Thrombosis
means the clotting of blood within an artery
or a vein. This is always abnormal and is
often dangerous, as it can reduce or stop
the flow of blood. When thrombosis affects
important arteries, such as the coronary
arteries (causing a heart attack) or the
arteries supplying the brain with blood
(causing a stroke), it is a major cause
of death and serious illness.
Thrombosis
of arteries supplying the legs leads to
pain on using the leg (or even when at rest
if the thrombosis is severe). If the blood
flow is cut off completely, the leg dies
and becomes gangrenous. If this happens
in the arteries to the intestines, gangrene
of a segment of bowel follows. This is a
surgical emergency. Thrombosis of the arteries
to the kidneys can cause serious kidney
damage.
Thrombosis
of deep leg veins causes swelling, redness
and pain in the leg. A clot may break off
and, carried with the flow of blood, lodge
in the lungs. This is called a pulmonary
embolism and is a common cause of sudden,
unexpected death (see articles on Embolism
and Pulmonary embolism).
Thrombosis
of superficial veins in the legs has no
connection with deep-vein thrombosis and
is not dangerous. It can be caused by skin
infection or repeated blows to the skin
over the veins. In intravenous drug abusers
it can occur where a vein is regularly punctured
with a needle.
Symptoms
The symptoms
of thrombosis depend on the effects of restriction
of the blood flow through the vessel it
affects.
Causes
In general,
thrombosis seldom occurs in a healthy artery,
because the smooth inner lining prevents
the clot from forming. Injury to a blood
vessel, or any disease process affecting
the smoothness of the inner lining, can
start the process of thrombosis.
The commonest
cause of thrombosis in arteries is atherosclerosis
(see article on Atherosclerosis). Atherosclerosis
causes strokes and heart attacks and is
now the number one killer of the Western
world. Atherosclerosis causes rough, raised
plaques (which contain cholesterol) on the
inner lining of arteries. These eventually
tear, and the thrombosis starts to build
up where the plaques are torn.
Even when
arteries are normal, a clotting tendency
can result from hormonal or biochemical
changes in the blood. The tendency to thrombosis
in arteries may be greater during pregnancy,
in women using oral contraceptives, in people
with cancer that has affected blood vessels,
and in people whose blood is thicker than
normal (those with polycythaemia, which
means there are too many cells in the blood).
Thrombosis
in veins is encouraged by local pressure,
inflammation (thrombophlebitis) and stagnation
of blood flow through inactivity.
Treatment
Clotbusting
drugs (fibrinolytic therapy) can be useful
in treating some forms of thrombosis. There
is good evidence that the combination of
fibrinolytic drugs such as streptokinase
with aspirin can significantly reduce the
death rate from coronary thrombosis.
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Thrombosis
