Surgical treatment such as coronary
angioplasty (see angioplasty,balloon)
may be recommended for those people
thought to be at high risk of severe
complications. If blood flow to the heart
is severely obstructed, a coronary by-
passoperation to restore blood flow
may be carried out.
athetosisA disorder of the nervous
system that is characterized by slow,
writhing, involuntary movements, most
often of the face, head, neck, and limbs.
These movements commonly include
facial grimacing, with contortions of the
mouth. There may also be difficulty in
balancing and walking. Athetosis tends
to be combined with chorea(jerky invol-
untary movements). Both athetosis and
chorea arise from damage to the basal
ganglia, clusters of nerve cells in the
brain that control movement. Causes of
athetosis include brain damage prior
to or at birth (see cerebral palsy), en-
cephalitis(brain infection), degenerative
disorders such as Huntington’s disease,
or as a side effect of phenothiazine
drugsor levodopa.
athlete’s footA common condition in
which the skin between the toes be-
comes itchy and sore, and may crack,
peel, or blister. It is due to a fungal
infection but may also be caused by
bacteria. Because the fungi thrive in
humid conditions, athlete’s foot is more
common in people with particularly
sweaty feet and with shoes and socks
made from synthetic fibres, which do
not absorb sweat. Self-treatment with
topical antifungal drugsis usually effec-
tive and should be combined with
careful washing and drying of the feet.
atlasThe topmost cervical vertebrain
the human spine. The atlas is attached
to and supports the skull. A pivot joint
attaching the atlas to the second cervi-
cal vertebra, the axis, allows the atlas to
rotate and therefore the head to turn
from side to side.
atonyLoss of tension in a muscle, so
that it is completely flaccid. Atony can
occur in some nervous system disorders
or after injury to nerves. For example,
the arm muscles may become atonic
after injury to the brachial plexus(nerve
roots in the neck passing into the arm).atopic eczemaThe most common form
of eczema. It usually begins in infancy
but may flare up during adolescence and
adulthood. The cause is unknown, but
people with atopyare more susceptible.
atopyA predisposition to various allergic
reactions (see allergy). Atopic indivi-
duals have a tendency to suffer from
one or more allergic disorders, such as
asthma, eczema, urticaria, and allergic
rhinitis(hay fever). The mechanism that
underlies the predisposition is unclear,
but atopy does seem to run in families.
ATPAn abbreviation for the compound
adenosine triphosphate, the principal
energy-carrying chemical in the body.
(See also ADP; metabolism.)
atresiaCongenitalabsence or severe nar-
rowing of a body opening or tubular
organ, due to a failure of development
in the uterus. Examples are biliary atresia,
in which the bile duct between the liver
and duodenum are absent; oesophageal
atresia, in which the oesophagus comes
to a blind end; and anal atresia (see
anus,imperforate), in which the anal
canal is shut off. Most forms of atresia
require surgical correction early in life.
atrial fibrillationA type of abnormal-
ity of the heartbeat (see arrhythmia,
cardiac) in which the atria (see atrium)
of the heart beat irregularly and rapidly.
The ventricles (lower chambers) also
beat irregularly. The heart’s pumping
ability is reduced as a result. Atrial fib-
rillation can occur in almost any
longstanding heart disease but is most
often associated with heart-valvedisor-
ders or coronary artery disease.
Sudden onset of atrial fibrillation can
cause palpitations, angina, or breathless-
ness. The heart’s inefficient pumping
action reduces the output of blood into
the circulation. Blood clots may form in
the atria and may enter the bloodstream
and lodge in an artery (see embolism).
Diagnosis of atrial fibrillation is con-
firmed by ECG. Digoxinor beta-blocker
drugsmay be given to control the heart-
rate. Atrial fibrillation of recentonset
may be reversed by defibrillation. In
most cases, anticoagulant drugsare
given to reduce the risk of embolism.
atrial flutterA type of abnormality of
the heartbeat (see arrhythmia,cardiac)ATHETOSIS ATRIAL FLUTTERA