Among the initial concerns about the Bjork-Shiley prosthetic valve??"although not nearly as serious as the fractured strut??"were concerns about the sounds emitted by the valve. According to researchers published in the Journal of Thoracic and Cardiovascular Surgery (07/83), the sound the valve made when it was closing could be heard not only by the patient with the device implanted, but by people in proximity to the patient.
"A clinical interrogation of 35 patients showed that 16 (46%) were disturbed by the clicking noise and 10 (29%) reported disturbance of those nearby," researchers wrote. The study's authors further noted that the sound pressure level was 35 dbA measured at 10 cm from the patient's chest. Although the sound was not life-threatening, it was unpleasant to some patients. Researchers suggested a new prosthesis could be designed to prevent the valve noise.
But the noise problem was overshadowed by a more serious concern: the risk of having a strut fracture, with potentially fatal consequences. Writing in 1991 for IEEE Technology and Society Magazine, J.H. Fielder argues that it was not just the defective nature of the heart valve that resulted in it being withdrawn, but that other ethical issues were at play and that if Shiley and Pfizer (which later bought Shiley) had responded to the failure issue properly, the Bjork Shiley valve might still be on the market.
As Fielder notes, most critics of the Bjork-Shiley heart valve would have put the valve's failure rate at less than one percent, meaning that the risk of a valve failure was not particularly high. Furthermore, heart valves are life-saving. When devices are life-saving, there is a different acceptable threshold for risks, because the consequence of not using the device could be death. Therefore, a one percent failure rate might be acceptable if many more patients survived because of the valve.
"While the number [of reported failures] was not large in relation to the number of valves implanted, the fact that all the fractures were similar??"occurring at the point where the outlet strut was welded to the ring??"strongly suggested that a design or manufacturing problem was responsible for the failures," Fielder wrote. In situations where both legs of the strut suffered a fracture, the valve failed, allowing unrestricted blood flow in the heart and preventing blood from flowing away from the heart.
Approximately two-thirds of patients who had both legs of the valve fail died.
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Fielder went on to note that a "Dear Doctor" letter to surgeons minimized problems and ignored hidden fractures, while misleading the FDA about problems with the struts. If Shiley had been upfront with the FDA, surgeons and patients, all might have felt that the benefits of the heart valve still outweighed the risks, but because of Shiley's handling of the fractures, the decision was made to pull the device from the market.