Mechanical heart valves
Drugs are not the only treatments that can have unexpected bad effects: non-drug treatments can pose serious risks too.
Mechanical heart valves are now a standard treatment for patients with serious heart valve disease and there have been many improvements in design over the years. However, experience with a particular type of mechanical heart valve showed how one attempt to improve a design had disastrous consequences.
Beginning in the early 1970s, a device known as the Björk-Shiley heart valve was introduced, but the early models were prone to thrombosis (clot formation) that impaired their function.
To overcome this drawback, the design was modified in the late 1970s to reduce the possibility of clots. The new device involved a disc held in place by two metal struts (supports), and many thousands of this new type of valve were implanted worldwide. Unfortunately, the structure of the valves was seriously flawed: one of the struts had a tendency to snap – a defect known as strut fracture – and this led to catastrophic and
often fatal valve malfunction.
As it happened, strut fracture had been identified as a problem during pre-marketing tests of the device, but this was attributed to defective welding and the cause was not fully investigated. The US Food and Drug Administration (FDA) nevertheless accepted this explanation, along with the manufacturer’s assurance that the lowered risk of valve thrombosis more than compensated for any risk of strut fracture.
When the evidence of disastrous valve failure became only too apparent, the FDA eventually acted and forced the valve off the market in 1986, but not before hundreds of patients had died unnecessarily.
Although product regulation systems have now improved to include better post-marketing patient monitoring and comprehensive patient registries, there is still a pressing need for greater transparency when new devices are introduced. 
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