Endocarditis is a bacterial infection of the mural endocardium and heart valves
Describe the pathogenesis of infective endocarditis
Trauma damages the heart valve endothelium. This can either be mechanical trauma or blood flow turbulence. Then a clot forms on the damaged endothelium. This is known as a non-bacterial thrombotic endocarditis. At the same time bacteria enter the blood from mucus membranes or other tissues (which may be associated with a form of traumatic event e.g. aggressive dental scaling). Bacteria then colonise the clot causing layers to form which makes a vegetation on the endothelium of the heart valve. Sometimes this can be prevented by the activation of complement or antibody.
Which valves are most affected by infective endocarditis?
Mitral and aortic valves
What is used to treat infective endocarditis?
What are MSCRAMMs?
MSCRAMMs are bacterial binding proteins that recognise ECM exposed in lesions (i.e. damaged heart endothelium)
Most bacteria with MMSCRAMs are Gram positive/negative?
How do vegetations cause regurgitation of blood and murmurs?
They can rupture the chordae tendinae which leads to valve insufficiency
List some of the causes of infective endocarditis
Streptococci and coagulase positive Staphylococcus
Bartonella (fungus - rare)
Why can there sometimes be problems with antibiotic treatment of endocarditis?
The vegetation hinders antibiotic penetration. The high concentration of microbes may stop multiplying which makes them less susceptible to Beta lactams.
What is a jet lesion?
When blood flowing from an area of high pressure through and orifice to an area of low pressure produces a high velocity jet
Which side of a jet lesion are the vegetations usually on: low or high pressure?
How do we identify the type of bacteraemia causing the infective endocarditis?
Blood cultures - ideally from three separate sites within a 24hr period
Why must you change the needle before depositing blood for culture into the bottle?
As you do not want to culture skin bacteria, only bacteria in the blood