M13 - Infective Endocarditis Flashcards
What is IE and infection of
The endocardium
What is the endocardium
Membrane layer of endothelial cells lining the heart that is continuous with the artery and vein lining and also forms the valve cusps
What happens to valves in patients with IE
They basically keep the valves open a little bit at rest and causes some back flow
What are the majority of IE cases caused by
Streptococci, mainly “oral streptococci” or enterococci
What is the next most common IE causing organism after strepto/enterococci
Staphylococci, S.aureus
Name the HACEK organisms and what they do
Haemophilus Aggregatibacter Cardiobacterium Eikenella Kingella These are gram -ve bacteria that are an unusual cause of infective endocarditis
Name some risk factors of IE
Rheumatic heart disease
Ageing population
Degenerative heart disease
Intravenous drug use
What parts of the body does IE tend to affect
Usually affects a heart valve but can involve a septal defect or mural endocardium in a left ventricular aneurysm. It can also complicate cardiac abnormalities such as arteriovenous shunts, coarctation (narrowing) of the aorta and developmental defects
What is a ventricular aneurysm
Balloon-like swelling in the wall (may develop after myocardial infarction)
Describe the pathogenesis of IE
- During a bacteraemia micro-organisms get deposited on, adhere to and multiply on an endothelial breach which has developed a platelet thrombus
- They then become encased in additional layers of fibrin and platelets and these layers help protect the bacteria from phagocytic cells
- Results in a “vegetation”, which is the characteristic lesions that form in endocarditis, mainly occur on valve leaflets and when blood flows from a high to a low pressure chamber
What types of IE are there
- Affecting previously normal valve
- Affecting previously abnormal native valve
- Affecting prosthetic valves
- Iatrogenic (a condition resulting from treatment)
What are the clinical features of abnormal native valve
- Rheumatic fever, degenerative (calcific) disease
- Congenital defects (especially turbulent flow)
- Mitral valve prolapse (5-10x risk)
- Degenerative valve disease
What pathogens tend to cause Abnormal Native Valve IE
Streptococcus spp. or Enterococcus spp.
usually mouth/gut/urinary tract?
Name some oral streptococci that can cause abnormal native valve IE
Strep sanguinis. S. mitis, S. mutans
Describe the virulence factors of oral streptococci that can cause IE
- Ability to bind to fibronectin - a protein on the surface of host cells including heart endothelium
- Production of extra-cellular polysaccharide
- Ability to bind to platelets (PAAP = platelet aggregation associated protein produced by the streptococci)
When does prosthetic valve IE happen
Greatest risk within first few months after surgery
>1 year after surgery - mainly as in native
What pathogens tend to cause prosthetic valve IE
S.aureus
Coagulase negative staphylococci
What are the virulence factors of staphylococcus aureus IE
MSCRAMMS - microbial surface components recognising adhesion matrix molecules:
- Surface exposed staphylococcal protein A
- fibrinogen binding protein
Evasion/defence against immune system:
- Leukocidin subunit
- Superantigen-like protein
What is used to diagnose IE
It is difficult to diagnose IE due to variable signs an symptoms
- Duke criteria is used: lab and clinical criteria that uses a major/minor scoring system
What are the major factors that fulfill the duke criteria for IE
- Blood culture:
- typical micro-orgs for endocarditis from 2 separate blood cultures e.g. oral streps, HACEK etc OR
- Persistently +ve blood cultures for ANY microbe OR
- all of 3 or most of 4 blood cultures - Evidence of endocardial involvement:
- echocardiogram +ve for IE, vegetation or abscess
- new damage to artificial valve
- new valvular regurgitation
What are the minor factors that fulfill the duke criteria for IE
- Predisposition - to heart condition, injecting drug use
- Fever > 37C
- Vascular phenomena - arterial embolism, septic pulmonary infarcts
- Immunological phenomena - glomerulonephritis
- Echocardiogram - findings consistent with IE BUT not meeting major criteria
- Microbiological - +ve blood culture but not meeting major criteria, antibody response indicating active infection with typical IE micro-org
What criteria of the Duke criteria must be fulfilled to diagnose definite IE
- 2 major;
- 1 major + 3 minor;
- 5 minor
What criteria of the Duke criteria must be fulfilled to diagnose possible IE
- 1 major + 1 minor
- 3 minor
What criteria of the Duke criteria must be fulfilled to reject IE
- Alternative diagnosis established OR
- Resolution within 4 days on antibiotics OR
- No pathological findings with 4 days on antibiotics OR
- Does not meet “possible” criteria
How are blood cultures processed for IE bacteria
- Incubate 5 days at 37C or longer in IE
- After growth detection do Gram stain
- Clue about ID: Gram positive cocci in chains, probably streps (presumptive)
- Full ID: culture on solid media
What +ve serology findings suggest culture negative endocarditis
Serology for Coxiella burnetii, chlamydia, mycoplasma, Bartonella
What treatment options are there for IE
- Vegetation impenetrable by phagocytes
- Bacteriocidal antibiotics required
- Synergisitic combination
- Intravenous minimum 2 weeks
- MIC of micro-organism essential
- Isolation of micro-organism essential
- Surgical backup essential
What medications are used to treat the acute presentation of IE
- Flucloxacillin 8-12g IV in 4-6 divided doses plus gentamicin 1mg/kg body weight IV 8 hrly (modified according to renal function_
What medications are used to treat the indolent presentation of IE
- Penicillin 7.2g IV daily in 6 divided doses or ampicillin/amoxicillin 2g IV 6 hrly gentamicin. 1mg/kg body weight IV 8 hrly (modified according to renal function)
What medications are used in penicillin allergic patients with inrtacardiac prosthesis or suspected MRSA
- 1g 12 hrly vancomycin IV modified according to renal function plus rifampicin 300-600mg twice daily orally plus gentamicin 1mg/kg 8 hrly (modified according to renal function)
What could be the causes of persistent fever after drug treatment of IE
- Abscess at aortic root/prosthetic valve ring
- Drug hypersensitivity
- IV line infection
- Other supervening nosocomial infection
