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Tetralogy of Fallot

Tetralogy of Fallot is characterised by:

  • VSD

  • Overriding aorta – Aorta directly over VSD, so deoxygenated blood enters the aorta straight from the RV

  • Pulmonary stenosis (RV outflow tract obstruction) – Ejection-systolic murmur

  • RV Hypertrophy

“Illustration of terratology of Fallot” © Centers for Disease Control and Prevention CC0 1.0 (https://commons.wikimedia.org/wiki/File:Truncus_arteriosus.jpg)

Risk factors - Rubella infection, Maternal alcohol and diabetes


The pulmonary stenosis has multiple effects including:

  • Providing resistance against RV outflow, therefore encouraging flow through the VSD instead → Cyanosis (deoxygenated blood enters LV + aorta)

  • RV trying harder to pump through this resistance → RV Hypertrophy


The degree of this pulmonary stenosis is very important to assess as it's the main determinant of the severity of cyanosis.


Presentation

N.B. Most are diagnosed during antenatal scans.

  • Ejection-systolic murmur

  • Cyanosis

  • Poor feeding and weight gain

  • Tet Spells


Tet Spells

These are intermittent episodes of Cyanosis and Tachypnoea, in which the Right-to-Left shunt becomes temporarily worsened. It can last minutes to hours and may resolve spontaneously, or it can lead to reduced consciousness, seizures and even death. It is potentially life-threatening, so it requires rapid intervention.


It's caused by increases in pulmonary resistance or decreases in systemic resistance e.g. physical exertion as the CO2 builds up and acts as a systemic vasodilator, therefore reducing its resistence. Examples of this physical exertion can be walking, exercising, and crying.


The main management option is through manoeuvres that help with pulmonary circulation. The usual way of doing this is by having the child sit/held with their knees bent to their chest. As a result, this increases systemic resistance, therefore encouraging blood to enter and stay in the pulmonary circulation.


Other options of management include:

  • Prophylactic propranolol to relax the RV

  • Supplementary O2

  • IVF – increase pre-load and systemic resistance

  • Phenylephrine infusion – increase systemic resistance

  • Morphine – decrease respiratory drive for more effective breathing

  • Sodium Bicarbonate – treat any metabolic acidosis that occurs


Management

  • Prostaglandin infusion - This helps to maintain patency of the Ductus Arteriosus, therefore allowing blood to flow from the aorta into the pulmonary vessels

  • Surgical repair


N.B. NSAIDs are therefore completely contraindicated in such patients as they'll decrease the amount of prostaglandin, causing the closure of the ductus arterious, and subsequent cyanosis.


N.B. Usually, the prostaglandins are given in the interim before surgery is done to definitively treat the heart defect.




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