the major advantage of mechanical over biological valves is their very low rate of failure. Their main disadvantage is thrombus formation
the major advantage of biological over mechanical valves is that long term anticoagulation is not needed. Their major disadvantage is the risk of structural deterioration over time because of leaflet degeneration and dystrophic calcifiication both of which are relatied to the position (mitral > aortic) and the patient age
"..The increasing confidence in bioprostheses, coupled with the increasing age of the patient population, is reflected in the increasing proportion of bioprosthetic valves, particularly pericardial valves, and the decreasing proportion of mechanical prostheses being implanted..."
risk of thromboembolism is on average 0.7% per year in patients with biological valves in sinus rhythm. Among patients > 65 years old undergoing primary aortic valve replacement (AVR) fewer than 10% of biological valves with require replacement for stutural valve deterioration over a 15 year period
a biological valve is the only option for patients who cannot take oral anticoagulants such as a young women planning to become pregnant
Reference:
1) BHF (factfile May 2009). Prosthetic heart valve.
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