A patient is suspected of having a myocardial infarction. The nurse assesses for elevations in which of the following isoenzyme values reported with the creatine kinase level?

Appeared in: JODHPUR AIIMS SNO-2018

Explanation

The question asks to identify the specific creatine kinase (CK) isoenzyme that elevates during a myocardial infarction (MI).
The correct isoenzyme is MB (CK-MB), as it is found predominantly in the heart muscle (myocardium).
When the heart muscle is damaged during an MI, it releases CK-MB into the bloodstream, causing its levels to rise.
CK-MB levels typically start to rise 4-6 hours after the onset of chest pain, peak within 18-24 hours, and return to baseline in 48-72 hours, making it a key diagnostic marker.

Option B: The BB isoenzyme (CK-BB) is primarily found in the brain and lung tissue. Its elevation is not associated with cardiac muscle damage.
Option C: The MM isoenzyme (CK-MM) is the most abundant type and is found in skeletal muscle. While it makes up a small percentage of the CK in heart muscle, its elevation is not specific to myocardial infarction.
Option D: MK stands for mitochondrial creatine kinase (Mi-CK). While present in heart muscle cells, it is not routinely measured in clinical practice for the diagnosis of acute MI. CK-MB and troponins are the standard markers.

Clinical Relevance

Nursing practice connection: Use the key finding related to Cardiac Biomarkers for Myocardial Infarction to guide bedside assessment, documentation, and the next nursing action.
Prompt identification of elevated CK-MB (along with troponins) is critical in the emergency department to confirm a diagnosis of MI and initiate timely reperfusion therapy (like angioplasty or thrombolytics) to save heart muscle.
Nurses play a key role in ensuring that blood samples for cardiac markers are drawn at the correct time intervals (e.g., on admission, and then serially every 6-8 hours) to track the rise and fall of these enzymes, which helps in diagnosis and prognosis.
What if? If a patient with chest pain has elevated CK-MM but normal CK-MB and troponin levels, the nurse should suspect a non-cardiac cause for the pain, such as a skeletal muscle injury, and assess the patient accordingly.

How to Approach the Question

First, identify the core of the question. It's asking about a specific laboratory value (a CK isoenzyme) related to a specific condition (myocardial infarction).
Recall the different types of creatine kinase isoenzymes and their primary locations in the body.
Associate each isoenzyme with the tissue it primarily represents: MM for skeletal Muscle, BB for Brain, and MB for Myocardium (heart muscle).
Based on this association, conclude that CK-MB is the specific marker for myocardial damage.
Evaluate the other options to confirm they are incorrect. CK-BB relates to the brain, CK-MM to skeletal muscle, and MK is not a standard diagnostic marker for MI.

Concept Tested & Keywords

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E6 PATHOLOGY QUICK REVIEWBased on Harsh Mohan Textbook of PATHOLOGY p. 196-198

E6 Textbook of Biochemistry for medical StudentsDM Vasudevan Part 2 — Subpart A (pp 1-239 of 478) p. 50-52

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