Infective Endocarditis (IE)

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The  infective  process  of  endocardial  layer  of  the  heart  can  involve  native  or  prosthetic  valve  and  congenital  defects/shunts.  Alpha–haemolytic  streptococci  are  the  most  common  causes  of  native  valve endocarditis but Staphylococcus aureus is more likely if the disease is rapidly progressive with  high fever or is related to a prosthetic valve (Staphylococcus epidermidis). 

Diagnostic Criteria 

  • Use Modified Dukes Criteria below and consult microbiologist where possible. Three sets of blood  cultures should be taken before starting treatment. 

Modified Dukes Criteria 
Major Criteria 

  • Positive blood cultures of typical organism for IE from at least two separate blood cultures
  • Evidence  of  endocardial  involvement  by  echocardiogram  (Trans–thoracic  Echo/Trans–oesophageal Echo)

Minor Criteria 

  • Fever > 38ºC
  • Presence of Rheumatic heart disease, congenital heart disease
  • Vascular phenomena; Major arterial emboli, septic pulmonary infarcts, mycotic aneurysm, intracranial haemorrhage, conjuctival hemorrhage, Janeway lesions
  • Immunological phenomena; glomerulonephritis, Osler's nodes, Roth's spots
  • Rheumatoid factor
  • Serologic  evidence  of  active  infective  endocarditis  or  blood  culture  not  meeting  major criterion

Definition of infective endocarditis according to the modified Duke criteria:  Definitive diagnosis of IE 

Pathological criteria  

Microorganisms demonstrated by culture or on histological examination of a vegetation, a vegetation that has embolized, or an intracardiac abscess specimen

OR

Pathological lesions: vegetation or intracardiac abscess  confirmed by histological examination showing active endocarditis

Clinical criteria 

  • Two major criteria OR
  • One major and three minor criteria OR
  • Five minor criteria

Possible Diagnosis of IE 

  • One major and one minor OR
  • Three minor criteria

Rejected IE 

  • Firm alternate diagnosis. 
  • Resolution of symptoms suggesting IE with antibiotic therapy for ≤4 days; or
  • No pathological evidence of IE at surgery or autopsy, with antibiotic therapy for ≤4 days; OR
  • Does not meet criteria for possible IE, as above.

Note 

  • Positive blood cultures remain the cornerstone of diagnosis and provide live bacteria for both identification and susceptibility testing
  • To  improve  yield  of  culturing  bacteria  at  least  three  blood  sample  sets  are  taken  at  30 minutes apart each containing 10mL of blood and should be incubated in both aerobic and anaerobic atmospheres
  • Sampling should be obtained from a peripheral vein using a meticulous sterile technique

Pharmacological Treatment 

Empirical Treatment 

Consider for negative blood culture, or if risk of delaying treatment for blood culture outweighs the benefit of starting treatment early  

Treatment for native valves: 

A: benzyl penicillin G (IV) 18–24milllion Units/24hours 4hourly in equally divided dose 4–6weeks 

OR 

B: ceftriaxone (IV) 2g 24hourly 4–6weeks 

AND 

B: cloxacillin (IV) 2g 6hourly 4–6 weeks 

AND 

A: gentamicin (IV) 1–1.5mg/kg 8 hourly for at least 2weeks 

OR 

If methicillin–resistant staphylococci anaerobes (MRSA) 

S: vancomycin (IV) 30mg/kg 24 hourly in two equally divided doses, not to exceed 2gm in 24hours unless serum levels are monitored 4–6weeks. 

Note: It  is  important  to  assay  serum  gentamicin  levels  every  3–4days.  One–hour  peak  concentration  should not exceed 10mg/l and trough concentration (2–hours pre–dose) should be less than 2mg/l. 

Prosthetic valve empirical treatment 

A:  benzyl  penicillin  G  (X–Pen)  (IV) 6 – 8 weeks 

OR 

B: ceftriaxone (IV) 2g 24hourly >6 weeks 

AND 

B: cloxacillin (IV) 2g 6 hourly >6 weeks 

AND 

A: rifampicin 300 – 600mg (IV) 8hourly >6 weeks 

AND 

A: gentamicin 1mg/kg (IV) 8hourly 2 weeks. 

Note 

  • It is important to assay serum gentamicin levels every 3–4days. One–hour peak concentration should not exceed 10mg/l and trough concentration (2-hour pre-dose) should be less than 2mg/L.
  • Gentamycin in renal failure should be given based on CrCl.
  • Patients with complicated IE should be evaluated and managed in high level of care or centre, with immediate surgical facilities and the presence of a multidisciplinary including an Infectious Disease specialist, a microbiologist, cardiologist, imaging specialists, and cardiac surgeons