Also Known As
Acute Myocardial Infarct
AMI
Myocardial Infarct
MI
ACS
This article was last reviewed on
This article waslast modified on
December 4, 2017.
What are heart attack and acute coronary syndrome?

A heart attack, also called an acute myocardial infarct (AMI), is caused by a blockage in the heart's arteries that completely cuts off the blood supply to a portion of the heart. Without prompt medical treatment, this blockage can damage or destroy heart tissue and can kill. According to the American Heart Association, about 735,000 people in the U.S. have heart attacks each year and about 120,000 of those affected die.

Acute coronary syndrome (ACS) is a group of signs and symptoms that are associated with insufficient blood flow to the heart. A heart attack differs from other forms of ACS in that the decreased blood flow persists, causing death of heart muscle cells. When someone is rushed to the emergency room, testing must be performed to determine whether or not a person's signs and symptoms (ACS) are due to a heart attack or to another cause.

The heart is a muscular organ that pumps blood throughout the body via a system of veins and arteries. Blood flows from the lungs, where it picks up oxygen, through the pulmonary veins into the heart, and then gets pumped out to the body, delivering oxygen to the tissues. The blood returns to the heart via the veins and gets pumped back to the lungs once again. In order to perform these tasks, the heart requires large amounts of oxygen that it obtains from its own dedicated network of veins and arteries.

The persistent blockage causing a heart attack is usually caused by a blood clot that becomes lodged in an artery that supplies blood to the heart (termed a coronary artery). This most frequently occurs in arteries that have narrowed, thickened walls. The thickening is caused by a gradual build-up of plaque in a process called atherosclerosis. The acute blockage of blood flow caused by a clot in a coronary artery, if present for more than an hour, can cause death of the heart muscle cells (infarct) and lead to scarring of the affected area of the heart.

Accordion Title
About heart attack and acute coronary syndrome
  • Risk Factors

    There are many risk factors for heart attack. These include:

  • Signs and Symptoms

    With both a heart attack and other forms of acute coronary syndrome (ACS), a person may experience a sudden onset of chest pain, often radiating into the jaw, arm or shoulder, that typically is not relieved by rest. This pain may be a first occurrence or a worsening of reoccurring pain.

    In someone who has had episodes of chest pain due to an inadequate blood supply through narrowed arteries (unstable angina), these symptoms may be more severe or longer-lasting than was previously experienced when the person developed chest pain on exertion (stable angina).

    Note that not everyone will experience chest pain, and women are more likely than men to have signs and symptoms that are not typical. In women, symptoms are often less dramatic and more likely to be misinterpreted as due to another cause than in men. Some heart attacks are sudden while other heart attacks start slowly. The pain and other symptoms may come and go.

    Signs and symptoms may include:

    • Chest pain, discomfort and/or pressure (most common)
    • Rapid heart rate, skipping a beat
    • Nausea and vomiting or stomach pain
    • Sweating
    • Sudden onset of shortness of breath 
    • Difficulty breathing
    • Feeling lightheaded
    • Change in blood pressure
    • Fatigue
    • Pain on other places such as the back, one or both arms, jaw or neck


    In some cases, some of these symptoms may occur without chest pain (particularly in older individuals and in those with diabetes).

    For more information on warning signs and the differences between those that occur in men and women, visit the links listed under Related Content, Elsewhere on the Web. If someone has one or more of these symptoms, the person should not ignore them and should call 911 or the local emergency number. If medical help is not received promptly, irreversible damage to the heart muscle may occur.

  • Tests

    When a person presents to the emergency room with symptoms of acute coronary syndrome (ACS), it is usually not clear whether the person is having a heart attack or unstable angina, or chest pain due to another cause. A number of tests are available to help evaluate whether a heart attack (AMI) has occurred.

    Laboratory Tests

    Blood tests are usually needed to tell whether a heart attack has occurred. Cardiac biomarkers, proteins that are released when muscle cells are damaged, are frequently ordered to help differentiate ACS from a heart attack. These include:

