Infective Endocarditis

Microbiology:
- Native valve:
  - S. aureus (30%)
  - Strep viridans (20%)
  - Enterococcus (10%)
  - Coag negative staph (10%)
  - Strep bovis (5%)
- Prosthetic valve:
  - S. aureus (40%)
  - Coag negative staph (20%)
  - Culture negative (20%)
  - Fungal (10%)
Diagnosis: IE results in persistent bacteremia, thus drawing multiple blood cultures is key
- Duke's criteria: serve as a guide, but do not trump clinical judgement
  - Major:
    - 1. Consistent blood cultures (any of below):
      - Typical organisms in two cultures: S. aureus, Strep viridans, Strep bovis, HACEK, enterococcus
      - Persistently positive cultures consistent with IE:
        
        Two cultures, >12h apart, or 3/3, or majority of 4 or more cultures, with one hour between first and last culture
      - Positive culture or IgG for Coxiella burnetti
    - Evidence of endocardial involvement (any of below):
      - New valvular regurgiation (new murmur insufficient)
      - Oscillating intracardiac mass
      - Abscess
      - Dehiscence of prosthetic valve
  - Minor:
    - Fever >38C
    - Vascular phenomena (e.g. emboli, Janeway's lesions)
    - Immunologic phenomena (e.g. glomerulonephritis, Osler's nodes, RF)
    - Blood cultures not meeting major criteria
  - Definite IE: 2 major, 1 major + 3 minor, 5 minor
- Studies:
  - ECG: may show conduction block
  - CXR: may show septic emboli
  - Echocardiography:
    - TTE: sensitivity 30-60% (30% in S. aureus bacteremia), specificity 100%
      - Sensitivity affected by windows, valvular abnormalities, prothetic valves
      - With totally normal TTE, sensitivity is 95%
    - TEE: more invasive and expensive
      - Incremental value may be in non-diagnostic TTE, or to evaluate prosthetic valves or for abscesses
    - Even if decision to treat for IE is made, echo can provide helpful information (e.g. size of vegetation, extension of infection)
    - In patients with S. aureus bacteremia, such as this case, you cannot hang your hat on a negative TTE
Therapy:
- Prompt initiation of therapy is critical, given high mortality (20-40%, even with modern therapy)
- Initial therapy should cover MRSA, with vancomycin being drug of choice
  - Daptomycin has only been studied in R-sided endocarditis
- If MSSA, should narrow to rapidly-cidal anti-staphylococcal agent (e.g. nafcillin or cefazolin)
- Adjuvant gentamicin clears bactermia more rapidly, but does not change mortality and is nephrotoxic - should only be used for 3-5 days
- Duration of therapy is typically 6 weeks

Surgery: indicated if there are complications
- Heart failure
- Severe valvular regurgitation
- Abscess
- Heart block
- Persistently positive cultures despite appropriate therapy
- Fungal endocarditis
- Embolization
- Extravalvular extension

(Christopher Woo MD, 8/10/10)