Infective Endocarditis

“Microbial infection of a heart valve, the lining of a cardiac chamber, or blood vessel”

Risk Factors

• Normal valves:
  • Dermatitis
  • IV injections
  • Renal failure
  • Organ transplantation
  • Diabetes
  • Post-op wounds
• Abnormal valves:
  • Aortic/mitral valve disease
  • Tricuspid valves in IV drug users
  • Coarctation
  • Patent ductus arteriosus
    Ventricular septal defect
  • Prosthetic valves

Aetiology

• Microbial infection:
  • Staph. aureus
  • Viridans streptococci
  • Coagulase-negative streptococci
• Other causes:
  • Rickettsia
  • Chlamydia,
  • Fungus

Pathophysiology

Typically occurs at sites of pre-existing endocardial damage (BUT infection with a  particularly virulent or aggressive organism e.g. S. aureus can cause endocarditis in a previously normal heart)

1. Cardiac lesions (congenital and acquired) → endothelial damage
2. Endothelial damage attracts platelets and fibrin
3. This aggregate is vulnerable to colonisation by blood-borne organisms
4. Once colonised, the avascular valve tissue + fibrin and platelet aggregates help protect proliferating organisms from host defences
5. Vegetations begin to grow and may become large enough to cause obstruction or embolism
6. Adjacent tissues are destroyed, and abscesses may form

Clinical Presentation

Fever + new heart murmur = endocarditis until proven otherwise

• Sub-acute – suspected when a patient with congenital or valvular disease:
  • Develops a persistent fever, complains of unusual tiredness, night sweats or weight loss, or develops new signs of valve dysfunction or heart failure
  • Other features; purpura, petechial haemorrhages, splinter haemorrhages, Osler’s nodes (rare), palpable spleen (common- especially in Coxiella infections), microscopic haematuria
• Acute:
  • Severe febrile illness, prominent and changing heart murmurs, petechiae *clinical stigmata of chronic endocarditis are usually absent
  • Embolic events are common, cardiac/renal failure may develop rapidly
• Post-operative:
  • Unexplained fever in a recent heart valve surgery patient may resemble acute and subacute endocarditis (depending on organism virulence)

Investigations

• Bloods:
  • Normochromic normocytic anaemia, neutrophilia, high ESR/CRP
  • Blood cultures – 3 sets before treatment, from different sites at different times at peak fever (should be taken for any fever lasting >1wk in those known to be at risk)
• Imaging:
  • Chest X-Ray – shows evidence of cardiac failure and cardiomegaly
  • Echocardiogram – vegetations may be hard to distinguish from an abnormal valve (failure to detect vegetations doesn’t rule out a diagnosis)
• Special:
  • Urinalysis – check for haematuria
  • ECG – may detect AV block (long PR interval)

Diagnosis

Using the Duke Criteria – definitive endocarditis with 2 major or 1 major + 3 minors or all 5 minors

• Major criteria:
  1. Positive blood culture – typical organism in 2 separate cultures or persistently +ve cultures
  2. Endocardium involved (positive ECHO or new valvular regurgitation)
• Minor criteria:
  • Predisposition (cardiac lesion, IV drug use etc)
  • Fever >38°C
  • Vascular/immunological signs
  • Positive blood culture that doesn’t meet major criteria
  • Positive ECHO that doesn’t meet major criteria

Management

• Remove the source of infection (e.g. infected tooth)
• Treatment depends on the presentation and suspected organism
  • Acute – flucloxacillin + gentamycin
  • Sub-acute – benzylpenicillin + gentamycin
  • Prosthetic valve/ MRSA or penicillin allergy – vancomycin + gentamycin + oral rifampicin
• Cardiac surgery is advised in most – debridement of infected material and valve replacement and this is only after commencement of Abx therapy

Complications

• Antibiotic prophylaxis solely to prevent IE is NOT recommended
• Give information about the importance of good oral hygiene
• Give clear information about the risks of invasive procedures (medical and non-medical e.g. piercings, tattoos)