Xenograft Tissue Valves (Bioprosthesis)
These valves are constructed from either the aortic valve or other tissue from various animals, e.g. porcine, calf pericardium. They are manufactured commercially and are widely available “on the shelf” of operating theatres in a similar way to mechanical valves.
Once the tissue is explanted (removed) from the animal , it is chemically treated and prepared for human use. Some tissue valves have a frame, or stent, that supports the valve, and some valves are stentless (no framework). A very thin polyester mesh cuff is sewn around the outside of the valve for easier implantation. Eliminating the stent makes it possible for the surgeon to implant a larger valve. Larger valves generally provide more surface area for blood flow; this allows more blood to flow through the valve to accommodate the body’s needs.
Tissue valves do not require long term Warfarin (after the initial six weeks or so), although they are limited by durability, which is worse in younger patients. For instance, in a 40 year old patient, durability is estimated at eight to 10 years, in a 60 year old patient at 10 to 12 years, and over the age of 70 years, 13 to 15 years can be anticipated. Thus, they are really most suitable for patients over the age of 65, and in particular, those over the age of 70, in whom the durability is better, and the chance of a re-operation being necessary are reduced, because of the patient’s older age.
Applicable Age Range Greater Than 65 Years
- Most patients who receive a biological valve replacement do not need to take life-long anticoagulant therapy after surgery, unless they have other conditions (such as atrial fibrillation) that require these medications.
- Easy insertion – relatively straightforward. Valves readily available.
- Limited durability in younger age groups, eg. less than 60 years.