What is Canine Bacterial Endocarditis?

Canine bacterial endocarditis (BE) is a serious cardiovascular disease affecting dogs, characterized by the formation of infected vegetations (thrombi) on the heart valves and endocardium. These vegetations consist of a fibrinous matrix interwoven with platelets, red and white blood cells, and most importantly, bacteria. While the condition can be acute or subacute, it’s a relatively common ailment, with a predisposition towards middle-aged and older, larger breed male dogs, often manifesting after the age of four.

Pathogenesis and Etiology:

The underlying cause is usually a bacteremia, a bacterial infection of the bloodstream. This bacteria adheres to the heart valves, typically the aortic valve, potentially exacerbated by pre-existing conditions like aortic stenosis. The resulting vegetations are friable, meaning they easily break off, forming emboli (traveling clots) that can lodge in various organs, causing further damage. The damage to the valves disrupts their structure and function, leading to regurgitation (backward flow of blood) or stenosis (narrowing of the valve opening). These functional impairments place significant strain on the heart, ultimately resulting in congestive heart failure.

In acute cases, the rapid destruction and necrosis of chordae tendineae (the tendons supporting the valves) and valvular tissue lead to severe valvular insufficiency and rapid onset of heart failure. Subacute cases progress more slowly, allowing for a longer period before clinical signs become apparent. The source of the bacteremia can vary; it can stem from other infections within the body, such as urinary tract infections, pneumonia, periodontal disease, or even skin infections. Underlying conditions, such as pre-existing valvular abnormalities, can significantly increase the risk of BE.

Clinical Presentation:

The clinical signs of canine bacterial endocarditis are often non-specific, making diagnosis challenging. Symptoms vary depending on the acuteness and severity of the infection, and the location of any emboli. Common signs include:

Lethargy and Weakness: Dogs may exhibit a marked decrease in energy levels, becoming less playful and more reluctant to exercise.

Exercise Intolerance: Even mild exertion may lead to rapid breathing and fatigue.

Cough: A persistent cough, often worse at night, is a common symptom due to fluid build-up in the lungs from heart failure.

Anorexia and Weight Loss: Loss of appetite and subsequent weight loss is often observed.

Fever: Intermittent or persistent fever may be present, reflecting the systemic infection.

Limb Swelling (Edema): Swelling in the legs and abdomen can occur due to fluid retention associated with heart failure.

Cardiac Murmurs: Auscultation (listening to the heart) may reveal abnormal heart sounds, such as a systolic murmur indicating valvular dysfunction.

Neurological Signs: Emboli lodging in the brain can cause neurological symptoms such as seizures, blindness, or altered mentation.

Arthritis: Emboli affecting the joints can lead to lameness and joint pain.

Diagnosis:

Diagnosing BE requires a combination of techniques:

Physical Examination: A thorough physical examination, including auscultation of the heart and lungs, is the first step.

Blood Tests: Complete blood count (CBC) and blood chemistry profiles may reveal anemia, inflammation, and organ damage. Blood cultures are crucial to identify the causative bacteria.

Echocardiography: Echocardiography (ultrasound of the heart) is essential for visualizing the heart valves, identifying vegetations, and assessing valvular function.

Electrocardiography (ECG): ECG helps to assess the heart’s electrical activity and detect any arrhythmias.

Treatment:

Treatment of canine bacterial endocarditis focuses on eradicating the infection with appropriate antibiotics and managing the consequences of valvular damage. Antibiotic selection should be guided by the results of blood cultures. However, given the urgency often associated with BE, treatment frequently begins empirically (before culture results are available), often with broad-spectrum antibiotics. Treatment usually involves:

Intravenous Antibiotics: Prolonged courses (4-6 weeks or longer) of intravenous antibiotics are typically required to effectively eliminate the infection. The specific antibiotic(s) used will depend on the identified bacterium and its susceptibility profile. Common choices include penicillin, cephalosporins, aminoglycosides, and combinations thereof.

Supportive Care: Management of heart failure symptoms may involve diuretics to reduce fluid retention, and medications to manage arrhythmias.

Surgical Intervention: In some cases, surgical intervention may be necessary, particularly if severe valvular damage is present. However, this is often a high-risk procedure.

Prognosis:

The prognosis for canine bacterial endocarditis varies depending on several factors, including the severity of the infection, the response to treatment, and the presence of other underlying health issues. Early diagnosis and aggressive treatment improve the chances of a positive outcome. However, even with effective treatment, some dogs may experience long-term complications or recurrence of the infection. Subacute cases generally carry a more guarded prognosis than acute cases.

Prevention:

Preventing BE is challenging since it often arises secondary to other infections. However, maintaining good oral hygiene, promptly treating any infections, and addressing underlying heart conditions can reduce the risk. Regular veterinary check-ups are essential for early detection of any potential heart problems.