Endocarditis: classification, etiology, pathogenesis, pathomorphology. Infective endocarditis - acute and subacute forms
This is the inflammation of the inner layers of the heart, the endocardium, and commonly affects the heart valves, interventricular septum and chordae tendineae. It is characterised by lesions, known as vegetations, formed of masses of platelets, fibrin and microorganisms.
Endocarditis can be infective or non-infective. Alternatively, it can be chronic or acute (which further divides into acute and subacute), or Left or Right. Risk factors for all forms include Pacemakers, artificial valves and other disruptions to the physiological endothelium.
- Infective endocarditis
- Caused by microbes, most commonly Strep, followed by Staph.
- Symptoms include fever, small areas of bleeding into the skin and tiredness. Complications may include valvular insufficiency (regurgitation), heart failure, stroke, sepsis and kidney failure
- Classic diagnostic triad: persistent fever, emboli, new/changing murmurs
- Risk factors include artificial valves, hemodialysis and pacemakers
- The most common bacteria are streptococci or staphylococci
- Non-infective endocarditis
- Also known as nonbacterial thrombotic endocarditis, usually occurs in hypercoagulability state - commonly system-wide bacterial infection, pregnancy or venous catheters.
Remember: sterile (non-infective) vegetations: NBTE, small bland vegetations on the lines of valve closure in hypercoagulable states, classically with mucinous adenocarcinoma (e.g. pancreas); and Libman–Sacks endocarditis in SLE, small vegetations on both surfaces of the leaflets. Both can embolize but do not destroy the valve.
An additional note about Right sided endocarditis, this is most common in IV drug users and patients who have pacemakers.
Endocarditis typically develops friable vegetations composed of necrotic debris, thrombus and organisms, commonly found in aorta, aneurysmal sacs and around the valves (aortic and mitral most common targets). These vegetations may be single or multiple, and can erose the underlying myocardium to produce an abscess cavity (ring abscess). Shedding of the vegetations is common due to their friability, it is this which leads to development of sub dermal septic infarcts and mycotic aneurysms.
Subacute bacterial endocarditis of the mitral valve: bulky, friable, irregular vegetations on the leaflets (CDC).
Image: “Haemophilus parainfluenzae Endocarditis PHIL 851 lores” by unknown author, Public domain, via Wikimedia Commons.
Acute form
- Refers to destructive and highly virulent forms, attacking a previously normal valve and capable of causing rapid death
Subacute form
- Low virulence organism, involving a previously abnormal heart (e.g. artificial valves).
- Can be insidious and even untreated for a long time