A heart attack is the death of or damage to heart muscle because the supply of blood to the heart is severely restricted or blocked. A heart attacks is also known as a myocardial infarctions (MI).
Heart attack is the leading cause of death in the United States.More than 1.5 million Americans experience a heart attack every year and between 500,000 and 700,000 die. Worldwide, heart attacks cause 12 million deaths each year. Most heart attacks are the result of years of silent but progressive coronary artery disease (CAD); a heart attack may be the first symptom of the disease. According to the American Heart Association, 63% of women and 48% of men who died suddenly of coronary artery disease had no previous symptoms.
A heart attack occurs when one or more of the coronary arteries that supply blood to the heart are completely or substantially blocked and not enough oxygen reaches the heart (a condition called ischemia). The blockage usually is caused by atherosclerosis, the build-up of plaque in the artery walls, and/or by a blood clot in a coronary artery. Much less often, a healthy coronary artery has a spasm, and blood flow to part of the heart suddenly decreases or stops. Coronary artery spasm in young, healthy individuals is most often brought on by methamphetamine or cocaine use.
About half of all people who have heart attacks wait at least two hours before seeking help. This increases their chance of death or being permanently disabled. The longer an artery remains blocked during a heart attack, the more damage will be done to the heart. Therefore, it is important to recognize the signs of a heart attack and seek prompt medical attention at the nearest hospital with 24-hour emergency cardiac care.
About one-fifth of all heart attacks are silent, that is, the individual does not know one has occurred. Although the person feels no pain, silent heart attacks still damage the heart.
The outcome of a heart attack depends onwhere the blockage is, whether heart rhythm is disturbed, and whether another coronary artery supplies blood to that part of the heart. Blockages in the left coronary artery usually are more serious than in the right coronary artery. Blockages that cause an arrhythmia, an irregular heartbeat, can cause sudden death.
Major risk factors
Major risk factors significantly increase the risk of coronary artery disease. Those which cannot be changed include:
- Heredity. People whose parents have coronary artery disease are more likely to develop it. The risk of heart attack is highest for those who have a male parent or sibling who has had a heart attack before age 45 or a female parent or sibling who has had a heart attack before age 55.
- Gender. Men under 60 years of age are more likely to have heart attacks than women of the same age.
- Age. Men over the age of 45 and women over the age of 55 are considered at risk. Older people (those over 65) are at increased risk of dying from a heart attack. Older women are twice as likely to die within a few weeks of a heart attack as men of the same age.
Major risk factors that can be modified through lifestyle changes include:
- Smoking. Smoking greatly increases both the chance of developing coronary artery disease and the change of dying from it. Smokers are more than twice as likely to have a heart attack and have two to four times the risk of non-smokers of sudden cardiac death. They also are more likely to die within an hour of a heart attack. Exposure to second-hand smoke also increases risk.
- High cholesterol. Cholesterol is a soft, waxy substance that is produced by the liver, as well as obtained from eating cholesterol-containing food, such as meat, eggs, and other animal products. Cholesterol level is affected by age, sex, heredity, and diet.
- Cholesterol does not dissolve in blood. Instead, it moves through the circulatory system in combination with carrier substances called lipoproteins. There are two types of carrier-cholesterol combinations, lowdensity lipoprotein (LDL) or ‘‘bad’’ cholesterol and high-density lipoprotein (HDL) or ‘‘good’’ cholesterol.
- LDL picks up cholesterol in the liver and carries it through the circulatory system. Most of the cholesterol in the body is LDL cholesterol. When too much LDL cholesterol is present, it begins to drop out of the blood and stick to the walls of the arteries. The sticky material on the artery walls is called cholesterol plaque. Plaque can reduce the amount of blood flowing through the arteries and encourage blood clots to form. Total cholesterol of 240 mg/dL and over poses a high risk, and 200–239 mg/dL a borderline high risk. For LDL cholesterol, high risk starts at 130–159 mg/ dL, depending on other risk factors.
- Researchers believe that HDL works opposite LDL. HDL picks up cholesterol off the walls of the arteries and takes it back to the liver where it can be broken down and removed from the body. This helps to keep the blood vessels open. Cholesterol can be measured by a simple blood test. To reduce the risk of cardiovascular disease, adults should keep their HDL cholesterol above 40 mg/dL.
