Health A-Z

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What Is It?

Endocarditis, also called infective endocarditis, is an infection and inflammation of the heart valves and the inner lining of the heart chambers, which is called the endocardium. Endocarditis occurs when infectious organisms, such as bacteria or fungi, enter the bloodstream and settle in the heart. In most cases, these organisms are streptococci ("strep"), staphylococci ("staph") or species of bacteria that normally live on body surfaces.

The infecting organism enters the bloodstream through a break in the skin caused by a skin disorder or injury; a medical or dental procedure; or a skin prick, especially among intravenous drug users.

Depending on the aggressiveness (virulence) of the infecting germ, the heart damage caused by endocarditis can be swift and severe (acute endocarditis) or slower and less dramatic (subacute endocarditis).

  • Acute endocarditis - Acute endocarditis most often occurs when an aggressive species of skin bacteria, especially a staphylococcus, enters the bloodstream and attacks a heart valve. Usually the affected heart valve was previously normal. Once staph bacteria begin to multiply inside the heart, they may send small clumps of bacteria called septic emboli into the bloodstream. The septic emboli enter other organs, especially the kidneys, lungs and brain. Intravenous (IV) drug users are at very high risk of acute endocarditis, because numerous needle punctures give aggressive staph bacteria many opportunities to enter the blood through broken skin. Dirty drug paraphernalia increases the risk. If untreated, this form of endocarditis can be fatal in less than six weeks.

  • Subacute endocarditis - This form of endocarditis most often is caused by one of the viridans group of streptococci (Streptococcus sanguis, mutans, mitis or milleri) that normally live in the mouth and throat. Streptococcus bovis or Streptococcus equinus also can cause subacute endocarditis, typically in patients who have a gastrointestinal problem, such as diverticulitis or colon cancer. Subacute endocarditis tends to involve heart valves that are abnormal, such as narrowed or leaky heart valves. Subacute bacterial endocarditis often causes non-specific symptoms that can persist for many weeks before a diagnosis is made.

Men develop endocarditis more often than women, and the illness is more common among people who have one or more of the following risk factors:

  • A congenital (present at birth) malformation of the heart or a heart valve, or mitral valve prolapse with mitral valve regurgitation

  • A heart valve damaged by rheumatic fever or by age-related valve thickening with calcium deposits

  • An implanted device in the heart (pacemaker wire, artificial heart valve)

  • A history of IV drug use

In about 20% to 40% of patients who do not have artificial heart valves and who do not use intravenous drugs, no heart problem can be identified that would increase their risk of endocarditis. In the 10% to 20% of endocarditis patients who have artificial heart valves, infections that follow within 60 days of valve surgery often are caused by a staphylococcus, while endocarditis that occurs later most frequently is caused by a streptococcus.

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From Health A-Z, Harvard Health Publications. Copyright 2007 by the President and Fellows of Harvard College. All rights reserved. Written permission is required to reproduce, in any manner, in whole or in part, the material contained herein. To make a reprint request, contact Harvard Health Publications. Used with permission of StayWell.

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