WHO WAS SHILEY INC.?
Shiley Inc. was a heart valve manufacturer based in Irvine, California. They began manufacturing mechanical artificial heart valves in the late 1960’s and produced several including the Bjork-Shiley Convexo-Concave, in 60-degree and 70-degree configurations.
As Shiley continued to rapidly increase their market penetration, they became a target for acquisition and in 1979 were acquired by Pfizer Inc.
By the early 1980’s, these valves had achieved a dominant position in the prosthetic valve market because of their claimed thrombo-embolic advantages over competitors. This effectively meant they were less prone to the development of blood clots in and around the flange, a major potential complication for heart valve recipients.
WHAT WERE THE BJORK SHILEY VALVES?
The Bjork Shiley 60 and 70-degree Convexo-Concave were prosthetic valves jointly developed by Dr. Viking Bjork, chairman of the Department of Surgery at Karaolinska Institute in Stockholm Sweden, and Donald Shiley a biomedical engineer from California. They would eventually come to be recognised by their abbreviated name of the “Bjork-Shiley C-C Valve”.
The valves were manufactured using state of the art materials and manufacturing processes between 1979 and 1985. The outer ring structure was made from titanium and the occluder (or disc) from carbon. The disc was held in place by two struts, a smaller outlet and a larger inlet. These were welded in place using the welding agent Haynes 25, a composite of cobalt, nickel, chromium, and tungsten.
This same material has historically been used in aerospace and military applications due to its strength and versatility. The important point to note is that this material, as strong as it is, needed to be welded at a specific temperature or the struts could be prone to failure.
WHY DID THE VALVES FAIL?
There is ongoing debate as to the cause of the failure of many of the valves. However there is evidence to suggest that the struts failed due to poor manufacturing practices i.e. incorrect welding temperatures resulting in pitting and weaknesses, and insufficient training of some welders.
Many valves were rewelded and reworked multiple times before eventually being approved for distribution.
CONSEQUENCES OF STRUT FAILURE
The propagation of a strut fracture could occur within days, weeks, or even years of implantation. When this did happen, the consequences would be dire.
In many cases one side of the outlet strut would fracture, and the other side would remain in place. This could have the effect of causing the carbon disc to periodically “lock open”, placing the patient in trauma until the disc freed itself and returned to its normal position.
Ironically this was preferable to the absolute failure of the strut as those circumstances would be fatal.
If the welds failed on both sides of the outlet strut, it would separate from the valve body and the disc would be ejected into the bloodstream. If a cardio thoracic hospital was not nearby, the patient would drown in their own blood.
In several cases where a fracture occurred, the ejected strut was later located in the ventricle or femoral artery after the death of the patient.
