Endocarditis is an inflammation of the inner layer of the heart, the endocardium. It usually involves the heart valves (native or prosthetic valves). Other structures which may be involved include the interventricular septum, the chordae tendineae, the mural endocardium, or even on intracardiac devices. Endocarditis is characterized by a prototypic lesion, the vegetation, which is a mass of platelets, fibrin, microcolonies of microorganisms, and scant inﬂammatory cells. In the subacute form of infective endocarditis, the vegetation may also include a center of granulomatous tissue, which may fibrose or calcify.
There are multiple ways to classify endocarditis. The simplest classification is based on etiology: either infective or non-infective, depending on whether a microorganism is the source of the inflammation. Regardless, diagnosis of endocarditis is based on the clinical features, investigations such as echocardiogram, as well as any blood cultures demonstrating the presence of endocarditis-causing microorganisms.
Since the valves of the heart do not receive any dedicated blood supply, defensive immune mechanisms (such as white blood cells) cannot directly reach the valves via the bloodstream. If an organism (such as bacteria) attaches to a valve surface and forms a vegetation, the host immune response is blunted. The lack of blood supply to the valves also has implications on treatment, since drugs also have difficulty reaching the infected valve.
Normally, blood flows smoothly through these valves. If they have been damaged (from rheumatic fever, for example) the risk of bacteria attachment is increased.
Nonbacterial thrombic endocarditis (NBTE) or marantic endocarditis is most commonly found on previously undamaged valves. As opposed to infective endocarditis, the vegetations in NBTE are small, sterile, and tend to aggregate along the edges of the valve or the cusps. Also unlike infective endocarditis, NBTE does not cause an inflammation response from the body (confusing, as the suffix "-itis" refers to inflammation). NBTE usually occurs during a hypercoagulable state such as system wide bacterial infection, or pregnancy, though it is also sometimes seen in patients with venous catheters. NBTE may also occur in patients with cancers, particularly mucinous adenocarcinoma where Trousseau syndrome can be encountered. Typically NBTE does not cause many problems on its own, but parts of the vegetations may break off and embolize to the heart or brain, or they may serve as a focus where bacteria can lodge, thus causing infective endocarditis.
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