Coronary Artery Disease

In order to perform the arduous task of pumping blood, the heart muscle needs a plentiful supply of oxygen-rich blood, which is provided through a network of coronary arteries. Coronary artery disease is the end result of atherosclerosis (commonly called "hardening of the arteries"), a process in which arteries narrow (a condition known as), preventing sufficient oxygen-rich blood from reaching the heart. Oxygen deprivation in vital cells (called ischemia) causes injury to the tissues of the heart. If the artery becomes completely blocked, damage becomes so extensive that cell death, a heart attack, occurs.

Atherosclerosis is triggered by excess amounts of unstable particles known as oxygen-free radicals, which bind with and alter other molecules, a process called oxidation. The particles are released as part of normal bodily processes, but environmental toxins, such as viruses or smoking, can produce excess amounts. When free radicals are released in artery linings, they react with and oxidize low-density lipoproteins (LDL, the so-called bad cholesterol). LDL then deposits mushy layers of oxidized cholesterol on the walls of the artery. The cholesterol accumulates and eventually hardens into plaques. But that isn't the end of the story. The injuries to the arteries signal the immune system to release white blood cells (particularly those called neutrophils and macrophages) at the site; this initiates a process called the inflammatory response. Macrophages literally "eat" foreign debris, in this case oxidized cholesterol, and become foamy cells that attach to smooth muscle cells causing them to build up. The immune system, sensing further harm, releases other factors called cytokines, which attract more white blood cells and perpetuate the whole cycle. They also stimulate the liver to produce blood-clotting factors called fibrinogen and C-reactive protein. Injured inner walls fail to produce enough nitric oxide, a substance critical for maintaining blood vessel elasticity. The arteries become calcified and lose elasticity. As this process continues, blood flow slows. A heart attack usually occurs when a blood clot forms completely sealing off the passage of blood. This typically happens when the plaque itself develops fissures or tears; blood platelets adhere to the site to seal off the plaque and a blood clot (thrombus) forms. 

Angina

Angina is not a disease itself but is the primary symptom of coronary artery disease. It is typically experienced as chest pain, which can be mild, moderate, or severe, but is often reported as a dull, heavy pressure that may resemble a crushing object on the chest. Pain often radiates to the neck, jaw, or left shoulder and arm. Less commonly, patients report mild burning chest discomfort, sharp chest pain, or pain that radiates to the right arm or back. Sometimes a patient experiences shortness of breath, fatigue, or palpitations instead of pain. Classic angina is precipitated by exertion, stress, or exposure to cold and is relieved by rest or nitroglycerin. Angina can also be precipitated by large meals, which place an immediate demand upon the heart for more oxygen. The intensity of the pain does not always relate to the severity of the medical problem. Some people may feel a crushing pain from mild ischemia, while others might experience only mild discomfort from severe ischemia. Some people have also reported a higher sensitivity to heat on the skin with the onset of angina.

Stable Angina. Stable angina can be extremely painful, but its occurrence is predictable; it is usually triggered by exertion or stress and relieved by rest. Stable angina responds well to medical treatment. Any event that increases oxygen demand can cause angina, including exercise, cold weather, emotional tension, and even large meals. Angina attacks can occur at any time during the day, but a high proportion seems to take place between the hours of 6:00 AM and noon.

Unstable Angina. Unstable angina is a much more serious situation and is often an intermediate stage between stable angina and a heart attack. A patient is usually diagnosed with unstable angina under the following conditions: pain awakens a patient or occurs during rest, a patient who has never experienced angina has severe or moderate pain during mild exertion (walking two level blocks or climbing one flight of stairs), or stable angina has progressed in severity and frequency within a two-month period. Medications are less effective in relieving pain of unstable angina.

Prinzmetal's Angina. A third type of angina, called variant or Prinzmetal's angina, is caused by a spasm of a coronary artery. It almost always occurs when the patient is at rest. Irregular heartbeats are common, but the pain is generally relieved immediately with treatment.

Silent Ischemia. Some people with severe coronary artery disease do not experience angina pain, a condition known as silent ischemia, which some experts attribute to abnormal processing of heart pain by the brain.