Fallot like physiology

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Fallot like physiology – cyanotic heart disease with low pulmonary blood flow

Basic components of this physiology are a large ventricular septal defect (or single ventricle) and severe pulmonary stenosis so that there is right to left shunt across the VSD and low pulmonary blood flow due to the pulmonary stenosis. They can develop hypercyanotic spells and cerebrovascular accidents while they seldom go in for heart failure, unlike the congenital cyanotic heart diseases with increased pulmonary blood flow. Chest X-ray shows pulmonary oligemia and cardiac size is seldom enlarged. The conditions included in this physiology are:

  1. Tetralogy of Fallot
  2. D- Transposition of great vessels (TGA) with ventricular septal defect (VSD) and pulmonary stenosis (PS)
  3. L- TGA with VSD and PS
  4. Tricuspid atresia with VSD and PS
  5. Double outlet right ventricle (DORV) with VSD and PS
  6. Single ventricle with PS

Beyond the age of 4 years, 90% of Fallot like physiology will be due to Tetralogy of Fallot. In almost all these conditions, if the pulmonary stenosis is absent, they have high pulmonary blood flow because of the VSD. In fact many cases of Tetralogy of Fallot in later life, may have a phase of increased pulmonary blood flow in early life before the development of right ventricular outflow tract obstruction. This type of conversion is known as Gasul variant or phenomenon.1


  1. Gasul BM, Dillon RF, Vrla V, Hait G. Ventricular septal defects; their natural transformation into the cyanotic or noncyanotic type of tetralogy of Fallot. J Am Med Assoc. 1957 22;164:847-53.

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