Also Known As
Acute Myocardial Infarct
AMI
Myocardial Infarct
MI
ACS
This article was last reviewed on
This article waslast modified on August 21, 2020.
Overview of the Heart

The heart is a muscular organ that pumps blood throughout the body via a system of arteries and veins. The heart has two sides and four chambers. The right side of the heart receives oxygen-depleted blood from the body and sends it to the lungs. Blood picks up oxygen in the lungs and flows through the pulmonary veins back to the left side of the heart. The left side of the heart receives the oxygen-rich blood from the lungs and pumps it through the aorta out to the body. In order to perform these tasks, the heart requires large amounts of oxygen that it obtains from its own dedicated network of arteries, which are called the "coronary arteries."

What are heart attacks and acute coronary syndrome?

Acute coronary syndrome (ACS) may present as a heart attack or unstable angina, which are conditions associated with decreased blood flow to the heart. ACS can cause a spectrum of signs and symptoms.

  • A partial blockage of blood flow to the heart may be due to arteries that have narrowed, thickened walls. The thickening is caused by a gradual build-up of plaque in a process called atherosclerosis. This can cause signs and symptoms such as pain and discomfort that may come and go and may occur even at rest.
  • These signs and symptoms may suddenly become more severe when the plaque ruptures, injuring the blood vessel. A blood clot can form that completely blocks blood flow to the heart. The blood clot can partially dissolve and then reform again later.
  • Signs and symptoms can also develop without any warning and may be serious (e.g., chest pain, shortness of breath, rapid heart rate). These may be caused by a sudden, partial, or complete blockage of blood flow to the heart.

When someone is rushed to the emergency room with possible signs and symptoms of ACS, testing must be performed to determine whether the symptoms are due to unstable angina, a heart attack, or to another cause when an ACS is excluded.

A heart attack, also called an acute myocardial infarction (AMI), differs from unstable angina in that most commonly, blood flow to the heart is persistently blocked. This persistent blockage is usually caused by a blood clot that develops in an artery that supplies blood to the heart (termed a coronary artery). Prolonged blockage can cause death of the heart muscle cells (infarct) and lead to later scarring of the affected area of the heart. The longer the blockage persists, the more damage to heart muscle can occur. Without prompt medical treatment, this blockage can even cause death.

According to the Centers for Disease Control and Prevention, about 805,000 Americans have heart attacks each year. In the United States, someone has a heart attack every 40 seconds.

Accordion Title
About Heart Attacks and ACS
  • Signs and Symptoms

    As mentioned above, ACS can cause a spectrum of signs and symptoms. With both a heart attack and unstable angina, you 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 recurring pain. People with unstable angina may have symptoms that may be more severe or longer-lasting than previously experienced with exertion (stable angina).

    Some signs and symptoms may develop suddenly while other symptoms start slowly or 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). Women are more likely than men to have signs and symptoms that are not typical. In women, symptoms are often less severe than in men and more likely to be misinterpreted as due to another cause.

    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 you have one or more of these symptoms, do not ignore them: seek medical care immediately. If medical help is not received promptly, irreversible damage to the heart muscle may occur.

  • Risk Factors

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

  • Tests

    If you go to the emergency room with symptoms of possible ACS, it is usually not clear whether you are having a heart attack or unstable angina, or chest pain due to another cause. A number of tests are available to help determine the cause of symptoms.

    Laboratory Tests

    Troponin—there are blood tests that detect heart damage. These are called cardiac markers. The most common one in use today is troponin. A troponin may be used to differentiate a heart attack from both stable angina and unstable angina. Troponin testing is usually ordered in the ER when you have chest pain or other signs and symptoms of a possible ACS. The initial test is typically followed by a series of troponin tests performed over the next several hours to look for changes in levels.

    • If there is a rise and/or fall in the series of troponin results above a specific threshold, then it is likely that you have had a heart attack or some other form of damage to the heart.
    • In people with angina, an elevated troponin may indicate that their condition is worsening, and they are at increased risk of a heart attack.

    One version of the test is called high-sensitivity (hs) troponin. It detects the same protein that the standard troponin test does, just at a lower level, sometimes allowing an earlier diagnosis of a heart attack.

    Other tests that may be performed include:

    Other, more general screening tests may also be ordered to help evaluate your general health status. These include:

    • Comprehensive metabolic panel (CMP)—a group of 14 tests that is used as a broad screening tool to assess the current status of your kidneys, liver, electrolyte and acid/base balance, blood glucose, and blood proteins
    • Complete blood count (CBC)—a test used to screen for a variety of disorders that can affect blood cells, such as anemia and infection

    Non-laboratory Tests

    Some non-laboratory evaluations and tests may be used to assess your heart and to help determine your risk of heart attack. Examples include:

    • A medical history, including an evaluation of risk factors such as age, coronary artery disease (CAD), diabetes, and tobacco use
    • 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 ECG.

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

    • An exercise stress test
    • Chest X-ray
    • Continuous ECG monitoring (ambulatory ECG, Holter monitoring)—this is a monitor that evaluates heart rhythm over time, during regular daily activities.
    • Nuclear heart scan (radionuclide imaging)—a radioactive compound is injected into the blood to evaluate how well your heart is pumping.
    • Echocardiography—ultrasound imaging of the heart
    • Cardiac computed tomography (CT) or magnetic resonance imaging (MRI)—imaging scans that create images of the heart and show damage from heart attacks, and calcium and blockages in your heart arteries
    • Coronary catheterization (angiogram)—a liquid dye is injected into the arteries of the heart through a long, thin tube (catheter) that is fed through an artery in the leg, groin, or arm to the arteries in the heart. The dye makes the arteries visible on X-ray, showing where arteries are blocked.

    For more information on these tests, visit the American Heart Association: Diagnostic Tests and Procedures for Heart Attack.

  • Treatment

    Acting fast, by seeking medical attention (calling 911) at the first symptoms of a heart attack, can save your life.

    Heart attacks must be treated promptly to minimize heart damage and open blocked arteries. This may include the use of medications, arteriography, and surgical procedures. Treatment is also given to relieve the acute symptoms associated with heart attacks and acute coronary syndrome.

    Some examples of medications prescribed for heart attacks include:

    • Aspirin—reduces blood clotting and may help blood flow through narrowed arteries; aspirin is often taken or given immediately when a heart attack is suspected.
    • Drugs that dissolve or split up blood clots (thrombolytic medications)
    • Pain medication, such as morphine
    • Nitroglycerin—helps relieve chest pain (angina), widens blood vessels to improve blood flow to the heart
    • Beta blockers—slows the heart rate, lowers blood pressure to relieve symptoms
    • ACE inhibitors—lowers blood pressure and decreases stress on the heart
    • Anticoagulants (blood thinners) and antiplatelet medicines—reduce blood clotting

    Sometimes medical procedures are needed, such as:

    • Angioplasty or percutaneous coronary intervention (PCI)—a procedure to widen the blood vessels that have become narrowed or blocked; in this procedure, a balloon-tipped catheter (usually through the groin) is inserted into the coronary arteries to flatten the blockage and open the vessel. Angioplasty is often combined with the insertion of a stent, a small, thin wire mesh tube to keep the vessel open.
    • Bypass surgery—uses a part of a healthy blood vessel from elsewhere in the body to re-direct blood flow around a blocked artery

    Once the initial attack or episode has been resolved, other treatments are frequently prescribed and implemented to help decrease the risk of repeated heart attacks. Your healthcare practitioner will likely prescribe diet and exercise changes appropriate to your condition.

    For more information, visit the National Heart, Lung, and Blood Institute: Heart Attack or the links in the Related Content section.

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