Heart Attack and Acute Coronary Syndrome

Description

Alternative Names

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 professional can rule out either a non-heart problem or possible other serious accompany conditions.
• An electrocardiogram (ECG) reading is taken, which records the waves made 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 physician 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 as follows:

• 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 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.

Physicians will 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. When this finding coincides with a heart attack, the condition is sometimes referred to as either as a Q-wave myocardial infarction or a STEMI (ST-segment elevation myocardial infarction). ST-elevations are strong indicators for aggressive treatments (thrombolytic drugs or angioplasty) to reopen blood vessels. (ST segment elevations do not always mean the patient has a heart attack. Also some heart attack patients do not have elevated ST segments. Other factors are important in making a diagnosis.)

Non-Elevated ST Segments: Angina and Acute Coronary Syndrome. A depressed or horizontal ST wave suggests some blockage and the presence of a 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). Most patients with angina can go home. (It should be noted that between 25% and 50% of people who suffer from angina or have 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 developing heart attack, but most likely, injury in the arteries is less serious than with a full-blown heart attack.

Exercise Stress Test

The primary value of exercise stress tests is not to detect coronary artery disease in people without symptoms but to help determine the severity and predict the outcome of an existing heart condition. It is considered for the following people:

• Patients with possible or probable angina and low or intermediate risk for adverse heart events.
• Selected adults who do not have symptoms of heart disease but are at moderate risk to high risk for developing heart disease (a 10% to 20% chance within ten years). In fact, heart blockage without angina (silent ischemia) may suggest a more severe condition, at least in men.

Basic Procedure. A stress test (exercise tolerance test) monitors the patient's heart rhythms, blood pressure, and clinical status. It can tell how well the heart handles work and if parts of the heart have decreased blood supply. A typical stress test involves the following:

• The patient walks on a treadmill or rides a stationary bicycle. Exercise continues until the heart is beating at least 85% of its maximum rate, until symptoms of heart trouble occur (e.g., changes in blood pressure, heart rhythm abnormalities, angina, fatigue) or the patient simply wants to stop.
• For patients who cannot exercise, the physician may administer dobutamine or arbutamine, which are agents that simulate the stress of exercise.
• An ECG is used to monitor heart rhythms during a stress test. (An echocardiogram or more advanced imaging technique may also be used to visualize the actions of the heart and blood flow.)

More than 25% of patients stop exercising before they reach their own maximum limits because of fear of a heart event. Patients should be reassured that the activities performed in the test under the guidance of a professional are safe.

[For more information on this test, see the Well-Connected Report #3 Coronary Artery Disease and Angina.]

Echocardiograms

An echocardiogram is a noninvasive test that uses ultrasound images of the heart. This test is more expensive than an ECG, but it can be very valuable, particularly when used with a stress test, to detect the location and extent of heart muscle damage.

Radionuclide Imaging

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 the following situations:

• To diagnose or determine the severity of unstable angina when less expensive diagnostic approaches are unavailable or unreliable.
• To determine the severity of chronic coronary artery disease.
• To assess the success of surgeries for coronary artery disease.
• To diagnose a heart attack.

Various imaging techniques may be used with radionuclide procedures, including the following:

• Planar scintigraphy. This uses a special overhead camera and is the oldest scanning technique.
• Single-photon emission computed tomography (SPECT) uses a camera that rotates around the patient and takes pictures of "slices" of the heart.
• Positron-emission tomographic (PET) scanners employ multiple rings that surround the patients, which detect and record atomic particles (photons) that are emitted by the tracer elements (such as radioactive oxygen, nitrogen, or carbon). It is more expensive and less widely available than SPECT.

Myocardial Perfusion (Blood Flow) Imaging Test (also called the Thallium Stress Test). This radionuclide test is typically used with an exercise stress test to determine blood flow to the heart muscles. It is a reliable measure of severe heart events and may prove to be cost effective in identifying patients at low risk for a heart attack. About a minute before the patient is ready to stop exercising, the physician administers thallium 201 (or more often now, sestamibi), a radioactive tracer, into the intravenous line. Immediately afterward the patient lies down and heart scans are performed, usually with a planar scintigraphy or with SPECT. If the scan detects damage, more images are taken three or four 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.

Radionuclide Angiography. This is a technique for visualizing the chambers and major blood vessels of the heart. It uses an injected radioactive tracer and can be performed during exercise, at rest, or with use of stress-inducing drugs. It is an excellent test for assessing the heart's pumping action both at rest and during exercise and for determining the severity of coronary artery disease. It is an alternative to echocardiograms in certain situations.

Advanced Noninvasive Imaging Techniques

Magnetic Resonance Angiography (MRA). MRA is a very promising noninvasive imaging technique that can provide three-dimensional images of the major arteries to the heart and identify disease with high accuracy. Experts believe this approach will eventually be a good alternative to angiography.

Click the icon to see an image of a MRI.

Computed Tomography (CT) Scans.Computed tomography (CT) scans used alone or with ECG may be used to detect calcium deposits on the arterial walls, strong indicators of current and future coronary artery disease. In fact, the absence of calcification in the arteries suggests virtually no risk at all for heart disease. (It should be noted that the presence of calcium does not always signify significant narrowing in the arteries.) Advanced CT techniques, such as electron beam computed tomography (EBCT) and helical multislice computed tomography (MSCT) are improving accuracy.

Some experts groups recommend them in selected patients who have an intermediate risk (i.e., a 10% to 20% chance of heart disease within 10 years). In general, the use of these expensive imaging tests are probably not very useful in people at low- or high risk people.

Angiography

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.

• 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.

Major complications include stroke, heart attacks, and kidney damage. These risks are very low (about 0.1%), however, if the procedure is done in an experienced medical center (one that performs at least 300 of these operations every year). Allergic reactions can also occur. The procedure is expensive, and between 10% to 30% of patients who have this procedure have normal results.

Biologic Markers

When heart cells become damaged, they release different enzymes and other molecules into the blood stream. 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. Some of these factors currently measured include the following:

• 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 are proving to identify many individuals with ACS, such as older women with serious other conditions, who might otherwise been 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.
• Myoglobin. Myoglobin is a protein found in heart muscles. It is released early in the injured heart and it may be useful in combination with CK-MB and the troponins.
• Other markers are proving to be helpful in identifying heart problems but are not routinely measured at this time except in clinical studies. They include fibrinogen (a protein involved in blood clotting) and C-reactive protein (a product of the inflammatory process). For example, persistently high levels of C-reactive protein in patients with unstable angina may be strong indicators of a future heart attack.