What are the diagnostic criteria and treatment guidelines for endocarditis?

Diagnostic Criteria and Treatment Guidelines for Infective Endocarditis

The diagnosis of infective endocarditis requires a combination of clinical, microbiological, and imaging findings, with treatment involving prolonged antimicrobial therapy and potentially surgical intervention based on the Modified Duke Criteria. 1

Diagnostic Criteria

Modified Duke Criteria

The diagnosis of IE is based on the Modified Duke Criteria, which includes:

Major Criteria:

1. Positive Blood Cultures:

   • Typical microorganisms from 2 separate blood cultures (viridans streptococci, S. bovis, HACEK group, S. aureus, or community-acquired enterococci)
   • Persistently positive blood cultures (≥2 positive cultures drawn >12 hours apart, or all 3 or majority of ≥4 cultures with first and last drawn ≥1 hour apart)
   • Single positive blood culture for Coxiella burnetii or phase I IgG antibody titer >1:800

2. Evidence of Endocardial Involvement:

   • Positive echocardiogram showing vegetation, abscess, new partial dehiscence of prosthetic valve
   • New valvular regurgitation

Minor Criteria:

• Predisposing heart condition or injection drug use
• Fever ≥38°C
• Vascular phenomena (major arterial emboli, septic pulmonary infarcts, mycotic aneurysm, intracranial hemorrhages, Janeway lesions)
• Immunologic phenomena (glomerulonephritis, Osler's nodes, Roth's spots, rheumatoid factor)
• Microbiological evidence not meeting major criteria

Definite IE diagnosis requires:

• 2 major criteria, OR
• 1 major and 3 minor criteria, OR
• 5 minor criteria 1

Initial Diagnostic Workup

1. Blood Cultures:

   • Obtain at least 3 sets of blood cultures from separate venipuncture sites before starting antibiotics
   • Each set should include aerobic and anaerobic bottles with at least 10 ml of blood per bottle in adults 1, 2

2. Echocardiography:

   • Transthoracic echocardiography (TTE) is the first-line imaging modality
   • Transesophageal echocardiography (TOE) is recommended when:
     • TTE is negative but clinical suspicion remains high
     • Prosthetic valve or intracardiac device is present
     • Complications are suspected 1, 2
   • Repeat echocardiography within 5-7 days if initial exam is negative but clinical suspicion remains high 1

3. For Culture-Negative Endocarditis:

   • Consider serological testing for:
     • Coxiella burnetii
     • Bartonella species
     • Brucella
     • Legionella
     • Mycoplasma
   • Consider PCR of surgical material for Tropheryma whipplei 1, 2

Treatment Guidelines

Antimicrobial Therapy

1. General Principles:

   • Bactericidal antibiotics administered intravenously
   • Prolonged therapy (typically 4-6 weeks)
   • Dosing based on organism sensitivity 1

2. Empiric Therapy (before culture results):

   • For native valve: Vancomycin plus gentamicin
   • For prosthetic valve: Vancomycin plus gentamicin plus rifampin 1

3. Specific Therapy (based on organism):

   • Staphylococcus aureus:
     • MSSA: Anti-staphylococcal penicillin (nafcillin, oxacillin)
     • MRSA: Vancomycin or daptomycin 6 mg/kg IV q24h 3
   • Streptococci: Penicillin G or ceftriaxone, with gentamicin for the first 2 weeks
   • Enterococci: Ampicillin plus gentamicin or vancomycin plus gentamicin

4. Duration:

   • Native valve IE: 4-6 weeks
   • Prosthetic valve IE: At least 6 weeks 1

Cardiac Device-Related IE (CDRIE)

1. Diagnosis:

   • Three or more sets of blood cultures before antibiotics
   • Lead-tip culture when device is explanted
   • TOE recommended regardless of TTE results 1

2. Treatment:

   • Complete hardware removal (device and leads) plus prolonged antibiotics
   • Percutaneous extraction recommended even with vegetations >10mm
   • Surgical extraction if percutaneous extraction is incomplete/impossible 1

3. Reimplantation:

   • Reassess need for reimplantation after device extraction
   • Postpone reimplantation for several days or weeks of antibiotic therapy
   • Blood cultures should be negative for at least 72h before new device placement
   • If valvular infection remains, delay implantation for at least 14 days 1

Surgical Indications

Surgery should be considered for:

• Heart failure due to valve dysfunction
• Uncontrolled infection (persistent bacteremia >72h despite appropriate antibiotics) 4
• Prevention of embolic events (large vegetations >10mm)
• Prosthetic valve endocarditis with valve dysfunction or abscess formation

Monitoring and Follow-up

1. During Treatment:

   • Repeat blood cultures to document clearance of bacteremia
   • Repeat echocardiography to monitor vegetation size and complications
   • Monitor for drug toxicity, especially with aminoglycosides and vancomycin 1, 4

2. After Treatment:

   • TTE recommended at completion of antibiotic therapy
   • Follow-up blood cultures if clinical suspicion of recurrence 1

Common Pitfalls and Caveats

• Delayed Diagnosis: Don't wait for positive blood cultures if clinical suspicion is high; if cultures remain negative after 48 hours, consider additional investigations for atypical organisms 1

• Inadequate Blood Cultures: Ensure proper volume (10ml per bottle) and timing (before antibiotics) 1

• Missing Prosthetic Valve IE: Always use TOE for prosthetic valves as TTE has lower sensitivity 1

• Premature Discontinuation of Therapy: Complete the full course of antibiotics even if clinical improvement occurs early 5

• Failure to Recognize Complications: Regularly assess for heart failure, embolic events, and conduction abnormalities 1