Infective Endocarditis

Risk Factors

• Structural heart disease: Rheumatic heart disease, congenital defects, prosthetic valves

• Intravascular devices: Cardiac implantable electronic devices (CIEDs), haemodialysis catheters​

• IV drug use: Strongly linked with right-sided endocarditis (tricuspid valve)​

• Immunosuppression: Diabetes, chemotherapy, long-term steroids

Symptoms & Signs

• Fever + new murmur = suspect IE

• Classic manifestations:

  • Constitutional: Fever, weight loss, malaise

  • Cardiac: New or changing murmur, heart failure signs (dyspnoea, oedema)

  • Embolic phenomena: Stroke, splenic infarct, renal infarction, Janeway lesions

  • Immunological: Osler’s nodes, Roth spots, glomerulonephritis​

  • Sepsis/shock: More common in S. aureus IE

Diagnosis

1. Modified Duke Criteria (Definitive = 2 major OR 1 major + 3 minor OR 5 minor)​

   • Major Criteria:

     • Positive blood cultures (Typical organisms in ≥2 separate blood cultures)

     • Echocardiographic evidence (vegetations, abscess, prosthetic valve dehiscence)

   • Minor Criteria:

     • Predisposing condition (e.g., prosthetic valve, IV drug use)

     • Fever >38°C

     • Vascular signs (e.g., Janeway lesions, embolic infarcts)

     • Immunological signs (Osler’s nodes, glomerulonephritis)

2. Investigations

   • Blood cultures x 3 sets from different venepuncture sites BEFORE antibiotics

   • Echocardiography:

     • TTE (initial; may miss small vegetations)

     • TOE (gold standard, especially in prosthetic valve IE)​

   • Other: FBC, CRP, ESR, urinalysis (for microscopic haematuria)

Management

1. Empirical IV Antibiotic Therapy (before cultures result) – Native Valve IE​

• Flucloxacillin 2g IV q4h + Benzylpenicillin 1.8g IV q4h + Gentamicin 4-5 mg/kg IV (single dose)

• If MRSA risk: Replace benzylpenicillin with vancomycin 25-30 mg/kg IV loading dose

2. Prosthetic Valve IE (higher mortality, requires aggressive treatment)​

• Flucloxacillin 2g IV q4h + Vancomycin 25-30 mg/kg IV loading + Gentamicin 4-5 mg/kg IV (single dose)

3. Directed Therapy (once culture results return)​

• MSSA: Flucloxacillin 2g IV q4h for 4-6 weeks

• MRSA: Vancomycin IV + Rifampicin ± Gentamicin (for prosthetic valve cases)

• Streptococci (Viridans group, S. bovis): Benzylpenicillin IV ± Gentamicin (synergistic)

• Enterococci: Amoxicillin or Vancomycin IV + Gentamicin (prolonged course)

Indications for Early Surgery​

• Severe valvular dysfunction (e.g., acute heart failure)

• Persistent infection despite appropriate antibiotics (≥7 days)

• Large mobile vegetations (>10 mm) with high embolic risk

• Prosthetic valve endocarditis

Complications

• Heart failure (most common cause of death)

• Septic emboli: Stroke, splenic or renal infarcts, pulmonary embolism (right-sided IE)

• Mycotic aneurysm: Rupture risk in cerebral circulation

• Sepsis and multi-organ failure

Prevention (Endocarditis Prophylaxis)​

• Antibiotic prophylaxis ONLY for high-risk patients undergoing high-risk procedures

  • High-risk conditions:

    • Prosthetic valves, previous IE, cyanotic congenital heart disease

  • High-risk procedures:

    • Dental: Manipulation of gingival tissue, tooth extraction

    • Respiratory: Tonsillectomy, bronchoscopy with biopsy

  • Regimen:

    • Amoxicillin 2g PO 60 min before procedure

    • If penicillin-allergic: Clindamycin 600mg PO

Notes:

• Suspect IE in any febrile patient with a murmur, embolic events, or sepsis

• Blood cultures x3 BEFORE starting antibiotics

• TOE is superior to TTE for detecting vegetations

• Empirical IV antibiotics should cover S. aureus, streptococci, and enterococci

• Early surgical consultation is critical in severe cases