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Infective endocarditis

  • Results from bacterial infection of the endothelial surface of the heart
  • Produces characteristic vegetations
  • Vegetations consist of platelets, fibrin and bacteria

Predisposing factors

  • Rheumatic valve disease
  • Degenerative heart disease
  • Mitral valve prolapse
  • Congenital heart disease
  • Hypertrophic cardiomyopathy
  • Intravenous drug abuse
  • Prosthetic valve

Microbiology

  • Relative proportions of infecting organisms depends on underlying valve disease
  • Native-valve endocarditis usually caused by:
    • viridans streptococci
    • Streptococcus bovis
    • Staphylococcus aureus
    • enterococci
    • Gram-negative coccobacilli (HACEK group)
  • Nosocomial native-valve endocarditis
  • Often occurs as a complication central venous catheter infection
  • Usually caused by:
    • Staphylococcus aureus
    • enterococci
    • coagulase-negative staphylococci
  • Prosthetic-valve endocarditis accounts for 10% cases of infective endocarditis
  • Greatest risk is during the first 6 months after surgery
  • MRSA responsible for most cases seen in the first year

Diagnosis

  • Clinical presentation can be varied
  • At one extreme acute systemic toxicity with rapid progression to cardiac complications
  • At other extreme indolent low-grade febrile illness with minimal cardiac dysfunction
  • 90% patients have a fever
  • 85% patients have murmur, usually that of underlying cardiac lesion
  • 10-40% have a changing murmur
  • Peripheral signs are rare
  • 95% patients have positive blood cultures
  • Echocardiography allows
    • visualisation of vegetations
    • detection of cardiac complications
  • Transthoracic echocardiography has a low sensitivity but high specificity
  • Transoesophageal echocardiography has a higher sensitivity

Duke clinical criteria

  • Requires the presence of :
    • Two major criteria or
    • One major and three minor criteria or
    • Five minor criteria

Major criteria

  • Positive blood cultures
  • Evidence of endocardial involvement

Minor criteria

  • Predisposing heart condition or intravenous drug abuse
  • Fever (>38.0 deg C)
  • Vascular phenomenon
    • Major arterial emboli
    • Septic pulmonary infarcts
    • Mycotic aneurysm
    • Intracranial haemorrhage
    • Conjunctival haemorrhages
  • Immunological phenomenon
    • Glomerulonephritis
    • Osler's nodes
    • Roth spots
  • Microbiological evidence (but less than major criteria)
  • Echocardiographic findings (but not meeting major criteria)

Management

  • Recommended antibiotic therapy depends on infecting organism
  • Parenteral therapy required to ensure bactericidal concentration
  • When empirical treatment is necessary need to consider
    • Risk factors for certain organisms
    • Local bacterial resistance patterns
  • Need to determine
    • Antibiotic sensitivities
    • Minimum inhibitory concentrations

Indications for surgical intervention

  • Moderate-to-severe heart failure as a result of valvular dysfunction
  • Partial dehiscence of a prosthetic valve
  • Persistent bacteraemia despite optimal antimicrobial therapy
  • Absence of effective bactericidal treatment
  • Fungal infective endocarditis
  • Relapse of prosthetic-valve endocarditis
  • Staphylococcus aureus prosthetic-valve endocarditis

Bibliography

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