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Acute Coronary Syndromes (Heart Attack; Myocardial Infarction; Unstable Angina)

By James Wayne Warnica, MD

Acute coronary syndromes result from a sudden blockage in a coronary artery. This blockage causes unstable angina or heart attack (myocardial infarction), depending on the location and amount of blockage.

  • People who experience an acute coronary syndrome usually have chest pressure or ache, shortness of breath, and fatigue.

  • People who think they are experiencing an acute coronary syndrome should call for emergency help and then chew an aspirin tablet.

  • Doctors use electrocardiography and measure substances in the blood to determine whether a person is experiencing an acute coronary syndrome.

  • Treatment varies depending on the type of syndrome but usually includes attempts to increase blood flow to affected areas of the heart.

In the United States, more than 1.5 million people have a heart attack each year. About 400,000 to 500,000 of them die, half before they reach the hospital. Almost all of them have underlying coronary artery disease and about two thirds of them are men.


An acute coronary syndrome occurs when a sudden blockage in a coronary artery greatly reduces or cuts off the blood supply to an area of the heart muscle (myocardium). The lack of blood supply to any tissue is termed ischemia. If the supply is greatly reduced or cut off for more than a few minutes, heart tissue dies. A heart attack, also termed myocardial infarction (MI), is death of heart tissue from ischemia.

A blood clot is the most common cause of a blocked coronary artery. Usually, the artery is already partially narrowed by a buildup of cholesterol and other fatty materials in the artery wall (atheroma). An atheroma may rupture or tear, which releases substances that make platelets stickier, encouraging clots to form. In about two thirds of people, the blood clot dissolves on its own, typically within a day or so. However, by this time, some heart damage has usually occurred.

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 such as cocaine. Sometimes the cause is unknown.


Doctors classify acute coronary syndromes based on electrocardiography (ECG) and on the presence of substances in the blood (serum markers) released by the damaged heart. The classification is important because treatments differ depending on the specific acute coronary syndrome. The classification consists of unstable angina and two types of heart attack.

  • Unstable angina is a change in the pattern of angina symptoms (see page Angina : Symptoms), including prolonged or worsening angina and new onset of severe angina symptoms. People who have unstable angina do not have signs of heart attack on their ECG or blood tests.

  • Non-ST-segment elevation MI is a heart attack that doctors can identify by blood tests but that does not produce typical changes (ST-segment elevation) on an ECG.

  • ST-segment elevation MI is a heart attack that doctors can identify by blood tests and also produces typical changes on an ECG.

Did You Know...

  • About one third of people who have a heart attack do not have chest pain.


Symptoms of the acute coronary syndromes are similar, and it is usually impossible to distinguish the syndromes based on symptoms alone. Symptoms of unstable angina are the same as those of angina pectoris, intermittent pressure, or an ache beneath the breastbone (sternum—see page Angina : Symptoms). However, in people with unstable angina, the pattern changes. People experience more frequent or more severe episodes of angina, or episodes occur at rest or after less physical exertion. About two of three people who have heart attacks experience unstable angina, shortness of breath, or fatigue a few days or weeks beforehand. Such a change in the pattern of chest pain discomfort 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. For unknown reasons, women often have different, less identifiable symptoms.

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, and those who have had a stroke.

Other symptoms include a feeling of faintness or actually fainting, sudden heavy sweating, nausea, shortness of breath, and a heavy pounding of the heart (palpitations).

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 ECG is routinely done some time afterward.

During the early hours of a heart attack, heart murmurs and other abnormal heart sounds may be heard through a stethoscope.


The complications of acute coronary syndromes depend on how much, how long, and where a coronary artery is blocked. If the blockage affects a large amount of heart muscle, the heart will not pump effectively. If the blockage shuts off blood flow to the electrical system of the heart, the heart rhythm may be affected.

Pumping problems

In a heart attack, part of the heart muscle dies. Dead tissue, and the scar tissue that eventually replaces it, does not contract. The scar tissue sometimes even expands or bulges when the rest of the heart contracts. Consequently, there is less muscle to pump blood. If enough muscle dies, the heart’s pumping ability may be so reduced that the heart cannot meet the body’s need for blood and oxygen. Heart failure, low blood pressure, or both develop. If more than half of the heart tissue is damaged or dies, the heart generally cannot function, and severe disability or death is likely.

