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:

Click the icon to see an image of stable angina.

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.

Acute Coronary 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 Angina.]
• 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.

Click the icon to see an image of an acute myocardial infarction.

The Process of Atherosclerosis

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.

Click the icon to see an image of atherosclerosis.

Increasingly, however, researchers are studying the interactions between cholesterol and processes known as oxidation and the inflammatory response:

Cholesterol and Lipoproteins. The story begins with cholesterol and sphere-shaped bodies called lipoproteins that transport cholesterol.

• 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.

Oxidation. The 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 walls.
  
  

  Click the icon to see an image of arterial plaque build-up.

Inflammatory 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 arteries.
• 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 the heart.
• 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 elasticity.
• 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.
  
  

  Click the icon to see an image of the developmental process of atherosclerosis.