Bma Illustrated Medical Dictionary

surgeryallows the treatment of most

types of heart defect present at birth

(see heart disease, congenital) and vari-

ous disorders of the heart valves.

Coronary artery bypassis performed to

treat obstruction of the coronary arter-

ies. Narrowing of the coronary arteries

can be treated by balloon angioplasty.

Angioplasty balloonshave also been

used to open up narrowed heart valves

in cases where the patient is unsuitable

for open heart surgery (see valvulo-

plasty). Heart transplant surgery can

offer hope to people with progressive,

incurable heart disease.

heart transplantReplacement of a

patient’s damaged or diseased heart

with a healthy heart taken from a donor

at the time of death. Typically, trans-

plant patients have advanced coronary

artery diseaseor cardiomyopathy. During

the operation, the function of the heart

is taken over by a heart–lung machine.

Most of the diseased heart is removed,

but the back walls of the atria (upper

chambers) are left in place. The ventricles

(upper chambers) are then attached to

the remaining areas of the recipient’s

heart. Once the immediate post-opera-

tive period is over, the outlook is good.

Patients face the long-term problems

associated with other forms oftransplant

surgery. (See also heart–lung transplant.)

The heart-rate is also regulated by the
autonomic nervous system. The parts of
this system concerned with heart action
are a nucleus of nerve cells, called the
cardiac centre, in the brainstem, and 2
sets of nerves (the parasympathetic and
sympathetic).
At rest, the parasympathetic nerves –
particularly the vagus nerve – act on the
sinoatrial node to maintain a slow
heart-rate. During or in anticipation of
muscular activity, this inhibition less-
ens and the heart-rate speeds up.
Sympathetic nerves release noradrenaline,
which further increases the heart-rate
and force of contraction. Sympathetic
activity can be triggered by fear or
anger, low blood pressure, or a reduc-
tion of oxygen in the blood.
Release of adrenalineand noradren-
aline by the adrenal glands also acts to
increase heart-rate.
The rate and rhythm of the heart can
be measured by feeling the pulse or by
listening with a stethoscope; a more
accurate record is provided by an ECG.
A resting heart-rate above 100 beats
per minute is termed a tachycardia, and a
rate below 60 beats per minute a brady-
cardia. (See also arrhythmia, cardiac.)
heart soundsThe sounds made by the
heartduring each heartbeat. In each
heart cycle, there are 2 main heart
sounds that can clearly be heard
through a stethoscope. The first is like a
“lubb”. It results from closure of the tri-
cuspidand mitral valvesat the exits of
the atria, which occurs when the ventri-
cles begin contracting to pump blood
out of the heart. The second sound is a
higher-pitched “dupp” caused by clo-
sure of the pulmonary and aortic valves
at the exits of the ventricles when the
ventricles finish contracting.
Abnormal heart sounds may be a sign
of various disorders. For example, high-
pitched sounds or “clicks” are due to
the abrupt halting of valve opening,
which can occur in people with certain
heart valvedefects. Heart murmursare
abnormal sounds caused by turbulent
blood flow. These may be due to heart
valve defects or congenital heart disease.
heart surgeryAny operation that is
performed on the heart. Open heart

HEART SOUNDS HEART TRANSPLANT

H

Aorta

SITE OF

INCISION

Pulmonary

artery

Back walls of atria

are left in place

HEART TRANSPLANT

Diseased area

to be replaced