Basic Facts

• The heart requires oxygen and nutrients so it can keep pumping, and this fuel is carried to the heart muscle within the blood that flows through the coronary arteries. So, the coronary arteries serve as fuel pipe lines to the heart muscle.

• Atherosclerosis (the build up of gunk or “plaque”) is by far the commonest cause of blockages in our arteries.
• When atherosclerosis affects the coronary arteries, it is referred to as “coronary artery disease” or CAD.

Back to Top

A More Detailed Explanation

The heart is a muscular organ that pumps blood to the body. Oxygen and nutrients are required by the heart so it can keep pumping, and this fuel is carried to the heart muscle within the blood that flows through the coronary arteries. So, the coronary arteries serve as fuel pipe lines to the heart muscle.

There are three major coronary arteries, and together with their respective branches, these arteries supply different parts of the heart muscle.  The left anterior descending coronary artery (LAD) supplies blood to the front part of the left ventricle (LV) as well as the septum (muscle partition that separates the LV and right ventricle (RV)). The circumflex coronary artery (“Circ” or CX) supplies the back portion of the LV. The right coronary artery (RCA) supplies the bottom portion of the LV and also the entire RV in 90% of cases. In 10% of cases, the CX supplies the bottom portion of the LV.

Coronary arteries have muscle fibers within their walls. By contracting those muscle fibers, the artery can reduce blood flow; relaxing the muscle fibers 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, markedly reducing blood flow. This uncommon condition is known as coronary spasm, and may be associated with chest pain.  The chest discomfort of coronary spasm usually 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, and the chest pain is relieved. Most chest pain is not caused by coronary spasm.  Rather it is a consequence of atherosclerosis.

Atherosclerosis (the build up of gunk or “plaque”) is by far the commonest cause of blockages in our arteries. Unlike coronary spasm which creates a temporary blockage, atherosclerosis results in a fixed blockage. Occasionally, atherosclerosis may be accompanied by coronary spasm. When atherosclerosis affects the coronary arteries, it is referred to as “coronary artery disease” or CAD.

The diagrams below show the various stages of progression of atherosclerosis and development of CAD. 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.

The inner lining of the normal coronary artery is smooth and free of blockages or obstructions. 

As we get older, lipids or fatty substances (cholesterol and triglycerides) are deposited as fatty streaks. The streaks are only minimally raised and thus do not produce any obstruction or symptoms - but they are precursors to bigger blockages down the road.  Fatty streaks can start to develop in childhood, so maintaining healthful lifestyle habits is important from an early age.

Patients with one or more risk factors for CAD are susceptible to the increased buildup of fatty deposits known as “atheroma”. This buildup begins to encroach upon the inner channel through which blood is flowing.

Back to Top

Risk Factors

Risk factors for developing CAD include:

• Hyperlipidemia (high cholesterol level, particularly the "bad" component known as Low-Density Lipoprotein (LDL))
• High blood pressure 
• Diabetes
• Cigarette smoking
• Obesity
• Poor dietary habits
• Lack of exercise
• Strong family history of CAD
• Increasing age
• Stress and tension

As CAD progresses, fibers begin to grow into and around the atheroma, causing the blockages to harden and turn into “plaque”. The enlarging plaque (above) increases the encroachment into the inner channel of the coronary artery. When the channel diameter is reduced by more than 50%, the artery may become obstructed enough to impact blood flow to the heart muscle during exercise, emotional stress, etc. During such times, the blood pressure and heart rate are both elevated and the need for oxygen and nutrients by the heart muscle is increased. 

The imbalance between the supply and demand of oxygen can cause chest discomfort (tightness, fullness, heaviness or pain) in the center of the chest and/or over the left breast). This is known as “angina” or angina pectoris.  Plaques can grow slowly or remain relatively stable for years.  So patients may not notice much worsening of angina during this time of stability and are said to have stable angina.

In other cases, plaques within the inner lining of the coronary artery may develop a slight crack or rupture. Note that the rupture involves only the surface of the plaque and does not go all the way through the wall of the artery.  Plaque rupture is recognized as an injury by the body which then produces a blood clot at the site of rupture in an attempt to seal off the superficial crack. The sudden increase in the obstruction caused by the clot can transform a mild blockage into a critical one within a matter of minutes (above). The decrease in blood flow to the heart muscle may be severely reduced and the patient will experience severe and prolonged chest pain that occurs at rest and may even awaken him or her from a sound sleep. This is known as unstable angina. If the clot does not fully close off the channel of the artery (as in the example above), some blood flow is maintained to the heart muscle, and a heart attack can be avoided if appropriate and prompt treatment is employed. 

However, the clot may continue to grow. This can completely fill the open channel of the artery (above) and cut off blood flow to the part of the heart muscle that the artery supplies.

Without oxygen and nutrients, the heart muscle is damaged and the patient suffers a heart attack ("myocardial infarction ”). The good news is that there are several forms of treatment that can get rid of the blood clot and restore flow across the artery.  The bad news is that all of these treatments are time sensitive and can only be employed if the patient is rushed to the emergency room of the nearest hospital. Every minute counts when it comes to salvaging heart muscle.  The really bad news?  Half of all heart attacks result in death. 

Uncontrolled risk factors (see above) all contribute to making the plaque more likely to rupture or crack.  So controlling risk factors not only prevents the development of blockages, but also prevents the development of a life altering or life limiting cardiac event “out of the blue”.

Coronary artery blockages and heart attacks may also be seen in patients who use stimulant drugs, especially "Crack" cocaine. This is becoming the commonest cause of heart attacks in young adults who are treated in emergency rooms in the United States.

 

Content originally developed and provided by HeartSite.com. Reviewed and modified for CardioSmart by ACC March 11, 2008.

Back to Top

---

Please note that the content on CardioSmart attempts to define practices that meet the needs of most patients in most circumstances. However, everyone is unique, and the extent to which the information applies specifically to you should be a key point of discussion between you and your cardiologist or health care provider. The ultimate judgment regarding your care must be made by you and your healthcare provider together, in light of circumstances specific to you as a patient.