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Endocarditis refers to inflammation of the inner layer of the heart, called the endocardium. Okay, but first, a bit of anatomy and physiology. The heart wall is made of three layers: the outer layer is the epicardium, the middle layer is the myocardium, and the inner layer is the endocardium. These layers line the four heart chambers, which are the two atria and two ventricles. The endocardium also lines the heart valves at the end of each chamber.
First, there are two atrioventricular valves, the mitral or bicuspid valve on the left, and the tricuspid valve on the right. The atrioventricular valves prevent blood from returning to the atria after filling the ventricles. And second, there are two semilunar valves called the aortic valve at the left, and the pulmonary valve at the right. The semilunar valves prevent blood from returning to the ventricles after being pumped out.
Okay, so depending on its cause, endocarditis can either be infective, or less frequently, non-infective. Infective endocarditis is most often caused by bacteria like Staphylococcus aureus or Staphylococcus epidermidis, which can be found in the skin, and may enter the bloodstream during surgical procedures, or through an infected intravenous catheter, skin wounds, or intravenous drug use.
Another common bacterial cause is Streptococcus viridans, which can be found in the mouth and may enter the bloodstream during a dental procedure. Additionally, Streptococcus gallolyticus is normally found in the intestinal flora; so when there’s colorectal bleeding, like with colorectal cancer, these bacteria can migrate into the bloodstream. On the other hand, Enterococci are a part of the normal urogenital flora, and can enter the bloodstream via genitourinary catheterization or surgery.
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