Tetralogy of Fallot
- It is the most common cyanotic heart defect
- The most common cause of blue baby syndrome.
- It occurs in approximately 3 to 6 per 10,000 births
- Represents 5-7% of congenital heart defects
- Its cause is thought to be due to environmental or genetic factors
or a combination
- It is associated with chromosome 22 deletions and diGeorge syndrome
- It occurs slightly more often in males than in females.
- The Tetralogy of Fallot has four components
- Right ventricular outflow tract obstruction (infundibular
stenosis)
- Ventricular septal defect
- Aorta dextroposition, overrides VSD
- Right ventricular hypertrophy
- The VSD and infundibular stenosis determine the pathophysiological
features
Pathology
- Underdevelopment of the right ventricular infundibulum results in
displacement of the infundibular septum
- This determines the degree of right ventricular outflow tract
obstruction
- A large subaortic ventricular septal defect results
- The aorta overrides the VSD into the right ventricle
- Tetralogy of Fallot with pulmonary stenosis (TOFPS)
- The hypoplastic RVOT is associated with pulmonary valve stenosis
- The branch pulmonary arteries are usually normal and are rarely
significantly hypoplastic
- Tetralogy of Fallot with pulmonary atresia (TOFPA)
- Variable pulmonary blood supply is present
- There may be a ductus arteriosus or aortopulmonary collaterals
- Prenatal remnants may be present with abnormal histological
characteristics
- The VSD is usually large and non restrictive
- The relative resistance of the RVOT and systemic vascular bed
determines the pathophysiology
- In TOFPA, the source of pulmonary blood flow heavily influences the
clinical presentation
- Natural history is determined by the severity of the RVOT
obstruction
- 25% of untreated infants die in 1st year of life
- Risk of death is greatest in 1st year, then constant until about age
25
Clinical features
- Cyanosis
- Usually constant
- May be intermittent with hypoxic spells
- Infants with severe infundibular stenosis and valvular stenosis
are deeply cyanotic from birth ·
- Cyanosis occurs later in infants with classic dominant
infundibular stenosis
- Moderate systolic ejection murmur
- The murmur disappears during a spell
- Continuous murmurs may be found in patients with aortopulmonary
collaterals
- Polycythaemia
- Clubbing
- Develops in older children, usually after 6 months of age
Investigation
- CXR shows a "boot-shaped" heart and is most common in older infants
and children
- ECG shows right ventricular hypertrophy and right axis deviation
- Echocardiography shows the VSD and RVOT obstruction
- Can also delineate coronary artery anatomy, AV valve morphology, and
central pulmonary arteries
Management
- The majority of patients have adequate saturation and can undergo
elective repair
- Progressive hypoxemia (saturation 75-80%) is an indication for
operation
- Occurrence of spells is a second indication for operation
- Asymptomatic children with TOFPS and uncomplicated morphology should
have elective repair between 3 and 24 months of age
- Very young infants with complicated morphology can be managed with a
staged shunt (usually modified Blalock-Taussig)
- Many centres now perform single-stage complete repair regardless of
age, avoiding:
- Prolonged RVOT obstruction and subsequent right ventricular
hypertrophy
- Prolonged cyanosis
- TOFPA treatment strategy depends on the pulmonary artery anatomy
- The goal is to repair the defect and provide blood flow from the RV
to as many pulmonary segments as possible
- There are many surgical options, including
- Shunting and second-stage repair
- Relieve RVOT obstruction and leave VSD open, adding a shunt as
necessary to maintain saturation
- The residual VSD can be closed after further development of the
pulmonary vasculature
- Ligation of aortopulmonary collaterals may be necessary
- Current hospital mortality is 2-5%
- Survival at 5 years is about 90%
Transposition of the great vessels
- Present in the immediate neonatal period, particularly if no
ventricular septal defect (VSD) is present
- Infants can present in shock and severely acidotic
- The infant is invariably cyanosed
- No murmur is present, unless there is a VSD or some other structural
cardiac lesion.
- Radiologically, the lungs appear to have increased blood flow and
increased pulmonary vascular markings.
- The mediastinum is narrow, as the great arteries are running
parallel.
- Diagnosis is made by echocardiography - important features to note
are
- The size of the ductus arteriosus
- Whether there is a VSD,
- How much atrial mixing of blood there is
- Infants with a large VSD or large atrial communication may present
later, within the first 2 weeks, with cyanosis.
- Cardiac failure may be present in the presence of a large VSD
- In the short-term, a prostaglandin infusion should be commenced to
ensure ductal patency
- A balloon atrial septostomy is usually performed within the first
day or two of life to assist with mixing at an atrial level.
- An arterial switch procedure is usually performed within the first
week
Bibliography
Shinebourne E A, Babu-Narayan S V, Carvalho J S.
Tetralogy of Fallot: from fetus to adult. Heart 2006;
92: 1353-1359. |