Heart Attack
Heart attack (myocardial infarction) is a medical emergency in which some of the heart's blood supply is suddenly and severely reduced or cut off, causing the heart muscle (myocardium) to die because it is deprived of its oxygen supply.
In the United States, more than 1.1 million people have a heart attack each year; about two thirds of them are men. Almost all of them have underlying coronary artery disease.
A heart attack usually occurs when a blockage in a coronary artery greatly reduces or cuts off the blood supply to an area of the heart. If the supply is greatly reduced or cut off for more than a few minutes, heart tissue dies.
Causes
A blood clot is the most common cause of a blocked coronary artery. Usually, the artery is already partially narrowed by atheromas. An atheroma may rupture or tear, narrowing the artery further and making blockage by a clot more likely. The ruptured atheroma not only reduces the flow of blood through an artery but also releases substances that make platelets stickier, further encouraging clots to form.
Uncommonly, a heart attack results when a clot forms in the heart itself, breaks away, and lodges in a coronary artery. Another uncommon cause is a spasm of a coronary artery that stops blood flow. Spasms may be caused by drugs. Sometimes the cause is unknown.
Symptoms
About two of three people who have heart attacks experience intermittent chest pain (angina (see Section 3, Chapter 33)), shortness of breath, or fatigue a few days or weeks beforehand. The episodes of pain may become more frequent and occur after less and less physical exertion. Such a change in the pattern of chest pain (unstable angina (see Section 3, Chapter 33)) may culminate in a heart attack.
Usually, the most recognizable symptom of a heart attack is pain in the middle of the chest that may spread to the back, jaw, or left arm. Less often, the pain spreads to the right arm. The pain may occur in one or more of these places and not in the chest at all. The pain of a heart attack is similar to the pain of angina but is generally more severe, lasts longer, and is not relieved by rest or nitroglycerin. Less often, pain is felt in the abdomen, where it may be mistaken for indigestion, especially because belching may bring partial or temporary relief.
About one third of people who have a heart attack do not have chest pain. Such people are more likely to be women, people who are not white, those who are older than 75, those who have heart failure or diabetes, or those who have had a stroke.
Other symptoms include a feeling of faintness, sudden heavy sweating, nausea, shortness of breath, and a heavy pounding of the heart.
Abnormal heart rhythms (arrhythmias) occur in more than 90% of people who have had a heart attack. Immediately and up to a few days after a heart attack, abnormal heart rhythms are a common reason that the heart cannot pump adequately. Abnormal heart rhythms originating in the ventricles (ventricular arrhythmias) may greatly interfere with the heart's pumping ability or may cause the heart to stop pumping effectively (cardiac arrest). A loss of consciousness or death can result. Sometimes loss of consciousness is the first symptom of a heart attack.
During a heart attack, a person may become restless, sweaty, and anxious and may experience a sense of impending doom. The lips, hands, or feet may turn slightly blue.
Older people may have unusual symptoms. In many, the most obvious symptom is breathlessness. Symptoms may resemble those of a stomach upset or a stroke. Older people may become disoriented. Nonetheless, about two thirds of older people have chest pain as do younger people. Older people, especially women, often take longer than younger people to admit they are ill or to seek medical help.
Despite all the possible symptoms, as many as one of five people who have a heart attack have only mild symptoms or none at all. Such a silent heart attack may be recognized only when electrocardiography (ECG) is routinely performed some time afterward.
During the early hours of a heart attack, heart murmurs and other abnormal heart sounds may be heard through a stethoscope.
Complications
The heart's ability to keep pumping after a heart attack is directly related to the extent and location of the damaged or dead tissue. Dead tissue is eventually replaced by scar tissue, which does not contract. Because each coronary artery supplies a specific area of the heart, the location of the damage is determined by which artery is blocked. If more than half of the heart tissue is damaged or dies, the heart generally cannot function, and severe disability or death is likely. Even when damage is less extensive, the heart may be unable to pump adequately, resulting in heart failure or shock. The damaged heart may enlarge, partly to compensate for the decrease in pumping ability (a larger heart beats more forcefully). Enlargement of the heart makes abnormal heart rhythms more likely.
