Mechanical and biological valves pave the way for the third generation...

In the early 1950s the first mechanical valve was developed, opening the way for the first generation of heart valves, mechanical valves. The main advantage of mechanical valves is durability: they last for over twenty years without failure. However, the main problem is the need for lifetime daily anticoagulation therapy because these valves promote the formation of blood clots.

To overcome this problem a new type of valve was developed in the late 1960s: tissue graft or xenograft, opening the way for the second generation of heart valves, called biological valves. The Hancock I bioprosthetic valve was the first biological valve approved in the United States market and was co-developed by Dr Norman Jaffe and Mr Warren Hancock.

These valves are made of animal tissue, and are preserved and sterilized by glutaraldehyde, a specific tanning solution. The harvested valve is sewn to an external frame, also called stent, and covered with a polyester fabric. The main advantages of these stented tissue valves are biocompatibility, limited anticoagulation therapy and improved hemodynamics.

In the 90s a new type of biological valve came into the market to overcome some of the problems of the stented tissue valves: stentless valves. Stentless valves create a larger orifice for blood flow, improve hemodynamics because of absence of an outer frame, and reduce friction. Their main disadvantage is that they are very difficult to implant and that the surgical procedure takes longer, increasing the peri-operative risk of complications. Only 10% of cardiac surgeons have the necessary skills to implant them. This is also one of the reasons why stentless valves have only 8% market share.

The advantages of biological valves over mechanical valves are summarised in the table below (to view these documents, deactivate the pop-up blocker)

Click here to view a comparison between mechanical and  biological heart valves

Click here to view a comparison  between stented and stentless heart valves