Coronary Artery Disease (Encyclopedia of Medicine)
Coronary artery disease is a narrowing or blockage of the arteries and vessels that provide oxygen and nutrients to the heart. It is caused by atherosclerosis, an accumulation of fatty materials on the inner linings of arteries. The resulting blockage restricts blood flow to the heart. When the blood flow is completely cut off, the result is a heart attack.
Coronary artery disease, also called coronary heart disease or heart disease, is the leading cause of death for both men and women in the United States. According to the American Heart Association, in 1995 one in every 4.8 deaths in the United States was caused by coronary artery disease. About every 29 seconds, one American will have a heart attack; about every minute, one American will die from a heart attack. Fourteen million Americans have active symptoms of coronary artery disease (heart attack or chest pains). Many millions more have silent coronary disease, the first indication of which can be sudden death.
Coronary artery disease occurs when the coronary arteries become partially blocked or clogged. This blockage limits the flow of blood from the coronary arteries, which are the major arteries supplying oxygen-rich blood to the heart. The coronary arteries expand when the heart is working harder and needs more...
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Coronary Artery Disease (Encyclopedia of Nursing & Allied Health)
Coronary artery disease is a stenosis (narrowing) or blockage of the arteries and vessels that provide oxygenated blood to the heart. It is caused by atherosclerosis (hardening of the arteries), an accumulation of fatty plaque on the inner linings of arteries. The resulting blockage restricts blood flow through the coronary arteries. When blood flow is completely cut off, the result is myocardial infarction (heart attack).
Coronary artery disease, also called coronary heart disease or atherosclerotic heart disease, is the leading cause of death for men and women in the United States. According to the American Heart Association, in 1998 one in every five deaths in the United States was caused by coronary artery disease. About every 29 seconds one American will have a heart attack; about every minute one American will die from a heart attack. Fourteen million Americans have active symptoms of coronary artery disease. Many millions more have asymptomatic (silent) coronary disease, the first indication of which can be sudden death.
Coronary artery disease occurs when the coronary arteries become partially blocked or clogged, thereby depriving the heart muscle of oxygen (myocardial ischemia). When the blockage is temporary or partial, angina (chest pain or pressure) may occur. When the blockage completely and suddenly cuts off the flow of blood, the result is myocardial infarction.
Healthy coronary arteries are clean, smooth, and slick. The artery walls are flexible and can expand to let more blood through when the heart needs to work harder. Atherosclerosis is thought to begin with an injury to the linings of the inner walls of the arteries. This injury makes them susceptible to atherosclerosis and thrombosis (blood clots).
Causes and symptoms
Coronary artery disease is usually caused by athero- sclerosis. Cholesterol and other fatty substances accumulate on the inner wall of the arteries. This attracts fibrous tissue, blood components, and calcium, which harden into flow-obstructing plaques. If a blood clot suddenly forms on one of these plaques it can convert a partial obstruction to a total occlusion. This is known as coronary thrombosis. Congenital defects and spasms of a coronary artery may also block blood flow. There is evidence that infection from organisms such as chlamydia bacteria may be responsible for some cases of coronary artery disease.
A number of major contributing factors increase the risk of developing coronary artery disease. Some risk factors can be modified and others cannot. Persons with more of these risk factors are at greater risk of developing coronary artery disease.
Major risk factors
Major risk factors significantly increase the chance of developing coronary artery disease. Risk factors that cannot be changed include:
- Heredity. People whose parents have coronary artery disease, particularly those who develop it at younger ages, are more likely to be diagnosed with it. African- Americans are also at increased risk because they experience rience a higher rate of severe hypertension than whites.
- Gender. Men under the age of 60 years of age are more likely to have myocardial infarctions than women of the same age. Over age 60, however, women have coronary artery disease at a rate equal to that of men.
- Age. Men over age 45 and women over age 55 years are more likely to have coronary artery disease. Occasionally, coronary disease affects individuals in the 30s. Older adults (those over 65) are more likely to die of a myocardial infarction. Older women are twice as likely as older men to die within a few weeks of a myocardial infarction.
Major risk factors that can be changed are:
- Smoking. Smoking greatly increases both the risk of developing coronary artery disease and resulting mortality. Smokers have two to four times the risk of nonsmokers for sudden cardiac death and are more than twice as likely to have a myocardial infarction. They are also more likely to die within an hour of a heart attack. Second-hand smoke may also increase risk.
