Congenital Heart Disease in the Emergency Department

Previous Lesson
Next Topic

Tetralogy of Fallot (ToF)

Right to Left Shunts

(1) Tetralogy of Fallot

TOF is the most common cause of cyanotic CHD.

In tetralogy of Fallot, as implied by the name, there are four cardinal anatomical features (see Fig 1):

  • A large VSD
  • Overriding of the aorta
  • Right ventricular outflow tract obstruction (pulmonary stenosis): this may be valvular, sub-valvular, and/or supra-valvular
  • Right ventricular hypertrophy

The most common cause of cyanotic CHD.

Comprises up to 10% of all CHD.

The pathophysiology relates to shunting of desaturated, systemic venous blood through the VSD to mix with the systemic cardiac output.

The greater the degree of obstruction to pulmonary blood flow, the larger the right-to-left shunt and the worse the desaturation.

Time of manifestation depends on the severity of right ventricular outflow tract obstruction and thus the amount of pulmonary blood flow; severe obstruction results in cyanosis in the newborn period and presents in the first week of life with cyanosis or collapse.

Right ventricular outflow tract obstruction: determines the amount of cyanosis.

The direction of shunt depends on the extent of right ventricular outflow tract obstruction. The VSD is almost never restrictive in tetralogy of Fallot.

Fig 1: Tetralogy of Fallot

tetralogyoffallot

Clinical presentation

Symptoms
  • Most are diagnosed antenatally or following the identification of a murmur in the first month or two of life.
  • The degree of RV outflow obstruction determines the age and symptoms at presentation
  • Newborn: Cyanosis at this stage may not be obvious, although a few with severe RVOTO may present with severe cyanosis in the first few days of life (secondary to reduced pulmonary blood flow)
  • Older Children: May present with pulmonary over-circulation and CHF (Net left-to-right flow through the VSD)- pink TOF (adequate pulmonary flow)
“Tet” spells

Sudden hypoxic spells, characterized by tachypnea and hyperpnea, followed by worsening cyanosis.

Occurs due to transient increase in right ventricular outflow tract obstruction that involvesnarrowing of the infundibulum (the sub-pulmonary outflow tract)

Precipitating factors: Agitation and dehydration. Spells often are precipitated by crying

The classical description of severe cyanosis, hypercyanotic spells and squatting on exercise, developing in late infancy.

It is important to recognize hypercyanotic spells, as they may lead to cerebrovascular accidents and even death if left untreated. They are characterised by a rapid increase in cyanosis, usually associated with irritability or inconsolable crying because of severe hypoxia, and breathlessness and pallor due to tissue acidosis.
Physical Signs
  • Systolic thrill at the lower and middle left sternal border
  • Loud single S2
  • Loud systolic ejection murmur at the lower left sternal border
  • With increasing right ventricular outflow tract obstruction, the murmur softens and cyanosis increases. When the severity of obstruction worsens, more blood is shunted across the VSD.
  • During a hypercyanotic spell, the murmur may be inaudible
  • Clubbing of the fingers and toes may be present in older children

Investigations

Chest radiograph
  • Boot shaped heart (with elevation of the cardiac apex due to right ventricular hypertrophy)
  • Normal heart size with decreased pulmonary vascular markings reflecting reduced pulmonary blood flow (may be normal or engorged in pink patients without significant PS)
ECG
  • Right axis deviation and Right ventricular hypertrophy
Echocardiography
  • This will demonstrate the cardinal features, but cardiac catheterisation may rarely be required to show the detailed anatomy of the coronary arteries

Management

Initial management is medical, with definitive surgery at around 6 months of age. It involves closing the VSD and relieving right ventricular outflow tract obstruction, sometimes with an artificial patch, which extends across the pulmonary valve.

Infants who are very cyanosed in the neonatal period require a surgically placed shunt to increase pulmonary blood flow. However, the trend now is to offer complete surgical repair when indicated without shunt palliation.

Hypercyanotic spells

Hypercyanotic spells are usually self-limiting and followed by a period of sleep. If prolonged (beyond about 15 minutes), they require prompt treatment with:

  • Hypercyanotic spells are usually self-limiting and followed by a period of sleep. If prolonged (beyond about 15 minutes), they require prompt treatment with:
  • Knee-chest position: May help to reduce venous return and increase systemic vascular resistance, thereby decreasing right-to-left shunting
  • Fluid: 20 ml/kg bolus
  • Oxygen: high-flow
  • Beta-blockers: intravenous esmolol
  • Antibiotics: assume infection was the precipitating factor
  • Morphine can be used sparingly, with care to avoid respiratory depression, (50 100 mcg/kg sc/im/iv)
  • Alpha-agonist: this can be lifesaving if other measures have not worked quickly. Use phenylephrine (0.1 mg in a 10 ml syringe, dilute to 10 ml with saline, and give very small aliquots until pulse and cardiac output return). The patients hands and feet will go white temporarily
  • Hypercyanotic spells are an indication for early surgery. Do not send a child home from the emergency department (ED) without obtaining a cardiology consultation.

(2) Transposition of the Great Arteries

Second most common cause of cyanotic CHD diagnosed by 1 year of age

The most common cyanotic CHD that presents in the first day of life.

The aorta lies anteriorly and arises from the right ventricle; the pulmonary artery is relatively posterior and connected to the left ventricle (ventriculoarterial discordance). Deoxygenated blood is therefore returned to the body and oxygenated blood is returned to the lungs. The pulmonary and systemic circuits are arranged in parallel. Unless there is mixing of blood between them, this condition is incompatible with life.

The presentation for infants with TGA depends on the degree of blood mixing. Fortunately, there are a number of naturally occurring associated anomalies, e.g. VSD, ASD and PDA. Initial survival depends on the presence of a shunt, allowing mixing between the systemic and pulmonary circulations.

These infants present with cyanosis at birth because of right-to-left shunting, and the cyanosis becomes more severe when the ductus arteriosus closes.