Pericarditis (inflammation of the membranes enveloping the heart) may develop in the first day or two after a heart attack or about 10 days to 2 months later. Symptoms of early developing pericarditis are seldom noticed, because symptoms of the heart attack are more prominent. However, pericarditis produces a scratchy rhythmic sound that can sometimes be heard through a stethoscope 2 to 3 days after a heart attack. Later developing pericarditis is usually called Dressler's (post-myocardial infarction) syndrome. This syndrome causes fever, pericardial effusion (extra fluid in the space between the two layers of the pericardium), pleurisy (inflammation of the pleura, which are the membranes covering the lungs), pleural effusion (extra fluid in the space between the two layers of the pleura), and joint pain.
Other complications after a heart attack include rupture of the heart muscle, a bulge in the wall of the ventricle (ventricular aneurysm), blood clots (emboli), and low blood pressure (hypotension). Nervousness and depression are common after a heart attack. Depression after a heart attack may be significant and may persist.
 See the sidebar Complications of a Heart Attack.
Diagnosis
Whenever a man over age 35 or a woman over age 50 reports chest pain, doctors usually consider the possibility of a heart attack. But several other conditions can produce similar pain: pneumonia, a blood clot in the lung (pulmonary embolism), pericarditis, a rib fracture, spasm of the esophagus, indigestion, or chest muscle tenderness after injury or exertion.
Electrocardiography (ECG) (see Section 3, Chapter 21) and certain blood tests can usually confirm the diagnosis of a heart attack within a few hours.
ECG is the most important initial diagnostic procedure when doctors suspect a heart attack. This procedure provides a graphic representation of the electrical current producing each heartbeat--the electrocardiogram (the ECG). In many instances, it immediately shows that a person is having a heart attack. Several abnormalities may be detected by ECG, depending mainly on the size and location of the heart muscle damage. If a person has had previous heart problems, which can alter the ECG, the current muscle damage may be harder for doctors to detect. Such people should carry a small copy of their ECG in their wallets, so that if they have symptoms of a heart attack, doctors can compare the previous ECG with the current ECG. If a few ECGs recorded over several hours are normal, doctors consider a heart attack unlikely.
Measuring levels of certain substances (called serum markers) in the blood also helps doctors diagnose a heart attack. The presence of these substances in the blood indicates damage to or death of heart muscle. These substances are normally found in heart muscle but are released into the bloodstream when heart muscle is damaged. Most commonly measured is an enzyme called CK-MB. Levels in the blood are elevated within 6 hours of a heart attack and remain elevated for 36 to 48 hours. Levels of CK-MB are usually checked when the person is admitted to the hospital and at 6- to 8-hour intervals for the next 24 hours. However, two proteins called troponin T and troponin I may be more specific markers for damage to the heart. These proteins are involved in muscle contraction and are released into the bloodstream when cells are damaged.
When ECG and serum marker measurements do not provide enough information, echocardiography or radionuclide imaging may be performed. Echocardiography may show reduced motion in part of the wall of the left ventricle (the heart chamber that pumps blood to the body). This finding suggests damage due to a heart attack. Radionuclide imaging may show a persistent reduction in blood flow to an area of the heart muscle, suggesting scar tissue due to a heart attack.
Dressler's syndrome (pericarditis that develops 10 days to 2 months after a heart attack) is diagnosed based on the symptoms it produces and on the time it occurs.
Treatment
A heart attack is a medical emergency. Half of deaths due to a heart attack occur in the first 3 or 4 hours after symptoms begin. The sooner treatment begins, the better the chances of survival. Anyone having symptoms that might indicate a heart attack should obtain prompt medical attention. Prompt transportation to a hospital's emergency department by an ambulance with trained personnel may save the person's life. Trying to contact the person's doctor, relatives, friends, or neighbors is a dangerous waste of time.