- High blood pressure (hypertension). High blood pressure makes the heart work harder and over timeweakens it. It increases the risk of heart attack, stroke, kidney failure, and congestive heart failure. A blood pressure of 140 over 90 or above is considered high. As the numbers increase, high blood pressure goes from being categorized as Stage 1 (mild) to Stage 4 (very severe). African Americans are at increased risk of developing severe hypertension.
- Obesity and lack of physical activity. The heart of an obese individual must work harder, while lack of physical activity increases the risk of coronary artery disease. Even modest physical activity is beneficial if done regularly.
- Use of certain drugs or supplements. In the late twentieth century, ephedra (ma huang) gained popularity as a weight-loss supplement. The herb can cause lifethreatening side effects, including heart attack, stroke, and seizures. Since April 2004, sale of products containing ephedra have been banned in the United States, although it may still be obtained illegally over the Internet. Hormone replacement therapy (HRT) was once believed to help prevent heart disease in postmenopausal women. However, the Women’s Health Initiative, a very large clinical trial, found the opposite to be true. Potential adverse effects of HRT include increased risk of heart attack, stroke and blood clots, and an increased risk of breast cancer.
Contributing risk factors
Contributing risk factors have been linked to coronary artery disease, but their significance or prevalence cannot always be demonstrated or quantified. Contributing risk factors include: #
- Diabetes mellitus. The risk of developing coronary artery disease is seriously increased for individuals with diabetes. More than 80% of diabetics die of some type of heart or blood vessel disease.
- Emotional factors. Long-term stress, anger, and guilt are thought to contribute to the development of coronary artery disease. Stress, the mental and physical reaction to life’s irritations and challenges, increases the 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 and more than doubles the risk of having a heart attack right after an episode of anger.
Causes and symptoms
Heart attacks generally are the result of severe coronary artery disease.Most heart attacks are caused by blood clots that form on atherosclerotic plaque. These may break lose and travel through the circulatory system causing heart attack or stroke (blockage of an artery to the brain). Certain major risk factors increase the chance of developing coronary artery disease. Some of these can be modified and some cannot. People with a greater number of risk factors are more likely to develop coronary artery disease.
More than 60% of people who have a heart attack experience symptoms before the heart attack occurs. These symptoms sometimes occur days or weeks before the heart attack. Sometimes, people do not recognize the symptoms of a heart attack or are in denial that they are having one. Typical symptoms include:
- Uncomfortable pressure, fullness, squeezing, or pain in the center of the chest (angina) that lasts more than 30 minutes. Warning pains before a heart attack may last a shorter time or may go away with rest and then return.
- Pain that spreads to the shoulders, neck, arms, or jaw.
- Chest discomfort accompanied by lightheadedness, fainting, sweating, nausea, or shortness of breath.
All of these symptoms do not occur with every heart attack, and most have other common causes. Nevertheless, person with any of these symptoms should immediately call an emergency rescue service (recommended) or be driven (but not drive themselves) to the nearest hospital with a 24-hour cardiac care unit. The advantage of calling an emergency rescue service is that life-saving treatment may begin while the individual is in transit to the hospital.
Experienced emergency care personnel usually can diagnose a heart attack simply by looking at the patient.
To confirm this diagnosis, they talk with the patient, check heart rate and blood pressure, perform an electrocardiogram, and take a blood sample. The electrocardiogram shows whether damage has occurred to the heart. Electrodes covered with conducting jelly are placed on the patient’s chest, arms, and legs. They send impulses of the heart’s electrical activity through an oscilloscope (a monitor) to a recorder, which traces them on paper. Damaged hearts produce a different electrical pattern from healthy hearts. The blood test shows the leak of cardiac enzymes or other biochemical markers from damaged cells in the bloodstream.
The goal of treatment is to restore adequate blood flow and oxygen delivery to the heart, relieve pain, and prevent complications. Heart attacks are treated with cardiopulmonary resuscitation (CPR) when necessary to start and keep the patient breathing and the heart beating. Beta-blocker drugs may be given to help control heart rate. Other drugs may be used to relieve pain and anxiety. These treatments may be started by trained emergency medical service personnel in the ambulance on the way to the hospital.
