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Usually the doctor can diagnose angina by
noting the symptoms and how they arise. However one or more diagnostic
tests may be needed to exclude angina or to establish the severity of
the underlying coronary disease. These include the electrocardiogram (ECG)
at rest, the stress test, and x- rays of the coronary arteries
(coronary "arteriogram" or "angiogram").
The ECG records electrical impulses of
the heart. These may indicate that the heart muscle is not getting as
much oxygen as it needs; they may also indicate abnormalities in heart
rhythm or some of the other possible abnormal features of the heart.
To record the ECG, a technician positions a number of small contacts
on the patient's arms, legs, and across the chest to connect them to
an ECG machine.
For many patients with angina, the ECG
at rest is normal. This is not surprising because the symptoms of
angina occur during stress. Therefore, the functioning of the heart
may be tested under stress, typically exercise. In the simplest stress
test, the ECG is taken before, during, and after exercise to look for
stress related abnormalities. Blood pressure is also measured during
the stress test and symptoms are noted.
A more complex stress test involves
picturing the blood flow pattern in the heart muscle during peak
exercise and after rest. A tiny amount of a radioisotope, usually
thallium, is injected into a vein at peak exercise and is taken up by
normal heart muscle. A radioactivity detector and computer record the
pattern of radioactivity distribution to various parts of the heart
muscle. Regional differences in radioisotope concentration and in the
rates at which the radioisotopes disappear are measures of unequal
blood flow due to coronary artery narrowing, or due to failure of
uptake in scarred heart muscle.
The most accurate way to assess the
presence and severity of coronary disease is a coronary angiogram, an
x-ray of the coronary artery. A long thin flexible tube (a "catheter")
is threaded into an artery in the groin or forearm and advanced
through the arterial system into one of the two major coronary
arteries. A fluid that blocks x-rays (a "contrast medium" or "dye") is
injected. X-rays of its distribution show the coronary arteries and
their narrowing.
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