Problems with artificial hearts include
the formation of blood clots within the
device, and infection. They are therefore
used as a temporary measure until a
heart transplantcan be performed.
heart attackSee myocardial infarction.
heartbeatA contraction of the heart
that pumps blood to the lungs and the
rest of the body. The different parts of
the heart contract in a precise sequence
that is brought about by electrical
impulses that emanate from the sino-
atrial nodeat the top of the right atrium.
Three phases make up a cycle of 1
heartbeat: the diastole (resting phase),
the atrial systole (atrial contraction),
and the ventricular systole (ventricular
contraction). The rate at which contrac-
tions occur is called the heart-rate. The
term pulserefers to the character and
rate of the heartbeat when it is felt at
certain points around the body (at the
wrist, for example).
heart blockA common disorder of the
heartbeatcaused by an interruption to
the passage of impulses through the
heart’s conducting system.
There are several grades of heart
block, from a slight delay between the
contractions of the atria (see atrium)
and ventricles(called a prolonged P-R
interval) to complete heart block, in
which the atria and ventricles beat in-
dependently. Heart block may be due to
coronary artery disease, myocarditis, over-
dose of a digitalis drug, or rheumatic fever.
A prolonged P-R interval causes no
symptoms. In more severe heart block,
the rate of ventricular contraction does
not increase in response to exercise.
This may cause breathlessness as a
result of heart failure, or chest pains or
fainting due to angina pectoris. If the
ventricular beat becomes very slow, or if
it stops altogether for a few seconds,
loss of consciousness and seizuremay
occur due to insufficient blood reaching
the brain. If the delay is prolonged, a
stroke may result.
Symptomless heart block may not
need treatment. Heart block that is
causing symptoms is usually treated by
the fitting of an artificial pacemaker.
Drugs, such as isoprenaline, that in-
crease the heart-rate and the strengthof the heart’s contractions, may be
given as a temporary measure.
heartburnA burning pain in the centre
of the chest, which may travel from the
tip of the breastbone to the throat. It
may be caused by eating rich or spicy
food, or by drinking alcohol. Recurrent
heartburn is a symptom of oesophagitis,
which is usually caused by acid reflux.
Heartburn is often brought on by lying
down or bending forwards.
heart disease, congenitalAny abnor-
mality of the heartpresent from birth.
Defects may affect the heart chambers,
valves, or main blood vessels. Major ab-
normalities are septal defects, coarctation
of the aorta, transposition of the great
vessels, patent ductus arteriosus, tetralogy
of Fallot, hypoplastic left heart syndrome,
pulmonary stenosis, and aortic stenosis.
Developmental errors leading to de-
fects arise early in the life of the
embryo. In most cases, there is no
known cause. Rubella in the mother is
the most common known cause.
The onset and severity of symptoms
depend on the defect. Some anomalies
cause cyanosisand breathlessness but
others may go undetected. Possible
complications of an untreated heart
defect include impaired growth, pneu-
moniaas a result of mild respiratory
infections, rapid tiring during exercise,
and Eisenmenger complex.
Antenatal diagnosis, using specialized
ultrasound scanning, is possible for
most defects. After birth, any suspected
defect is investigated using chest X-
rays, ECG, or echocardiography.
Oxygenand various drug treatments
may improve the symptoms of heart
block. Some conditions, such as small
septal defects or patent ductus arteri-
osus, may get smaller or disappear of
their own accord. Other defects will
require surgical correction. Narrowed
heart valves can often be treated by
balloon valvuloplasty. In other cases,
open heart surgeryor a heart transplant
may be required.
Children with heart defects are at an
increased risk of bacterial endocarditis;
to prevent this, they are given antibiotic
drugsbefore all surgical procedures
including dental treatments.HEART ATTACK HEART DISEASE, CONGENITALH