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We tend to think of heart disease in terms of clogs of cholesterol, but one of the deadliest disease of the heart, infective endocarditis, is caused by infection with the same Staphylococcus and Streptococcus bacteria that cause other common infections.

Infective endocarditis: infection with Staphylococcus and Streptococcus bacteria

Any form of endocarditis involves inflammation of the inner layer of the heart known as the endocardium. Infections may also involve heart valves, including implanted heart values. Endocarditis may also affect the interventricular septum that separates the two lower chambers of the heart, the ventricles.

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Endocarditis is recognized by "vegetation." This is a mass of bacteria, some white blood cells that cause inflammation, platelets (the blood cells that enable blood to clot), and fibrin, the stringy protein on which blood clots form.

These tissues inside the heart are especially at risk for infection because they do not receive their own dedicated blood supply. Whtie blood cells do not eve have an opprotunity to "lodge" on their surfaces to get rid of infectious bacteria.

Just how serious infective endocarditis is for the heart depends on the "incubation time" of the bacteria infecting its tissues. Short incubation endocarditis involves infections that occur over six weeks or less. Usually involving Staphylococcus bacteria, short incubation endocarditis causes much more serious symptoms. Long incubation endocarditis, usually involving Streptococcus bacteria, develops over a period of months or years and causes relatively mild symptoms.

What are the symptoms of infective endocarditis?

The symptoms of infective endocarditis have nothing to do with chest pain:

  • 97 per cent of people who have infective endocarditis develop a fever.
  • 90 per cent of people who have infective endocarditis suffer endurance fatigue, usually with a vague kind of depression that does not stem from life events and what a layperson might call a "blah" attitude (malaise).
  • 35 per cent of people who have infective endocarditis have a combination of cough and weight loss

Another frequent but overlooked symptom of infective endocarditis is a phenomenon known as Janeway lesions. These are painless "blood blisters" on the soles of the feet and palms of the hands. They resemble the kind of changes in the skin caused by peripheral arterial disease, but they do not extend up the legs or arms, and they usually are not infected. These lesions may start with raised "blistering," but they quickly flatten out and form a bruise. The outermost layer of skin will not be affected, only the skin just beneath it.

Infective endocarditis more rarely manifests itself as:

  • Night sweats,
  • Stiff muscles and muscle aches,
  • Osler's nodes, painful lesions on the fingertips,
  • Anemia, stroke, bloodshot eyelids rather than bloodshot eyes, kidney failure, spots on the retina, and clubbed fingers and toes.

How does infective endocarditis get started?

To cause an infection in the heart, massive numbers of bacteria have to find their way into the bloodstream.

At one time researchers thought that infective endocarditis was usually caused by dental procedures releasing large numbers of strep and staph bacteria into the blood vessels around the root canal. While dental procedures can cause the infections that lead to endocarditis, researchers now believe that urinary tract infections and colon infections, including those acquired during colonoscopy, are more frequent sources of the bacteria that cause the disease.

Intravenous drug use, including insulin injections, can cause infective endocarditis. People who get infections from infected needles usually develop infections on the right side of the heart, because blood returns from the veins that receive the drugs to the right side of the heart. Treatment for rheumatoid arthritis, ankylosing spondylitis, Sjögren's syndrome, and interstitial pneumonia with steroid drugs can lead to the immune deficiencies that invite infections in the heart, and even simply daily brushing and flossing the teeth can introduce bacteria into the bloodstream that lodge in the valves of the heart.

People who have colon cancer sometimes get heart infections with a different kind of microorganism, Clostridium. This infectious agent gets into poorly treated drinking water. People who have gum disease sometimes get infections with the HACEK organisms:

  • Haemophilus (Haemophilus influenzae)
  • Aggregatibacter (Aggregatibacter actinomycetemcomitans, Aggregatibacter aphrophilus)
  • Cardiobacterium hominis
  • Eikenella corrodens
  • Kingella (Kingella kingae)

These microorganisms live on the surface of the gums.

Diagnosis and treatment of infective endocarditis

How do doctors diagnose infective endocarditis?

Doctors very seldom diagnose infective endocarditis in patients admitted for treatment in the emergency room, because the symptoms of endocarditis are usually gradual, even when the infectious agent is Streptococcus. The disease usually takes at least a few weeks to manifest symptoms, and, unless the patient is seeking care in the emergency room because of lack of money, very few people with this disease will be diagnosed in the ER.

Infective endocarditis is mostly commonly diagnosed when the doctor is looking for something else. No single test is absolutely conclusive all the time. Ultrasound of the heart will detect only 65 to 95 per cent of cases. Unless there is a telltale sign like Osler's nodes or Janeway lesions, the doctor will also run several blood tests to look for the bacteria that cause the condition. Usually these blood tests are run at least 12 hours apart.

How is infective endocarditis treated? Infective endocarditis is usually treated with high-dose antibiotics delivered by intravenous injection (IV) for two to six weeks. It is relatively difficult to get antibiotics to the inside of the heart because blood is constantly flowing in and out. For this reason, the dosage has to be high and the treatment period has to be long to get rid of the infection for good.

In some cases, the lining of the valves will be surgically "scraped" to remove the infection. If infection destroys the mitral valve, between the upper and lower chambers of the heart, then another operation may be needed to replace it. Careful adherence to doctor's orders and completing antibiotics is necessary, because, even when treated, infective endocarditis results in death about 25 per cent of the time.