What is Tetralogy of Fallot?
Tetralogy of Fallot is rare and estimated to occur in 1 in 4,000 dogs at birth. Since dogs are born with the disease, they are most likely to be brought in for treatment between the age of two and eight months. Because the disease means that an affected dog’s tissues are in a constant state of oxygen deprivation, Tetralogy of Fallot is deadly if left untreated, as most dogs will die before they reach a year old if they do not receive treatment. As it is congenital, it is more likely to occur in purebred dogs, and specifically, English Bulldog and Keeshond breeds have a higher occurrence of Tetralogy of Fallot than other breeds.The broader definition of Tetralogy of Fallot entails a congenital heart defect that is rare. Caused by the convergence of four heart abnormalities: right ventricular hypertrophy (thickening of heart muscle on right ventricle), an overriding aorta, pulmonic stenosis (obstruction of blood flow through the pulmonary valve) and a the hole between the two ventricles (technically known as the ventricular septal defect).
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Symptoms of Tetralogy of Fallot in Dogs
- Dyspnea, or shortness of breath
- Low or decreased exercise intolerance
- Slower rate of growth than littermates
- Cyanosis, or blue or purple coloration of skin and mucous membranes due to low oxygen saturation
Causes of Tetralogy of Fallot in Dogs
Tetralogy of Fallot is congenital.
Diagnosis of Tetralogy of Fallot in Dogs
The veterinarian will start the visit with a wellness examination, which involves a thorough physical examination throughout the entirety of your dog. This will include listening to your dog’s heart with a stethoscope, which may or may not reveal a heart murmur. The presence of a heart murmur is an indicator of Tetralogy of Fallot; however, if the stethoscope fails to validate a heart murmur, or irregular beat, that does not always mean that your dog does not have the disease. A complete blood count measuring red and white blood cells and an chemical blood profile will be taken in order to examine your dog’s overall health and discover any other issues or alternative diagnoses. Pulse oximetry will be taken in order to measure the oxygen saturation level in your dog’s blood, as low blood oxygen is an indicator of Tetralogy of Fallot. X-rays of your dog’s heart and an echocardiogram (ultrasonic test of the hearts functioning) will be conducted in order to examine the state of your dog’s heart. Additional tests may include an ECG or electrocardiogram and angiocardiography, both of which can further measure the functioning of your dog’s heart in order to determine if she has all four of the defects that make of Tetralogy of Fallot.
Treatment of Tetralogy of Fallot in Dogs
Phlebotomy treatment may be utilized in order to restore the balance of red blood cells (known as hematocrit, or packed cell volume) to ideal levels. Blood will be removed and replaced with IV fluid at a ratio of one to two times the amount of blood drawn.
Hydroxyurea, a myelosuppressive agent, is a treatment that produces reversible bone marrow suppression and is an alternative to phlebotomy in order to restore hematocrit to ideal levels. Side effects include anorexia, vomiting, sloughing of nails and bone marrow hypoplasia.
Beta Blockers can be successful at treating hypoxemia, or low levels of blood oxygen. The most common beta blockers prescribed is propranolol.
Corrective Surgery includes open heart surgery and has not been studied extensively. Surgical methods such as cardiopulmonary bypass and anastomosis of the left subclavian artery to a pulmonary artery have been attempted few times with varying success. There is a high mortality rate in the surgery itself and a bad prognosis for dogs post-surgery. In addition to the risks associated with heart surgery and the limited success of surgeries in the past, there are financial and logistical impediments to finding a surgeon with the knowledge to perform such surgeries.
Recovery of Tetralogy of Fallot in Dogs
Since surgery is not a highly attractive option because of its poor prognosis, most dogs with Tetralogy of Fallot must be managed through medication and behavioral treatment. If your dog is prescribed medication, be sure to administer proper doses and monitor your dog’s health. Regular checkups will be required in order to monitor health and may include phlebotomy treatments. Behaviorally, it is important to keep your dog on strict exercise restriction in order to reduce the strain on the heart and stress to tissues.