Mechanical prostheses: old and new

The four mechanical valve prostheses currently available on the U.S. market have evolved from a field of more than 50 valves produced for human implantation since the early 1950s (Tables 11-1 to 11-4). This literature establishes that good results can be achieved with a number of cardiac prostheses if properly used and monitored after implant. The current generation of valves have demonstrated ease of implantation, improved durability, good hemodynamic performance, and reduced thromboembolism and thrombosis with proper anticoagulation. The cost and complexity of completing PMA by the FDA, concern over product liability, and patent rights on design and raw materials have narrowed the choice of devices for surgeons in the United States and slowed the pace of new market entries. The evolution of mechanical valves has been reviewed and modes of valve failure reviewed when pertinent. Clinical expectations for earlier generation devices and present valves also are reviewed. Prostheses under evaluation are discussed along with considerations for valve implantation, surveillance, and anticoagulation. We have employed the SJM valve since about 1985. The proven good hemodynamic performance in small sizes and low profile have made its application well suited to the pediatric population and for smaller aortic roots. The well-guarded hinge mechanism and low probability for disc entrapment have facilitated its use in chordal sparing mitral replacements in our experience. Application in the tricuspid position also has been successful but requires close attention to anticoagulation.