and the amount supplied. There are several possible causes of this condition.
Firstly, the blood flow through the coronary arteries may be reduced because
of mechanical blockages, such as atheroma (plaque), thrombosis (a clot),
spasm, ostial stenosis, arteritis or any sort of blockage (an embolism) due
to, for example, tumor cells or an air bubble. Secondly, a decreased flow
of oxygenated blood to the myocardium because of anemia (Chapter 13),
hypotension (low blood pressure) or carbon monoxide poisoning (Chapter
12 ). Thirdly, an increased demand for oxygen caused by exercise or myocardial
hypertrophy that requires an increase in cardiac output. Note that in the last
two scenarios, the coronary arteries may be healthy. The commonest cause
of ischemic heart disease is coronary atheroma, which obstructs the flow of
blood through the coronary arteries.
14.10 Cardiomyopathies
Cardiomyopathy is a progressive disorder that impairs the function of the
ventricular muscle walls. It may come about as a result of a number of diseases
or may have no identifiable cause.
Dilated Congestive Cardiomyopathy
Dilated congestive cardiomyopathy is not a single condition but a group of
heart disorders in which the ventricles have enlarged but are still not able to
pump enough blood to meet the needs of the body. Heart failure may result.
The commonest cause of the defect in developed countries is widespread
coronary artery disease, which leads to an inadequate blood supply to the
heart muscle. This causes damage and the undamaged muscle then stretches in
compensation. If this is inadequate to meet body needs, then dilated congestive
cardiomyopathy develops. Its symptoms are shortness of breath on exertion
and a rapid onset of tiredness due to the weakening of the heart’s pumping
action. The heart rate speeds up so blood pressure is normal or low, but fluid is
retained in the legs, abdomen and lungs. Enlargement of the heart can mean
that the valves do not close properly, leading to leakage, and this improper
closing may be heard as murmurs using a stethoscope. The stretching may
also increase the potential for arrhythmias. Electrocardiography or magnetic
resonance imaging (MRI, see Chapter 18) may be used to confirm the initial
diagnosis.
About 70% of people with the condition die within five years from the onset
of symptoms and the prognosis declines as the heart walls become thinner
with reduced contractibility. Men tend to survive only half as long as women
and blacks half as long as whites. In about half of the cases there is sudden
death. Treating the underlying cause, for example reducing alcohol abuse
can prolong life. When there is coronary artery disease there may be angina
(Section 14.13), which is treated with glyceryltrinitrate, A-blockers or calcium
channel blockers. There may also be pooling of blood in the swollen heart
that can cause clots to form and therefore the patient is given anticoagulants
(Chapter 13 and Box 14.3).
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