Endocarditis Flashcards
Which common congenital heart defect increases the risk of endocarditis?
Bicuspid aortic valve, due to abnormal flow of blood so there is a greater risk of microbes in the bloods sticking to the valve cusps.
What does endocarditis often link to?
Structural heart defects.
What is endocarditis?
Inflammation of the endocardium.
What is the most common feature of endocarditis?
Vegetations (aggregation) on the surface of heart valves.
What are vegetation of heart valves?
They are the accumulation of fibrin, platelets and inflammatory cells on the surface of valves, that occurs due to disrupted flow of blood (turbulent) through the valve.
How do vegetation of heart valves cause infection?
The vegetation on the heart valve allows microorganisms in the blood stream to bind to the vegetation.
Invasion of the microorganisms in the endocardium can cause endocarditis.
Which pathogen most frequently causes endocarditis, and why?
Staphylococcus aureus. This is because it contains fibronectin binding proteins that are capable of binding to the intact endothelium.
It also contains the enzyme coagulase, meaning that it can convert fibrinogen to fibrin, increasing the risk of vegetations.
How does the coagulase test differentiate between staphylococci?
It tests for the ability to form fibrin. Staphylococcus aureus is the only staphylococcus that contains coagulase, which can convert fibrinogen to fibrin.
This means that staphylococcus aureus will give a positive result.
All other staphylococcus will return a negative test, and so they are termed coagulase negative staphylococcus.
Vegetations are classed as biofilms. What is the formation process of biofilms?
Biofilms are formed through the adherence of bacteria to a surface. With vegetations, this is the valvular surface.
The aggregation of bacteria allow an extracellular matrix to be formed and surround the pathogens, forming a microcolony.
The bacteria proliferate and the extracellular matrix grows. Once it reaches a macrocolony, cells can detach and cause infection elsewhere.
What are the issues with biofilms?
The extracellular matrix is hard to penetrate with antibiotics.
The biofilm can embolise and form biofilms elsewhere in the body.
The bacteria produce autoinducers which induce the bacteria to upregulate genes that confer antibiotic resistance.
The biofilm can cause persistent inflammation.
They can only really be treated with removal, which carries its own risks.
What are the issues with deep and superficial bacterial microcolonies?
Deep colonies are dormant, but are difficult to eradicate.
Superficial colonies can embolise or cause re-infection of the vegetation. This can cause:
- Spread of the infection causing destruction of the myocardium.
- Distal blood-borne septic embolisation; infection at distal sites due to movement of the bacterial colonies through the blood.
Clinical features of endocarditis.
Fever.
Heart murmur.
Cardiac complications - incompetant valves can lead to ventricular hypertrophy, heart failure, etc.
Embolic features, such as Janeway lesions, splinter haemorrhages, Oslers nodes and Roth spots.
What are Janeway lesions?
Haemorrhagic nodular lesions on the palms and soles.
What are splinter haemorrhages?
Small linear capillary engorgements on the distal third of the nail bed.
What are Oslers nodes?
Painful, erythematous (red) nodules on the pads of the fingers and toes.
They are related to septic micro-emboli and immune-related vasculitis.
What are Roth spots?
They are haemorrhagic spots seen in the retina of the eye.
These are caused by thrombocytopenia, caused by low-grade DIC - a complication of bacterial endocarditis.