Once at the hospital, certain patients may receive intravenous drug therapy to dissolve blood clots (thrombolytic therapy). If started within six hours after the start of the heart attack, these drugs are successful in dissolving blood clots in about 80% of patients. If these drugs are given in a window 6–12 hours after the start of pain, the success rate drops to 50%. Thrombolytic therapy is not used if more than 12 hours has passed since chest pain started. Throughout treatment, the patient is monitored closely. Additional treatment can include, electric shock, additional drug therapy, revascularization procedures, percutaneous transluminal coronary angioplasty(see percutaneous coronary intervention), and coronary artery bypass surgery. An electrical-shock device (defibrillator), may be used to restore a normal rhythm if the heart is fluttering and contracting uncontrollably (arrhythmia). Supplemental oxygen often is used to ease the heart’s workload. If oxygen is used within hours of the heart attack, it may help limit damage to the heart. Additional drugs may be used to stabilize the patient and limit damage to the heart, including aspirin, anticoagulants, painkillers, tranquilizers, beta-blockers, ace-inhibitors, nitrates, rhythmstabilizing drugs, and diuretics. Once the patient has been stabilized, he or she is usually moved to the cardiac care unit (CCU) for special monitoring.
To prevent additional heart attacks, aspirin and an anticoagulant drug often follow the thrombolytic drug. These help to prevent new blood clots from forming and existing blood clots from growing. Anticoagulant drugs help prevent the blood from clotting. The most common anticoagulants are heparin and warfarin. Heparin, an anticoagulant, often is given intravenously while the patient is in the hospital. Warfarin (Coumadin), taken orally, often is given later, and sometimes must be taken for life. Aspirin helps to prevent the dissolved blood clots from reforming.
To relieve pain, a nitroglycerine tablet taken under the tongue may be given. If the pain continues, morphine sulfate may be prescribed. Tranquilizers such as diazepam (Valium) and alprazolam (Ativan) may be prescribed to lessen the trauma of a heart attack.
To slow the heart rate and give the heart a chance to heal, beta-blockers often are given intravenously right after the heart attack. These can also help prevent sometimes-fatal ventricular fibrillation. Betablockers include atenolol (Tenormin), metoprolol (Lopressor), nadolol, pindolol (Visken), propranolol (Inderal), and timolol (Blocadren).
Nitrates, a type of vasodilator, also are given right after a heart attack to help improve the delivery of blood to the heart and ease heart failure symptoms. Nitrates include isosorbide mononitrate (Imdur), isosorbide dinitrate (Isordil, Sorbitrate), and nitroglycerin (Nitrostat).
When a heart attack causes an abnormal heartbeat, arrhythmia drugs may be given to restore and maintain the heart’s normal rhythm. These include amiodarone (Cordarone), atropine, bretylium, disopyramide (Nor Pace), lidocaine (Xylocaine), procainamide (Procan), propafenone (Rythmol), propranolol (Inderal), quinidine, and sotalol (Betapace).
Angiotensin-converting enzyme (ACE) inhibitors reduce the resistance against which the heart beats and are used to manage and prevent heart failure. They are used to treat heart attack patients whose hearts do not pump well or who have symptoms of heart failure. Taken orally, they include Altace, Capoten, Lotensin, Monopril, Prinivil, Vasotec, and Zestril. Angiotensin receptor blockers, such as losartan (Cozaar), may be substituted.
Diuretics can help get rid of excess fluids that sometimes accumulate when the heart is not pumping effectively. They also help reduce hypertension. Usually taken orally, they cause the body to increase urine output. Common diuretics include: bumetanide (Bumex), chlorthalidone (Hygroton), chlorothiazide (Diuril), furosemide (Lasix), hydrochlorothiazide (HydroDIRUIL, Esidrix), spironolactone (Aldactone), and triamterene (Dyrenium).
Percutaneous transluminal coronary angioplasty (see percutaneous coronary intervention) and coronary artery bypass surgery are invasive revascularization procedures that open blocked coronary arteries and improve blood flow. They usually are performed only on patients for whom clot-dissolving drugs do not work, who have poor exercise stress tests, poor left ventricular function, or ischemia. Generally, angioplasty is tried before coronary artery bypass surgery is attempted.