- High cholesterol. Cholesterol is produced by the body, and obtained from eating animal products such as meat, eggs, milk, and cheese. Age, gender, heredity, and diet affect cholesterol level. Risk of developing coronary artery disease increases as blood cholesterol levels increase. When combined with other factors, the risk is even greater. Total cholesterol of 240 mg/dL or more poses a high risk, and 20039 mg/dL a borderline high risk. For LDL (low-density lipoprotein) cholesterol, high risk starts at 13059 mg/dL, depending on other risk factors. Low levels of HDL (high-density lipoprotein) increases the risk of coronary disease; high HDL protects against it.
- Hypertension (high blood pressure). High blood pressure makes the heart work harder, and over time, weakens it. It increases the risk of myocardial infarction, stroke, kidney failure, and congestive heart failure. Blood pressure of 140 over 90 or above is considered high. When hypertension is combined with obesity, smoking, high cholesterol, or diabetes, the risk of myocardial infarction or stroke increases several times.
- Sedentary lifestyle and lack of physical activity. Inactivity increases the risk of coronary artery dis- ease. Even modest physical activity is beneficial if done regularly.
- Diabetes mellitus. The risk of developing coronary artery disease is significantly increased for diabetics. More than 80% of diabetics die of some type of cardiovascular disease.
Contributing risk factors
Contributing risk factors have been linked to coronary artery disease, but their precise contribution to the development of disease is not known yet. Contributing risk factors are:
- Obesity. Excess weight increases the strain on the heart and increases the risk of developing coronary artery disease, even if no other risk factors are present. Obesity increases both blood pressure and blood cholesterol, and can lead to diabetes.
- Stress and anger. Stress and anger can produce physiological changes that contribute to the development of coronary artery disease, in part by increasing the risk of thrombosis. Stress, the mental and physical reaction to life's irritations and challenges, increases heart rate and blood pressure and can injure the lining of the arteries. Evidence shows that anger increases the risk of dying from heart disease. The risk of heart attack is more than double after an episode of anger.
Angina (chest pain) is the main symptom of coronary heart disease but it is not always present. Symptoms of angina typically include chest pain that may be described as heaviness, tightness, a burning sensation, squeezing, or pressure behind the breastbone. This pain may radiate to the left arm, neck, or jaw. Many people have no symptoms of coronary artery disease before having a heart attack; 63% of women and 48% of men who died suddenly of coronary artery disease had no previous symptoms of the disease, according to the American Heart Association.
The diagnosis of coronary artery disease is made by the physician after a medical history, physical examination, and basic screening tests have been performed. The diagnostic work-up includes evaluation of body weight, blood pressure, blood lipid levels, and fasting blood glucose levels. Other diagnostic tests include resting and exercise electrocardiogram (ECG), echocardiography, radionuclide scans, and coronary angiography. A treadmill exercise (stress) test also may be used as a screening test for patients with significant risk factors but are asymptomatic.
An ECG may reveal if a patient has had a previous myocardial infarction (MI) or is having a MI. An ECG taken on a patient with coronary artery disease, who is not having chest pain during the ECG and has not had a prior MI, may be completely normal. An ECG technician places electrodes on the patient's chest, arms, and legs. These electrodes send impulses of the heart's activity through an oscilloscope (a monitor) to a recorder that traces them on
paper. The test takes about 10 minutes and is performed in a physician's office. A definite diagnosis cannot be made from electrocardiography. About 50% of patients with significant coronary artery disease have normal resting electrocardiograms. Another type of electrocardiogram, known as an exercise stress test, measures how the heart and blood vessels respond to exertion when the patient is exercising on a treadmill or a stationary bike. This test is performed in a physician's office or an exercise laboratory. It takes 15-30 minutes. Like many medical tests, it does not have 100% accuracy. It sometimes gives a normal reading when the patient has a heart problem or an abnormal reading when the patient does not.
If the electrocardiogram reveals a problem or is inconclusive, the next step is exercise echocardiography or nuclear myocardial scanning (radionuclide angiography). Echocardiography, cardiac ultrasound, uses sound waves to create an image of the heart's chambers and valves. A technician presses a hand-held transducer against the patient's chest to obtain an image that can be displayed on a monitor. It does not visualize the coronary arteries, but can detect abnormalities in heart wall motion caused by coronary disease. Performed in a cardiology outpatient diagnostic laboratory, the test takes about 30- 60 minutes.
Nuclear myocardial scanning enables physicians to see if the myocardium (heart muscle) is being adequate- ly perfused by the coronary arteries. Performed by radiologists and radiology technicians, nuclear scans involve injecting a small amount of radiopharmaceutical, such as thallium or sestamibi, into a vein. A camera that uses gamma rays to produce an image of the radioactive material records pictures of the heart. A radionuclide scan is comparable, in terms of radiation exposure, to a chest x ray. The tiny amount of radioactive material used disappears from the body in a few days. Radionuclide scans cost about four times as much as exercise stress tests but provide more information.
