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Angina is
usually a warning sign of the presence of significant coronary artery disease.
Patients with angina are at risk of developing a heart attack (myocardial
infarction). A heart attack is the death of heart muscle precipitated by the
complete blockage of a diseased coronary artery by a blood clot. For further
information, please read the Heart Attack article.
During angina,
the lack of oxygen (ischemia) to the heart muscle is temporary and reversible.
The lack of oxygen to the heart muscle resolves and the chest pain disappears
when the patient rests. The muscle damage in a heart attack is permanent. The
dead muscle turns into scar tissue with healing. A scarred heart cannot pump
blood as efficiently as a normal heart, and can lead to heart
failure.
Up to 25% of
patients with significant coronary artery disease have no symptoms at all, even
though they clearly lack adequate blood and oxygen supply to the heart muscle.
These patients have "silent" angina. They have the same risk of heart attack as
those with symptoms of angina. The resting electrocardiogram (EKG) is a
recording of the electrical activity of the heart muscle, and can detect heart
muscle which is in need of oxygen. The resting EKG is useful in showing the
changes which are caused by a heart attack. It is less useful in patients with
angina, since the chest pain and lack of oxygen supply to the heart only become
evident during exertion or excitement.
In patients with
a normal resting EKG, exercise treadmill or bicycle testing can be useful
screening tools for coronary artery disease. During an exercise treadmill test,
EKG recordings of the heart are performed continuously as the patient undergoes
increasing levels of exercise. The occurrence of chest pain during exercise can
be correlated with changes on the EKG which demonstrate the lack of oxygen to
the heart muscle. When the patient rests, the angina and the changes on the EKG
which indicate lack of oxygen to the heart can both disappear. The accuracy of
exercise treadmill tests in the diagnosis of significant coronary artery disease
is 60% to 70%.
If the exercise
treadmill test does not show signs of coronary artery disease, a nuclear agent
(thallium) can be given intravenously during exercise treadmill tests. The
addition of thallium allows nuclear imaging of blood flow to different regions
of the heart, using an external camera. A reduced blood flow in an area of the
heart during exercise, with normal blood flow to the area at rest, signifies
significant artery narrowing in that region of the heart.
Stress
echocardiography combines echocardiography (ultrasound imaging of the heart
muscle) with exercise treadmill testing. Like the exercise thallium test, stress
echocardiography is more accurate than an exercise treadmill test in detecting
coronary artery disease. When a coronary artery is significantly narrowed, the
heart muscle supplied by this artery does not contract as well as the rest of
the heart muscle during exercise. Abnormalities in muscle contraction can be
detected by echocardiography. Stress echocardiography and thallium stress tests
are both about 80% to 85% accurate in detecting significant coronary artery
disease.
When a patient
cannot undergo exercise stress test because of neurological or arthritic
difficulties, medications can be injected intravenously to simulate the stress
on the heart normally brought on by exercise. Heart imaging can be performed
with a nuclear camera or echocardiography.
Cardiac
catheterization with angiography (coronary arteriography) is a technique that
allows x-ray pictures to be taken of the coronary arteries. It is the most
accurate test to detect coronary artery narrowing. Small hollow plastic tubes
(catheters) are advanced under x-ray guidance to the openings of the coronary
arteries. Iodine contrast "dye," is then injected into the arteries while an
x-ray video is recorded. Coronary arteriography gives the doctor a picture of
the location and severity of coronary artery disease. This information can be
important in helping doctors select treatment options.
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