PROSTHETIC CARDIAC VALVES

Even after 30 years of experience and success, problems associated wit h heart valve prostheses have not been eliminated. The most serious pr oblems and complications are: (i) thrombosis and thromboembolism, (ii) anticoagulation-related hemorrhage, (iii) tissue overgrowth, (iv) inf ection, (v) paravalvular leaks due to healing defects, and (vi) valve failure due to material fatigue or chemical change. Degeneration remai ns a major concern for long-term success of porcine bioprosthetic valv es, while there is a more even distribution of failure causes in mecha nical valves. Direct comparison of the performance of artificial heart valves is difficult, and it is impossible to categorize any particula r valve as the best. Nonetheless, clear characteristics can be identif ied: mechanical valves tend to have greater durability at the expense of requiring life-long anticoagulant therapy because of their tendency toward thrombosis, while bioprostheses tend to deteriorate more rapid ly due to degenerative processes but do not require anticoagulation th erapy. The choice between bioprosthetic nonthrombogenicity and mechani cal valve durability depends upon characteristics of the specific pati ent. Further advances in prosthetic heart valves have three promising directions: (i) improved nonthrombogenicity with artificial materials; (ii) improved durability for tissue valves; and (iii) improved hemody namic characteristics, especially reduction or elimination of low shea r stress regions near valve and vessel surfaces and of high turbulent shear stresses along the edges of jets produced by valve outflow or le akage of flow. Nonetheless, while current artificial valves leave room for further advances, the superior prognosis for patients with prosth etic replacement is dramatic and convincing.