Tetralogy of Fallot

Tetralogy of Fallot

is the most common Cyanotic heart disease in children. The condition causes mixing of deoxygenated blood with the oxygenated blood being pumped out of the heart and into the circulatory system of blood vessels, Causing-

• hypoxemia.
  
  
• cyanosis, a bluish color of the skin, lips, and membranes inside the mouth and nose.

The 4 abnormalities (tetralogy) of the heart described by Fallot include the following:

• Right ventricular hypertrophy: Narrowing or blockage of the pulmonary valve and/or muscle under the pulmonary valve coming out of the right ventricle. This restriction to blood outflow causes an increase in right ventricular work and pressure, leading to right ventricular thickening or hypertrophy.
  
  
• Ventricular septal defect (VSD): This is a hole in the heart wall (septum) that separates the 2 ventricles. The hole is usually large and allows oxygen-poor blood in the right ventricle to pass through, mixing with oxygen-rich blood in the left ventricle. This poorly oxygenated blood is then pumped out of the left ventricle to the rest of the body. The body gets some oxygen, but not all that it needs. This lack of oxygen in the blood causes cyanosis.
  
  
• Abnormal position of the aorta: The aorta, the main artery carrying blood out of the heart and into the circulatory system, exits the heart from a position overriding the right and left ventricles. (In the normal heart, the aorta exits from the left ventricle.) This is not of major importance in infants.
  
  
• Pulmonary valve stenosis (PS): The major issue with tetralogy of Fallot is the degree of pulmonary valve stenosis, since VSD is always present. If the stenosis is mild, minimal cyanosis occurs, since blood still mostly travels to the lungs. However, if the PS is moderate to severe, a smaller amount of blood reaches the lungs, since most is shunted right-to-left through the VSD

Investigations:

CXR - baseline
ECG - yearly to assess rhythm and QRS duration
TTE - regularly (yearly or more frequent if severe PR and RV dysfunction, can be 2 or 3 yearly if very good surgical result and no new symptoms) (NB. It is easy to under estimate the degree of PR by colour follow alone) To assess pulmonary valve function, proximal PA anatomy, RV size and function, LV function, aortic root size and degree of aortic regurgitation.
Catheterisation - for dilatation / stenting of pulmonary arteries
MRI - becoming investigation of choice for proximal pulmonary artery anatomy, RV size and function and assessment of pulmonary regurgitation
Holter - for symptoms and screening for VT or high grade ectopy in those with marked RV dilatation or QRS > 180ms
Exercise test / CPEX - exercise capacity serial assessment, pre-pregnancy counselling

Additional investigations - EP studies for those with symptomatic atrial or ventricular arrhythmias or unexplained syncope or pre-syncope


Indications for intervention

Unrepaired tetralogy of Fallot (at any age)
Significant RVOT or branch PA stenosis (RV pressure > half systemic)
Severe pulmonary regurgitation with dilatation and dysfunction of the RV
Aortic regurgitation
Arrhythmias in presence of repairable haemodynamic sequela

TREATMENT OPTIONS
Surgery (+/- anti-arrhythmia procedures)

Percutaneous pulmonary valve implantation (for those with an RV to PA conduit of suitable size only)

Percutaneous pulmonary artery angioplasty and stenting