Coronary Heart Disease

Coronary Heart Disease, chronic illness in which the coronary arteries, the vessels that supply oxygen-carrying blood to the heart, become narrowed and unable to carry a normal amount of blood. Most often, the coronary arteries become narrowed because of atherosclerosis, a process in which fatty deposits called plaque build up on the inside wall of an artery (see Arteriosclerosis). Plaque is made of oily molecules known as cholesterol, fibrous proteins, calcium deposits, tiny blood cells known as platelets, and debris from dead cells. Plaque formation often begins in adolescence and progresses very slowly over the course of decades. Gradually, the growing plaque thickens the wall of the artery, reducing the space for blood to flow through.

When its blood supply is reduced, the heart does not receive sufficient oxygen. This oxygen deficit leads to two main consequences: chest pain known as angina pectoris, and heart attack, in which part of the heart dies because of oxygen deprivation. Coronary heart disease is the leading cause of death in the United States, responsible for about 515,000 deaths each year.

II ANGINA PECTORIS

A person who suffers from angina pectoris has coronary arteries that are wide enough to supply blood to the heart during normal activities, but too narrow to deliver sufficient blood and oxygen when extra work is required of the heart. An attack of angina develops when the heart must work harder than normal and the muscle cells that make up the heart do not receive enough oxygen.

Angina is typically felt as a heavy, squeezing pain in the center of the chest. The pain may also spread to the neck, jaw, back, and left arm. An attack of angina may last for several minutes and is often brought on by physical activity, emotional stress, cold weather, or digestion of a heavy meal—all factors that can increase the heart’s workload. Angina affects more than 6.6 million Americans.

III HEART ATTACK

A heart attack, also known as a myocardial infarction, usually occurs when a blood clot forms inside a coronary artery at the site of an atherosclerotic plaque. The blood clot severely limits or completely cuts off blood flow to part of the heart. In a small percentage of cases, blood flow is cut off when the muscles in the artery wall contract suddenly, constricting the artery. This constriction, called vasospasm, can occur in an artery that is only slightly narrowed by atherosclerosis or even in a healthy artery. Regardless of the cause of a heart attack, the oxygen deprivation is so severe and prolonged that heart muscle cells begin to die for lack of oxygen. About 1.1 million people in the United States have a heart attack every year; the heart attacks prove fatal for about 40 percent of these people.

A person having a heart attack typically feels an intense, crushing pain in the chest, especially on the left side. The pain may radiate to the person’s neck, jaw, and left arm. The pain is often similar to an attack of angina, but more intense and longer lasting. Other signs of a heart attack include profuse sweating, nausea, and vomiting. However, heart attack symptoms can vary greatly among people. In one study, about one-quarter of people who had a heart attack felt only mild symptoms and did not seek medical attention, and about 12 percent experienced no symptoms at all.

Some people have gradually worsening bouts of angina before having a heart attack. For others, a heart attack may be the first signal of heart trouble. No matter what a person’s medical history, anyone who experiences symptoms of a heart attack should go to a hospital without delay. Oxygen deprivation can cause permanent damage to the heart within hours or even minutes, so the faster a heart attack patient receives treatment, the better the chance of survival.

IV RISK FACTORS

Some of the risk factors for coronary heart disease are beyond a person’s control. For example, a person’s risk of developing coronary heart disease increases with age. Hereditary factors may also increase the risk for the disease. Males were once thought to be at greater risk of coronary heart disease, but more recent studies show this is not true. About equal numbers of women and men develop coronary heart disease. Heart attacks in women are more likely to be fatal than in men. Women tend to develop the disease later in life than men do. This is because the sex hormone estrogen that circulates in women’s bodies helps protect them against atherosclerosis. Therefore, most women do not develop coronary heart disease until after menopause, when levels of protective estrogen markedly decrease.

Other risk factors for coronary heart disease can be changed depending on a person’s lifestyle. These modifiable risk factors include cigarette smoking, a sedentary lifestyle, obesity, diabetes mellitus, and hypertension (high blood pressure). Perhaps the most important modifiable risk factor, however, is high blood cholesterol. When excess cholesterol circulates in the blood, it deposits in the wall of the arteries, hastening the progression of atherosclerosis.

The amount of cholesterol in a person’s bloodstream is partially determined by heredity, but it also depends on the amount of cholesterol and animal fat in the diet (see Human Nutrition). In some parts of Asia and Africa where people consume very little fat and cholesterol, total blood cholesterol averages less than 150 milligrams per deciliter (mg/dl) and heart attacks are very rare. In the United States, where the typical diet includes many foods high in fat and cholesterol, total blood cholesterol averages about 200 mg/dl, and coronary heart disease is the leading cause of death.

Scientists have learned that cholesterol is especially dangerous when it is carried through the bloodstream as low-density lipoprotein (LDL), which is often known as “bad” cholesterol. By contrast, cholesterol in the form of high-density lipoprotein (HDL) actually lowers a person’s risk of heart attack, and HDL is often referred to as “good” cholesterol.

V DIAGNOSIS

A variety of simple diagnostic methods may identify coronary heart disease before it becomes life threatening. Regular physical examinations, coupled with a person’s family medical history, may alert a physician that a patient has a high risk for heart disease. Cholesterol screening, a blood test that measures cholesterol levels, can identify people at risk for atherosclerosis. In 2003 the United States Food and Drug Administration approved a new blood test that measures an enzyme called lipoprotein-associated phospholipase A2. Elevated levels of this enzyme indicate that a person is at increased risk for coronary heart disease. Studies have found that this blood test, known as the PLAC test, is a better indicator of coronary heart disease than cholesterol screening.

Chest pain, shortness of breath, and an abnormal pulse are some of the symptoms of coronary heart disease, but symptoms of heart disease may be different for every patient, and similar symptoms may also indicate a variety of other medical conditions. In a patient with chest pain, shortness of breath, or an abnormal pulse who also has risk factors for coronary heart disease, several types of tests help doctors make an accurate diagnosis.

An electrocardiogram (ECG, sometimes known as EKG) provides a graphical picture of the different phases of the heartbeat (see Electrocardiography). An ECG recorded when a patient is at rest may indicate that the blood supply of the heart is not normal, and the ECG can often detect damage from a previous heart attack. In an exercise stress test, an ECG is recorded while a patient is performing physical activity such as walking on a treadmill or riding a stationary bicycle. As the intensity of exercise increases, the doctor looks for specific changes in the ECG that indicate the heart is not getting enough oxygen.

In cardiac catheterization, a long, thin, flexible tube called a catheter is threaded through an artery or vein to the patient’s heart. Doctors collect information about the heart’s function, such as pressure and blood flow in different chambers of the heart, by means of a device attached to the catheter. The catheter can also be used to perform coronary angiography, in which a dye that is visible on X rays is injected through the catheter into the coronary arteries. Moving and still X-ray pictures of the heart are taken, and the resulting images enable doctors to see where the coronary arteries are narrowed or obstructed by atherosclerosis.