Infective endocarditis affects the endocardium (the lining of the heart) and usually one or more of the heart valves. Though uncommon, the condition occurs when bacteria (and rarely, other pathogens) enter the bloodstream and settle in the heart lining, a heart valve, or a blood vessel. Because it so often is caused by bacteria, infective endocarditis is also referred to as bacterial endocarditis.
Definition & Facts
Streptococcus and staphyloccocus are the most common bacterial agents that cause infective endocarditis. Infective endocarditis can be acute or subacute. The subacute form typically takes longer to recognize and diagnose due to subtler symptoms than acute infective endocarditis which has a sudden and severe onset.
Prosthetic valve endocarditis (PVE) afflicts prosthetic heart valve replacements. Abnormal, damaged, or prosthetic valves are more susceptible to infection. Prosthetic valve endocarditis is typically categorized as a subacute form of endocarditis.
Patients with some preexisting cardiac conditions are at greater risk than others of developing this condition. Patients with artificial heart valves or certain congenital heart defects need to take antibiotics before certain dental or surgical procedures to prevent endocarditis.
Symptoms & Complaints
Subacute bacterial endocarditis symptoms develop more gradually as milder fatigue, low grade fever, a slightly faster heart rate, perspiration, and a low red blood cell count. Such symptoms progress subtly over weeks to months and in some cases, ultimately cause fatalities.
Small arteries may clog if accumulations of bacteria on the endocardium or valves loosen, become emboli or clots, travel through the bloodstream, and lodge in an artery. This can block the artery and sometimes cause fatal consequences.
A blocked cranial artery may precipitate a stroke, and a heart attack may follow blockage of a coronary artery. Emboli can cause infections that damage the lungs, kidneys, spleen, and brain among other organs. Abscesses may form at the bases of infected heart valves or wherever infected emboli settle.
Heart valves may perforate and leak. Some patients go into septic shock with full organ failure. Arterial infections can weaken the walls, causing bulges or ruptures, which may be fatal in some areas. Other symptoms of acute and subacute bacterial endocarditis are chills, joint pains, pallor (pale skin), and painful subcutaneous nodules.
Small red spots resembling freckles may appear on the skin, in the eyes, and under the fingernails. These are tiny clots or emboli from the heart valves. Larger emboli may appear as blood in the urine or cause pain or numbness in a limb. The spleen may enlarge (splenomegaly). Sepsis, a severe blood infection, is not uncommon.
Bacteria introduced into the bloodstream sometimes lodge on heart valves and infect the endocardium. Bacteria normally do not populate the blood, but a puncture to the skin or an irritated lining of the mouth or gums in the predisposed from chewing or brushing the teeth may draw bacteria into the bloodstream as may gingivitis (inflammation of the gums), and certain dental, medical, and surgical procedures.
Normal heart valves usually suffer no harm as the body's immune system destroy such bacterial infections; however, damaged heart valves may harbor such bacteria, upon which they lodge on the endocardium and proliferate.
If the cause of a case of infective endocarditis is prolonged abuse of intravenous illicit drugs, the tricuspid valve between the right atrium and right ventricle becomes infected most often. In most other cases, the mitral valve between left atrium and left ventricle or the aortic valve is infected. Risk factors for infective endocarditis include:
- Congenital disorders (or birth defects) of the heart, heart valve, or major blood vessels
- Heart valve damage from rheumatic fever
- Heart valve deterioration with aging
- Intravenous drug injections with contaminated needles
- A prosthetic or replacement heart valve
Risk factors for children and young adults are birth defects of the heart, particularly when they allow blood to leak from one chamber of the heart to another. A risk factor for older people is heart valve degeneration or calcium deposits in the mitral or aortic valve.
Patients with prosthetic or replacement heart valves are at high risk during the first year after heart valve surgery; the risk then decreases but remains higher than for the general population. The risk is always greater with aortic or mechanical rather than with mitral and natural-tissue replacement valves.
Infective endocarditis of a prosthetic heart valve, acute or subacute, is more likely than an infected natural valve to spread to adjacent cardiac muscle. Infection may cause an interference with the heart's electrical conduction system, slow the heartbeat, cause a loss of consciousness, and possibly cause death.
Diagnosis & Tests
Many symptoms are vague and undifferentiated, so diagnosis may be difficult. Patients with suspected acute or subacute infective endocarditis are hospitalized for prompt study, diagnosis, and treatment. Reasons for suspicion are a heart valve disorder, a replacement heart valve, recent surgical or dental procedures, and drug abuse by intravenous injection.
Echocardiography detects damaged heart valves, and blood cultures identify the microorganism(s) infecting them. Echocardiography uses ultrasound waves to show heart valve images that reveal growths on and damage to the heart. Transesophageal echocardiogram with an ultrasound probe in the esophagus behind the heart, though more invasive, is more accurate and reliable than is the transthoracic method usually performed first with the probe on the chest.
Treatment & Therapy
Untreated infective endocarditis is always fatal. With treatment, the risk of death depends on patient age and history, the virulence of the infection, the presence of a prosthetic heart valve, the infecting microorganism, and heart valve damage. With aggressive antibiotic regimens, most patients survive.
Treatment typically involves two to eight weeks of high doses daily of antibiotics administered intravenously. Antibiotic therapy ordinarily begins in a hospital but may be completed at home with help from a nurse. Antibiotics do not cure all infections, particularly if the infected valve is a replacement.
Some bacteria are resistant to antibiotics. Because antibiotics precede heart valve replacement surgery to prevent infection, any bacteria that survive this preventive measure are likely resistant. It is also generally harder to cure infections of artificial, implanted material than of natural, human tissue. Cardiac surgery is often necessary to repair or replace injured valves, remove bacterial growths, or drain abscesses.
Prevention & Prophylaxis