Disease Description: A specific four-way developmental abnormality of the structures of the heart and associated great vessels.

Inherit Mode: While it can occur in any breed of dog, the keeshond is most commonly affected. Based on studies with affected keeshonden, the mode of inheritance is believed to be autosomal recessive with variable expression. This means that the problem can be transmitted from either the dam or the sire (or both) to a puppy, and that the degree of severity is unpredictable: in the same litter, some puipies may be gravely affected, some not at all, and some in between, in varying proportions.

Disease Symptom: As with other heart defects, the presence of symptoms and overall impact of tetralogy of Fallot depends on the severity of the defect. If a dog has tetralogy of Fallot with a very mild degree of pulmonic stenosis and a small ventricular septal defect, for example, then he or she may only have a heart murmur and a normal life with no associated problems. More serious cases are common, where puppies with this combination of defects experience weakness, failure to thrive and grow, a reduced tolerance for exercise, and general cyanosis (blue-grey coloration of the mucous membranes of the mouth and eyes, instead of the normal pale pink). These signs are the result of the delivery of poorly oxygenated blood to the different parts of the body. Mildly affected dogs may enjoy a normal life, but dogs with symptoms such as those described above often have a shortened lifespan. Tetralogy of Fallot does not cause suffering (there is no pain associated with it) but in its most severe forms it can confine a dog to a quiet, easygoing lifestyle.

Disease Cause: -

Disease Diagnose: Puppies with severe cases of this disorder may be weak and may grow poorly, and such symptoms are initial clues to a veterinarian that tetralogy of Fallot may be present. On closer physical examination, a veterinarian may identify cyanosis, and a heart murmur is apparent on listening to the heart with a stethoscope in all cases of tetralogy of Fallot. Definitive confirmation comes with thoracic radiographs (X-rays of the chest) and an echocardiogram (ultrasound of the heart; cardiac sonogram), both of which are noninvasive tests that can be performed without sedation in a majority of dogs.

Treat Method: Complex open-heart surgery is required to correct the condition, and this is routinely performed successfully in children. In dogs, however, surgery has a high mortality rate and is not considered a viable treatment option at this time. In the absence of definitive correction through surgery, tetralogy of Fallot is managed by giving daily medication at home to reduce the impact of sympathetic activity ("adrenaline rushes") on the heart, which can be especially strenuous on sick hearts like those with tetralogy of Fallot. These medications are called beta-blockers and include such prescription medications as atenolol, metoprolol, or carvedilol. Some dogs with tetralogy of Fallot develop a very high red blood cell count, which further hampers adequate tissue oxygenation. In these dogs, periodic phlebotomy (bloodletting) may restore a more normal viscosity or thickness to the blood, and thus improve circulation, or a medication to reduce red blood cell formation in the body (hydroxyurea) may be prescribed for this purpose. Regardless, dogs with tetralogy of Fallot that require medications need to have regular medical checkups, often every few months.

Breeder Advice: Affected pups and their parents (assumed to be carriers) should not be bred. Siblings that appear normal after careful physical examination may be used for breeding, with meticulous follow-up of offspring. The offspring should be examined with echocardiography at age 8-12 weeks and, if affected, the breeding of the parents should be discontinued.

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