Drugs such as beta-blockers and especially angiotensin-converting enzyme (ACE) inhibitors can reduce the extent of the abnormal areas by reducing the workload of and the stress on the heart. Thus, these drugs help the heart maintain its shape and function more normally.

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.

Rhythm problems

Abnormal heart rhythms (arrhythmias) occur in more than 90% of people who have had a heart attack. These abnormal rhythms may occur because the heart attack damaged part of the heart’s electrical system. Sometimes there is a problem with the part of the heart that triggers the heartbeat, so heart rate may be too slow. Other problems can cause the heart to beat rapidly or irregularly. Sometimes the signal to beat is not conducted from one part of the heart to the other, and the heartbeat may slow or stop.

In addition, areas of heart muscle that have poor blood flow but that have not died can be very irritable. This irritability can cause heart rhythm problems, such as ventricular tachycardia or ventricular fibrillation. These rhythm problems greatly interfere with the heart’s pumping ability and may cause the heart to stop beating (cardiac arrest). A loss of consciousness or death can result. These rhythm disturbances are a particular problem in people who have an imbalance in blood chemicals, such as a low potassium level.

Other problems

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. Pericarditis is more common in people who have not had the blocked artery opened by percutaneous coronary intervention (PCI) or coronary artery bypass grafting (CABG). People seldom notice symptoms of early developing pericarditis because their heart attack symptoms 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. Sometimes, the inflammation causes a small amount of fluid to collect in the space between the two layers of the pericardium (pericardial effusion). Later developing pericarditis is usually called Dressler (post-myocardial infarction) syndrome. This syndrome causes fever, pericardial effusion, inflammation of 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 malfunction of the mitral valve, 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.


Whenever a man over age 35 or a woman over age 40 reports chest pain, doctors usually consider the possibility of an acute coronary syndrome. But several other conditions can cause 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.

ECG (see page Electrocardiography) and certain blood tests can usually confirm the diagnosis within a few hours.

ECG is the most important initial diagnostic procedure when doctors suspect an acute coronary syndrome. This procedure provides a graphic representation of the electrical current producing each heartbeat. In many instances, it immediately shows that a person is having a heart attack. Abnormalities detected by ECG help doctors determine the type of treatment needed. The abnormalities on ECG also help show where the heart muscle was damaged. If a person has had previous heart problems, which can alter the ECG, the most recent 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 an acute coronary syndrome, doctors can compare the previous ECG with the current ECG. If a few ECGs recorded over several hours are completely normal, doctors consider a heart attack unlikely.

Measuring levels of certain substances (called cardiac markers) in the blood also helps doctors diagnose acute coronary syndromes. These substances are normally found in heart muscle but are released into the bloodstream only when heart muscle is damaged or dead. Most commonly measured are a heart muscle proteins called troponin I and troponin T and an enzyme called CK-MB (creatinine kinase, muscle and brain subunits). Levels in the blood are elevated within 6 hours of a heart attack and remain elevated for 36 to 48 hours. Levels of cardiac markers are usually measured when the person is admitted to the hospital and at 6- to 8-hour intervals for the next 24 hours.

When ECG and serum marker measurements do not provide enough information, echocardiography or radionuclide imaging may be done. 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.

Dressler 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.

Other testing

Other tests may be done during or shortly after hospitalization. These tests are used 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 Holter Monitor: Continuous ECG Readings). 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 done during exercise—see page Stress Testing) 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 doing percutaneous coronary intervention or coronary artery bypass grafting to restore blood flow to the heart.


Many people who have unstable angina go on to have a heart attack within about 3 months.

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. 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.


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%. Doctors usually recommend that people who have not yet had a heart attack or stroke who are over 50 years of age and have 2 or more risk factors (see page Overview of Coronary Artery Disease : Risk Factors) should take low-dose aspirin every day to prevent heart attacks and stroke. People with an allergy to aspirin may take clopidogrel instead.

Usually, doctors also prescribe a beta-blocker (such as metoprolol) because these drugs 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 and modifying diet will reduce the risk of death after a heart attack. People at high risk (especially obese people with diabetes) who have not yet had a heart attack or stroke may benefit from lipid-lowering drugs.

Angiotensin-converting enzyme (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.

People should also make changes in their lifestyle. They should eat a low-fat diet and increase the amount of exercise they get. People who have high blood pressure or diabetes should try to keep those disorders under control. People who smoke should quit.


