INFECTIVE ENDOCARDITIS: INTRODUCTION
The prototypic lesion of infective endocarditis, the vegetation (Fig. 118-1), is a mass of platelets, fibrin, microcolonies of microorganisms, and scant inflammatory cells. Infection most commonly involves heart valves (either native or prosthetic) but may also occur on the low-pressure side of the ventricular septum at the site of a defect, on the mural endocardium where it is damaged by aberrant jets of blood or foreign bodies, or on intracardiac devices themselves. The analogous process involving arteriovenous shunts, arterioarterial shunts (patent ductus arteriosus), or a coarctation of the aorta is called infective endarteritis.
Endocarditis may be classified according to the temporal evolution of disease, the site of infection, the cause of infection, or a predisposing risk factor such as injection drug use. While each classification criterion provides therapeutic and prognostic insight, none is sufficient alone.
Acute endocarditis is a hectically febrile illness that rapidly damages cardiac structures, hematogenously seeds extracardiac sites, and, if untreated, progresses to death within weeks.
Subacute endocarditis follows an indolent course; causes structural cardiac damage only slowly, if at all; rarely metastasizes; and is gradually progressive unless complicated by a major embolic event or ruptured mycotic aneurysm.
In developed countries, the incidence of endocarditis ranges from 2.6 to 7.0 cases per 100,000 population per year and remained relatively stable from 1950 to 2000. While rates of congenital heart diseases remain constant, other predisposing conditions in developed countries have shifted from chronic rheumatic heart disease to illicit IV drug use, degenerative valve disease, intracardiac devices, and health care–associated infection. The incidence of endocarditis is notably increased among the elderly. In reported series, 10–30% of endocarditis cases involve prosthetic valves. The risk of prosthesis infection is greatest during the first 6 months after valve replacement; gradually declines to a low, stable rate thereafter; and is similar for mechanical and bioprosthetic devices.
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