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Heart attack and acute coronary syndrome

Description

An in-depth report on the causes, diagnosis, treatment, and prevention of heart attack.

Alternative Names

Acute coronary syndrome; Myocardial infarction

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 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 two major pumping chambers in the heart.)
• T and U. These waves follow the ventricular contractions.

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. 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). STEMI heart attacks are very severe and usually have complete artery blockage. 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 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. (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 developing heart attack, but most likely, injury in the arteries is less serious than with a full-blown heart attack.

Echocardiogram

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 an exercise stress test, to detect the location and extent of heart muscle damage.

Nuclear Ventriculography (Thallium Stress Test)

Nuclear ventriculography (also known as a radionuclide test) uses radioactive materials called tracers to make heart chambers and blood vessels visible. 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

Angiography, also known as cardiac catheterization, 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.

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 - 30% of patients who have this procedure have normal results.

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.

Kidney Tests

Tests that measure kidney function can help predict which patients are at greatest risk of heart attack, stroke, or death from heart disease. Kidney tests measure proteins in the blood that are filtered through the kidneys. These proteins include creatinine and blood urea nitrogen (BUN). A more recent type of kidney test measures the protein cystatin C. Recent research suggests that the cystatin C kidney test may be better at predicting cardiovascular risks in elderly patients.

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 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 help identify many individuals with ACS, such as older women with other serious conditions that might otherwise have 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 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.

• Review Date: 4/15/2006
• Reviewed By: Harvey Simon, M.D., Editor-in-Chief, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital

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