Introduction
Coronary artery disease is a condition in which the blood supply to the heart muscle is partially or completely blocked.
Coronary artery disease was once widely thought to be a man's disease. On average, men develop it about 10 years earlier than women, because until menopause, women are protected from the disease by high levels of estrogen. However, after menopause, the disease becomes more common among women. Among people aged 75 and older, a higher proportion of women have the disease, because women live longer.
In the United States, cardiovascular disease is the leading cause of death among both sexes, and coronary artery disease is the most common type of cardiovascular disease, occurring in about 5 to 9% (depending on sex and race) of people aged 20 and older. The death rate increases with age and overall is higher for men than for women, particularly between the ages of 35 and 55. After age 55, the death rate for men declines, and the rate for women continues to climb. After age 70 to 75, the death rate for women exceeds that for men who are the same age.
Coronary artery disease affects people of all races, but the incidence is extremely high among blacks and southeast Asians. The death rate is higher for black men than for white men until age 60 and is higher for black women than for white women until age 75.
Coronary artery disease is almost always due to the buildup of cholesterol and other fatty materials (called atheromas or atherosclerotic plaques) in the wall of a coronary artery. However, occasionally, the cause is spasm of an artery, and rarely, the cause is a birth defect, a viral infection (such as Kawasaki syndrome), lupus erythematosus, inflammation of the arteries (arteritis), or physical damage (from an injury or radiation therapy).
Fatty materials can build up gradually in arteries; this process, called atherosclerosis (see Section 3, Chapter 32), can affect different arteries. Coronary artery disease is due to atherosclerosis that develops in the arteries that encircle the heart and supply it with blood--the coronary arteries and their branches. As the atheromas grow, they bulge into the arteries, narrowing the interior (lumen) of the arteries and partially blocking blood flow. With time, calcium accumulates in the atheromas. An atheroma may rupture. Blood may enter a ruptured atheroma, making it larger, so that it narrows the artery even more. The rupture of an atheroma triggers the formation of a blood clot (thrombus). The clot may further narrow or even block the artery, or the clot may detach (becoming an embolus) and block another artery further downstream.
As an atheroma blocks more and more of a coronary artery, the supply of oxygen-rich blood to the heart muscle (myocardium) can become inadequate. An inadequate blood supply to the heart muscle is called myocardial ischemia. If the heart does not receive enough blood, it can no longer contract and pump blood normally. If an atheroma blocks an artery completely, the area of the heart muscle supplied by the artery dies, and a heart attack results.
Coronary artery disease is the most common cause of myocardial ischemia. The major complications of coronary artery disease are chest pain due to myocardial ischemia (angina) and heart attack (myocardial infarction).
 See the animation Fatty Deposits in a Coronary Artery.
Risk Factors
Some factors that affect whether a person develops coronary artery disease cannot be modified. They include advancing age, male sex, and a family history of early coronary artery disease (that is, having a close relative who developed the disease before age 50 to 55).
Other risk factors for coronary artery disease involve a person's lifestyle, which can be modified to reduce risk. These factors include high cholesterol levels, high blood pressure, smoking (the most important modifiable risk factor), a high-fat diet, physical inactivity, and obesity.
Reducing high levels of total and low-density lipoprotein (LDL) cholesterol (see Section 3, Chapter 32 and Section 12, Chapter 157) and high blood pressure (hypertension) (see Section 3, Chapter 22) is important because these disorders increase the risk of coronary artery disease. Changes in lifestyle or use of drugs can modify both disorders.
Smoking more than doubles the risk of developing coronary artery disease and having a heart attack. Secondhand smoke appears also to increase risk and should be avoided. Obesity (see Section 12, Chapter 156), which is becoming more common (especially in North America and Europe), also contributes greatly to the risk of coronary artery disease, particularly when fat is stored in the abdomen.
High levels of lipoprotein(a)--another type of cholesterol--and of triglycerides--another fat in the blood--may also increase risk. But high levels of high-density lipoprotein (HDL) cholesterol--the good cholesterol--may reduce risk. It may be increased by lifestyle changes.
Risk is also increased by a diet that is low in fiber, vitamins C and E, and phytochemicals (which are present in fruits and vegetables and which are thought to promote health). For some people, a diet low in fish oils (omega-3 polyunsaturated fatty acids) increases risk.
Having one or two drinks of alcohol a day appears to slightly reduce the risk of coronary artery disease (while slightly increasing that of stroke). However, having more than two drinks a day increases the risk, and the larger the amount, the greater the risk.
Certain disorders increase the risk of coronary artery disease. They include high levels of the amino acid homocysteine in the blood (hyperhomocysteinemia) (see Section 3, Chapter 32), diabetes, and low levels of thyroid hormones (hypothyroidism). Diabetes greatly increases the risk. Many people with diabetes have high blood pressure, have high cholesterol levels, are obese, and tend to be physically inactive. The cause of death in more than 80% of people with diabetes is a heart or blood vessel disorder.
Whether infection with certain organisms contributes to the development of coronary artery disease is uncertain. The organisms suspected include Chlamydia pneumoniae (which can cause pneumonia), Helicobacter pylori (which can contribute to stomach ulcers), and a virus (as yet unidentified). Nonetheless, inflammation, whether caused by infection or not, appears to contribute to the development of coronary artery disease. If an atheroma becomes inflamed, it softens and is more likely to rupture, and blood clots are more likely to form.
