What is Tetralogy of Fallot?

Tetralogy of Fallot is a rare but dangerous combination of defects that are developed when the puppy is still an embryo. In a dog with Tetralogy of Fallot, the heart and great blood vessels have not been properly formed. These dogs have four defects: ventricular septal defect, pulmonic stenosis, over riding aorta and right ventricular hypertrophy secondary to the pulmonic stenosis.

A dog with a ventricular septal defect has a defect or hole in the wall that separates the right and left ventricles of the heart. A dog with pulmonic stenosis suffers from partial obstruction of the blood flow that runs from the right side of the heart through the pulmonic valve. When it comes to the aorta, it is not positioned in its correct place in dogs with Tetralogy of Fallot.

Dog breeds at higher risk of Tetralogy of Fallot

The mode of inheritance for this problem is believed to be austosomal recessive with variable expression, and affected pups should not be used for breeding, nor should their parents. Siblings can be used for breeding, but only after meticulous examination. Relative to other breeds, the Keeshond and the English bulldog is at a higher risk of being born with Tetralogy of Fallot. 

Tetralogy of Fallot symptoms in dogs

The severity of the Tetralogy of Fallot symptoms will depend on how severe the abnormality is. In dogs with mild Tetralogy of Fallot, the only symptom can be a heart murmur that the vet can notice during a physical examination. The pulmonic stenosis can be so mild that it never causes any significant problems for the dog.

In many cases, Tetralogy of Fallot will however cause problems for the dog. The symptoms can often be seen when the dog is still a puppy. An affected puppy can for instance be weak and exercise intolerant. It can also fail to grow as big and heavy as it should. In some dogs, the pink mucous membranes will become grey since the blood is too poorly oxygenated.

In dogs where the Tetralogy of Fallot is not mild, the average life span is no more than 1-2 years without treatment. The available treatment can prolong the life of the dog, but it is only effective in roughly 50 percent of the cases. Even with treatment, the dog must be forced to a limited activity level throughout its entire life. 

Tetralogy of Fallot treatment for dogs

Medical and surgical treatments can be used to manage this condition, but open heart surgery is necessary if your want to cure the problem. Open heart surgery is very dangerous for the dog. If your dog weighs at least 10 kilograms, a less dangerous type of heart surgery is available but this will only serve to milder the effects of Tetralogy of Fallot, not cure the condition. This procedure will reroute poorly oxygenated blood to the lungs of the dog. This type of heart surgery is helpful for roughly 50% of the dogs, but even in cases where the procedure is a success you need to limit the activity level of your dog. In addition to heart surgery, medications can create a better life for dogs with Tetralogy of Fallot. Beta-adrenergic blockers can for instance reduce the muscular obstruction that can occur as a result of pulmonic stenosis. This will make it possible for a greater amount of blood to flow to the lungs.

Cardiovascular and circulatory problems in dogs: (click for more info)
Aortic stenosis in dogs
Congestive heart failure in dogs
Degenerative mitral valve disease in dogs
Dilated cardiomyopathy in dogs
Heart valve dysplasia in dogs
Hemolytic anemia in dogs
Patent ductus arteriosus in dogs
Pericardial effusion in dogs
Pulmonary hypertension in dogs
Pulmonic stenosis in dogs
Thrombocytopenia in dogs
Ventricular septal defect in dogs
Atrial septal defect in dogs
Tetralogy of Fallot in dogs
Von Willebrand disease in dogs