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Written By:

Nick A. Schroeder, DVM, DACVIM

Endocarditis is infection of the heart valves. Fortunately, this tends to be an uncommon problem in the dog and is rare in cats. Working dogs (i.e. police dogs, German Shepherds, Belgian Malinois, etc.), Doberman Pinschers, Boxers, Golden Retreivers and Rottweilers may be predisposed. The most commonly affected heart valve in dogs and cats is the aortic valve. The second most common valve seen is the mitral valve. Both of these are on the left side of the heart, and if severe enough of a leak develops, this may lead to heart chamber enlargement and eventually left-sided congestive heart failure (CHF, LCHF). Other associated conditions may include arrhythmias, seeding of other organs with bacteria, enlargement of the spleen, arthritis, inflammation in the muscles, and kidney problems. Endocarditis occurs because bacteria in the bloodstream colonize the valve tissues, which may lead to “vegetative” growth-like lesions. These in turn cause the affected valve to leak blood backwards (regurgitation) with each heartbeat, increasing the workload of the heart itself. Occasionally, a narrowing of the valve (stenosis) occurs, further exacerbating the problem.

Bacteremia (bacteria in the bloodstream) is an absolute requirement for endocarditis to develop. Minute amounts of bacteria normally will periodically be shed into the bloodstream associated with simple activities such as eating and defecation. If a large amount of bacteria colonize a portion of a heart valve, and the body’s immune defenses are overwhelmed, then vegetative growths may occur. The colonization process is facilitated by pre-existing changes on the surface of the valve itself. These lesions typically lead to incompetence of the affected valve and a leak (insufficiency or regurgitation) will ensue. Occasionally concurrent narrowing (stenosis) of the valve will develop. If a bad enough leak on the valve evolves, then secondary heart chamber enlargement can result, predisposing to heart failure. Portions of these lesions may break off and travel downstream, seeding other organs with bacteria, causing infarctions, and leading to systemic illness. Gingivitis (inflammation and infection of the gum tissues) and dental disease is frequently cited as a risk factor for developing endocarditis. This may be true in humans, but has not been demonstrated in dogs and cats. “Bad teeth” does NOT lead to a “bad heart” in small animals. Most older, small breed dogs have age-associated dental disease and concurrent, unrelated valvular degeneration (chronic mitral valvular disease). These conditions are associated with one another due to age and not from a cause and effect relationship.

Diagnosis of endocarditis may be fraught with difficulty. Many patients display symptoms that may mimic many other disease processes, which can delay definitive diagnosis. Patients with endocarditis may have no symptoms at all or have cyclical fevers, vomiting, diarrhea, difficulty breathing, coughing, lethargy, weight loss, a new heart murmur, or sometime syncope (fainting episodes). Bloodwork may show evidence of infection/inflammation. Chest x-rays may show heart enlargement and signs of heart failure (congestion, fluid in the lungs, etc.). Blood cultures may or may not be culture positive for bacteria. Echocardiography (ultrasound of the heart) may show leaky valves and lesions on heart valves consistent with endocarditis. Ultrasound of the abdomen may show lesions suggestive of infarctions, enlargement of the spleen, etc. There are major and minor criteria for a diagnosis of endocarditis that have been developed, and a combination of positive tests is used to make the call.

Treatment of endocarditis is typically expensive and prolonged. Generally days of hospitalization on intravenous antibiotic followed by a long-course (6-8 weeks or more) of oral antibiotics is necessary. Concurrent therapy for congestive heart failure may be required, and diuretics, blood pressure medication and drugs for heart muscle pump function support may be prescribed. Surgical valvular replacement is generally not attempted.

The prognosis for endocarditis is always guarded. Some patients succumb to systemic infection rather quickly and others may eventually pass from refractory congestive heart failure. IF the lesions can be sterilized with antibiotic, and the heart enlargement/symptoms of heart failure controlled on medication, some patients can do okay for months to even years, depending on the severity of the initial infection. Consultation with a board-certified veterinary cardiologist is recommended for all patients with known or suspected endocarditis.