Review Question - QID 210646

This patient is presenting with multiple risk factors for myocardial infarction (diabetes, dyslipidemia, and recent myocardial infarction (MI) requiring percutaneous coronary intervention) and squeezing/substernal chest pain suggesting a diagnosis of a MI. The best diagnostic test for an MI within 10 days of a previous MI is a creatine kinase-muscle/brain (CK-MB) level.

When ischemia damages cardiac tissues, cardiac enzymes leak out and these markers are detected in the blood. The most specific enzyme for diagnosis are cardiac troponins, and they should be used to confirm the diagnosis in most cases. However, this enzyme stays elevated in the blood for up to 10 days, thus it cannot be used to diagnose another infarction that occurs within this time frame. Instead, the diagnosis can be confirmed/further supported with a CK-MB level which is a less specific enzyme that stays elevated for roughly only 2 days thus making it the test of choice for diagnosing a repeat infarction.

Incorrect Answers:
Answer 1: Angiography is the most accurate test and would be obtained after an ECG was performed and a CK-MB level was ordered.

Answer 2: Cardiac troponins (a single set) would not be useful in this situation since they are likely still elevated due to the previous/recent MI. However, serial troponins demonstrating a 20% increase from the first set could be used to diagnose a reinfarction.

Answer 4: Myoglobin rises most rapidly after a MI occurs; however, it is not particularly specific when it comes to making the diagnosis.

Answer 5: Stress testing would not be indicated in this patient who already has clear symptoms of ischemic pain at rest.

Bullet Summary:
A creatine kinase-muscle/brain (CK-MB) can be used to diagnose repeat myocardial infarctions that occur within 10 days of another infarction.