Endocarditis in Dogs

By Malcolm Weir, DVM, MSc, MPH; Catherine Barnette, DVM

What is endocarditis?

Endocarditis refers to an infection of a heart valve. While endocarditis can affect any of the heart valves, the most commonly affected valves are the mitral and aortic valves.

Endocarditis occurs when bacteria enter the bloodstream and lodge on the valves of the heart. These bacteria may originate from a systemic (body-wide) infection such as pyometra or urinary tract infection, a skin wound, an abscess, a surgical procedure, dental disease, or immune suppression.

Some dogs are more susceptible to endocarditis than others. In many cases, endocarditis affects a heart valve that has already been damaged. This damage may be caused by a defect in the heart (resulting in abnormal blood flow over the valve, which can lead to scar tissue formation), inflammation of the heart tissues, or surgical procedures.

Endocarditis is most common in middle-aged and older dogs, especially large breeds. Males are more commonly affected than females. The most commonly affected breeds include Labrador Retrievers, German Shepherds, German Shepherd mixes, Golden Retrievers, and Rottweilers.

Endocarditis is relatively uncommon in dogs.

What are the clinical signs of endocarditis? 

Signs of endocarditis are often nonspecific early in the course of the disease. Affected dogs show vague signs of illness, such as weight loss and lethargy. They may develop signs related to the spread of bacteria throughout their body, such as lameness and joint pain. Affected dogs may also have a fever.

In later stages, endocarditis begins to affect the functioning of the heart. Dogs may develop signs of heart failure, such as a cough, exercise intolerance, and weakness. You may also notice that your dog has shortness of breath or difficulty breathing.

How will my veterinarian diagnose endocarditis?

There are a number of physical examination findings that might lead your veterinarian to suspect that your dog has endocarditis. Your veterinarian may hear a heart murmur, which indicates abnormal blood flow over a heart valve. Blood pressure abnormalities are also often associated with endocarditis; in some cases, these abnormalities may be dramatic enough that your veterinarian can detect them when assessing your dog's hindlimb pulses.

Your veterinarian will likely perform a number of additional tests in order to diagnose your dog’s endocarditis. These tests may include:

  • Blood tests (including a complete blood cell count and serum biochemistry) may show abnormalities consistent with endocarditis or other infection.
  • Chest radiographs (X-rays) often show heart enlargement or signs of heart failure.
  • Electrocardiography (ECG) may show an irregular heartbeat (arrhythmia).
  • Echocardiography (ultrasound of the heart) allows visualization of the heart valves. This is often one of the most helpful tests in arriving at a diagnosis of endocarditis.
  • Infectious disease testing, including blood cultures and tests for specific pathogens, (sometimes using polymerase chain reaction [PCR] tests) may be used to help determine what agent is involved in endocarditis. Unfortunately, false negative tests on these results are common.

Endocarditis can be a challenge to definitively diagnose. Diagnosis is based upon how well your dog meets the diagnostic criteria for endocarditis, because there is no definitive 'yes or no' test to determine whether he has endocarditis.

If your dog has multiple findings consistent with endocarditis, this suggests a high likelihood of the condition and warrants treatment.

How is endocarditis treated?

Endocarditis is treated with prolonged courses of antibiotics. These antibiotics are often continued for 4-6 months. The choice of antibiotics is often based on bacterial cultures, which can help determine the most effective antibiotic for a particular infection.

Treatments may also be provided for supportive care of affected patients. These treatments may include pain medications (for joint pain), IV fluids (for dehydration), and medications to treat heart failure.

Dogs are monitored throughout treatment, with chest X-rays, blood tests, and additional heart testing as indicated.

What is the prognosis for endocarditis?

The prognosis for endocarditis in dogs varies, depending on factors such as which heart valve is affected, what bacteria is causing the infection, and the dog's overall health. Endocarditis that affects the aortic valve typically carries a poor prognosis, while mitral valve endocarditis often progresses much more slowly (over a period of months to years).

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