Infective endocarditis (IE) is a microbial infection, implanted on a heart valve or on the mural endocardium after bacteremia or fungemia. It is characterized by fever, valvular destruction, and peripheral embolization. Acute IE is most commonly caused by Staphylococcus aureus, occurs on normal valves, is rapidly destructive, produces metastatic foci, and is fatal in < 6 weeks unless treated. Subacute EI is usually caused by Streptococcus viridans, occurs on damaged valves, does not produce metastatic foci, and takes >6 weeks (up to one year) to be fatal.
Causes of Infective Endocarditis
Characteristic lesions of IE are vegetations on valves or elsewhere on endocardium. Usually arises secondary to colonization by microbes of sterile vegetations composed of platelets/fibrin. Sterile vegetations represent nonbacterial thrombotic endocarditis; these form over areas of trauma to endothelium (intracardiac foreign bodies), in areas of turbulence (deformed valves), over scars, or in setting of wasting disease (e.g., malignancy with marantic endocarditis). Vegetations of IE then result from deposition of platelets/fibrin over bacteria, which forms a “protective site” into which phagocytic cells penetrate poorly. Clinical features result from vegetations and immune reaction to infection. With fungal IE, vegetations may be large, occluding valve orifice and forming large peripheral emboli. S. aureus can cause rapid valve destruction; healing forms scar, with resulting valvular stenosis or regurgitation. Abscesses may form in myocardium. Other complications include conduction abnormalities, fistulas, or rupture of chordae, papillary muscle, or ventricular septum. Vegetations can embolize to heart, brain, kidney, spleen, liver, extremities, lung, with resultant infarcts and abscesses. Circulating immune complexes may result in glomerulonephritis, arthritis, or various mucocutaneous manifestations of vasculitis.
Symptoms of Infective Endocarditis
- Night sweats (may be severe)
- Weight loss
- Muscle aches and pains
- Heart murmur
- Red, painless skin spots on the palms and soles (Janeway lesions).
- Nail abnormalities (splinter hemorrhages under the nails)
- Joint pain
- Abnormal urine color
- Red, painful nodes (Osler’s nodes) in the pads of the fingers and toes
- Fatigue
- Weakness
- Fever
Diagnosis
Clinical diagnosis of IE is made in the following manner:
I. Definite IE: 2 major criteria or 1 major + 3 minor criteria or 5 minor criteria.
A. Major criteria.
- Isolation of S. viridans, S.bovis, HACEK-group organisms, or (in the absence of a primary focus) communityacquired S. aureus or enterococcus from two separate blood cultures or isolation of a microorganism consistent with endocarditis in (1) blood culture 12 h apart or (2) all of three or most of four or more blood cultures, with first and last at least 1 h apart.
- Evidence of endocardial involvement on echocardiography: oscillating intracardiac mass or abscess or new partial dehiscence of prosthetic valve or new valvular regurgitation.
B. Minor criteria.
- Predisposing lesion or IVDU.
- Fever of 38.0°C.
- Major arterial emboli, septic pulmonary infarcts, mycotic aneurysm, intracranial hemorrhage, conjunctival hemorrhages, Janeway lesions.
- Glomerulonephritis, Osler’s nodes, Roth’s spots, rheumatoid factor.
- Positive blood cultures not meeting the major criterion (excluding single cultures positive for organisms that do not typically cause endocarditis) or serologic evidence of active infection with an organism that causes endocarditis.
- Echocardiogram consistent with endocarditis but not meeting the major criterion.
II. Possible IE: Findings that fall short of “definite” but do not fall into the “rejected” category
III. Rejected: Alternative diagnosis or resolution of syndrome or no evidence of IE at surgery or autopsy with 4 days of antibiotic therapy
Treatment
Cure of IE requires eradication of all microbes from vegetation(s). Microbicidal drug regimens must produce high enough concentrations for long enough duration to sterilize vegetation(s).
Antimicrobial Therapy Appropriate IV antibiotic therapy, depending on the sensitivity of the infecting organism.
Surgery Most common indication, congestive heart failure. Valve replacement.
Prevention
Infective endocarditis occurs when there is an infection in the blood. Antibiotics can prevent such an infection from occurring in the first place. Antibiotic prophylaxis is recommended before medical procedures with a high probability of introducing bacteria into the blood.
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