Heart Valve Diseases

Problems associated with the heart valves constitute the most common form of heart disease in dogs.

Types of Heart Valve Diseases

Chronic Valve Disease

For unknown reasons, the flaps of the valves between the atria and ventricles (lower chembers) can become thickened and distorted until their edges no longer meet when the valve shuts. This defect allows some blood to be forced back into one or both of the atria when the ventricles contract to expel blood from the heart. The seepage increases as the valve defect worsens. Sometimes, some of the muscular cords (cordae tendinae) holding the valve flaps in place rupture. If this happens, that part of the valve becomes useless.

Diagnosis of Chronic Valve Disease

During the initial stages of the valvular heart disease, there may be no obvious signs that anything is wrong. This condition is usually discovered during a routine examination, when a vet hears a heart murmur. When valve disease is present, the mitral valve, which lies between the atrium and the ventricle on the left side of the heart, is usually affected. The equivalent valve on the right of the heart, the tricuspid valve, is affected in only about one third of cases.

Treatment of Chronic Valve Disease

Chronic valve disease is an important cause of heart failure, a condition in which the heart cannot keep up with the workload. Treatment of valvular heart disease will not prolong a dog's life expectancy.

Congestive Heart Failure

A heart affected by a disease that reduces its pumping efficiency (most often chronic valve disease) can usually "compensate" for months or years. It usually does so by increasing in size. Eventually, the underlying disease leads to congestive heart failure, in which blood becomes backed up in the veins. This buildup, in turn, forces fluid out of the circulation into the body tissues, in the lungs and elsewhere.

Congestive heart failure can occur gradually or suddenly. The early signs include reduced exercise tolerance (becoming out of breath very quickly during exercise) and lethargy. Because congestive heart failure occurs in older dogs, these signs are often mistaken as natural age-related changes. Soon, a dry, non-productive cough develops, initially after exercise and at night.

As heart failure persists, more changes are noticed. Some dogs lose their appetite, lose weight, and breathe more rapidly. In some cases, fluid that has been forced out of the veins may cause ascites and swelling of the limbs. Eventually, fluid back up in the lungs may cause a frothy cough or production of a bubbly pink fluid.

In the late stages of heart failure, a dog braces itself on its elbows and extends its head to breathe. The dog's gums and tongue become blue. The pulse becomes rapid and irregular. Fainting usually occurs with the slightest exertion.

Diagnosis of Congestive Heart Failure

A veterinarian diagnoses congestive heart failure when the typical signs are present and are consistent with known heart disease. If there is no known heart disease, chest and abdominal X-rays, ECG, and echocardiography are performed. If the heart failure primarily affects the right side of the heart, a blood test may be carried out for heartworm infestation.

Treatment of Congestive Heart Failure

Dogs with heart disease but no signs of heart failure aree treated normally and given a full exercise routine. When the first signs of heart failure develop, a dog benefits from treatment from a combination of ACE (angiotensin-converting enzyme) inhibitors and diuretics such as frusemide (furosemide). The ACE inhibitors reduce the workload on the heart by causing blood vessels to widen. The diuretic is a "water pill": it makes your dog urinate more, which clears fluid congestion from the lungs and veins.

Other medications that act on the heart and circulation, such as digitalis, calcium channel blockers, beta blockers, and antiarrhythmic drugs, may also be used in some cases. nitroglycerin may be recommended in some advanced cases.

Dietary treatment for heart failure remains controversial. Excess salt in the diet should be avoided, but the benefit of low-salt diets is, as yet, not proven. Antioxidants may be of value for some dogs with congestive heart failure such as selenium and vitamin E. Routine, daily light exercise is beneficial as long as it does not cause the dog to cough, tire easily, or breathe rapidly.

Bacterial Endocarditis

This condition is an infection of the heart valves and the lining of the heart muscle. Bacteria enter the bloodstream from wounds or infections elsewhere in the body and invade the heart valves, where they produce cauliflower-like masses called vegetations. Some of the vegetations break off and spread via the blood stream to infect other parts of the body. Gum disease is one possible source of bacteria. In addition, dogs being treated with immunosuppressant drugs, including corticosteroids, are at increased risk of bacterial endocarditis.

The fact that infection can and does affect other parts of the body means that dogs often have nonspecific signs suggestive of a number of diseases. These signs include lethargy, loss of appetite, fever, shaking, lameness, and personality changes.

Diagnosis of Bacterial Endocarditis

An affected dog usually has a heart murmur, often changing in intensity from day to day. Chest X-rays, ECG , and echocardiography are used to confirm the diagnosis. A blood culture identifies the bacteria and the antibiotic drugs that are likely to be effective against them.

Treatment of Bacterial Endocarditis

An appropriate antibiotic, selected according to bacterial culture, is given intravenously for the first week (through a tube called an indwelling cannula). Oral antibiotic therapy will continue for the long term. Affected dogs are monitored closely. Repeat X-rays and echocardiography will show the vegetations shrinking in size. Even so, the outlook is not good; congestive heart failure may occur at any time.

Breeds at Risk

The risk of valvular heart disease is related to the type of dog. While the condition is known to affect around 50% of Calvalier King Charles spaniels, it is relatively uncommon in medium, large, and giant breeds. A veterinarian may take into account the breed of the dog (as well as other factors, such as the animal's age) in making a diagnosis of valvular heart disease. The causes of the difference in susceptibility between one breed and another are genetically based, though not, as yet, fully understood. Breeds with a high incidence of valvular heart disease include Miniature schanauzer, Calvalier King Charles spaniel, Chihuahua, Lhasa Apso, Miniature Poodle, and Yorkshire Terrier.