Echocardiography visualizes endocardial and valvular vegetations measuring 2 mm or greater. Transesophageal echocardiography is more sensitive than transthoracic echocardiography for adolescents and adults and for patients with prosthetic valves but is often unnecessary in children.
Infective endocarditis must be differentiated from other causes of bacteremia or other cardiac conditions using the Modified Duke Criteria for categorizing the strength of the endocarditis diagnosis (Table 111-2). Noninfectious causes of endocardial vegetations must be excluded, such as sterile clots and vegetations associated with rheumatoid disease and lupus erythematosus. Prolonged bacteremia can be caused by infectious endothelial foci outside of the heart, often associated with congenital malformations, vascular trauma, an infected venous thrombosis, and previous vascular surgery.
Severely ill patients must be stabilized with supportive therapies for cardiac failure, pulmonary edema, and low cardiac output (see Chapter 145). Empirical antibiotic therapy may be started for acutely ill persons after blood cultures are obtained. With subacute disease, awaiting results of blood cultures to confirm the diagnosis is recommended to direct therapy according to the susceptibility of the isolate. Because antibiotics must reach the organisms by passive diffusion through the fibrin mesh, high doses of bactericidal antibiotics are required for an extended period of treatment (4 to 8 weeks). Infective carditis from susceptible viridans streptococci can be treated with monotherapy penicillin G for 4 weeks. A 2-week regimen of penicillin G plus an aminoglycoside is effective in adults. Surgery is indicated if medical treatment is unsuccessful, with persistent bacteremia, an unusual or difficult to treat pathogen (fungal endocarditis), valve annulus or myocardial abscess, rupture of a valve leaflet, valvular insufficiency with acute or refractory heart failure, recurrent serious embolic complications, or refractory prosthetic valve disease.
The major complications of infective endocarditis are direct damage to the heart and heart valves and distant complications secondary to sterile and septic emboli from vegetations. Damage to the heart and heart valves may include regurgitation with vegetations or actual defects in the leaflets resulting from embolization of the leaflet tissue, abscess of the valve
Histopathologic Criteria Microorganisms shown by culture or histopathologic examination in a vegetation, emboli, intracardiac abscess or Active endocardial lesions on pathologic examination Clinical Criteria Two major criteria or one major and three minor criteria or five minor criteria) Major Criteria Positive blood cultures Two or more separate cultures positive with typical organisms for infective endocarditis Two or more positive cultures of blood drawn more than 12 hours apart or 4 positive blood cultures irrespective of timing of obtaining specimen A positive blood culture for Coxiella burnetii or positive IgG titer >1:800 Evidence of endocardial involvement Positive findings on echocardiogram (vegetation on valve or supporting structure, abscess, new valvular regurgitation) Minor Criteria Predisposition—predisposing heart condition or injection drug use Fever—temperature >38° C (>100.4° F) Vascular phenomena (major arterial emboli, septic pulmonary infarcts, mycotic aneurysm, intracranial hemorrhage, conjunctival hemorrhages, Janeway lesions) Immunologic phenomena (glomerulonephritis, Osler nodes, Roth spots, rheumatoid factor)
Microbiologic evidence (positive blood culture result, but not meeting major criteria, or serologic evidence of active infection with organism consistent with infective endocarditis)
Firm alternative diagnosis for manifestations of endocarditis or
Resolution of manifestations of endocarditis with antibiotic therapy for <4 days or