Tetralogy of Fallot

Anatomy & Physiology

The 4 components are a ventricular septal defect, pulmonary stenosis, right ventricular hypertrophy and an overriding aorta. The VSD is always large and the murmur is generated by the increased flow across the pulmonary valve. The degree if right to left shunting and hence the amount of cyanosis depends upon the severity of the pulmonary stenosis. The right ventricular hypertrophy is a consequence of the pressure load on the ventricle.

Presentation

Presentation depends on degree of pulmonary stenosis. If severe then lung blood flow is reduced & cyanosis is observed as a neonate. If it is less severe as the degree of pulmonary stenosis increases with age it presents later in infancy. Clubbing develops by around 6 months of age.

Sometimes it may present with hypercyanotic spells. In these the degree of cyanosis markedly & suddenly increases often without warning due to reduced pulmonary blood flow. Hypoxaemia leads to acidosis & sometimes death. It is therefore treated as a medical emergency.

An ejection systolic murmur is present at the mid LSE 3/6 due to pulmonary stenosis.

The features of the 22q- syndrome may be present.

Investigations

Electrocardiogram

Right ventricular hypertrophy is the hallmark of the ECG - demonstrated as here with right axis deviation, upright T waves & tall R waves in V_1-3

Chest X-ray

The pulmonary artery bay is empty (arrow) & the apex upturned thus giving the “boot shaped” heart appearance.

The lung fields are oligaemic.

Echocardiogram

The VSD is usually large (arrow) & the aortic override (ventricular septum pointing at the midline of the aortic valve - starred) is easily demonstrated.

The pulmonary artery can be imaged (right) and the Doppler velocity (below) in the pulmonary artery is increased (4 m/s) due to the PS. Note the double envelope due to the fixed (valvar) and dynamic (subvalvar muscular) obstruction

. Doppler

Natural History

Only 50% survive to the age of 2 years (Bertanou et al. Am J Cardiol 1978) and increasing cyanosis throughout early life leads to limitation from breathlessness & the complications of extreme cyanosis (thromboses, bleeding, cerebral abscess formation) limits both the quality and length of survival of the remainder.

Management

If symptomatic in early infancy then palliation is undertaken with a modified BT shunt.

Routine repair is usually undertaken at 6-18 months age with VSD closure by a tangential patch (see right) to correct the override & the pulmonary stenosis is relieved with a patch).

VSD patch

Prognosis

For the majority is excellent. The perioperative mortality is less than 5% and the long term survival is excellent - 76% at 40 years (Moller et al Am J Cardiol 2001). As significant number require re-operation for residual pulmonary stenosis or regurgitation. This may involve a replacement homograft. There is also a risk of late sudden death due to arrhythmias.

This page was last edited 16/2/2004

Acknowledgements