For men and women, the use of male steroids (androgens)--either the hormone testosterone or the synthetic anabolic steroids (see Section 7, Chapter 108)--may also increase the risk of coronary artery disease. These drugs lower HDL (the good) cholesterol levels, increase LDL (the bad) cholesterol levels, and cause high blood pressure. All of these effects may contribute to having a heart attack at an early age or to having a stroke. What effects the use of anabolic steroids early in life have later in life are unclear.
Prevention
Modifying risk factors can help prevent coronary artery disease. Some of these factors are interrelated, so that modifying one also modifies another.
Smoking: Quitting smoking is most important. People who quit smoking decrease their risk of developing coronary artery disease by half compared with those who continue to smoke. How long people smoked before quitting does not matter. Quitting also decreases the risk of death after coronary artery bypass surgery or after a heart attack.
Diet: Limiting the amount of fat to no more than 25 to 35% of daily calories is recommended to promote good health. However, some experts believe that fat must be limited to 10% of daily calories to reduce the risk of coronary artery disease. A low-fat diet also helps lower high total and LDL (the bad) cholesterol levels, another risk factor for coronary artery disease.
The type of fat consumed is important. There are three types: saturated, monounsaturated, and polyunsaturated. Saturated fats are found in meats, non-skim dairy products, and artificially hydrogenated vegetable oils. The more solid the product, the higher the proportion of saturated fats. Monounsaturated fats are found in olive oil and canola oil. Polyunsaturated fats include omega-3 fats, contained in deep-sea fatty fish (such as mackerel, salmon, and tuna), and omega-6 fats, contained in vegetable oils. The ideal combination of types of fats is unknown. However, a diet high in saturated fats is known to promote coronary artery disease, and a diet high in monounsaturated or omega-3 fats is less likely to do so. Thus, eating fish regularly is recommended.
Eating at least five servings of fruits and vegetables daily can decrease the risk of coronary artery disease. Such foods contain many phytochemicals. Whether the phytochemicals are responsible for the risk reduction is unclear because people who consume such diets also tend to eat less fat, more fiber, and more foods containing vitamins C and E. One group of phytochemicals called flavonoids (found in red and purple grapes, red wine, and black teas) appears to be particularly protective.
A high-fiber diet is also recommended. There are two kinds of fiber. Soluble fiber (which dissolves in liquid) is found in oat bran, oatmeal, beans, peas, rice bran, barley, citrus fruits, strawberries, and apple pulp. It helps lower high cholesterol levels. It may decrease or stabilize high blood sugar levels and increase low insulin levels. Thus, soluble fiber may help people with diabetes reduce their risk of coronary artery disease. Insoluble fiber (which does not dissolve in liquid) is found in most grains and grain products and in fruits and vegetables such as apple skin, cabbage, beets, carrots, brussels sprouts, turnips, and cauliflower. It helps with digestive function. However, eating too much fiber can interfere with the absorption of certain vitamins and minerals.
Eating soy products, such as tofu and tempeh, also seems to reduce the risk of coronary artery disease. Eating foods high in folic acid, such as citrus fruits, tomatoes, vegetables, and grain products, may lower homocysteine levels and thus help reduce risk. However, this effect has not been proved.
Overall, a person should maintain a healthy weight and eat a variety of foods. The Mediterranean diet, which consists of large portions of fruits, vegetables, nuts, and olive oil, appears to reduce the risk of coronary artery disease.
The diet should contain the recommended daily requirements of vitamins and minerals. Vitamin supplements are not considered an acceptable substitute for a healthy diet. The role of supplements in reducing the risk of coronary artery disease is somewhat controversial. There is no proof that taking supplements of vitamin E or vitamin C prevents coronary artery disease. Taking folic acid or vitamins B6 and B12may lower homocysteine levels, but evidence supporting their use by the general population is scanty.
 See the sidebar Butter, Margarine, or Cholesterol-Lowering Margarine?
Physical Inactivity: People who are physically active are less likely to develop coronary artery disease and high blood pressure. Exercise that promotes endurance (aerobic exercise such as brisk walking, bicycling, and jogging) or muscle strength (resistance training with free weights or weight machines) helps prevent coronary artery disease (see Section 1, Chapter 6). People who are out of shape or who have not exercised in a long time should consult their doctor before they start an exercise program.
Obesity: Modifying the diet and engaging in physical activity can help control obesity. Decreasing alcohol consumption can also help because alcohol is high in calories. A loss of even 10 to 20 pounds can reduce the risk of coronary artery disease.
High Cholesterol Levels: High total and LDL (the bad) cholesterol levels can be lowered by exercising and by quitting smoking as well as by reducing the amount of fat in the diet. Drugs that lower levels of total and LDL cholesterol in the blood (lipid-lowering drugs) may be used (see Section 12, Chapter 157). The benefits of lowering cholesterol levels are greatest in people with other risk factors, such as smoking, high blood pressure, obesity, and physical inactivity.
Increasing the level of HDL (the good) cholesterol also helps reduce the risk of coronary artery disease. The same lifestyle changes that lower total and LDL cholesterol levels can help increase HDL cholesterol levels. For people who are overweight, losing weight can also help.
High Blood Pressure: Lowering high blood pressure reduces the risk of coronary artery disease. Treatment of high blood pressure begins with lifestyle changes: eating a healthy diet that is low in salt and, if needed, losing weight and increasing physical activity. Drug therapy (see Section 3, Chapter 22) may also be necessary.
Diabetes Mellitus: Good control of diabetes reduces the risk of some complications of diabetes, but the effects of such control on the development of coronary artery disease are less clear. Good control of diabetes may also reduce the risk of complications of coronary artery disease.
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