When the valve between the two right chambers of the heart (the "tricuspid" valve, between the right atrium and right ventricle) fails to form a tight seal, the blood pumped from the atrium into the ventricle tends to be "regurgitated" back into the atrium.
Some background: The heart muscle is a pump that moves blood through the four chambers with involuntary contractions that promote the one-directional flow of the blood. The valves between the chambers prevent the backflow of blood into the preceding chamber, thus keeping the blood flowing in the direction it should. When the valves are misshapen or otherwise poorly formed, blood moves backwards, not forwards in the heart. This means the heart has to work harder to pump the volume of blood the body needs for normal functions.
In tricuspid valve dysplasia, the developing embryo fails to allow the flaps of the valve to "loosen" from their normally flattened position during development. The upshot is the unfortunate inability of a poorly shaped valve to keep some of the blood from moving backwards. The degree of dysplasia (it varies) will determine how much of this blood moves the wrong way and, hence, the severity of symptoms.
Large breed dogs are most commonly afflicted, with male dogs overrepresented.
Symptoms and Identification
Most dogs will be diagnosed with a heart murmur before the onset of any symptoms of tricuspid valve dysplasia. If the murmur is progressive or significant, veterinarians will recommend X-rays, EKGs (electrocardiograms) and echocardiograms (heart ultrasounds).
X-rays may show an enlarged right side of the heart while the EKG may reveal abnormal heart rhythms caused by this enlargement. The best tool, however, is the echocardiogram. This kind of ultrasonography identifies the abnormal shape of the valve.
The most common symptoms of tricuspid valve dysplasia are related to right-sided heart failure. With this condition, dogs will have distended abdomens (ascites) due to the fluid accumulation that occurs when the blood "backs up" on its way back to the heart. They may also pant or faint if they're unable to get enough oxygen into their blood as a result of the poor volume of blood reaching their lungs (blood from the right side of the heart flows into the lungs to receive oxygen).
Occasionally, life-threatening abnormal heart rhythms may result. These can lead to sudden death.
Larger breed dogs are predisposed to this hereditary disease, especially the Borzoi, Boxer, German Shepherd, Great Dane, Great Pyrenees, Irish Setter, Labrador Retriever, Newfoundland, Old English Sheepdog, and Weimaraner.
Treatment for severe cases of tricuspid valve dysplasia is currently not available. Though "open-heart" surgeries have been attempted, the high risks assumed with this kind of surgery are not usually considered worthwhile given the alternatives: drugs, low-sodium diets and exercise restriction.
Drugs employed are designed to treat the symptoms of the disease rather than the problem itself. Diuretics for fluid removal, beta-blockers for central blood pressure reduction and others to relieve the heart failure are typically prescribed.
The good news: Tricuspid valve dysplasia is not typically terribly expensive to treat. Now the bad news: That's because there are no definitive therapies available. Diagnosing the condition, however, may be expensive. Since echocardiograms can cost up to $500-$600, diagnosing and monitoring the disease can really add up.
New heart drugs can also add up. For large dogs, this can mean $100-$200 a month in medication for some unfortunate cases.
Thankfully, many patients don't require any treatment at all. Others may not need any until later in life, thus limiting the lifelong expenses associated with the condition.
Preventing tricuspid valve dysplasia is all about careful weeding out of affected dogs from the breeding pool. Preventing reproduction in any affected pet is critical. Since very mild forms of the disease may be undetected through conventional means, screening dogs of highly affected breeds (with echocardiography) prior to breeding is strongly recommended.
Work is currently being undertaken to identify the gene(s) involved in tricuspid valve dysplasia. The goal is to develop a genetic test so that veterinarians may screen dogs inexpensively at an early age.
Patterson, D.F. 1996. The genetics of canine congenital heart disease. ACVIM-Proceedings of the 14th Annual Veterinary Medical Forum: 225-226.