Bjork–Shiley valve
The Bjork–Shiley valve is a mechanical heart valve prosthesis. Beginning in 1971, it has been used to replace the aortic or mitral valves. It marks the first example of a successfully used tilting-disc valve. It was manufactured first by Shiley Inc., then later by Pfizer after that company purchased Shiley. One model of the Bjork–Shiley valve became the subject of a famous lawsuit and recall after it was shown to malfunction.
The valve was co-invented by Donald Shiley.
Construction
The Bjork valve consists of a single carbon-coated disc in a tantalum housing. The discs are held in place by two metal struts, an inflow and an outflow strut. The standard design Bjork–Shiley valve is a very durable valve and was widely used in the 1970s.[1] According to the literature the housing is actually an alloy called Haynes 25 which is a chromium cobalt alloy <http://www.ajnr.org/cgi/reprint/24/3/512>
Convexo-concave valves
Attempts to improve the design of the valve and speed manufacturing, however, led to a weaker structure, with serious consequences. Beginning in 1979, Bjork–Shiley valves with the convexo-concave design had a tendency to develop fractures in the outflow strut which could result in catastrophic valve failure and possibly sudden cardiac death. Later analysis revealed that the strut was fracturing at the place where it was welded onto the metal valve ring. One end of the strut would fracture first, followed by the second strut some months later. Eventually, 619 of the 80,000 convexo-concave valves implanted fractured in this way, with the patient dying in two thirds of those cases. The convexo-concave valve was forced off the market by the FDA in 1986.[2] Valves welded by specific welders were at greater risk of fracture. The Convexo-Concave valve was withdrawn from the market and multiple lawsuits filed. This recall and legal struggle have been described as "perhaps the most infamous recall case on record".[3]
Not all of these valves were removed and replaced. The risk of valve fracture must be balanced against the risk of the surgery to replace the valve. Decision tools have been published and are available from a trust set up for this purpose during the litigation surrounding the valve "recall". The tools take into account patient age, the size and location of the valve (aortic or mitral) and other factors to come up with a recommendation as to whether surgery to replace the valve is worthwhile. In some patients the risk of surgery to replace the valve is higher than the risk of the valve fracturing. A compensation fund was also established to provide money for patient compensation and to pay for the costs of heart surgery to replace the valve.
More recent models of the Bjork–Shiley valve did away with the convexo-concave design and are reliable valves that do not require replacement.
References
- ↑ "Valves". http://www.rjmatthewsmd.com/Definitions/valves.htm. Retrieved 2006-05-28.
- ↑ "Bjork–Shiley Heart Valve". http://www.yourlawyer.com/topics/overview/bjork_shiley_heart_valve. Retrieved 2005-05-28.
- ↑ Pringle, Evelyn. "Lethal Defects of Bjork–Shiley Heart Valve". http://www.lawyersandsettlements.com/articles/bjork.html. Retrieved 2006-05-28.