In nuclear myocardial scanning, a camera passes back and forth over the patient who lies on a table. Usually performed in a hospital's nuclear medicine department, the procedure takes 30-60 minutes.
Nuclear myocardial scanning is usually performed in conjunction with an exercise stress test. When the stress test is completed, thallium or sestamibi is injected. The patient resumes exercise for one minute to absorb the thallium. For patients who cannot exercise, cardiac blood flow and heart rate may be increased by intravenous dipyridamole (Persantine) or adenosine. Thallium or sestamibi scanning is done twice, immediately after injecting the radiopharmaceutical and again four hours (and maybe 24 hours) later. Usually performed in a hospital's nuclear medicine department, each scan takes about 30- 60 minutes.
Coronary angiography is the gold standard (most accurate method) for establishing the diagnosis of coronary artery disease, but it is also the most invasive. During coronary angiography the patient is awake but sedated. ECG electrodes are placed on the patient's chest and an intravenous line is inserted. A local anesthetic is injected into the site where the catheter will be inserted. The invasive cardiologist inserts a catheter into a groin artery and guides it into the aorta. A contrast dye is injected directly into the coronary arteries to determine whether they are obstructed. Coronary angiography is performed in a cardiac catheterization laboratory either in an outpatient or inpatient surgery unit. It takes from 30 minutes to two hours.
Coronary artery disease can be treated many ways. The choice of treatment depends on the severity of the disease. Treatments include lifestyle changes and drug therapy, percutaneous transluminal coronary angioplasty, and coronary artery bypass surgery. Coronary artery disease is a chronic disease requiring lifelong care. Angioplasty or bypass surgery is not a "cure."
Patients with less severe coronary artery disease may gain adequate control through lifestyle changes and drug therapy. Many of the lifestyle changes that prevent disease progression low-fat, low-cholesterol diet, weight loss if needed, exercise, and not smokinglso help prevent the disease from developing.
Drugs such as nitrates, beta-blockers, and calcium- channel blockers relieve chest pain and complications of coronary artery disease, but they cannot clear blocked arteries. Nitrates (nitroglycerin) improve blood flow to the heart. Beta-blockers (acebutelol, propranolol) reduce the amount of oxygen required by the heart during stress. One type of calcium-channel blocker (verapamil, diltiazem hydrochloride) helps keep the arteries open and reduces blood pressure. Aspirin helps prevent blood clots from forming on plaques, reducing the likelihood of myocardial infarction. Cholesterol-lowering medications are also indicated in most cases.
Percutaneous transluminal coronary angioplasty and bypass surgery are invasive procedures to improve blood flow in the coronary arteries. Percutaneous transluminal coronary angioplasty, usually called coronary angioplasty or PTCA, is a non-surgical procedure. A catheter tipped with a balloon is threaded through an artery in the groin into the blocked coronary artery. The balloon is inflated, compressing the plaque to enlarge the blood vessel and open the blocked artery. The balloon is deflated, and the catheter is removed. Coronary angioplasty is performed by an invasive cardiologist in a hospital and generally requires a stay of one or two days. Coronary angioplasty is successful about 90% of the time, but one- third of the time the artery restenoses (narrows again) within six months. The procedure can be repeated. It is less invasive and less expensive than coronary artery bypass surgery.
In coronary artery bypass surgery, a healthy vein from an arm, leg, or the internal mammary artery is used to build a detour (bypass) around the coronary artery blockage. Bypass surgery is appropriate for those patients with blockages in two or three major coronary arteries, those with severely narrowed left main coronary arteries, and those who have not responded to other treatments. It is performed in a hospital under general anesthesia. A heart-lung machine is used to support the patient while the healthy vein or artery is attached past the blockage to the coronary artery. About 70% of patients who have bypass surgery experience complete relief from angina; about 20% experience partial relief. Only about 3-4% of patients per year experience a return of symptoms. Survival rates after bypass surgery decrease over time. At five years after surgery, survival expectancy is 90%; at 10 years about 80%, at 15 years about 55%, and at 20 years about 40%.
Three newer surgical procedures for unblocking coronary arteries are currently being evaluated. Atherectomy is a procedure in which the cardiologist shaves off and removes strips of plaque from the blocked artery. In laser angioplasty, a catheter with a laser tip is inserted into the affected artery to burn or break down the plaque. A metal coil, called a stent, may be implanted permanently to keep a blocked artery open. Stenting is gaining popularity as an alternative to more invasive surgery.