Percutaneous transluminal coronary angioplasty, usually called coronary angioplasty, is a procedure in which a catheter (a tiny plastic tube) tipped with a balloon is threaded from a blood vessel in the thigh or arm into the blocked artery. The balloon is inflated and compresses the plaque to enlarge the blood vessel and open the blocked artery.The balloon is then deflated and the catheter is removed. Coronary angioplasty is performed in a hospital and generally requires a two-day stay. It is successful about 90% of the time. For one-third of patients, the artery narrows again within six months after the procedure. The procedure can be repeated. It is less invasive and less expensive than coronary artery bypass surgery.
In coronary artery bypass surgery, a detour is built around the coronary artery blockage using a healthy leg or chest wall artery or vein. The healthy vein then supplies oxygen-rich blood to the heart. Bypass surgery is major surgery done most often only when patients have blockages in two or three coronary arteries or a severely narrowed left main coronary arteries, or who have not responded to other treatments. It is performed in a hospital under general anesthesia using a heartlung machine to support the patient while the heart is stopped and a healthy vein is attached to the coronary artery. About 70% of patients who have bypass surgery experience full relief from angina; about 20% experience partial relief. Long term, symptoms recur in only about 3 or 4% of patients per year. Five years after bypass surgery, survival expectancy is 90%, at 10 years it is about 80%, at 15 years it is about 55%, and at 20 years it is about 40%.
There are several other surgical procedures for unblocking coronary arteries including: atherectomy, where the surgeon grinds out and removes strips of plaque from the blocked artery and laser angioplasty, where a catheter with a laser tip is inserted to burn or break down the plaque. After the artery is opened, a tiny metal tube called a stent may be implanted permanently to help the artery remain open.
Alternative therapies aim at preventing the progression of heart disease that leads to a heart attack. Changes in lifestyle can also prevent second heart attacks.
Herbal medicine offers a variety of remedies that may have a beneficial effect on coronary artery disease. Oats (Avena sativa), garlic (Allium sativum), and guggul (Commiphora mukul), may help reduce cholesterol; linden (Tilia europaea) and hawthorn (Crataegus spp.) are sometimes recommended to control high blood pressure, a risk factor for heart disease. Tea (Camellia sinensis), especially green tea, is high in antioxidants, which studies have shown may have a preventive effect against atherosclerosis.
Nutritional therapies have been shown to prevent coronary artery disease and stop, or even reverse, the progression of atherosclerosis.Alow-fat, high-fiber diet is often recommended. It is essential to reduce the amount of meat and animal products consumed, as they are high in saturated fats.Whole grains, fresh fruits and vegetables, legumes, and nuts are recommended. Vitamin and mineral supplements that reduce, reverse, or protect against coronary artery disease include chromium; calcium and magnesium; B complex vitamins; the antioxidant vitamins B and E; L-carnitine; and zinc.
Yoga and other bodywork, massage, relaxation therapies, aromatherapy, and music therapy may also help by reducing stress and promoting physical and mental well being. By evoking the body’s relaxation response through meditation and deep breathing, blood pressure, metabolic rate, and heart rate can all be reduced.
Successful recovery from a heart attack requires a substantial amount of rehabilitation. Most patients follow a three-stage rehabilitation program. Phase 1 begins in the hospital with low-level exercise to prevent complications from prolonged bed rest. Phase 2 begins after hospital discharge and usually takes place in an outpatient rehabilitation setting. The goals of phase 2 are to increase physical endurance and to promote return to normal daily activities. Phase 3 continues in an outpatient setting, It begins 3–6 months after the heart attack and may last up to one year. In phase 3, the level of exercise is gradually increased, ideally to the point where swimming, light jogging, or bicycling is possible. The effectiveness of rehabilitation, however, may be limited by other medical conditions
Early recognition of a heart attack substantially improves survival. More than half or all people who have heart attacks die before they reach the hospital. Another 10% die in the hospital. Of people who leave the hospital after a heart attack, 27% of men and 44% of women die within one year. Within six years, 23% of men and 31% of women have another heart attack, 13% of men and 6% of women experience sudden death, and about 20% have heart failure. People who survive a heart attack have a chance of sudden death that is four to six times greater than others and a chance of illness and death that is two to nine times greater.
