Faulty Valve

 

Shiley, Inc., a Pfizer subsidiary, was a pioneer in artificial heart valves. From 1965 to the late 1970s, Shiley manufactured and sold artificial heart valves that never had a fracturing problem. In the 1970s it came up with a new model, the C-C, that allowed better blood flow than other models, thereby reducing the risk of blood clots. The new valve consisted on a metal ring through which blood flows, with two wire struts protruding from the ring that hold a small disk in place. The disk tilts up and down within the struts, opening and closing the valve according to the natural flow of blood. About 86,000 C-C valves have been implanted in patients.

Unfortunately, about 450 fractured C-C valves have been reported so far, with nearly 300 resulting deaths. Investigators have come up with disturbing findings. Since fractures can be fatal, Shiley inspectors were told to look very carefully (through microscopes) for any evidence of cracks. Each valve was hand-built, with one strut welded to the valve’s metal ring at a much sharper angle than in earlier models. Then the wire strut was bent up and down, often several times, to insert the disk. Scratches had to be polished off to let blood flow through smoothly. If any cracks were discovered, the valve was to be rewelded or discarded. Each valve was accompanied by a card recording dates and the manufacturing operations performed. What investigators discovered was that many cards indicating rewelding were falsified. Many cards were signed off by Inspector No. 2832, an employee who had left Shiley six months before the valve was first manufactured.

Investigators learned that some cracks were simply polished over rather than rewelded. Further investigation revealed skepticism about the notion that rewelding was an acceptable practice. Nancy Wilcox, a Shiley employee, testified in a Houston court case that she had talked with Cabot Corp., supplier of the metal alloy Shiley used with its struts. She reported that a Cabot official said they do not normally recommend rewelding.

Shortly after this conversation, Shiley stopped rewelding, and it disposed of any valves observed to have cracks. Shiley also reduced the angel of the outlet strut, thereby making the initial weld of strut to ring easier.

A 1984 internal memo written by a member of Shiley’s task force on valve fractures expressed concern about pressure on quality control inspectors to inspect valves at a rat that causes eye fatigue, increasing the probability of not noticing some defects.

Pfizer apparently takes a different view. It is reported as holding that the major reason for fractures was an abnormal closure of the disk, causing it to hit the tip of one strut with too much force. Repeated striking can produce metal fatigue, ultimately resulting in a broken strut. In addressing this problem, Pfizer says that, in early 1984, it made design changes that avoided the abnormal disk closure--and that no valves with the new design have fractured.

The Federal Drug Administration’s position is that no specific cause of fractures has been proven.

Identify and discuss the ethical issues this case raises. Discuss the safety issues this case should raise for engineers.