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 past these valves. If they have been damaged (from rheumatic fever, for example) the risk of bacteria attachment is increased.
Rheumatic fever is common worldwide and responsible for many cases of damaged heart valves. Chronic rheumatic heart disease is characterized by repeated inflammation with fibrinous resolution. The cardinal anatomic changes of the valve include leaflet thickening, commissural fusion, and shortening and thickening of the tendinous cords. The recurrence of rheumatic fever is relatively common in the absence of maintenance of low dose antibiotics, especially during the first three to five years after the first episode. Heart complications may be long-term and severe, particularly if valves are involved. While rheumatic fever since the advent of routine penicillin administration for Strep throat has become less common in developed countries, in the older generation and in much of the less-developed world, valvular disease (including mitral valve prolapse, reinfection in the form of valvular endocarditis, and valve rupture) from undertreated rheumatic fever continues to be a problem.
In an Indian hospital between 2004 and 2005, 4 of 24 endocarditis patients failed to demonstrate classic vegetatations. All had rheumatic heart disease (RHD) and presented with prolonged fever. All had severe eccentric mitral regurigitation (MR). (One had severe aortic regurgitation (AR) also.) One had flail posterior mitral leaflet (PML).
Read more about this topic: Endocarditis
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