There are two varieties of valve that can be used to replace the diseased
one in the patient:
1. Prosthetic
2.
Artificial, man-made valves, sometimes called “plastic” valves,
although they have little plastic in them.
Biological
Valves made from human or specially treated animal tissue.
Both types of valve have advantages and disadvantages; both are good
but neither is perfect.
The man-made artificial valves of today are manufactured from very
strong materials and have been put through strict tests for function and wear
before they are marketed; as the valves have to open and close about 40
million times a year, this is obviously necessary.
Because they are made of hard substances, many of these artificial
valves make clicking sounds once they have been implanted the great majority of people soon grow accustomed to this: to some it is irritating, to some
an
Also, because they are made of artificial materials, these valves, like any
other foreign bodies lying exposed in the blood stream, tend to form a clot on
themselves. This makes it necessary for people who have these valves to take
anti-coagulant drug (e.g., Warfarin) which modifies the normal blood
clotting process and so protects the valve from clot formation. This prevents
the serious consequence of a piece of clot breaking off and becoming loose in
the circulation. It is a life-time commitment to take the anti-coagulant drug and,
because the dose has to be right, blood tests have to be made at intervals to
ensure that this is so. For most people this means attending an anti-coagulant
clinic at their local hospital at intervals – at first this may be once a week — later
it is usually once every six or eight weeks. Leaflets setting out advice on the
problems of living with anti-coagulant therapy are given to patients when they
leave hospital.
The most commonly used biological valve today is the xenograft (pig)
valve. The valves are specially treated so that they not only become tougher and
more resistant to wear, but are also rendered incapable of causing rejection by
the human body.
These valves are silent, and anti-coagulants are needed only for a short
period (4-6 weeks) while the valve is “bedding in” after which they can be
stopped. Sometimes, for special reasons, patients who have received xenograft
valves may be advised to stay on anti-coagulant treatment permanently, but this
is the exception rather than the rule.