People who may be having a heart attack are usually admitted to a hospital that has a cardiac care unit. Heart rhythm, blood pressure, and the amount of oxygen in the blood are closely monitored so that heart damage can be assessed. Nurses in these units are specially trained to care for people with heart problems and to handle cardiac emergencies.
If no complications occur during the first few days, most people can safely leave the hospital within a few more days. If complications such as abnormal heart rhythms develop or the heart can no longer pump adequately, hospitalization can be prolonged.
Initial Treatment: People who think they may be having a heart attack should call an ambulance, then chew an aspirin tablet. If aspirin is not taken at home or given by emergency personnel, it is usually immediately given at the hospital. This therapy improves the chances of survival by reducing the size of the clot (if present) in the coronary artery. People with an allergy to aspirin may be given clopidogrel or ticlopidine instead. Because decreasing the heart's workload also helps limit tissue damage, a beta-blocker is usually given to slow the heart rate, to enable the heart to work less hard, and to reduce the area of damaged tissue.
Often, oxygen is given through nasal prongs or a face mask. By increasing oxygen pressure in the blood, this therapy provides more oxygen to the heart and helps keep heart tissue damage to a minimum.
If a blocked coronary artery can be cleared quickly, heart tissue may be saved. Often, blood clots in an artery can be dissolved by a thrombolytic drug such as streptokinase, recombinant tissue plasminogen activator (alteplase), or reteplase. To be effective, a thrombolytic drug must be given intravenously within 6 hours of the start of heart attack symptoms. After 6 hours, most damage is permanent, and removing the blockage may not help. Early treatment increases blood flow in 60 to 80% of people and helps keeps heart tissue damage to a minimum. Aspirin, which prevents platelets from forming blood clots, or heparin, which stops clotting, may enhance the effectiveness of a thrombolytic drug.
Because thrombolytic drugs can cause bleeding, they are not usually given to people who have bleeding in the digestive tract, who have severe high blood pressure, who have recently had a stroke, or who have had surgery during the month before the heart attack. Older people who do not have any of these conditions can be safely given a thrombolytic drug.
In some cardiovascular treatment centers, angioplasty or coronary artery bypass surgery (see Section 3, Chapter 33) is performed immediately after the heart attack to clear the arteries instead of using a thrombolytic drug. This approach is preferred for people who cannot take thrombolytic drugs and for those who are very ill after having a massive heart attack. For some people, a thrombolytic drug is used with angioplasty or with an antiplatelet drug, such as a glycoprotein IIb/IIIa inhibitor (for example, abciximab or tirofiban).
Because most people who have had a heart attack are experiencing severe discomfort and anxiety, morphine is often used. This drug has a calming effect and reduces the workload of the heart. Most people are given nitroglycerin, which relieves pain by reducing the workload of the heart and possibly by dilating arteries. Usually, it is first given under the tongue, then intravenously.
Angiotensin-converting enzyme (ACE) inhibitors (see Section 3, Chapter 22) can reduce heart enlargement and increase the chance of survival for many people. Therefore, these drugs are usually given in the first few days after a heart attack and prescribed indefinitely.
Subsequent Treatment: Because physical exertion, emotional distress, and excitement stress the heart and make it work harder, a person who has just had a heart attack should stay in bed in a quiet room for a few days. Visitors are usually limited to family members and close friends. Watching television may be permitted if the programs do not cause stress.
Smoking, a major risk factor for coronary artery disease and heart attack, is prohibited in hospitals and in cardiac care units. Moreover, a heart attack is a compelling reason to stop smoking.
Stool softeners and gentle laxatives may be used to prevent constipation, so that the person does not have to strain. If the person cannot pass urine or if the doctors and nurses must keep track of the precise amount of urine produced, a urinary catheter is used.