Many heart attacks can be prevented through a healthy lifestyle that reduces risk factors for developing coronary artery disease. For patients who have already had a heart attack, a healthy lifestyle, participation in a cardiac rehabilitation program, and carefully following doctor’s orders may prevent another heart attack. A heart-healthy lifestyle includes eating a heart-healthy diet, regular exercise, maintaining a healthy weight, no smoking, moderate drinking, no illegal drugs, controlling high blood pressure, and managing stress.
A heart-healthy diet includes a variety of foods that are low in fat (especially saturated fat), low in cholesterol, and high in fiber; plenty of fruits and vegetables; and limited sodium (salt). Saturated fat raises cholesterol. Polyunsaturated and monounsaturated fats are relatively better for the heart. Fat should comprise no more than 30 percent of total daily calories. The American Heart Association has information on heart-healthy living on its Web site and publishes several heart-healthy cookbooks.
Cholesterol comes from eating foods such as meat, eggs, and other animal products. It also is produced in the liver. Soluble dietary fiber can help lower cholesterol. Cholesterol intake should be limited to about 300 mg per day. Many lipid-lowering drugs can reduce LDL-cholesterol by an average of 25–30% when combined with a low-fat, low-cholesterol diet. Fruits and vegetables are rich in fiber, vitamins, and minerals. They are also lowin calories and nearly fat free. Vitamin C and beta-carotene, found in many fruits and vegetables, also are beneficial. Excess sodiumincreases the risk of high blood pressure. Many processed foods contain large amounts of sodium, which should be limited to a daily intake of 2,400 mg—about the amount in a teaspoon of salt. In the United States, cholesterol, fats, fiber, sodium, and calories are listed on nutritional labels of all processed foods.
Regular aerobic exercise can lower blood pressure, help control weight, increase HDL(‘‘good’’) cholesterol, and reduce stress. Moderate intensity aerobic exercise lasting about 30 minutes four or more times per week is recommended for maximum heart health. Three 10- minute exercise periods also are beneficial. Aerobic exercise— activities such as walking, jogging, and cycling— uses the large muscle groups and forces the body to use oxygen more efficiently. It also can include everyday activities, such as active gardening, climbing stairs, or brisk housework. However, any regular exercise, no matter how mild, is better than not exercising.
Maintaining a desirable body weight also is important in preventing heart attacks. In 2009, about one third of all adult Americans were overweight or obese. People who are 20% or more over their ideal body weight have an increased risk of developing coronary artery disease. Losing weight can help reduce total and LDL cholesterol, reduce triglycerides, and boost relative levels of HDL cholesterol. It also may reduce blood pressure.
Smoking has many adverse effects on the heart. It increases the heart rate, constricts major arteries, and can create irregular heartbeats. It also raises blood pressure, contributes to the development of plaque, increases the formation of blood clots, and causes blood platelets to cluster and impede blood flow. Quitting can repair heart damage caused by smoking; even heavy smokers can return to heart health, and the health of their lungs also improves. Several studies have shown that ex-smokers face the same risk of heart disease as non-smokers within 5 to 10 years of quitting.
Drinking alcohol should always be done in moderation. Modest consumption of alcohol may protect against coronary artery disease; however, even small amounts of alcohol may have other negative effects depending on the individual’s health status and medications being taken. The American Heart Association defines moderate consumption as one ounce of alcohol per day—roughly one cocktail, one 8-ounce glass of wine, or two 12-ounce glasses of beer. Excessive alcohol use is always bad for the heart, and illegal drugs, such as methamphetamines and cocaine, can seriously harm the heart and cause a fatal heart attack.
High blood pressure, one of the most common and serious risk factors for coronary artery disease, can be controlled through lifestyle changes and medication. People with moderate hypertension may be able to lower it through dietary changes, such as reducing sodium intake combined with exercising regularly, managing stress, quitting smoking, and drinking alcohol in moderation. If these changes do not work, or if hypertension is severe, drugs that lower blood pressure may be prescribed.
Stress management means controlling mental and physical reactions to life’s irritations and challenges. Techniques for controlling stress include taking life more slowly, spending time with family and friends, thinking positively, getting enough sleep, exercising, and practicing relaxation techniques. (See: anxiety, treat anxiety with relaxation).
Daily aspirin therapy has been proven to help reduce blood clots associated with atherosclerosis. It also can lower the risk of strokes.
- Acute coronary syndrome - detailed technical article
- Percutaneous coronary intervention- detailed technical article