The heart is the human
body?s hardest-working organ. Throughout life it
continuously pumps blood enriched with oxygen and vital
nutrients through a network of arteries to all parts of
the body's tissues. In order to perform the arduous task
of pumping blood to the rest of the body, the heart muscle
itself needs a plentiful supply of oxygen-rich blood,
which is provided through a network of coronary arteries.
These arteries carry oxygen-rich blood to the heart?s
muscular walls (the myocardium).
Coronary artery disease
is the most common cause of heart attacks, which occur
when blood flow to the myocardium is interrupted. The
following syndromes suggest different degrees of severity
among patients with heart disease:
the icon to see an image of stable angina.
This condition can usually be managed with life-style
measures and medications, such as low-dose aspirin. The
more severe the angina, however, the greater the chance
for progressing to a more serious condition.
Syndromes.These are severe and sudden heart conditions
that require aggressive treatment but have not developed
into a full-blown heart attack. Acute coronary syndromes
include the following:
- Unstable Angina.
Unstable angina is a much more serious situation than
stable angina. It is often an intermediate stage
between stable angina and a heart attack. [See Box
- Non Q-wave Myocardial
Infarction. This condition is diagnosed when blood
tests and ECG suggest a developing heart attack. In
such cases, injury in the arteries appears to be less
severe than with a full-blown heart attack.
Heart Attack. The
full-blown heart attack occurs when blood flow is blocked
and tissue death occurs from loss of oxygen, severely
damaging the heart. In such cases, an injury known as an infarct
occurs, or in other words, a myocardial infarction,
more commonly known as a heart attack.
the icon to see an image of an acute myocardial
The Process of
Coronary artery disease
is the end result of a complex process called atherosclerosis
(commonly called "hardening of the arteries").
This causes blockage of arteries (ischemia) and
prevents oxygen-rich blood from reaching the heart. There
are many steps in the process leading to atherosclerosis
and some are not fully understood.
the icon to see an image of atherosclerosis.
researchers are studying the interactions between
cholesterol and processes known as oxidation and
the inflammatory response:
Lipoproteins. The story begins with cholesterol
and sphere-shaped bodies called lipoproteins that
- Cholesterol is a
white, powdery nutrient that is found in all animal
cells and in animal-based foods. It is critical for
many functions, but under certain conditions
cholesterol can have harmful effects.
- The lipoproteins that
transport cholesterol are referred to by their size.
The most commonly known are low-density lipoproteins (LDL)
and high-density lipoproteins (HDL). LDL is often
referred to as the "bad" cholesterol and HDL
as the "good" cholesterol.
damaging process called oxidation is an important trigger
in the atherosclerosis story.
- Oxidation is a
chemical process in the body caused by the release of
unstable particles known as oxygen free radicals.
It is one of the normal processes in the body, but
under certain conditions (such as exposure to
cigarette smoke or other environment stresses) these
free radicals are over-produced.
- In excess amounts,
they can be very dangerous, including damaging cells
and even effecting genetic material.
- In heart disease,
free radicals are released in artery linings and
oxidize low-density lipoproteins (LDL). The oxidized
LDL is the basis for cholesterol buildup on the artery
the icon to see an image of arterial plaque
Response. For the arteries to harden there must be a
persistent reaction in the body that causes ongoing harm.
Researchers now believe that this reaction is an immune
process known as the inflammatory response. The following
is one theory about how the inflammatory response
contributes to heart disease:
- The injuries to the
arteries during oxidation signal the immune system to
release white blood cells (particularly those called neutrophils
and macrophages) at the site. These factors
initiate the inflammatory response.
- Macrophages consume
foreign debris, in this case oxidized LDL cholesterol.
- The process converts
LDL cholesterol into foamy cells that attach to the
smooth muscle cells of the arteries. The cholesterol
becomes mushy and accumulates on artery walls.
- Over time the
cholesterol dries and forms a hard plaque,
which causes further injury to the walls of the
- In response to this
additional harm, the immune system releases other
factors called cytokines. These are powerful
inflammatory molecules that attract more white blood
cells and perpetuate the whole cycle, causing
persistent injury to the arteries.
Evidence is growing that
the inflammatory response may be present not just in local
plaques in single arteries but that it occurs throughout
the arteries leading to the heart.
Blockage in the
Arteries. Eventually these calcified (hardened)
arteries become narrower (a condition known as stenosis).
- As this narrowing and
hardening process continues, blood flow slows and
prevents sufficient oxygen-rich blood from reaching
- Such oxygen
deprivation in vital cells is called ischemia.
When it affects the coronary arteries, it causes
injury to the tissues of the heart.
- Injured inner vessel
walls also fail to produce enough nitric oxide,
a substance critical for maintaining blood vessel
- These narrow and
inelastic arteries not only slow down blood flow but
also become vulnerable to injury and tears.
The End Result: Heart
Attack. Heart attack can occur as a result of one or
two effects of atherosclerosis:
- If the artery becomes
completely blocked and ischemia becomes so extensive
that oxygen-bearing tissues around the heart die.
- If the plaque itself
develops fissures or tears. Blood platelets adhere to
the site to seal off the plaque and a blood clot
(thrombus) forms. A heart attack can then occur if the
formed blood clot completely blocks the passage of
oxygen-rich blood to the heart.
the icon to see an image of the developmental
process of atherosclerosis.