Tetralogy of Fallot in Cats

Severe cases of Tetralogy of Fallot in kittens are often detectable very early in life because of slow development and failure to thrive. The most severe cases are often fatal within the first year of life as corrective surgery for this condition is not a viable option in small animals. The symptoms of less severe cases, however, may not be detected until later in life and range from a low tolerance for physical exertion to heart murmur. These milder cases can often be managed with medication and by limiting physical activity, allowing some cats with Tetralogy of Fallot to live a normal life.

Tetralogy of Fallot is a rare congenital heart condition that is a combination of four simultaneous heart defects that are present even before birth. These defects overtax the heart, increase the mass of the heart muscle to an unhealthy size, cause low levels of oxygen in the bloodstream, and can thicken the blood. If you have a kitten that seems delayed in growth, has shortness of breath, and is chronically fatigued, make an appointment with your veterinarian so that tests may be done to determine if your cat suffers from this condition. 

Tetralogy of Fallot can be a very serious condition in a cat. If you notice the following symptoms, you should contact your veterinarian immediately. The prevalence of these symptoms will be dependent upon the severity of each case.

• Slow growth as compared to other littermates 
• Chronic fatigue
• Difficulty breathing
• Low tolerance for exercise
• Cyanosis (blue/purple coloring of skin and mucous membranes)
• Heart murmur
• Irregular heartbeat

The cause of this congenital heart condition is a recessive gene that can be carried by either the mother or the father that results in a failure of proper development of the heart while the animal is an embryo. It can only be avoided if cats that are known to be carriers of this gene are prevented from breeding. This gene results in four simultaneous developmental abnormalities in the heart. These abnormalities are:

• Pulmonic Stenosis: obstruction of blood flow from the right side of heart
• Ventricular Septal Defect: defect/hole in the wall that separates the right and left ventricles
• Dextroaorta: the aorta diverts blood away from the lungs where it would be oxygenated, resulting in unoxygenated blood in the circulatory system
• Right Ventricular Concentric Hypertrophy: thickening of the heart’s right ventricular wall

If Tetralogy of Fallot is suspected, a veterinarian will begin with a thorough physical examination of the cat, listening to breathing, looking for blue or purple coloration of areas of skin and mucous membranes, and listening for a heart murmur. In addition to these initial steps, the veterinarian may run the following tests that will allow the vet to see if the heart abnormalities that are associated with Tetralogy of Fallot are present:

• Thoracic radiograph (X-rays of the Chest)
• Echocardiogram (ultrasound of the heart)

If it is determined that your cat has Tetralogy of Fallot, treatment will be dependent upon the severity of the heart defects that are present and the age of the animal. Corrective surgery for Tetralogy of Fallot in small animals is extremely rare because of high mortality rates. Since corrective surgery is not a viable option, treatments for Tetralogy of Fallot in cats will likely be for the entire life of the animal. The following treatments will likely be explored by your veterinarian:

Exercise Restriction 

Often the first and most basic form of treatment for a cat weakened by Tetralogy of Fallot. A cat living with this condition will likely need to stay indoors.

Medication

Beta Blockers may be used to reduce adrenal “shocks” to the heart and hydroxyurea used to lower red blood cell production

Periodic Phlebotomy

A procedure commonly known as bloodletting may improve circulation.

Surgical Procedures 

Rarely, due to their high risk, palliative procedures may be performed to increase blood flow.

Since corrective surgery for Tetralogy of Fallot is not a viable option for cats, animals that are born with this combination of developmental defects will live with this condition for the entirety of their lives. The goal of treatment for cats with Tetralogy of Fallot is not to heal or cure them, but rather to help them live as full a life as possible while coping with this condition. While severe cases will often be fatal for kittens, for milder cases exercise restriction, medication, regular veterinary examinations to monitor treatment, and perhaps more invasive palliative veterinary procedures can provide a fuller and longer life, though still sometimes shorter than average. Cats with this condition should likely be kept indoors and free from as many stressors as possible such as loud noises, other rambunctious pets, and small children.