What Materials Are Used To Replace Heart Valves?
A defective heart valve or aortic valve needs to be replaced with a duplicate valve, which can function just like the original aortic valve. This duplicate valve can be either mechanical or biological. The mechanical valves are made of strong and durable materials like titanium or carbon whereas the biological valves are made of human or animal tissues.
Why the Aortic Valve Is Replaced?
The aortic valve is a one way opening which separates the heart and aorta. When the heart pumps the blood the aortic valve opens so that the blood passes through it and back flow of blood is prevented. The aortic valve malfunctions in two ways:
Aortic Regurgitation: In this condition, the aortic valve does not close properly resulting in back flow or leakage of blood.
Aortic Stenosis: In this condition, the valve does not open completely or properly, so the required amount of blood is not able to pass through the aorta.
If any of the above two defects occur in the aorta, there will be a need of replacement of the aortic valve as this defect cannot be treated only with medications. This is called a replacement surgery. The surgeon replaces malfunctioning valve with an artificial valve. The artificial valve contains an orifice which allows the blood to pass, a system which opens and closes the valve. Depending on the type of material, there are two types of valves which are generally used for replacement. They are:
Mechanical Valves: They are artificial valves made up of plastic, titanium or carbon. These valves are durable, strong and long lasting. Once they are fitted they do not need to be replaced for a long term. The problem with these valves is that blood tends to adhere to it and may create a problem of blood clotting, so the patients have to take anticoagulant drugs like warfarin or blood thinning agents throughout their life. The mechanical valves are good for children and young patients who are under the age of 40 because they do not require replacement.
The mechanical valve is of three types depending on the opening and closure system. These three types include:
Reciprocating Ball Type: The first type of mechanical valve has a ball in cage like design in which a rubber ball is used that moves to and fro in a cobalt chromium alloy cage. When the pressure of the blood comes, the valve opens and the blood flows via primary and the secondary orifice and between the ball and the metal cage.
Tilting Disk Type: This type includes a circular disk held by wire-like arms, which extend out in to the orifice. When the disk is opened the main orifice gets divided into two unequal orifices.
Two Semicircular-Hinged Leaflet Type: As the name suggests, it consists of two-hemispherical leaflets joined to the orifice through a hinge mechanism. When the valve opens, the leaflet separates allowing the blood flow in one direction.
Biological Valves: These types of valves are made up of human or animal tissues. If taken from animal, it is known as Xenograft. If these tissues are taken from human heart it is called a Homograft or Allograft. Sometimes the biological valve is made out of the patient’s own tissues, which is known as Autograft. The biological valves are not as strong as the mechanical valves and lasts up to 10 to 20 years, after which they have to be replaced. The patient need not take any anti-coagulants as in the case of mechanical valves. Biological valves are used more often in the elderly patients, specially those who are above 65 because in children and young patients there is a danger of breakage of the biological valve.