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Aina Meducci 2012


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Tetralogy of fallot (ToF)

I have been out all weekends; to classes, clinics, farms and studying for tests. So far I have encountered many interesting cases that I thought it will be nice to share with you dear readers.

In past 2 weeks, I have come into pathology about circulatory system involving heart and vessels. Above all matters what interest me the most is the Tetralogy of fallot of which it is quite rare to happen but it existed in certain breed of dogs. Lets us review.


What is Tetralogy of fallot (ToF)?

Tetralogy of Fallot (TOF) is one of the most common congenital heart disorders. This condition is classified as a cyanotic heart disorder, because tetralogy of Fallot results in an inadequate flow of blood to the lungs for oxygenation (right-to-left shunt).Patients with tetralogy of Fallot initially present with cyanosis shortly after birth, thereby attracting early medical attention.

Normal heart vs ToF

Louis Arthur Fallot, after whom the name tetralogy of Fallot is derived, was not the first person to recognize the condition. Stensen first described it in 1672; however, it was Fallot (1888) who first accurately described the clinical and complete pathologic features of the defects. It was detected in human and later were discovered in animal as well.

Tetralogy of fallot (TOF) in dogs is consists of four heart abnormalities that result in insufficiently oxygenated blood being pumped into the dog’s body. It is the most common cyanotic heart diseasein dogs. TOF consists of pulmonic stenosis, a ventricular septal defect, ventricular hypertrophy defect, and an overriding aorta (altering position of aorta). For this there are not so many dog medications options available.


Features of ToF

Common dogs breed with ToF


English bulldog

Etiology and pathophysiology

The cause(s) of most congenital heart diseases are unknown, although genetic studies suggest a multifactorial etiology.

The hemodynamics of tetralogy of Fallot depend on the degree of right ventricular (RV) outflow tract obstruction (RVOTO). The ventricular septal defect (VSD) is usually nonrestrictive, and the RV and left ventricular (LV) pressures are equalized. If the obstruction is severe, the intracardiac shunt is from right to left, and pulmonary blood flow may be markedly diminished. In this instance, blood flow may depend on the patent ductus arteriosus (PDA) or bronchial collaterals.

Clinical signs and symptoms
  • Difficulty with feeding
  • Blue (pale-cynotic)
  • Failure to thrive
  • Heart Murmur – Since this is a congenital heart disorder, the likelihood that the heart will exhibit a murmur is great. The heart will often have a loud murmur due to the fact that the heart chambers will be abnormal in their function and capacities of blood. The murmur can change over time if the Tetralogy of Fallot does not cause the death of the child early on
  • Difficulty in Gaining Weight – Since the body relies on the blood circulation to send andreceive nutrients throughout the body,animal that survive to may see a reduced gain in weight because the nutrients needed for growth are not as readily available as is in animal thatdo not have the Tetralogy of Fallot.
  • Dyspnea – Shortness of breath, also known as dyspnea, is very possible as the lungs will not be able to get enough blood flow to properly saturate the blood with oxygen. This will create a much more difficult time for those who have Tetralogy of Fallot to breathe correctly.

Differential diagnosis

  • Aortic Stenosis
  • Pediatric Acute Respiratory Distress Syndrome
  • Pediatric Apnea
  • Pediatric Bronchiolitis
  • Pediatric Foreign Body Ingestion
  • Pediatric Patent Ductus Arteriosus Surgery
  • Pediatric Pneumonia
  • Pneumothorax
  • Pulmonic Valvular Stenosis
  • Sickle Cell Anemia


  • Complex surgery can be done to achieve, e.g. systemic to pulmonary shunts (subclavian to pulmonary or Blalock-Taussig, ascending aorta to pulmonary artery or Potts)
  • Drugs (e.g. beta-blocker) can even be used.AVOID SYSTEMIC VASODILATORS as they compromise venous return
  • Address item with phlebotomy and replace blood volume with crystalloids.
  • Cage rest, oxygen and supportive therapy for metabolic acidosis.

Source: Tetralogy of fallot; emedicine.medscape.com, Tetralogy of fallot; www.tetralogyoffallot, Common heart disease in dogs; Cute home pets,

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