Your heart is a strong muscular pump that is responsible for moving about 3,000 gallons of blood through your body every day. Like other muscles, your heart requires a continuous supply of blood to work properly. Your heart muscle gets the blood it needs to do its job from the coronary arteries.
What is coronary artery disease?
Coronary artery disease is the narrowing or blockage of the coronary arteries, usually caused by atherosclerosis. Atherosclerosis (sometimes called "hardening" or "clogging" of the arteries) is the buildup of cholesterol and fatty deposits (called plaques) on the inner walls of the arteries. These plaques can restrict blood flow to the heart muscle by physically clogging the artery or by causing abnormal artery tone and function.
Without an adequate blood supply, the heart becomes starved of oxygen and the vital nutrients it needs to work properly. This can cause chest pain called angina. If blood supply to a portion of the heart muscle is cut off entirely, or if the energy demands of the heart become much greater than its blood supply, a heart attack (injury to the heart muscle) may occur.
Who is affected by coronary artery disease?
Heart disease is the leading cause of death among men and women in the United States. Coronary artery disease affects 16.5 million Americans. The American Heart Association (AHA) estimates that someone in the US has a heart attack about every 40 seconds. In addition, for patients with no risk factors for heart disease, the lifetime risk of having cardiovascular disease is 3.6% for men and less than 1% for women. Having 2 or more risk factors increase the lifetime risk of cardiovascular disease to 37.5% for men and 18.3% in women.
Reference: Heart Disease and Stroke Statistics 2017 Update: A Report from the American Heart Association Statistics Committee and Stroke Statistics Subcommittee. Circulation. 2017, January 25, http://circ.ahajournals.org/content/early/2017/01/25/CIR.0000000000000485.
What are acute coronary syndromes?
Unstable angina: This may be a new symptom or a change from stable angina. The angina may occur more frequently, occur more easily at rest, feel more severe, or last longer. Although this can often be relieved with oral medications (such as nitroglycerin), it is unstable and may progress to a heart attack. Usually more intense medical treatment or a procedure are required to treat unstable angina.
Non-ST segment elevation myocardial infarction (NSTEMI): This type of heart attack, or MI, does not cause major changes on an electrocardiogram (ECG). However, chemical markers in the blood indicate that damage has occurred to the heart muscle. In NSTEMI, the blockage may be partial or temporary, so the extent of the damage is usually relatively small.
ST segment elevation myocardial infarction (STEMI): This type of heart attack, or MI, is caused by a sudden blockage in blood supply. It affects a large area of the heart muscle, and causes changes on the ECG as well as in blood levels of key chemical markers.
Although some people have symptoms that indicate they may soon develop an acute coronary syndrome, some may have no symptoms until something happens, and still others have no symptoms of the acute coronary syndrome at all.
All acute coronary syndromes require emergency evaluation and treatment.
As the size of the blockage in a coronary artery increases, the narrowed coronary artery may develop "collateral circulation." Collateral circulation is the development of new blood vessels that reroute blood flow around the blockage. However, during times of increased exertion or stress, the new arteries may not be able to supply enough oxygen-rich blood to the heart muscle.
What is ischemia?
Ischemia is a condition described as "cramping of the heart muscle." Ischemia occurs when the narrowed coronary artery reaches a point where it cannot supply enough oxygen-rich blood to meet the heart's needs. The heart muscle becomes "starved" for oxygen-rich blood to meet the heart's needs. The heart muscle becomes "starved" for oxygen.
Ischemia of the heart can be compared to a cramp in the leg. When someone exercises for a very long time, the muscles in the legs cramp up because they're starved for oxygen and nutrients. Your heart, also a muscle, needs oxygen and nutrients to keep working. If the heart muscle's blood supply is inadequate to meet its needs, ischemia occurs, and you may feel chest pain or other symptoms.
Ischemia is most likely to occur when the heart demands extra oxygen. This is most common during exertion (activity), eating, excitement or stress, or exposure to cold.
When ischemia is relieved in less than 10 minutes with rest or medications, you may be told you have "stable coronary artery disease" or "stable angina." Coronary artery disease can progress to a point where ischemia occurs even at rest.
Ischemia, and even a heart attack, can occur without any warning signs and is called "silent" ischemia. Silent ischemia can occur among all people with heart disease, though it is more common among people with diabetes.
Learn more about ischemia.
What are the risk factors for coronary artery disease?
Nonmodifiable risk factors (those that cannot be changed) include:
- Male gender. Men have a greater risk of heart attack than women do, and men have heart attacks earlier in life than women. However, beginning at Age 70, the risk is equal for men and women.
- Advanced age. Coronary artery disease is more likely to occur as you get older, especially after Age 65.
- Family history of heart disease. You have an increased risk of developing heart disease if you have a parent with a history of heart disease, especially if they were diagnosed before Age 50. Ask your doctor when it's appropriate for you to start screenings for heart disease so it can be detected and treated early.
- Race. African Americans have more severe high blood pressure than Caucasians and, therefore, have a higher risk of heart disease. The risk of heart disease is also higher among Mexican Americans, American Indians, native Hawaiians and some Asian Americans. This is partly due to higher rates of obesity and diabetes in these populations.
Modifiable risk factors (those you can treat or control) include:
- Cigarette smoking and exposure to tobacco smoke
- High blood cholesterol and high triglycerides – especially high LDL ("bad") cholesterol over 100 mg/dL and low HDL ("good") cholesterol under 40 mg/dL. Some patients who have existing heart or blood vessel disease, and other patients who have a very high risk, should aim for a LDL level less than 70 mg/dL. Your doctor can provide specific guidelines.
- High blood pressure (140/90 mmHg or higher)
- Uncontrolled diabetes (HbA1c >7.0)
- Physical inactivity
- Being overweight (body mass index [BMI] 25–29 kg/m2) or being obese (BMI higher than 30 kg/m2)
- NOTE: How your weight is distributed is important. Your waist measurement is one way to determine fat distribution. Your waist circumference is the measurement of your waist, just above your navel. The risk of cardiovascular disease increases with a waist measurement of over 35 inches in women and over 40 inches in men.
- Uncontrolled stress or anger
- Unhealthy Diet
The more risk factors you have, the greater your risk of developing coronary artery disease.
What causes the coronary arteries to narrow?
Your coronary arteries are shaped like hollow tubes through which blood can flow freely. The muscular walls of the coronary arteries are normally smooth and elastic and are lined with a layer of cells called the endothelium. The endothelium provides a physical barrier between the blood stream and the coronary artery walls, while regulating the function of the artery by releasing chemical signals in response to various stimuli.
Coronary artery disease starts when you are very young. Before your teen years, the blood vessel walls begin to show streaks of fat. As you get older, the fat builds up, causing slight injury to your blood vessel walls. Other substances traveling through your blood stream, such as inflammatory cells, cellular waste products, proteins and calcium begin to stick to the vessel walls. The fat and other substances combine to form a material called plaque.
Over time, the inside of the arteries develop plaques of different sizes. Many of the plaque deposits are soft on the inside with a hard fibrous "cap" covering the outside. If the hard surface cracks or tears, the soft, fatty inside is exposed. Platelets (disc-shaped particles in the blood that aid clotting) come to the area, and blood clots form around the plaque. The endothelium can also become irritated and fail to function properly, causing the muscular artery to squeeze at inappropriate times. This causes the artery to narrow even more.
Sometimes, the blood clot breaks apart, and blood supply is restored. In other cases, the blood clot (coronary thrombus) may suddenly block the blood supply to the heart muscle (coronary occlusion), causing one of three serious conditions, called acute coronary syndromes.