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.
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; will be elevated within a few hours of heart damage and remain elevated for up to two weeks. A series of troponin tests is typically performed over several hours. A rise and/or fall in the series of results indicates a heart attack.
- 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.
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.
One or more of these 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 these cardiac biomarkers 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.
Other more general screening tests may also be ordered to help evaluate the person's major body organs, electrolyte balance, blood sugar, and red and white blood cells to see whether there are any excesses, deficiencies, or dysfunctions that may be causing or exacerbating 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 sugar, and blood proteins.
- Complete Blood Count – a test used to determine a person's general health status and to screen for a variety of disorders.
A range of non-laboratory evaluations and tests are used to assess chest pain and other symptoms. These include:
- A medical history, including an evaluation of risk factors such as age, 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 show 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?