horse with tetralogy of Fallot

Tetralogy of Fallot

What is tetralogy of Fallot?


  • Tetralogy of Fallot is a set of four defects of the heart and blood vessels that can occur in foals at birth (congenital).
  • Tetralogy of Fallot affects the flow of blood through the heart, which can cause shortness of breath, fatigue, and exercise intolerance, among other signs.
  • Treatment for tetralogy of Fallot in horses is primarily supportive.
  • There are currently no identified strategies to prevent tetralogy of Fallot in horses.

Tetralogy of Fallot is a set of four cardiovascular defects that are present at birth (congenital) and affect the flow of blood through the heart:

  1. the obstruction of blood flow from the right ventricle (pulmonic stenosis),
  2. an opening between the right and left ventricles of the heart that causes the blood to flow from the left to the right ventricle when the heart contracts (ventricular septal defect),
  3. a rightward abnormal positioning of the origin of the aorta,
  4. thickening of the muscles in the right ventricle.

This condition is named after Étienne-Louis Arthur Fallot, a 19th century French physician who recognized that these four heart defects occurred together. In Latin, the word “tetra” means four - hence “tetralogy”.

Tetralogy of Fallot has been identified in several species, including horses, humans, dogs, and others. It is rare and caused by abnormal development of the embryonic heart during organogenesis.

What are the clinical signs of tetralogy of Fallot?

Clinical signs of tetralogy of Fallot can include a bluish tinge to skin and membranes (cyanosis), fatigue, shortness of breath, exercise intolerance, collapse, and seizures due to reduced blood flow to the lungs. Stunted growth may be observed in affected horses. A heart murmur is often present.

How is tetralogy of Fallot diagnosed?

Tetralogy of Fallot is diagnosed by cardiac auscultation (listening to the heart with a stethoscope), electrocardiography (cardiac ultrasound), x-rays, and blood work.

How is tetralogy of Fallot treated?

Treatment for tetralogy of Fallot is primarily supportive and may include medication. Heart surgery is rarely performed in horses.

What is the prognosis for tetralogy of Fallot?

The prognosis for horses diagnosed with tetralogy of Fallot varies depending on the severity of the defects, but is generally guarded to poor. Some affected horses reach adulthood.

How can tetralogy of Fallot be prevented?

There are currently no known preventative measures for tetralogy of Fallot in horses.

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