Artificial heart valve

An artificial heart valve is a device which is implanted in the heart of patients who suffer from valvular diseases in their heart. When one or two of the four heart valves of the heart have a malfunction, the choice is normally to replace the natural valve by an artificial valve. This requires Open-Heart Surgery.

There are two types of artificial heart valves: the mechanical and the biological valves.

A mechanical artificial heart valve with a pivoting disc

There are several varieties of mechanical valves. Some mechanical valves are made of a metal ring covered by a tissue, into which the suture threads are stitched, in order to keep the valve in place once implanted. The metal ring holds, by means of two metal supports, a disc which opens and closes as the heart pumps blood through the valve. The disc is usually made of an extremely hard carbon material (pyrolitic carbon), in order to allow the valve to function during years without wearing out. In some models of mechanical valves, the disc is divided into two parts, which open and close as a door. Another variety, utilizes a metal cage to house a metal ball. When blood pressure in the in the chamber of the heart exceeds that of the pressure on the outside of the chamber the ball is pushed against the cage and allows blood to flow. When the chamber has emptied the majority of the blood and the pressure outside the chamber exceeds that inside the chamber the ball moves back against the base of the valve forming a seal. The Ball valve was invented by Miles "Lowell" Edwards and Albert Starr in 1960 (commonly referred to as the Starr-Edwards Silastic Ball Valve). The first human inplant occured on Sept 21, 1960.

Mechanical heart valves are today very reliable and allow the patients to live a normal life. One of the main advantages of these valves is that they are well tolerated by the body. Only a small amount of blood thinner is needed to be taken by the patient each day, in order to prevent clotting of the blood when flowing through the valve. Any medication however can lead to other complications.

Biological valves are valves of animals, like pigs, which undergo several chemical procedures in order to make them suitable for implantation in the human heart. The porcine (or pig) heart is most similar to the human heart, and therefore represents the best anatomical fit for replacement. Implantation of a porcine valve is a type of Xenograft which means a transplant from one species (in this case a pig) to another. There are some risks associated with a Xenograft such as the human bodies tendency to reject foreign material. Medication can be used to retard this effect, but is not always successful.

Another type of biological valve utilizes biological tissue to make leaflets that are sewn into a metal frame. This tissue is typically harvested from the Pericardial Sac of either Bovine (cows) or Equine (horses). The pericardial sac is particularly well suited for a valve leaflet due to it's extremely durable physical properties. This type of biological valve is extremely effective means of valve replacement. The tissue is sterilized so that the biological markers are removed eliminating a response from the host's immune system. The leaflets are flexible and durable and do not require the patient to take blood thinners for the rest of their life.

The most used heart valves in the US and EU are those utilizing tissue leaflets. Mechanical valves are more commonly used in Asia and Latin America. The following companies manufacture artifical heart valves: Medtronic, Edwards Lifesciences, and St. Jude.