Tetralogy of Fallot and the hypercyanotic spell

What it is

Tetralogy of Fallot is the most common form of cyanotic congenital heart disease. Four things make it:

• Ventricular septal defect
• Pulmonary stenosis
• Right ventricular hypertrophy
• Overriding aorta

How severe it runs depends on the degree of right ventricular outflow obstruction, which is the pulmonary stenosis.

How it presents

Cyanosis, SOB on exertion and on feeding, cyanotic spells, clubbing, poor development, squatting during episodes of cyanosis, metabolic acidosis, fatigue and dyspnoea.

The physical signs seen are central cyanosis, clubbing of the fingers and toes, and a loud harsh ejection systolic murmur with split S2. The murmur is that of the pulmonary stenosis.

The hypoxic or tet spell is an episodic central cyanosis due to total occlusion of right ventricular outflow. During a spell the child typically becomes restless and agitated and may cry inconsolably; toddlers may squat; the skin turns bluish during episodes of crying or feeding. In severe spells prolonged unconsciousness and convulsions, hemiparesis, or death may occur.

How it is diagnosed

• ECG: right axis deviation and right ventricular hypertrophy
• Chest X ray: boot shaped heart
• ECHO confirms the diagnosis and shows the anatomical features, including the pulmonary stenosis