ARROWROOT
A
heart muscle is either partially or com-
pletely
blocked,
leading
to
a
slow,
irregular heartbeat. Periods of bradycar-
dia
may
alternate
with
periods
of
tachycardia due to a fault in impulse
generation (see
sick sinus syndrome).
CAUSES
A common
cause
of arrhythmia is
coronary artery disease,
in which the
coronary
arteries
are
narrowed
by
atherosclerosis
(fat deposits on the artery
walls),
particularly
when
following
myocardial infarction
(heart attack). Some
tachycardias are the result of a
congenital
(present
from
birth)
defect
in
the
heart's conducting system.
Caffeine
can
cause
tachycardia
in
some
people.
Amitriptyline
and some
other
antidepressant drugs
can cause seri-
ous cardiac arrhythmias if they are taken
in high doses.
SYMPTOMS
An arrhythmia may be felt as pal-
pitations,
in
which
the
individual
becomes aware of an abnormally rapid
heartbeat.
However,
in
some
cases,
arrhythmias
cause
fainting
and diz-
ziness as a result of reduced blood
flow to the brain, or chest pain and
breathlessness if there is a reduction in
blood flow to the lungs. These may be
the first symptoms.
DIAGNOSIS
Arrhythmias are diagnosed by an
ECG,
which shows the pattern of electrical
activity within heart muscle.
If the
arrhythmia is intermittent, a continuous
recording may need to be made using
an
ambulatory ECG.
TREATMENT
Treatments for arrhythmias include
anti-
arrhythmic drugs,
which prevent or slow
tachycardias. With an arrhythmia that
has developed suddenly, it may be pos-
sible to restore normal heart rhythm by
using electric shock to the heart (see
defibrillation
).
Repeated attacks of tachycardia can
sometimes be treated by radio frequency
ablation (the removal of dead or diseased
tissue) of the heart’s abnormal conduc-
tion pathway This may be carried out
during
cardiac
catheterization
(see
catheterization, cardiac).
In some cases, a
pacemaker can be fitted to restore nor-
mal heartbeat by overriding the heart’s
abnormal rhythm.
arrowroot
A starchy substance that is obtained
from the roots of the West Indian plant
MAEANTA ARUNDINACEA. Arrowroot was
traditionally used an an easily digestible
invalid
or
baby
food,
being
either
mixed to a paste with milk or water or
used as an ingredient in biscuits.
arsenic
A
poisonous
metallic
element
that
occurs naturally in its pure form and
various compounds. Arsenic poisoning,
which is now rare, once occurred as a
result of continuous industrial or pesti-
cide exposure.
arterial reconstructive surgery
An operation to repair
arteries
that are
narrowed, blocked, or weakened.
WHY IT IS DONE
Arterial reconstructive surgery is most
often performed to repair arteries that
have been narrowed by
atherosclerosis
(fatty deposits on artery walls). It is also
used to repair
aneurysms
(ballooning of
arteries)
and arteries damaged as a
result of injury.
HOW IT IS DONE
A narrowed or blocked section of artery,
particularly a coronary artery, can be
bypassed by sewing in a length of vein
above and below the constricted area.
Elsewhere in the body, the affected sec-
tion is commonly replaced using an
artificial tube or a section of vein. (See
also
angioplasty, balloon
;
coronary artery
bypass; endarterectomy.)
arteries, disorders of
Disorders of the arteries may take the
form of abnormal narrowing (which
reduces blood flow and may cause tis-
sue
damage),
complete
obstruction
(which may cause tissue death), or
abnormal widening and thinning of an
artery wall (which may cause rupture
of the blood vessel).
TYPES
Atherosclerosis,
in which fat deposits
build up on the lining of artery walls, is
the most common arterial disease. It
can
involve
arteries
throughout
the
body, including the brain
(see
cere-
brovascular disease),
heart (see
coronary
artery disease),
and legs (see
peripheral
vascular disease
). Atherosclerosis is the
main type of
arteriosclerosis,
a group of
disorders that cause thickening and loss
of elasticity of artery walls.
Hypertension
(high blood pressure) is
another common cause of thickening
and narrowing of arteries. Hyperten-
sion predisposes people to coronary
artery disease and increases the risk of a
stroke
or
kidney failure.
Arteritis
is inflammation of artery walls
that causes narrowing and sometimes
blockage.
Aneurysm
is ballooning of an artery
wall caused by the pressure of blood
flowing through a weakened area.
Thrombosis
occurs when a thrombus
(blood clot) forms in a blood vessel,
causing obstruction of the blood flow.
An
embolism
is blockage of an artery
by a fragment of blood clot or other
material travelling in the circulation.
Raynaud’s disease
is a disorder in
which there is intermittent spasm of
small arteries in the hands and feet,
usually precipitated by the cold.
arteriography
An alternative name for
angiography,
an
X-ray technique for imaging arteries.
arteriole
A blood vessel that is a branch from an
artery
and which branches further to
form
capillaries.
Arterioles have mus-
cular walls,
and their nerve supply
enables
them
to
be
narrowed
or
widened to meet the blood-flow needs
of tissues they supply.
arteriopathy
Any disorder of an artery (see
arteries
,
disorders of
).
arterioplasty
Surgical repair of an artery (see
arterial
reconstructive surgery
).
arteriosclerosis
A group of disorders that cause thicken-
ing and loss of elasticity of artery walls.
Atherosclerosis
is the most common type
of arteriosclerosis, and the two terms are
often used synonymously.
Other types are medial arteriosclero-
sis (in which muscle and elastic fibres
in larger arteries are replaced by fibrous
tissue) and Monckeberg’s arteriosclero-
sis (in which there are calcium deposits
in the arterial lining).
arteriovenous fistula
An abnormal communication directly
between an artery and a vein. An arteri-
ovenous fistula may be present at birth
or may result from injury. A fistula can
also be created surgically for easy access
to the bloodstream, as occurs in
dialysis.
If the fistula is close to the skin sur-
face it may cause a small, pulsating
swelling. If several are present in the
lungs, uptake of oxygen into the blood
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