Chapter 16 Prosthetic Cardiac Valves

Abstract

Even after 30 years of experience and success, problems associated with heart valve prostheses have not been eliminated. The most serious problems and complications are: (i) thrombosis and thromboembolism, (ii) anticoagulation-related hemorrhage, (iii) tissue overgrowth, (iv) infection, (v) paravalvular leaks due to healing defects, and (vi) valve failure due to material fatigue or chemical change. Degeneration remains a major concern for long-term success of porcine bioprosthetic valves, while there is a more even distribution of failure causes in mechanical valves. Direct comparison of the performance of artificial heart valves is difficult, and it is impossible to categorize any particular valve as the best. Nonetheless, clear characteristics can be identified: 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 rapidly due to degenerative processes but do not require anticoagulation therapy. The choice between bioprosthetic nonthrombogenicity and mechanical valve durability depends upon characteristics of the specific patient. 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 hemodynamic characteristics, especially reduction or elimination of low shear stress regions near valve and vessel surfaces and of high turbulent shear stresses along the edges of jets produced by valve outflow or leakage of flow. Nonetheless, while current artificial valves leave room for further advances, the superior prognosis for patients with prosthetic replacement is dramatic and convincing.