PROSTHETIC VALVES



Prosthetic valves may be either mechanical or bioprosthetic. The two basic designs of mechan­ical valves are the ball and cage and the tilting disk (like a toilet seat cover). Bioprosthetic valves are made from porcine valve tissue mounted on metal struts.

All prosthetic valves are somewhat stenotic, and residual gradients over both aortic and mitral valves occur. Any prosthetic valve can develop a perivalvular leak, that is, a leak exterior to the valve sewing ring, resulting in aortic or mitral re­gurgitation. In addition to hemodynamic effects, the turbulence from a perivalvular leak can cause red cell hemolysis. Even normally functioning prosthetic valves can cause hemolysis in some pa­tients. The mechanical portion of a prosthetic valve may clot or otherwise malfunction. The long-term durability of mechanical valves has been well documented, but the durability of bio­prosthetic porcine valves is not established, and many appear to degenerate, especially in younger patients.

All prosthetic valves carry a risk of thromboem­bolism. Valves in the aortic position are less likely to cause emboli than valves in the mitral position. Bioprosthetic valves are less likely to cause em­boli than mechanical valves; however, a patient with a high embolic risk (for example, atrial fi­brillation, markedly dilated left atrium, previous history of peripheral emboli, or documented in­tracardiac thrombus) requires chronic anticoa­gulation despite the presence of a porcine valve. All prosthetic valves are prone to developing en­docarditis, and vigorous endocarditis prophylaxis should be administered prior to dental, GI, or GU surgery .





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