Streptococcus viridans( α hemolytic) most common cause
Enterococci( streptococcus fecalis and S bovis) are oral commensals.
All of the above only infect damaged valves, and cause what was known as Sub acute bac endocarditis in the past( SABE)
Staph aureus( coagulase +ve) infects native valves, esp in IV drug abusers and result in acute fulminant endocarditis with valve rupture
HACEK group of organisms( Hemophilus, Actinobacillus, Cardiobacterium, Eikenella corodens, Kingella)
Staph epidermidis( coagulase –ve skin flora) infects prosthetic valves
Fungi like Candida can also cause IE resulting in large vegetations formation
Predisposing factors:
Jet lesions in the endocardium as a result of VSD, coarctation of aorta, MS, AR, etc( note: ASD doesn’t result in significant jet lesion)
Damaged valves, eg due to RHD, MVPS
Prosthetic valves
Episodes of bacteremia, eg dental, urogenital, gastrointestinal procedures, endoscopy, indwelling catheters, etc
IV drug users: rt sided valves affected
immunosupression
Site:
Site of Involvement
mitral valve 25-30%,
aortic valve 25-35%,
tricuspid valve 10%, esp inIVDU
valve prosthesis 10%,
congenital defect 10%
Valves being relatively avascular, it is difficult to eradicate the infection by the body’s defence mechanism
Morphology:
Vegetations are the hallmark- consisting of fibrin, RBC, bacteria and necrotic debris; are friable, and can be large in fungal endocarditis
Bulky vegetations might obstruct the lumen of the valve
Ring abscess in perivalvular myocardium
M/E brisk neutrophilic response is seen after the infection extends to the vascular myocardium
Fibrosis, calcification and chronic inflammatory infiltrate develop later
Embolisation of vegetations can cause metastatic abscesses and infarction in spleen, kidney, brain.
Aortic valve acute endocarditis. The probe extends through a perforated leaflet. Acute
endocarditis is very destructive of the valves and often embolizes too.
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