Heart Attack and Acute Coronary Syndrome

  • Diagnosis

    When a patient comes to the hospital with chest pain, the following diagnostic steps are usually taken to determine any heart problems, and, if present, their severity:

    • The patient will report all symptoms so that a health care provider can rule out either a non-heart problem or possible other serious accompanying conditions.
    • An electrocardiogram (ECG) reading is taken, recording the electrical activity of the heart. It is the key tool for determining if heart problems are causing chest pain and, if so, how severe they are.
    • Blood tests showing elevated levels of certain factors (troponins and CK-MB) indicate heart damage. (The doctor will not wait for results, however, before administering treatment if a heart attack is strongly suspected.)
    • Imaging tests, including echocardiogram and perfusion scintigraphy, help rule out a heart attack if there is any question.

    Electrocardiogram (ECG)

    An electrocardiogram (ECG or EKG) measures and records the electrical activity of the heart. The waves measured by the ECG correspond to the contraction and relaxation pattern of the different parts of the heart. Specific waves seen on an ECG are named with letters:

    • P. The P wave is associated with the contractions of the atria (the two chambers in the heart that receive blood from outside).
    • QRS. The QRS is a series of waves associated with ventricular contractions. (The ventricles are the two major pumping chambers in the heart.)
    • T and U. These waves follow the ventricular contractions.
    Click the icon to see an image of a normal sinus rhythm.

    Doctors use a term called the P-Q or P-R interval, which is the time taken for an electrical impulse to travel from the atria to the ventricle.

    The most important wave patterns in diagnosing and determining treatment for a heart attack are called ST elevations and Q waves.

    Elevated ST Segments: Heart Attack. Elevated ST segments are strong indicators of a heart attack in patients with symptoms and other indicators. They suggest that an artery to the heart is blocked and that the full thickness of the heart muscle is damaged. The kind of heart attack associated with these findings is referred to as either a Q-wave myocardial infarction or a STEMI (ST-segment elevation myocardial infarction.)

    However, ST segment elevations do not always mean the patient has a heart attack. An inflammation in the sack around the heart (pericarditis) is another cause of ST-segment elevation.

    Non-Elevated ST Segments: Angina and Acute Coronary Syndrome. A depressed or horizontal ST wave suggests some blockage and the presence of heart disease, even if there is no angina present. It occurs in about half of patients with other signs of a heart event. This finding, however, is not very accurate, particularly in women, and can occur without heart problems. In such cases, laboratory tests are needed to determine the extent, if any, of heart damage. In general, one of the following conditions may be present:

    • Stable Angina (blood test results or other tests show no serious problems and chest pain resolves). Between 25 - 50% of people who have angina or silent ischemia have normal ECG readings.
    • Acute Coronary Syndrome (ACS). This includes severe and sudden heart conditions that require aggressive treatment but have not developed into a full-blown heart attack. ACS, refers to either unstable angina or NSTEMI (non ST-segment elevation myocardial infarction) -- also referred to as non Q-wave myocardial infarction. Unstable angina is potentially serious, and chest pain is persistent, but blood tests do not show markers for heart attack. With NSTEMI, the blood tests suggest a heart attack, but most likely, injury to the heart is less serious than with a full-blown STEMI heart attack.


    An echocardiogram is a noninvasive test that uses ultrasound images of the heart. Your doctor can see whether a part of your heart muscle has been damaged and is not moving. An echocardiogram may also be used as part of an exercise stress test, to detect the location and extent of heart muscle damage at the time of discharge or soon after you leave the hospital after a heart attack.

    Radionuclide Imaging (Thallium Stress Test)

    Radionuclide procedures use imaging techniques and computer analyses to plot and detect the passage of radioactive tracers through the region of the heart. Such tracing elements are typically given intravenously. Radionuclide imaging is useful for diagnosing and determining:

    • Severity of unstable angina when less expensive diagnostic approaches are unavailable or unreliable
    • Severity of chronic coronary artery disease
    • Success of surgeries for coronary artery disease
    • Whether a heart attack has occurred
    • The location and extent of heart muscle damage at the time of discharge or soon after you leave the hospital after a heart attack

    The procedure is noninvasive. It is a reliable measure of severe heart events and can help identify if damage has occurred from a heart attack. A radioactive isotope such as thallium (or technetium) is injected into the patient's vein. The radioactive isotope attaches to red blood cells and passes through the heart in the circulating blood. The isotope can then be traced through the heart using special cameras or scanners. The images may be combined with an electrocardiogram. The patient is tested while resting, then tested again during an exercise stress test. If the scan detects damage, more images are taken 3 or 4 hours later. Damage due to a prior heart attack will persist when the heart scan is repeated. Injury caused by angina, however, will have resolved by that time.


    Angiography is an invasive test. It is used for patients who show strong evidence for severe obstruction on stress and other tests and for patients with acute coronary syndrome. In the procedure:

    • A narrow tube is inserted into an artery, usually in the leg or arm, and then threaded up through the body to the coronary arteries.
    • A dye is injected into the tube, and an x-ray records the flow of dye through the arteries.
    • This process provides a map of the coronary circulation, revealing any blocked areas.
    Click the icon to see an image of cardiac catheterization.Click the icon to see an image of dye injected into the coronary arteries.

    Biologic Markers

    When heart cells become damaged, they release different enzymes and other molecules into the bloodstream. Elevated levels of such markers of heart damage in the blood or urine may help predict a heart attack in patients with severe chest pain, and help determine treatment. Tests for these markers are often performed in the emergency room or hospital when a heart attack is suspected. Some markers include:

    • Troponins. The proteins cardiac troponin T and I are released when the heart muscle is damaged. Both are proving to be among the best diagnostic indications of heart attacks. They can help diagnose heart attack and identify patients with ACS who might otherwise be misdiagnosed.
    • Creatine kinase myocardial band (CK-MB). CK-MB has been a standard marker, but the MB fraction is not as accurate as troponin levels, since elevated levels can appear in people without heart injury.