Infective Endocarditis

Infective Endocarditis

·        = Infection of mural endothelium or heart valves.  May also include the proximal aorta

·        See also Rheumatic Fever(Topic)

Classification

·        Now all called infective endocarditis

·        Acute bacterial endocarditis (ABE):

o   < 6 weeks duration

o   Virulent organisms

o   Normal valves (eg IVDU)

o   Bulky friable vegetations: may extend to adjoining endocardium and chordae tendinae. Destructive (directly proportional to virulence of organism). Much more destructive than Rheumatic Fever. Microscopically vegetations show a suppurative exudate, fibrinous thrombi, and large bacterial colonies destroying valve substance

·        Sub-acute bacterial endocarditis (SBE)

o   > 6 weeks duration

o   Avirulent organisms: normal flora

o   Abnormal valves

o   Evolution slower, gradual valvular dysfunction, flatter vegetations with deeper chronic inflammatory component including a vascular fibrous tissue healing response

Predisposing Factors

·        1950s: rheumatic heart disease (most cases) – affect 15 – 35 year olds

·        1990s: degenerative, rheumatic, congenital (low pressure side of a septal defect gets infected), prosthetic valves – affects 50 year olds

·        Circulatory factors:

o  Regurgitant blood stream (incompetent valve)

o  Large pressure gradient across valve (i.e. rarely right heart except IVDU)

Anatomic sites of infection

·        Nearly always where there‟s a pre-existing abnormality

·        Usually on the top of the valve

·        Incompetent mitral and aortic valves: 40% mitral, 40% mitral and aortic valve

·        Calcific aortic stenosis

·        Prosthetic heart valves

·        Congenital septal or valve defects

·        Also in Intra-venous drug users (IVDU) with normal hearts (Right side commonly affected).

Causal organisms

·        In theory: any organism (including fungi and chlamydiae)

·        In practice:

o  Native valves:

§  Streptococci: 70%

§  Staph: 20 – 25%

§  Miscellaneous (including enteroccoci) 5%

§  Culture negative 5%

o  Prosthetic valves:

§  < 3 months (early PVE): staphylococci > streptococci

§  > 3 months: staph = streptococci

·        Streptococcal causes of endocarditis:

o  Oral Commensals: Viridians Streps – more in younger people, good at sticking, don‟t cause much

o   infection elsewhere: S. sanguis, s. salivarius, s. mitis, s. milleri, s. mutans

o  Faecal: called enterococcal

·        Staphylococcal causes:

o  S. aureus: coag +ive – 60% mortality (common in intravenous drug user)

o  S. epidermidis + 20 others: coag –ive – 40% mortality

·        Miscellaneous causes: Haemophilus, Actinobacillus, Cadriobacterium/Candida Albicans (­in prosthetic valves, mortality 100%), Eikenella, Kingella

Pathogenesis of infection

·        Abnormal valve ®

o   NBTE (non-bacterial thrombotic endocarditis) – little blood clots – we all have them but ­risk on a deformed valve ®

§  Transient bacteraemia from possibly trivial infection ® adherence of bacteria ® Acute inflammatory reaction – WBCs, fibrin & platelets laid down ®

o   Mature vegetation – sheds bacteria

Diagnosis

·        Always a differential in pyrexia of unknown origin.  Malaise, weakness

·        Existing immunosuppression, neutropenia, diabetes, and alcohol increases risk

·        Heart murmur, isolated petechiae (eg nail beds, retinal) and splenomegaly significant

·        Blood culture: 3 times – organism load in blood may be low

·        Echocardiogram (although may miss flat vegetations)

Complications

·        Valvular insufficiency or stenosis (aortic stenosis ® LV hypertrophy ® coronary artery insufficiency)

·        Local extension: down septum, into wall of aorta, perforated valve, suppurative pericarditis, ring abscesses

·        Embolism: small infarcts (e.g. in kidney cortex) or abscess (each emboli has bacteria in it) eg in lungs 

·        Mycotic aneurysms, focal and diffuse glomerulonephritis

·        Septicaemia

·        Antigenaemia: antigen/antibody complexes ® skin lesions, clogged up kidneys

Treatment

·        Identify causal organism with antibody sensitive tests (MIC & MBC)

·        Empiric antibiotic therapy - regimes:

o   Staphylococcal: Flucloxacillin (or vancomycin) 2g iv 4 hourly for 2 weeks, then 1 g orally 6 hourly for 4 weeks

o   Streptococcal: penicillin + gentamycin or amoxycillin + gentamycin iv for 2 weeks, then 4 weeks oral