The heart is a muscular organ that pumps blood to the body at an average of 72 times
per minute. Oxygen and nutrients serve as a fuel supply to the pump and are carried
to heart in the form of blood that flows through the coronary arteries. Thus, the
coronary arteries serve as fuel pipe lines to the heart muscle.
The three major coronary arteries (Left Anterior Descending (LAD), Circumflex (Circ) and Right Coronary Artery (RCA)) and their respective branches each supply a designated portion of the heart, as follows: The LAD supplies blood to the front (anterior) portion of the heart and the septum (muscle partition that separates the Left Ventricle (LV) and Right Ventricle (RV)). The Circ supplies the back (posterior) portion of the LV. The RCA supplies the bottom (inferior) portion of the ventricle and also the RV in 90% of cases. In the other 10%, the Circ sends a branch to the inferior wall of the LV.
Coronary arteries have muscle fibers within their walls. By contracting the muscle, the artery can reduce blood flow; relaxing the muscle increases flow. In this way, the coronary arteries can regulate blood flow to different portions of the heart. Occasionally, the muscle within a coronary artery may go into spasm and markedly reduce blood flow to the heart muscle. This condition is known as coronary spasm. Typically, the chest discomfort of coronary artery spasm occurs at rest, and usually during the early morning hours. When the spasm is relieved (spontaneously or with the use of medications), the blood vessel goes back to its normal appearance and function. A temporary decrease in blood supply can cause chest discomfort while a persistent decrease can result in permanent muscle damage or a heart attack.
Atherosclerosis is by far the commonest cause of coronary artery blockage. Unlike coronary spasm which creates a temporary blockage, atherosclerosis results in a fixed blockage. Occasionally, atherosclerosis may be accompanied by coronary spasm. The diagrams below show the various stages of progression of atherosclerosis and development of coronary artery blockages. The round picture on the left of each illustration is a cross-sectional view of the coronary artery, while the picture on the right is a longitudinal section at the same level.
Major risk factors for developing CAD include:
- Hyperlipidemia (high cholesterol level, particularly the "bad" component known as Low-Density Lipoprotein (LDL))
- High blood pressure
- Cigarette smoking
- Strong family history of CAD
- Male gender, obesity, age above 50 years, lack of exercise, stress and tension can also predispose to the development of atherosclerosis