For severe nervousness (which can stress the heart), a mild antianxiety drug (for example, a benzodiazepine such as lorazepam) may be prescribed. To deal with mild depression and denial of illness, which are common after a heart attack, patients and their family members and friends are encouraged to talk about their feelings with doctors, nurses, and social workers. Some patients require an antidepressant.
After about 5 to 7 days in the hospital, people who have had a heart attack are usually discharged. Nitroglycerin, aspirin, a beta-blocker, an ACE inhibitor, and a lipid-lowering drug (most often, a statin) (see Section 12, Chapter 157) are usually prescribed. Soon after discharge, people should see their primary care doctor, who can refer them to a cardiologist or to a cardiac rehabilitation program if needed.
People who develop Dressler's syndrome are usually given aspirin. Even with treatment, the syndrome can recur. If the syndrome is severe, a corticosteroid or a nonsteroidal anti-inflammatory drug other than aspirin (such as ibuprofen) may be needed for a short time.
Prognosis and Prevention
Most people who survive for a few days after a heart attack can expect a full recovery, but about 10% die within a year. Most deaths occur in the first 3 or 4 months, typically in people who continue to have angina, abnormal heart rhythms originating in the ventricles (ventricular arrhythmias), and heart failure. All of these disorders may result from a heart attack. The prognosis is worse if the heart has enlarged after a heart attack than if heart size remains normal. Older people are more likely to die after a heart attack and to have complications, such as heart failure. The prognosis for smaller people is worse than that for larger people. This finding may help explain why the prognosis for women who have had a heart attack is, on average, worse than that for men. Women also tend to be older and to have more serious disorders when they have a heart attack. Also, they tend to wait longer after a heart attack to go to the hospital than do men.
Other procedures may be performed to determine whether a person needs additional treatment or is likely to have more heart problems. For instance, a person may have to wear a Holter monitor, which records the heart's electrical activity for 24 hours (see Section 3, Chapter 21). This procedure enables doctors to detect whether the person has abnormal heart rhythms (arrhythmias) or episodes of inadequate blood supply without symptoms (silent ischemia). An exercise stress test (electrocardiography performed during exercise) (see Section 3, Chapter 21) before or shortly after discharge can help determine how well the person is doing after the heart attack and whether ischemia is continuing. If these procedures detect abnormal heart rhythms or ischemia, drug therapy may be recommended. If ischemia persists, doctors may recommend coronary angiography to evaluate the possibility of performing angioplasty or bypass surgery to restore blood flow to the heart.
Taking one baby aspirin, one half of an adult aspirin, or one full adult aspirin daily after a heart attack is recommended. Because aspirin prevents platelets from forming clots, it reduces the risk of death and the risk of a second heart attack by 15 to 30%. People with an allergy to aspirin may take clopidogrel or ticlopidine instead. Usually, doctors also prescribe a beta-blocker (such as metoprolol, propranolol, or timolol) because they reduce the risk of death by about 25%. The more serious the heart attack, the more benefit beta-blockers provide. However, some people cannot tolerate the side effects (such as wheezing, tiredness, and cold limbs), and not everyone benefits.
Taking lipid-lowering drugs may reduce the risk of death after a heart attack.
ACE inhibitors, such as captopril, enalapril, lisinopril, and ramipril, are often prescribed after a heart attack. They help prevent death and the development of heart failure, particularly in people who have had a massive heart attack or who have heart failure.
Rehabilitation
Cardiac rehabilitation, an important part of recovery, begins in the hospital. Remaining in bed for longer than 2 or 3 days leads to physical deconditioning and sometimes to depression and a sense of helplessness. Barring complications, people who have had a heart attack can usually progress to sitting in a chair, passive exercise, use of a commode chair, and reading on the first day. By the second or third day, people are encouraged to walk to the bathroom and engage in nonstressful activities, and they can perform more activities each day (see Section 3, Chapter 21).
| 
