Right to left shunt: tetralogy of Fallot
This, the most common cyanotic
CHD, is characterized by 4 cardinal ana-tomical cardiac anomalies:
·Large VSD.
·Overriding aorta.
·Right ventricular outflow
obstruction (infundibular and valvular pulmonary stenosis).
·Right ventricular hypertrophy.
Systemic venous return to the
right side of the heart is normal. In the pres-ence of pulmonary stenosis,
however, blood is shunted across the VSD into the aorta and arterial desaturation
and cyanosis result. The severity of cyanosis is dependent on the degree of
right ventricular outflow obstruc-tion and, when this is moderate, a balanced
shunt across the VSD occurs and cyanosis may be mild or absent.
Tetralogy of Fallot presents in
early infancy with the following.
·Cyanosis:
usually not present at birth and
leading to clubbing.
·Paroxysmal
hypercyanotic spells (infancy): spontaneous/unpredictable onset;
tachypnoea; restlessness; and increasing cyanosis, then becoming white and
floppy. Potentially dangerous. Duration ranges from a few minutes to hours; severe episodes result in syncope and
occasionally convulsions/hemiparesis.
Severe tetralogy of Fallot with
worsening cyanosis in early neonatal period requires prostagladin E infusion;
and surgery (e.g. modified Blalock–Taussig shunt) in order to maintain
pulmonary blood flow and oxygenation. Definitive surgery to repair the
underlying heart defects is carried out from 4mths of age onwards.
Untreated, the combination of
right to left shunt, chronic cyanosis, and polycythaemia predispose to:
·Cerebral thrombosis and ischaemia.
·Brain abscess.
·Bacterial endocarditis.
·Congestive cardiac failure.
Patients are often asymptomatic
after surgical corrections. Long-term follow-up (up to 30yrs) suggest that
improved quality of life is maintained and most are able to lead unrestricted
lives. Some will require pulmonary valve replacement in teenage years. Cardiac
conduction defects, including complete heart block, are seen post-operatively
and require treatment.
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