Because the vsd is usually large pressures may be

Because the VSD is usually large, pressures may be equal in the right and left ventricles.
Therefore the shunt direction depends on the difference between pulmonary and systemic
vascular resistance. If pulmonary vascular resistance is higher than systemic resistance, the shunt
is from right to left. If systemic resistance is higher than pulmonary resistance, the shunt is from
left to right. PS decreases blood flow to the lungs and consequently the amount of oxygenated
blood that returns to the left side of the heart. Depending on the position of the aorta, blood
from both ventricles may be distributed systemically.
Clinical manifestations—Some infants may be acutely cyanotic at birth; others have mild
cyanosis that progresses over the first year of life as the PS worsens. There is a characteristic
systolic murmur that is often moderate in intensity. There may be acute episodes of cyanosis and
hypoxia, called blue spells or tet spells (see p. 1337). Anoxic spells occur when the infant's

oxygen requirements exceed the blood supply, usually during crying or after feeding. Patients are
at risk for emboli, seizures, and loss of consciousness or sudden death after an anoxic spell.
Surgical Treatment
• Palliative shunt—In infants who cannot undergo primary repair, a palliative procedure to
increase pulmonary blood flow and increase oxygen saturation may be performed. The preferred
procedure is a modified Blalock-Taussig shunt operation, which provides blood flow to the
pulmonary arteries from the left or right subclavian artery via a tube graft (see Table 42-2). In
general, however, shunts are avoided because they may result in pulmonary artery distortion.
• Complete repair—Elective repair is usually performed in the first year of life. Indications for
repair include increasing cyanosis and the development of hypercyanotic spells. Complete repair
involves closure of the VSD and resection of the infundibular stenosis, with placement of a
pericardial patch to enlarge the RVOT. In some repairs, the patch may extend across the
pulmonary valve annulus (transannular patch), making the pulmonary valve incompetent. The
procedure requires a median sternotomy and the use of cardiopulmonary bypass.
Prognosis—The operative mortality for total correction of tetralogy of Fallot is less than 3%. With
improved surgical techniques, there is a lower incidence of dysrhythmias and sudden death;
surgical heart block is rare. Heart failure may occur postoperatively.
31. Patent ductus arteriosus:
In utero fetal Po2 is 20 to 30 mm Hg. After birth, when the Po2 level in the arterial blood
approximates 50 mm Hg, the ductus arteriosus constricts in response to increased oxygenation.
Circulating hormone prostaglandin E (PGE2) levels also have an important role in closure of the
ductus arteriosus. In term infants it functionally closes within the first hours after birth;
permanent closure usually occurs within 3 to 4 weeks, and the ductus arteriosus becomes a