Cardiovascular System >
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)
- Cardiac lesions (congenital and acquired) → endothelial damage
- Endothelial damage attracts platelets and fibrin
- This aggregate is vulnerable to colonisation by blood-borne organisms
- Once colonised, the avascular valve tissue + fibrin and platelet aggregates help protect proliferating organisms from host defences
- Vegetations begin to grow and may become large enough to cause obstruction or embolism
- 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:
- Positive blood culture – typical organism in 2 separate cultures or persistently +ve cultures
- 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)