An agent that is smaller than a virus causes scrapie. It is either a protein called a prion or it is another substance closely associated with the prion protein. Scientists still have a lot to learn about the scrapie agent and exactly how it works.
Tissue valves are made with tissues from porcine (pig) heart valves or bovine (cow) cardiac tissue because they function like human heart valves. Once the tissue is removed from the animal, it is chemically treated to preserve the tissue and prevent immulogic reactions once it is placed in a patient.
Information and photographs posted with permission from Edwards LifesciencesÂ®. The porcine stented valve was the first generation of porcine tissue valves. They have been available for more than 30 years. The valves are made from natural porcine aortic valves, but may be used for aortic or mitral valve replacement. They are trimmed and then fixed in buffered glutaraldehyde at high pressure.