Myocardial ischemia may be caused by the partial or complete blockage of a blood vessel or by a narrowed or constricted blood vessel. A blockage can decrease or prevent blood flow to the heart. It can cause a heart attack (myocardial infarction, MI) and permanently damage or kill heart muscle cells.
Temporary myocardial ischemia may be seen with angina, an episodic condition associated with the gradual narrowing of one or more blood vessels and with arterial spasms. Angina is triggered when the body cannot respond adequately to increased oxygen demands, and it usually resolves with rest. In some cases, angina can become unstable, occurring at rest or becoming more severe, and can escalate to cause a heart attack. Both unstable angina and MI are collectively known as acute coronary syndrome (ACS). Symptoms vary but may include chest pain and pressure that occurs at rest or persists despite rest, shoulder pain, neck pain, nausea, and shortness of breath.
People with these symptoms are typically evaluated in the emergency room. There, the doctor must try to rapidly differentiate ACS from other conditions with similar presentations and try to distinguish between the various causes of ACS. To do this, he may order cardiac biomarkers, tests such as troponin and myoglobin, to detect damage to the heart, and an electrocardiogram (ECG) to look for heart damage. If these tests are clearly abnormal, then the person is started on treatment for MI.
If the tests are not definitive, then determining whether someone is experiencing temporary angina, is at a significant risk of having a heart attack in the near future, or if they can be safely sent home can be a challenge. Researchers are looking for tests that can help guide the doctor's decision-making in this situation. The ischemia-modified albumin test is a potential candidate for this role.
How is the sample collected for testing?A blood sample is obtained by inserting a needle into a vein in the arm.
Is any test preparation needed to ensure the quality of the sample?No test preparation is needed.
How is it used?Ischemia-modified albumin (IMA) is a fairly new test that has been FDA approved to help rule out cardiac ischemia in people with chest pain whose diagnosis is not clear. It is a cardiac biomarker that is meant to be ordered along with or following a troponin test and an ECG.
If the troponin test, which may take several hours to start to increase after an MI, is negative and the ECG is not definitive, then the ischemia-modified albumin test may add valuable information about whether cardiac ischemia is occurring. IMA may be ordered along with a myoglobin test in the first few hours of chest pain to try to stratify the person's risk of having a heart attack in the near future.
When is it ordered?
What does the test result mean?Ischemia-modified albumin is a marker of decreased oxygen availability. Studies have shown IMA to be sensitive for ischemia but not very specific, which means that it can be elevated with ischemia in other areas of the body. Its primary value is in its negative predictive value.
When IMA is not present in a person who has been having chest pain for a few minutes to a few hours, then it is unlikely that ischemia has occurred. When IMA and myoglobin are negative, an ECG is normal, and a troponin is negative at initial and repeat testing, then it is unlikely that the person's chest pain has or will result in a heart attack in the near future.
If someone has been experiencing chest pains for several hours, then the IMA test may not be as valuable because it may have already risen and fallen back to normal or near normal levels by the time the blood sample is collected.
Is there anything else I should know?Research and current studies are evaluating whether a significantly elevated IMA may be useful as a positive indicator that myocardial ischemia is occurring. Increases in IMA have also been seen with ischemia that is occurring in other parts of the body, such as the skeletal muscles and gastrointestinal tract.
The IMA test is not widely used at present. Although it is regarded as a promising cardiac biomarker, its ultimate clinical utility has yet to be determined. Many physicians are adopting a wait-and-see attitude. They want to see more data accumulated on its use and on the factors, such as underlying diseases and decreased albumin levels, that may affect or interfere with its interpretation.
Can an IMA test be done in a doctor's office?No, the test must be run with specialized equipment. In most cases, the IMA test is ordered when a person is being evaluated for chest pain in the Emergency Room.
If a person has not had a heart attack, why are they still considered at risk?