    • Troponin – the most commonly ordered and cardiac-specific of the markers. Blood levels of troponin will be elevated within a few hours of heart damage and remain elevated for up to two weeks. Troponin tests are usually ordered initially in the ER when a person presents with symptoms of acute coronary syndrome and then a few more times in the next several hours to look at changes in concentrations. If levels are normal, then it is much less likely that the symptoms and chest pain are due to heart muscle damage and is more likely that the pain is due to stable angina. A rise and/or fall in the series of results indicates a heart attack.
    • A test called high-sensitivity troponin detects the same protein that the standard test does, just at much lower levels. Because this version of the test is more sensitive, it becomes positive sooner and may help detect heart injury and acute coronary syndrome earlier than the standard test. The hs-troponin test may also be positive in people with stable angina and even in people with no symptoms. When it is elevated in these individuals, it indicates an increased risk of future heart events, such as heart attacks. Currently, this test is not approved in the U.S., but research is ongoing and it may become available in the near future. It is already routinely used as a cardiac biomarker in clinical practice in Europe, Canada, and other countries as well.
    • CK-MB – one particular form of the enzyme creatine kinase that is found mostly in heart muscle and rises when there is damage to the heart muscle cells. This test is performed less frequently now that troponin testing is available.


    Other tests that may be performed include:

    • Myoglobin – a protein released into the blood when heart or other skeletal muscle is injured; this test is used less frequently now.
    • BNP or NT-proBNP – released by the body as a natural response to heart failure; increased levels of BNP, while not diagnostic for a heart attack, indicate an increased risk of cardiac problems in persons with acute coronary syndrome.


    Other more general screening tests may also be ordered to help evaluate the person's major body organs, electrolyte balance, blood glucose, and red and white blood cells to see whether there are any excesses, deficiencies, or dysfunctions that may be causing or worsening the person's symptoms. These include:

    • Comprehensive Metabolic Panel – a group of usually 14 tests that is used as a broad screening tool to assess the current status of an individual's kidneys, liver, electrolyte and acid/base balance, blood glucose, and blood proteins.
    • Complete Blood Count – a test used to screen for a variety of disorders that can affect blood cells, such as anemia and infection.


    Non-laboratory Tests

    A range of non-laboratory evaluations and tests may be used to assess chest pain and other symptoms. These include:

    • A medical history, including an evaluation of risk factors such as age, coronary artery disease (CAD), diabetes, and smoking
    • A physical examination
    • An electrocardiogram (ECG or EKG) – a test that looks at the heart's electrical activity and rhythm; the diagnosis of a heart attack may be made by changes seen on an electrocardiogram and by a number of blood tests. An ECG is performed within the first few minutes after a person with ACS arrives in the emergency room. It evaluates heart rhythm and can be used to detect changes that prove that a severe heart attack has occurred. Most commonly, the ECG only confirms that the heart is not getting enough blood or has non-specific changes that do not prove that a heart attack has occurred.
    • Continuous ECG monitoring – a person wears a monitor that evaluates heart rhythm over a period of time.


    Based on the findings of these tests, other procedures may be necessary, including:

    • An exercise stress test
    • Chest X-ray
    • Radionuclide imaging – a radioactive compound is injected into the blood to evaluate blood flow and examine images of narrowed blood vessels around the heart.
    • Echocardiography – ultrasound imaging of the heart
    • Cardiac catheterization – in this procedure, a thin flexible tube is inserted into an artery in the leg and threaded up to the coronary arteries to evaluate blood flow and pressure in the heart and the status of the arteries in the heart.
    • Coronary angiography – X-rays of arteries using a radiopaque dye to help diagnose CAD; this procedure is performed during cardiac catheterization.

    For more information on these, visit the National Heart, Lung, and Blood Institute: How is a Heart Attack Diagnosed?

  • Treatment

    Heart attacks must be treated promptly to minimize heart damage and address blockages. This may include the use of both drugs and surgical procedures. Treatment is also given to relieve the acute symptoms associated with heart attacks and acute coronary syndrome. Once the initial attack or episode has been resolved, other treatments and lifestyle changes are frequently prescribed and implemented to help decrease the risk of recurrence.

    As in all heart diseases, controlling blood pressure (reducing hypertension) is a primary concern. Drugs, such as digoxin, which helps the heart increase contractions, and antiarrhythmics, such as procainamide, which help synchronize the contractions, may also be used, depending on how the heart is reacting. Other medications may also be prescribed, including beta blockers, ACE inhibitors, anticoagulants, antiplatelet medicines, and drugs that dissolve or split up blood clots (thrombolytic medications). For unstable angina, a baby aspirin is considered a first-line treatment. Sometimes medical procedures are needed, such as angioplasty or coronary artery bypass grafting. Your healthcare practitioner may also prescribe diet and exercise changes appropriate to your condition.

    For more information, visit the National Heart, Lung, and Blood Institute: How is a Heart Attack Treated?

View Sources

NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used. To access online sources, copy and paste the URL into your browser.

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