What are the diagnostic criteria and treatment options for infective endocarditis?

Diagnostic Criteria and Treatment for Infective Endocarditis

The diagnosis of infective endocarditis should be made using the Modified Duke Criteria, which classifies cases as "definite," "possible," or "rejected" based on specific major and minor criteria, while treatment typically involves prolonged antimicrobial therapy with vancomycin for MRSA endocarditis or vancomycin plus an aminoglycoside for enterococcal endocarditis. 1

Diagnostic Criteria: Modified Duke Criteria

Major Criteria

1. Microbiological Evidence:

   • Typical microorganisms for IE in 2 separate blood cultures (e.g., Streptococcus viridans, S. bovis, Staphylococcus aureus) 1
   • Persistently positive blood cultures (≥2 positive cultures obtained >12 hours apart) 1
   • Single positive blood culture for Coxiella burnetii or anti-phase 1 IgG antibody titer >1:800 1, 2

2. Echocardiographic Evidence:

   • Oscillating vegetation on valve or supporting structures 1
   • Abscess, pseudoaneurysm, or intracardiac fistula
   • Valvular perforation or aneurysm
   • New partial dehiscence of prosthetic valve 1

Minor Criteria

1. Predisposition: Predisposing heart condition or intravenous drug use
2. Fever: Temperature >38°C (100.4°F)
3. Vascular phenomena: Major arterial emboli, septic pulmonary infarcts, mycotic aneurysm, etc.
4. Immunologic phenomena: Glomerulonephritis, Osler's nodes, Roth spots, rheumatoid factor
5. Microbiological evidence not meeting major criteria 1

Diagnostic Classification

• Definite IE: 2 major criteria, OR 1 major + 3 minor criteria, OR 5 minor criteria 1
• Possible IE: 1 major + 1 minor criteria, OR 3 minor criteria 2
• Rejected IE: Firm alternate diagnosis, resolution with ≤4 days of antibiotics, or no pathological evidence of IE at surgery/autopsy 1

Diagnostic Approach

1. Blood Cultures:

   • Obtain at least 3 sets of blood cultures from different venipuncture sites before starting antibiotics 1
   • Critical for establishing microbiological diagnosis

2. Echocardiography:

   • Transesophageal echocardiography (TEE) recommended for patients with prosthetic valves, possible IE, or complicated IE with paravalvular abscess 1
   • TEE has higher sensitivity than transthoracic echocardiography (TTE) for detecting vegetations and abscesses

3. Serological Testing:

   • For blood culture-negative endocarditis (BCNE), test for fastidious organisms:
     • Coxiella burnetii (Q fever)
     • Bartonella species
     • Brucella
     • Legionella
     • Tropheryma whipplei 1

4. Molecular Techniques:

   • PCR of valve tissue can detect non-cultivable pathogens 1

Treatment Approach

Antimicrobial Therapy

1. Staphylococcal Endocarditis:

   • For MRSA: Vancomycin IV is indicated 3
   • For methicillin-susceptible S. aureus: Nafcillin or oxacillin preferred

2. Streptococcal Endocarditis:

   • For S. viridans or S. bovis: Vancomycin alone or in combination with an aminoglycoside 3
   • Penicillin G or ceftriaxone are alternatives for susceptible strains

3. Enterococcal Endocarditis:

   • Vancomycin in combination with an aminoglycoside (e.g., gentamicin) 3

4. Early Prosthetic Valve Endocarditis:

   • Vancomycin in combination with rifampin, an aminoglycoside, or both for S. epidermidis or diphtheroids 3

5. Duration of Therapy:

   • Native valve endocarditis: 4-6 weeks
   • Prosthetic valve endocarditis: 6-8 weeks

Surgical Intervention

Consider surgery for:

• Heart failure due to valve dysfunction
• Uncontrolled infection (abscess, persistent bacteremia)
• Prevention of embolic events (large vegetations)
• Prosthetic valve endocarditis with complications

Pitfalls and Caveats

1. Blood Culture Negativity:

   • Prior antibiotic use is a common cause of BCNE 4
   • Consult infectious disease specialists and microbiologists for culture-negative cases 1

2. Diagnostic Limitations:

   • Modified Duke Criteria have lower sensitivity in prosthetic valve and right-sided endocarditis 1
   • The criteria are more accurate when applied at the end of patient evaluation rather than initially 1

3. Regional Variations:

   • In some regions, Bartonella endocarditis is common enough that elevating Bartonella serology to a major criterion would improve diagnostic sensitivity 5

4. Empiric Treatment:

   • Obtain cultures before starting antibiotics whenever possible
   • When empiric therapy is necessary, cover the most likely pathogens based on clinical presentation and local epidemiology 3