Tuesday, 7 May 2013

The Perfect Human Valve Substitute ?

The quest for the perfect heart valve substitute goes on. This article in recent edition of the Circulation journal shows how little has changed in the 50 years we have been implanting prostheses to replace diseased human aortic valves. Patients who have mechanical heart valves still require anticoagulants and are at greater risk of strokes or anticoagulant related haemorrhages. The new anticoagulants have not and will not change that reality. Patients who receive biological valves are at higher risk of requiring reoperations due to degeneration of the prosthesis. The cut off age for the use of mechanical prosthesis used to be 70 years. (Below 70 mechanical, above biological). Over the past decade, it has drifted downwards first to 65 then to 60. Although the rate of bioprosthetic degeneration does slow with age (possibly related to calcium turnover) the main determinant of whether degenerative changes become clinically significant is years of life with the prosthesis in situ I.e. longevity or prognosis. As life span of both women and men has increased rapidly over the past 20 years, the cut off age should in my opinion, be going up and not down. This downward drift in cut off age has not occurred because of new evidence or because of dramatic new developments in the design or manufacture of biological valve prosthesis. What has driven this change is marketing and the advent of TAVI (Transcutaneous Aortic Valve Implantation) or valve on a catheter. This device ( which is essentially a biological prosthesis that is collapsed around a catheter ) can be used to treat a stenosed native aortic valve or a degenerating surgically implanted prosthesis without the need for open surgery. A TAVI device inside a degenerating biological prosthesis is a very imperfect solution for many people who might still have 10 or more years of like ahead of them. What is needed and what has not yet been invented is a biological valve that does not degenerate over time or a mechanical valve that is completely non-thrombogenic. The advent of stem cell technology and the emerging concept of using acellular valves that get seeded by autologous cells suggest that the former I.e. a perfect biological valve is more likely to be invented than the latter. I won't however be holding my breath.