Coronary Heart Disease.

Coronary Heart Disease. I INTRODUCTION 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. VI TREATMENT There is no cure for coronary heart disease. However, proper treatment can slow or even halt the progression of atherosclerosis so that the coronary arteries do not become further narrowed. Treatment can also help reduce the risk of a heart attack in people who have coronary heart disease. The first step in fighting coronary heart disease is to make lifestyle changes to reduce risk factors. Doctors recommend that heart patients eat a low-fat diet and keep their blood cholesterol low. Most physicians believe LDL should be less than 100 mg/dl for patients with coronary heart disease. Patients are also encouraged to quit smoking, exercise regularly, and control high blood pressure and diabetes mellitus through diet or medication. If a low-fat diet cannot reduce a person's cholesterol sufficiently, doctors may prescribe a cholesterol-lowering drug such as lovastatin, simvastatin, or pravastatin. Many different drugs are available to control angina. Nitroglycerin and similar drugs are the oldest such medications. More recently, two other types of drugs have become available, beta blockers and calcium channel blockers. All of these medications decrease the heart's oxygen demand (by slowing the heart rate or making the heart contract less vigorously), increase the heart's blood supply, or both. Sometimes patients may take a combination of these angina-relieving drugs. Finally, aspirin is sometimes recommended to help prevent a heart attack. Aspirin interferes with platelets, blood cells that are involved in blood clotting. In this way, the drug helps prevent the formation of a clot in a coronary artery. Some patients may still suffer from angina even after making lifestyle changes and taking various medications. These patients may undergo coronary artery bypass surgery or percutaneous transluminal coronary angioplasty (PTCA) to help relieve their symptoms. In bypass surgery, a surgeon removes a length of blood vessel from elsewhere in the patient's body--usually a vein from the leg or an artery from the wrist. The surgeon then attaches one end of the blood vessel to the aorta and the other end to the coronary artery downstream of the blockage. Surgeons today commonly use an artery from the inside of the chest wall because bypasses made from this artery are very durable. The surgery creates a conduit for blood to flow through that bypasses the area narrowed by atherosclerosis. Sometimes multiple bypasses are created if more than one blockage exists. Bypass surgery became widely used in the early 1970s and is now performed on about 519,000 patients in the United States each year. PTCA, often known as balloon angioplasty, is an alternative to bypass surgery, especially for patients with less extensive coronary artery disease. In this procedure, first performed in 1977, a catheter with a deflated balloon at its tip is threaded through the patient's arteries to the site of a blockage. The balloon is then inflated, crushing the atherosclerotic plaque and restoring normal flow of blood through the artery. Although balloon angioplasty is initially effective in most cases, a blockage may return after only a few months, resulting in a repeat artery narrowing known as restenosis. Cardiologists, physicians specializing in treating heart disorders, may use an expandable metal scaffolding called a stent to help prevent restenosis. The stent is placed in the artery at the time of angioplasty and helps keep the artery open. Nearly 600,000 balloon angioplasty procedures are performed in the United States each year. When a person who may be having a heart attack arrives in the emergency room, doctors usually perform an ECG, which shows telltale changes when a heart attack is occurring. They may also order blood tests to detect the presence of chemicals released by injured heart muscle cells. The patient may be given drugs such as nitroglycerin and beta blockers, which decrease the heart's oxygen demand and help limit the amount of tissue damaged in the heart attack. Some patients are treated with a drug that dissolves blood clots, such as streptokinase or tissue-type plasminogen activator (t-PA). These drugs are most effective when given within an hour of the onset of chest pain. Other patients may have emergency balloon angioplasty or bypass surgery to restore blood flow to the heart muscle. After a heart attack, a patient may remain in the hospital for several days. At first, he or she may stay in a coronary care unit (CCU), an intensive care unit designed specifically for heart attack patients. In the CCU, the patient is monitored constantly with an ECG, and specially trained doctors and nurses are on hand to treat abnormal heart rhythms or other complications that may develop. Before the patient leaves the hospital, doctors may order an exercise stress test, coronary angiography, or other tests to evaluate whether the person should have angioplasty or bypass surgery. VII HISTORY OF FIGHTING CORONARY HEART DISEASE The first description of angina pectoris was published by English physician William Heberden in 1772. However, heart attacks and coronary heart disease were not well understood at the time. In fact, throughout the 19th century, sudden death that occurred during an attack of angina was usually ascribed to indigestion. It was not until 1912 that American physician James Herrick clearly described the relationship between blood clots in the coronary arteries and heart attack. In the early decades of the 20th century, deaths from coronary heart disease began to increase, particularly in the United States and many other industrialized nations. Better hygiene, immunization, and the advent of antibiotics reduced deaths from infectious diseases, which had previously been the leading cause of death. More people were living longer, causing the prevalence of coronary heart disease to increase simply because the disease often does not cause problems until people are middle-aged or older. At the same time, standards of living improved in industrialized countries, and people began to eat more meat and more fatty food, and exercised less. By the 1940s, coronary heart disease had reached epidemic proportions in the United States. Scientists began to investigate the risk factors that made people vulnerable to the disease. One of the most influential studies was the Framingham Heart Study, which began in 1948 and continues today. Initially, scientists tracked more than 5,000 residents of a small town in Massachusetts, collecting data about possible risk factors and the prevalence of heart attacks in the community. This study helped scientists identify three key risk factors for coronary heart disease--high blood pressure, cigarette smoking, and high blood cholesterol. Today, the study also includes the children of the original participants, and scientists continue to gather information on coronary risk factors. In the United States, the death rate from coronary heart disease has been declining in recent years. In part, this decline is due to medical advances such as the development of CCUs and clot-dissolving drugs, which have made fewer heart attacks fatal. Other advances, such as various medications, angioplasty, and bypass surgery, prevent some heart attacks. While the incidence of coronary heart disease has lessened as many people have adopted healthier lifestyles, many other people still have habits that put them at risk for coronary heart disease. Experts estimate that more than 46 million adults in the United States smoke, 105 million have cholesterol above 200 mg/dl, 73 million have hypertension, 61 million are obese, 17 million have diabetes, and more than 90 million do not exercise at all. Many experts hope that as more people adopt healthier lifestyles, deaths from coronary heart disease will continue to decline. Contributed By: Eugene Passamani Microsoft ® Encarta ® 2009. © 1993-2008 Microsoft Corporation. All rights reserved.