Artificial valves

Related Information: • Congenital heart defects or disease in children • Artificial valves • Mitral valve prolapse and other valvular disorders • Congenital heart problem descriptions • Endocarditis • The future of heart disease

Replacement of diseased natural heart valves with artificial ones has been life saving for those who require them. However, as in so much of medicine today, the replacement valves are never as good as natural, healthy valves.

Prosthetic (artificial) heart valves have been used for the past several decades. The manufacture of prosthetic heart valves has been studied so intensively that valves are considered successful when they have performed well for 20 years and more.

There are two general types of valves: mechanical and bioprosthetic (usually taken from pigs). The mechanical valves last longer but require the person to take blood thinners (anticoagulants).

Mechanical valves

• The Starr-Edwards valve has a caged-ball design and has performed well since 1965.
• The Bjork-Shiley, with a tilting-disk design, has been in use since 1970.
• The newer St. Jude and Medtronic-Hall valves also have a tilting-disk design. Of the tilting-disk designs, the St. Jude appears to have the most favorable properties especially in children and small-framed adults.

Bioprosthetic valves
The bioprosthetic valves do not require long-term anticoagulation, but frequently must be replaced after only about 10 years or so in adults. They are often selected by women who wish to become pregnant, and by elderly people. They often need to be replaced much more quickly in children and in people with diseased kidney function who are on hemodialysis.

Risk of stroke
The major risk of prosthetic heart valves is stroke. The reason seems to be that, despite considerable engineering research and development, the flow of blood across the prosthetic valve is turbulent, not smooth. This leads to formation of blood clots ("thrombi", technically, since they form inside the body), which can float into the brain. When they reach the brain, they float into smaller and smaller arteries until they reach arteries that are thinner than they are. They plug up these arteries, which prevents oxygen from reaching the part of the brain supplied by those arteries, which in turn causes a stroke. In general, the risk of stroke is higher for mitral valve replacement than for aortic valve replacement, perhaps because blood flows more slowly across the mitral valve and therefore has more time to form thrombi.

Source: National Institutes of Health