Heart Valve Malformation in Dogs

In dogs, as in humans, the heart is made up of four chambers: two atria and two ventricles. On either side, the atrium and ventricle are separated by a valve which allows the blood to flow only one way. Blood coming from the body enters the right atrium; it passes through the tricuspid valve into the right ventricle before being pumped to the lungs when the heart contracts. Returning from the lungs, the oxygen-rich blood enters the left atrium and passes through the mitral valve before being pumped back into the body. Congenital defects can cause malformation of either of these two valves, called atrioventricular valve dysplasia. Deformities in either the mitral or tricuspid valve allow a small amount of blood to leak back through the valve in the wrong direction (called valve regurgitation) so that the heart has to work harder to pump the same amount of blood. With mild deformities, dogs may have very few symptoms, but severely affected dogs will develop congestive heart failure at a young age. Puppies may have trouble with strenuous exercise or fail to grow properly. Other symptoms may develop as heart dysfunction gets worse, including a swollen abdomen from fluid accumulation, difficulty breathing, and bluish discoloration of mucus membranes. Inherited atrioventricular dysplasia is present at birth and symptoms typically become apparent in puppies or young dogs as opposed to valve degeneration which may cause congestive heart failure to develop with age. Tricuspid valve dysplasia has been defined as an autosomal recessive trait in Labradors, but in most cases the mode of inheritance isn’t known. Puppies may have more severe symptoms than their parents, so even mildly affected dogs shouldn’t be bred.

Congenital malformation can occur in the either of the valves that connect the atrium and ventricle chambers in the heart. This is called atrioventricular dysplasia. The deformity will force the heart to work harder and dogs may develop congestive heart failure at a young age.

These are some of the symptoms you might notice in a dog with heart valve malformation.

• Exercise intolerance
• Stunted growth
• Enlarged jugular veins on the neck
• Labored breathing
• Fainting (syncope)
• Heart murmur or irregular heartbeat
• Rapid breathing (tachypnea)
• Crackle sounds in the chest
• Swollen abdomen (ascites) 
• Enlarged jugular veins in the neck
• Bluish discoloration to the gums and other mucus membranes (cyanosis)

Types

• Tricuspid valve dysplasia causes right-sided congestive heart failure because the heart is no longer pumping the right amount of blood to the lungs; fluid accumulation in the abdomen, lungs, and even the legs is common
• Mitral valve dysplasia causes left-sided congestive heart failure with low cardiac output and dogs will be more likely to show symptoms or weakness, fainting, and bluish gums

Atrioventricular dysplasia is inherited. These are some factors which might make it more likely in your dog.

• More common in certain breeds
• Tricuspid valve dysplasia  (Labrador Retrievers , German Shepherds, Gray Pyrenees, Old English Sheepdogs)
• Mitral valve dysplasia  (Bull Terriers, Newfoundlands, Great Danes, Golden Retrievers, Dalmatians)
• One of both parents has the condition
• More common in males

Many dogs with atrioventricular dysplasia have a heart murmur which is audible before symptoms become apparent. The veterinarian may notice this on a routine check-up. Any heart murmur that persists for more than 2 or 3 weeks should be tested further. Sometimes a vibration called a thrill may be palpable above the affected chamber. The veterinarian may suspect atrioventricular dysplasia, especially if your dog is young and belongs to an affected breed, but further testing will be necessary. Heart valve malformation will be diagnosed with chest x-rays, electrocardiography, and echocardiography, an ultrasound of the heart. The x-ray may show chamber enlargement while abnormal rhythms will be recorded on the electrocardiogram. If fluid is present in the lungs or abdomen, this will also be visible on an x-ray. Echocardiography gives the clearest picture and will usually show specifically where the deformation is located. The veterinarian may also be able to tell you how severe the defect it is and possibly give you an idea of your dog’s outlook.

Treatment will depend on the severity of the problem. Prosthetic heart valve replacement is not common in dogs, so it’s unlikely that surgical treatment will be a possibility. Mildly affected dogs may remain asymptomatic for years and don’t need to be treated. Dogs that are showing signs of congestive heart failure will be given appropriate medication, including diuretics and Ace inhibitor to help eliminate fluids and support heart function. Abdominocentesis, insertion of a tube to remove fluid from the abdomen, may be necessary especially with tricuspid valve dysplasia. The veterinarian may also prescribe a low-sodium diet.

A complete recovery from atrioventricular dysplasia is unlikely, but dogs with mild cases may live for a numbers of years with careful management. Severe malformation doesn’t have a good outlook since the heart will have to work too harder to maintain a normal oxygen level and will weaken over time. The veterinarian can usually give you a good idea of how severe your dog’s problem is upon diagnosis.