Right to left shunt: tetralogy of Fallot
This, the most common cyanotic CHD, is characterized by 4 cardinal ana-tomical cardiac anomalies:
·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.
·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.