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Coronary artery disease (CAD) occurs when the arteries that supply blood to
the heart muscle (the coronary arteries) become hardened and narrowed. The
arteries harden and narrow due to buildup of a material called plaque on their
inner walls. The buildup of plaque is known as atherosclerosis.
As the plaque increases in size, the insides of the coronary arteries get
narrower and less blood can flow through them. Eventually, blood flow to the
heart muscle is reduced, and, because blood carries much-needed oxygen, the
heart muscle is not able to receive the amount of oxygen it needs. Reduced or
cutoff blood flow and oxygen supply to the heart muscle can result in:
- Angina. Angina is chest pain or
discomfort that occurs when the heart does not get enough blood.
- Heart attack. A heart attack
happens when a blood clot develops at the site of plaque in a coronary
artery and suddenly cuts off most or all blood supply to that part of the
heart muscle. Cells in the heart muscle begin to die if they do not
receive enough oxygen-rich blood. This can cause permanent damage to the
heart muscle.
Over time, CAD can weaken the heart muscle and contribute to:
- Heart
failure. In heart failure, the heart can’t pump blood
effectively to the rest of the body. Heart failure does not mean that the
heart has stopped or is about to stop. Instead, it means that the heart is
failing to pump blood the way that it should.
- Arrhythmias. Arrhythmias are changes in the normal beating rhythm of
the heart. Some can be quite serious.
CAD is the most common type of heart disease. It is the leading cause of
death in the United States in both men and women.
Symptoms and Diagnosis
The most common symptoms of coronary artery disease (CAD) are:
- Chest
pain or chest discomfort (angina) or pain in one or both arms or in
the left shoulder, neck, jaw, or back
- Shortness of breath
The severity of symptoms varies widely. Symptoms may become more severe as
coronary arteries become narrower due to the buildup of plaque (atherosclerosis).
In some people, the first sign of CAD is a heart
attack. A heart attack happens when plaque in a coronary artery breaks
apart, causing a blood clot to form and block the artery.
There is no single test to diagnose coronary artery disease (CAD). Your
doctor will ask about your medical history and your family’s medical
history, assess your risk factors, and do a physical exam and several tests.
These procedures are used to:
- Decide if you have CAD
- Determine the extent and severity of the disease
- Rule out other possible causes of your symptoms
Based on the results of these procedures, your doctor may order one or more
of the following tests:
- EKG
(electrocardiogram). This test measures the rate and regularity of your
heartbeat.
- Echocardiogram.
This test uses sound waves to create a moving picture of your heart.
Echocardiogram provides information about the size and shape of your heart
and how well your heart chambers and valves are functioning. The test also
can identify areas of poor blood flow to the heart, areas of heart muscle
that are not contracting normally, and previous injury to the heart muscle
caused by poor blood flow.
- There are several different types of echocardiograms,
including a stress echocardiogram. During this test, an echocardiogram is
done both before and after your heart is stressed either by having you
exercise or by injecting a medicine into your bloodstream that makes your
heart beat faster and work harder. A stress echocardiogram is usually done
to find out if you have decreased blood flow to your heart.
- Stress Test. Some heart problems are easier to diagnose when your heart
is working harder and beating faster than when it's at rest. During stress
testing, you exercise (or are given medicine if you are unable to
exercise) to make your heart work harder and beat faster while heart tests
are performed.
- During exercise stress testing, your blood pressure and
EKG readings are monitored while you walk or run on a treadmill or pedal a
bicycle. Other heart tests, such as nuclear heart scanning or
echocardiography, also can be done at the same time. These would be
ordered if your doctor needs more information than the exercise stress
test can provide about how well your heart is working.
- If you are unable to exercise, a medicine can be
injected through an intravenous line (IV) into your bloodstream to make
your heart work harder and beat faster, as if you are exercising on a
treadmill or bicycle. Nuclear heart scanning or echocardiography is then
usually done.
- During nuclear heart scanning, radioactive tracer is
injected into your bloodstream, and a special camera shows the flow of
blood through your heart and arteries. Echocardiography uses sound waves
to show blood flow through the chambers and valves of your heart and to
show the strength of your heart muscle.
- Your doctor also may order two newer tests along with
stress testing if more information is needed about how well your heart
works. These new tests are magnetic resonance imaging (MRI) and positron
emission tomography (PET) scanning of the heart. MRI shows detailed images
of the structures and beating of your heart, which may help your doctor
better assess if parts of your heart are weak or damaged. PET scanning
shows the level of chemical activity in different areas of your heart.
This can help your doctor determine if enough blood is flowing to the
areas of your heart. A PET scan can show decreased blood flow caused by
disease or damaged muscles that may not be detected by other scanning
methods.
- Chest
x ray. A chest x ray takes a picture of the organs and structures
inside the chest. These include the heart, lungs, and blood vessels.
- Cardiac
catheterization. A thin, flexible tube is passed through an artery in
the groin or arm to reach the coronary arteries. The tube allows your
doctor to examine the inside of your arteries to see if there is any
blockage. Your doctor also can determine the pressure and blood flow in
the heart's chambers, collect blood samples from the heart, and examine
the arteries of the heart by x ray.
- Coronary
angiography. This test is usually performed along with cardiac
catheterization. A dye that can be seen by x ray is injected through the
catheter into the coronary arteries. The doctor can see the flow of blood
through the heart and the location of blockages.
- Nuclear
heart scan. This test provides your doctor with moving pictures of the
blood passing through your heart's chambers and arteries and shows the
level of blood flood to the heart muscle. A small amount of a radioactive
tracer is injected into your bloodstream through a vein, usually in your
arm. A special camera is placed in front of your chest to show where the
tracer lights up in healthy heart muscle and where it doesn't light up (in
heart muscle that has been damaged or has a blocked artery).
- There are different types of nuclear heart scans. Most
scans have two phases—taking pictures of the heart at rest and while it
is beating faster (called a stress test), although sometimes only a rest
scan is done. Many heart problems show up more clearly when your heart is
stressed than when it is at rest. By comparing the nuclear heart scan of
your heart at rest to your heart at "stress," your doctor can
determine if your heart is functioning normally or not.
- Electron beam computed tomography. This test identifies and measures
calcium buildup in and around the coronary arteries.
Your doctor may also order the following blood tests:
- A fasting glucose test to check your blood sugar level
- A fasting
lipoprotein profile to check your cholesterol levels
Causes
Coronary artery disease (CAD) is caused by atherosclerosis (the thickening
and hardening of the inside walls of arteries). Some hardening of the arteries
occurs normally as a person grows older.
In atherosclerosis, plaque deposits build up in the arteries. Plaque is
made up of fat, cholesterol, calcium, and other substances from the blood.
Plaque buildup in the arteries often begins in childhood. Over time, plaque
buildup in the coronary arteries can:
- Narrow the arteries. This reduces the amount of blood and oxygen that
reaches the heart muscle.
- Completely block the arteries. This stops the flow of blood to the heart
muscle.
- Cause blood clots to form. This can block the arteries that supply blood
to the heart muscle.
Plaque in the arteries can be:
- Hard and stable. Hard plaque causes the artery walls to thicken and
harden. This condition is associated more with angina than with a heart
attack, but heart attacks frequently occur with hard plaque.
- Soft and unstable. Soft plaque is more likely to break open or to break
off from the artery walls and cause blood clots. This can lead to a heart
attack.
Reference:
National Heart, Lung, and Blood Institute, USA.
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