Definition and pathogenesis

The term infective endocarditis (IE) denotes an infection of the endothelial surface of the heart. This is usually a valvular surface, but nonvalvular extracardiac endothelium can also be infected. Previously, IE was classified as acute or subacute, depending on the severity of clinical presentation; however, now classification and therefore therapeutic decisions are based on the bacteriology and the valvular tissue involved, that is, native valve versus prosthetic valve.

Structural abnormalities that cause turbulent blood flow across a high to low pressure gradient denude epithelium from surfaces impacted on by the turbulence; such damaged areas (most commonly valvular surfaces) are predisposed to platelet and fibrin deposition and eventually to the formation of sterile vegetation, also known as nonbacterial thrombotic endocarditis (NBTE). When transient bacteremia occurs after injury to mucosal surfaces in the oropharynx, genitourinary tract, or gastrointestinal tract, organisms can become fixed onto the NBTE, where they adhere firmly, multiply, and stimulate further deposition of platelets and fibrin. The infected site is sustained by inaccessibility of the organisms to host defenses. Complications may arise through local bacterial spread or through embolization of fragments of the vegetation. The endovascular location of the lesions causes multiorgan bacterial seeding as well as organ damage through immune complex deposition.