the pulmonary artery.
(B)
Atrial septal defect. Blood is shunted from left to
right.
(C)
Ventricular septal defect. Blood is usually shunted from left to right.
(D)
Endocardial cushion
defect. Blood flows between the chambers of the heart.
(E)
Pulmonary stenosis, with decreased
pulmonary blood flow and right ventricular hypertrophy.
(F)
Tetralogy of Fallot.This involves a
ventricular septal defect, dextroposition of the aorta, right ventricular outflow obstruction, and right
ventricular hypertrophy. Blood is shunted from right to left.
(G)
Transposition of the great vessels.The
pulmonary artery is attached to the left side of the heart and the aorta to the right side.
(H)
Postductal
coarctation of the aorta.