In many cases, coronary artery disease can be successfully treated. Advances in medicine and healthier lifestyles have caused a substantial decline in death rates from coronary artery disease since the mid-1980s. New diagnostic techniques enable doctors to identify and treat coronary artery disease in its earliest stages. New technologies and surgical procedures have extended the lives of many patients who would otherwise have died. Research on coronary artery disease continues.
Health care team roles
Patients with coronary artery disease are most often treated by primary care physicians with consultation from cardiologists and cardiovascular surgeons when needed. Nurses, ECG technicians, laboratory technologists, and other allied health professionals have important roles in the diagnosis of coronary artery disease as well as in the institution of timely treatment. Nurses and other practitioners involved in triage or screening in the emergency department must accurately assess patients with chest pain or other indications of coronary artery disease.
ECG technicians, radiology technicians, and laboratory technologists are responsible for performing the diagnostic imaging studies, ECG and blood chemistries, to confirm the diagnosis of coronary artery disease. During the hospitalization, nurses, dieticians, respiratory and physical therapists collaborate to plan a cardiac rehabilitation program and provide patient and family education.
Nurses, physical therapists and dieticians work together to educate patients and their families. Patients are taught to recognize and accurately describe symptoms such as pain, pressure, or heaviness in the chest, left arm, or jaw. Patients are advised to report any changes in the intensity or quality of their pain to nurses or other health care professionals while in the hospital. When necessary, they are counseled by nursing or pharmacy technicians about the use of sublingual (under the tongue) nitroglycerin to relieve chest pain. They are instructed to seek medical attention immediately should serious symptoms return after they have been discharged.
Along with instruction about medication, follow-up care, and the importance of participating in cardiac rehabilitation, patients are informed about ways to reduce their risk for myocardial infarction or other complications of coronary artery disease. This education is tailored to the individual patient's needs. It may include referral to a smoking cessation program; nutritional counseling to reduce dietary fat and sodium and achieve a desirable body weight; and recommendations to increase physical activity. Patient education also addresses treatment of any coexisting illnesses such as diabetes; and instruction about ways to more effectively manage stress and anger.
A healthy lifestyle can help prevent coronary artery disease and help keep it from progressing. A heart- healthy lifestyle includes eating right, regular exercise, maintaining a healthy weight, no smoking, moderate drinking, no recreational drugs, controlling hypertension, and managing stress. Cardiac rehabilitation programs are excellent to help prevent recurring coronary problems for patients at risk and those with a history of coronary events and procedures.
Anginahest pain that happens when diseased blood vessels restrict the flow of blood to the heart. Angina is often the first symptom of coronary artery disease.
Atherosclerosis process in which the walls of the coronary arteries thicken due to the accumulation of plaque in the blood vessels. Atherosclerosis is the cause of coronary artery dis- ease.
Beta-blocker drug that blocks some of the effects of fight-or-flight hormone adrenaline (epinephrine and norepinephrine), slowing the heart rate and lowering the blood pressure.
Calcium-channel blocker drug that blocks the entry of calcium into the muscle cells of small blood vessels (arterioles) and keeps them from narrowing.
Coronary arterieshe main arteries that provide blood to the heart. The coronary arteries surround the heart like a crown, coming out of the aorta, arching down over the top of the heart, and dividing into two branches. These are the arteries in which coronary artery disease occurs.
HDL cholesteroligh-density lipoprotein cholesterol is a component of cholesterol that helps protect against heart disease. HDL is nicknamed "good" cholesterol.
LDL cholesterolow-density lipoprotein cholesterol is the primary cholesterol molecule. High levels of LDL increase the risk of coronary heart disease. LDL is nicknamed "bad" cholesterol.
Plaque deposit of fatty and other substances that accumulate in the lining of the artery wall.
Triglyceride fat that comes from food or is made from other energy sources in the body. Elevated triglyceride levels contribute to the development of atherosclerosis.
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Coronary Artery Disease (Encyclopedia of Public Health)
The heart, a powerful muscle that beats over 50,000 times in one day, is fed the blood and energy it needs through small tubes called coronary arteries (see Figure 1). Coronary artery disease (CAD) is the most common cause of death and disability in the United States and other industrialized countries, and it can be manifested if these arteries become narrowed by cholesterol to about half their normal diameter (see Figure 2). Cholesterol, a waxy substance, deposits slowly inside the artery. These deposits, which cause CAD, are called atherosclerotic plaques, having a central soft cholesterol core wrapped in hard fibrous tissue.
