A myocardial infarction (heart attack) occurs when a patient’s heart does not receive enough oxygen, causing heart muscle to die. Although many causes can reduce oxygen delivery to the heart, the death of heart muscle (myocardial necrosis) usually occurs due to a blockage of a blood vessel to the heart. The dead heart muscle releases many different chemicals into the blood, and doctors often order blood tests on patients with chest pain in order to look for these chemicals to substantiate the diagnosis of a heart attack. Finding these chemicals helps a physician to diagnose a patient with a heart attack, and start appropriate treatment. But, not all the chemicals released my dead heart muscle are the same, there are different chemicals, each with distinct properties.
Myoglobin
Myoglobin is released by dead heart muscle soon after a heart attack, but it is also released by many other dead cells. This means that a doctor in the emergency department has a difficult time interpreting this test because so many different things can produce an abnormal result. Doctors do not often use this test in diagnosing myocardial infarctions because of the lack of clear information offered by an elevated myoglobin. A myoglobin/ carbonic anhydrase III ratio makes this test more specific, but this ratio is not often readily available.
Creatine-Kinase
Creatine-kinase (CK) is another chemical located within the heart that is released by dead heart muscle. CK is also released by other types of dead tissue, but there are different subtypes of creatine-kinase that are only released from specific types of tissue. Creatine-kinase subtype MB (CK-MB) is only released from dead heart muscle and is useful in diagnosing heart attacks. The amount in a patient’s blood increases about 4 hours after a heart attack, peaks at 18-24 hours, and then it starts to disappear from the blood. This means that a patient with a heart attack may have levels too low to diagnose a heart attack when measured less that four hours after the event. This test is even better for diagnosing a heart attack when it is measured in a patient’s blood every few hours for a full day.
Troponin I
Troponin I is only released from dead heart muscle and reaches a detectable level in a patient’s blood 3-6 hours after a heart attack, and stays elevated for 14 days. This means it elevates quicker than CK-MB after a heart attack and stays elevated longer also! This makes it a more valuable test in the diagnosis of a heart attack than CK-MB.
All of these chemicals are invaluable in the diagnosis and treatment of a myocardial infarction. Scientist are currently working on even better test for use in the diagnosis of a heart attack. The ideal test will look for a chemical that is only released from heart muscle, is released immediately and stays elevated for a long time after a heart attack.