Endocarditis

What is it?

Endocarditis is an infection or inflammation of the endocardium, typically involving the heart valves. It can be broadly classified into:

  • Infective endocarditis (IE): Caused by microbial infection, primarily bacterial but sometimes fungal.
  • Non-infective endocarditis: Typically sterile, involving thrombus formation on the valves due to underlying systemic conditions.

Categorisation of Causes

  • Infective causes: Bacterial, fungal, or other microbial infections.
  • Non-infective causes: Include Libman-Sacks endocarditis (associated with systemic lupus erythematosus) or nonbacterial thrombotic endocarditis (NBTE), often linked to malignancy or hypercoagulable states.

Pathogenesis of Infective Endocarditis

  • Initial Damage: Injury or abnormality of the valve endothelium (congenital, rheumatic, or degenerative) leads to platelet and fibrin deposition.
  • Bacteremia: Microorganisms enter the bloodstream and adhere to the damaged endocardium.
  • Vegetation Formation: Pathogens, platelets, and fibrin aggregate to form vegetations, which can damage the valve and cause systemic emboli.

Risk Factors

  • Cardiac risk factors: Prosthetic heart valves, prior history of endocarditis, congenital heart disease, rheumatic heart disease.
  • Non-cardiac risk factors: Intravenous drug use, long-term indwelling catheters, haemodialysis, immunosuppression.

Typical Organisms and Their Sources

  • Native valve endocarditis (NVE):
    • Streptococcus viridans: Often from the oral cavity.
    • Staphylococcus aureus: Commonly from skin infections or IV drug use.
    • Enterococci: Often from the gastrointestinal or genitourinary tracts.
  • Prosthetic valve endocarditis (PVE):
    • Early PVE (<1 year post-surgery): Staphylococcus epidermidis and other coagulase-negative staphylococci from surgical contamination.
    • Late PVE (>1 year post-surgery): Organisms more similar to those seen in NVE.

Organisms with Particular Associations

  • Streptococcus gallolyticus (Strep bovis): Associated with colorectal cancer and gastrointestinal lesions.
  • Fungal endocarditis: Candida species and Aspergillus are associated with immunosuppression or long-term antibiotic use, usually causing large vegetations and systemic emboli.

HACEK Group

  • HACEK organisms: A group of Gram-negative bacteria (Haemophilus, Aggregatibacter, Cardiobacterium, Eikenella, Kingella) that are part of the normal oropharyngeal flora but can cause endocarditis, particularly in patients with poor dental hygiene. They are important because they can cause culture-negative endocarditis and require specific identification techniques.
💡
Eikenella corrodens gets its name from its ability to "corrode" agar in the lab, leaving pits or depressions in the culture medium where the bacteria have grown. It is infamous for causing infections following human bites or fistfights ("fight bites"). It can also cause abscesses and wound infections, making it a true opportunistic pathogen in cases of trauma.
💡
While they were originally classified as common culprits in culture-negative endocarditis due to their slow growth, modern blood culture systems have become better at identifying them. They are no longer a major cause of true culture-negative endocarditis, but the slow-growing label stuck.

Tricuspid Valve Endocarditis in IV Drug Users

  • The tricuspid valve is most commonly affected in IV drug users because the injected contaminants first reach the right side of the heart, where they can adhere to the tricuspid valve, leading to right-sided endocarditis.

Clinical Features of Endocarditis

  • Cardiac symptoms: Fever, new or changing heart murmur, heart failure (due to valve damage).
  • Extra-cardiac symptoms: Septic emboli (e.g., stroke, splenic infarcts), immune complex deposition (e.g., glomerulonephritis), and peripheral stigmata such as:
    • Osler’s nodes: Painful, tender nodules on fingers or toes.
    • Janeway lesions: Non-tender, erythematous macules on palms or soles.
    • Splinter haemorrhages: Tiny blood spots under the nails.
    • Roth spots: Retinal haemorrhages.

Diagnosis of Infective Endocarditis

  • Modified Duke Criteria:
    • Major criteria:
      1. Positive blood cultures (consistent with typical organisms).
      2. Evidence of endocardial involvement on echocardiography (e.g., vegetations).
    • Minor criteria:
      1. Predisposing heart condition or IV drug use.
      2. Fever > 38°C.
      3. Vascular phenomena (e.g., arterial emboli).
      4. Immunological phenomena (e.g., glomerulonephritis).
      5. Microbiological evidence (e.g., single positive blood culture). Diagnosis is made with 2 major, or 1 major + 3 minor, or 5 minor criteria.

Investigations

  • Blood cultures: At least 3 sets, taken before starting antibiotics.
  • Echocardiography: Transthoracic echocardiogram (TTE) or transoesophageal echocardiogram (TOE) to detect vegetations.
  • Other investigations: Full blood count, CRP/ESR, urinalysis (for haematuria), ECG, and imaging to detect complications.

Management of Infective Endocarditis

  • Medical management: Prolonged course of IV antibiotics (usually 4-6 weeks) tailored to the organism and valve involvement.
  • Surgical management: Considered in cases of:
    • Heart failure due to valve dysfunction.
    • Persistent infection despite antibiotic treatment.
    • Large vegetations (>10mm) with risk of embolism.
    • Fungal or highly resistant infections.

Complications

  • Cardiac: Heart failure, valve rupture, abscess formation.
  • Embolic: Stroke, pulmonary emboli, splenic or renal infarcts.
  • Infectious: Persistent sepsis, perivalvular abscess.
  • Immunological: Glomerulonephritis, vasculitis.

Non-Infective Endocarditis

  • Libman-Sacks endocarditis: Associated with systemic lupus erythematosus, characterised by sterile vegetations on both sides of the valve leaflets.
  • Non-bacterial thrombotic endocarditis (NBTE): Often seen in hypercoagulable states such as malignancy, leading to sterile thrombi on valve leaflets.