Acute coronary syndromes are medical emergencies. 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 an acute coronary syndrome 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 heart 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.

Did You Know...

  • Half of deaths due to a heart attack occur in the first 3 or 4 hours after symptoms begin.

Drug treatment

People who think they may be having a heart attack should chew an aspirin tablet immediately after calling an ambulance. If aspirin is not taken at home or given by emergency personnel, it is 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 instead. Some people are given both aspirin and clopidogrel.

Because decreasing the heart’s workload also helps limit tissue damage, a beta-blocker is usually given to slow the heart rate. Slowing the rate enables the heart to work less hard and reduces the area of damaged tissue.

Most people are also given an anticoagulant drug, such as heparin, to help prevent the formation of additional blood clots.

Often, oxygen is given through nasal prongs or a face mask. Providing more oxygen to the heart helps keep heart tissue damage to a minimum.

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.

ACE inhibitors (see page Drug therapy) 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.

Statins (see page Dyslipidemia : Treatment) have long been used to help prevent coronary artery disease, but doctors have recently found that they also have short-term benefit for people with an acute coronary syndrome. Doctors give a statin to people who are not already taking one.

Opening the arteries

The decision on the timing and method of opening a blocked coronary artery depends on the type of acute coronary syndrome and on how quickly the person got to the hospital.

In people who have an ST-segment elevation MI, immediately clearing the coronary artery blockage saves heart tissue and improves survival. Doctors try to clear the blockage within 90 minutes after the person arrives at the hospital. Because the sooner the artery is cleared the better the outcome, the method of clearing is probably not as important as the timing. If available within 90 minutes, percutaneous cardiac interventions (PCI) such as angioplasty and stent placement (see page Overview of Coronary Artery Disease : Percutaneous coronary intervention) appear to be the best way to open blocked arteries during an ST-segment elevation MI. If these procedures are not available within that time frame, doctors give clot-dissolving (thrombolytic, or fibrinolytic) drugs intravenously to open the arteries. Thrombolytic drugs include streptokinase, tenecteplase (TNK-tPA), alteplase, and reteplase. Although better if given immediately, these drugs can work well within 3 hours and may be of some benefit for up to 12 hours after the person arrives at the hospital. In some areas, thrombolytic drugs are given before hospital arrival by specially trained paramedics. Most people who are given a thrombolytic drug still need to have PCI before they leave the hospital.

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.

People who have a non-ST-segment elevation MI or unstable angina do not usually benefit from immediate PCI or thrombolytic drugs. However, doctors usually do PCI within the first day or two of hospitalization. If the person’s symptoms worsen or certain complications develop, doctors may do PCI earlier.

In some people, coronary artery bypass grafting (CABG—see page Overview of Coronary Artery Disease : Coronary Artery Bypass Grafting) is done during an acute coronary syndrome instead of using PCI or a thrombolytic drug. For example, CABG may be used for people who cannot be given a thrombolytic drug (for example, because they have a bleeding disorder or have had a recent stroke or recent major surgery). CABG may also be used for people who cannot undergo PCI because of the severity of their arterial disease (for example, because there are many areas of blockage or heart function is poor, especially if the person also has diabetes).

General measures

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, is prohibited in hospitals. Moreover, an acute coronary syndrome 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 need to 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 acute coronary syndromes, people are encouraged to talk about their feelings with doctors, nurses, social workers, and their family members and friends. Some people require an antidepressant.


After about 3 to 4 days in the hospital, people who have had an uncomplicated heart attack and successful PCI are usually discharged. Other people may require a longer stay.

Nitroglycerin, aspirin and sometimes clopidogrel, a beta-blocker, an ACE inhibitor, and a lipid-lowering drug (most often, a statin—see page Lipid-Lowering Drugs) are usually prescribed.

People who develop Dressler syndrome are usually given aspirin. Colchicine is often rapidly effective. Even with treatment, the syndrome can recur. If Dressler syndrome is severe, a corticosteroid or a nonsteroidal anti-inflammatory drug other than aspirin (such as ibuprofen) may be needed for a short time.


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 do more activities each day (see page Rehabilitation for Heart Disorders). If everything goes well, people are usually back to their normal activities within about 6 weeks. Participation in a regular exercise program consistent with the person’s age and heart health is beneficial.

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