Plaque buildup stems from lifestyle and other coronary risk factors, including harmful diets, physical inactivity, smoking, stressful behavior patterns, elevated blood cholesterol, high blood pressure, and diabetes. The wide differences in CAD deaths among countries are largely lifestyle related. Racial differences in susceptibility tend to be minor. Diets overloaded with meat, eggs, butter, whole milk, cheese, and ice cream contain excessive cholesterol and saturated fat, which raise blood cholesterol, thus producing atherosclerosis.
Sedentary lifestyles in America are increasing. From 1991 to 1997, participation by high school students in physical education fell from 42 percent to 27 percent. Obesity increased by 60 percent in the United States in the 1990s because of decreasing physical activity and larger size and frequency of restaurant meals, especially inexpensive high-calorie fast foods. Obesity contributes to atherosclerosis in four ways. It raises blood pressure, cholesterol, and triglycerides (a type of blood fat), and it promotes diabetes, a strong and increasingly common CAD risk factor. A poor diet, and especially one containing excessive amounts of salty foods, can also increase blood pressure.
Smoking cigarettes promotes CAD by damaging the artery's inside lining and by lowering high-density lipoprotein (HDL) cholesterol, a protective fraction of the blood cholesterol. Fortunately, smoking rates have declined in the United States,
and ex-smokers who also exercise benefit by increasing HDL and lowering triglycerides.
In the United States in 1997, CAD caused over 1 million heart attacks and almost 500,000 deaths (one per minute), almost equally affecting men and women. Forty percent of deaths were sudden (within a few hours), usually from ventricular fibrillation, a very rapid beating of the ventricles, the heart's major muscle. A nonfatal heart attack damages the part of the ventricle deprived of blood (a myocardial infarction, or MI; see Figure3) with a 30 percent chance of recurrence within six years. Angina, less serious than an MI, is diagnosed by noting chest pain or "squeezing" after eating, exercise, emotional stress, or exposure to cold. About 350,000 new angina cases occur in the United States yearly; some of which progress to an MI, either nonfatal or fatal, especially if not treated.
The nearly 1 million new nonfatal MI or angina cases that occur yearly in the United States are treated aggressively, using relatively new surgical and nonsurgical technologies. The most common surgeries are coronary artery bypass graft surgery (CABGS) or angioplasty. About 1 million of these are performed yearly, at a cost of $3 billion. CABGS uses short lengths of veins (taken from the patient's legs) to bypass as many as five blocked or severely narrowed arteries. Angioplasty opens narrowed arteries by inflating a strong balloon, fracturing a plaque, and widening that artery segment. A metal tube (a stent) is often inserted to prevent that segment's closure. Nonsurgical approaches seek to change diet, exercise, smoking, body weight, and stress factors. Recently many new anticholesterol drugs, especially the statins, have reduced CAD extensively when used with lifestyle changes.
America's lost earnings and medical and disability payments from CAD cost about $130 billion yearlyn especially tragic burden since scientists now believe that most CAD events are preventable. Optimism regarding CAD's preventability stems from noting a 55 percent fall in CAD rates in the United States between its peak in 1967 and 1995. In turn, the peak represented a 50 percent rise from 1940.
The rise was caused by increases in smoking and rich diets associated with prosperity during and after World War II; the decline resulted from extensive health education that produced major decreases in smoking and dietary intake of saturated fat, and more recently by improved blood-pressure control from medications. CAD rates stopped declining in the United States in 1996, indicating an urgent need for more aggressive prevention. However, without the 55 percent decline since 1967, the human and financial burden would now be even greater.
The international picture has cause for great concern. Although CAD declined in developed countries from 1980 to 2000, the World Health Organization predicts that CAD will become the major cause of death in almost all countries by 2020, with over 10 million deaths per year predicted. Developing countries are repeating the earlier lifestyle mistakes of developed countries, ironically aided by aggressive promotion and export of cigarettes and unhealthy fast foods by the United States. Economists predict that rising CAD costs will greatly sap these countries' resources, delay economic growth, and cause unnecessary suffering.
Thus, the main lesson that the observed large fluctuations in CAD prevalence teaches is that social and environmental factors, not genetic, predominate in its cause. Therefore, CAD is an excellent example of how public health measures on lifestyle (and human behavior) can either benefit or harm our human potential.
JOHN W. FARQUHAR
(SEE ALSO: Atherosclerosis; Blood Lipids; Blood Pressure; Cardiovascular Diseases; Chronic Illness; Diabetes Mellitus; HDL Cholesterol; LDL Cholesterol; Lifestyle; Physical Activity; Smoking Behavior; Smoking Cessation; Tobacco Control)
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