Tetralogy of Fallot

Question 1

TOF - overview

Answer 1

1. Most common cyanotic congenital heart disease

Characterised by four cardinal anatomical cardiac anomalies:

2. Large VSD
3. Overriding aorta
4. RV outflow obstruction (infundibular and valvular pulmonary stenosis)
5. RVH

Incidence = 10% of congenital heart disease cases, 3-6:10,000 births

Question 2

TOF - pathophysiology (3)

Answer 2

1. Systemic venous return to the right side of the heart is normal.
2. In the presence of pulmonary stenosis, however, blood is shunted across the VSD into the aorta and arterial desaturation and cyanosis result.
3. The severity of cyanosis is dependent on the degree of right ventricular outflow obstruction. When this is moderate, a balanced shunt across the VSD occurs and cyanosis may be mild or absent.

Question 3

TOF - clinical features

Answer 3

1. Tetralogy of Fallot presents in early infancy with the following:
2. Cyanosis: usually not present at birth and leading to clubbing.
3. Paroxysmal hypercyanotic spells (‘tet spells’, seen in infancy): (5)
   i. Spontaneous/unpredictable onset
   ii. Tachypnoea; restlessness
   iii. Increasing cyanosis, then becoming white and floppy. Potentially dangerous.
   iv. Duration ranges from a few minutes to hours
   v. Severe episodes result in syncope and occasionally convulsions/hemiparesis.

Question 4

TOF - ix (4)

Answer 4

Bedside

1. ECG
   - Usually shows RVH

Imaging

2. CXR
   - Heart size normal
   - Uptilted apex and concave pulmonary segment associated with reduced lung vascularity (oligaemia)
   - Severe case: cardiac contour may resemble the shape of a wooden clog (coeur en sabot) - often referred to as ‘boot-shaped
3. Echo** - diagnostic.
4. Cardiac catheterisation is rarely performed, but may be indicated if coronary anatomy is unclear on U/S imaging

Question 5

TOF - mx

Answer 5

1. Severe tetralogy of Fallot with worsening cyanosis in early neonatal period requires prostagladin E infusion; (see b p.58) and surgery (e.g. modified
   Blalock–Taussig shunt) in order to maintain pulmonary blood flow and oxygenation.
2. Definitive surgery to repair the underlying heart defects is carried out from 4mths of age onwards.
3. Mx of ‘tet spells’: (5)
   i. Place the patient in the knee-to-chest position
   ii. Administer oxygen
   iii. Insert IV line and administer phenylephrine, morphine sulphate, and propranolol
   iv. Prolonged attacks require sodium bicarbonate
   v. Refer to cardiac centre

More on ‘tet spells’:
- Patients may have attacks of paroxysmal hyperpnoea and increased cyanosis that occur spontaneously or after early morning feeds, prolonged crying, or defecation

Question 6

TOF - prognosis

Answer 6

Untreated, the combination of right to left shunt, chronic cyanosis, and polycythaemia predispose to:
1. Cerebral thrombosis and ischaemia.
2. Brain abscess.
3 Bacterial endocarditis.
4. Congestive cardiac failure.
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5. 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.