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A 56-year-old white male is recovering well from his acute anterior wall MI that was treated with thrombolytic therapy 4 days ago. On day 4 of his hospitalization, he develops new chest pain that is similar to his previous pain of myocardial infarction in severity, radiation and character. The pain is not relieved by sublingual nitroglycerin. He is hemodynamically stable. His lung fields are clear and heart sounds are normal. EKG shows hyperacute T waves and new ST segment elevation in leads V1, V2, and V3. He is suspected to have re-infarcted. Which of the following biomarkers of cardiac injury can establish the diagnosis of re-infarction in this setting?
A. Cardiac troponin T
B. Cardiac troponin I
C. LDH
D. CK-MB
E. Myoglobin
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yes, D, a Goljan well-taught topic !
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yeah reinfarctions
ck-mb
d..........
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CK-MB fraction has a high specificity for an acute MI (slightly lower than cardiac troponins). It begins to rise within 4-6 hours after MI and returns to baseline within 48-72 hours. It™s high specificity and rapid return to the baseline makes it the biomarker of choice for the diagnosis of a recurrent MI.
Cardiac troponins T and cardiac troponins I are proteins that control the interaction of actin and myosin. They are more specific than all the other biomarkers of cardiac injury being used for the diagnosis of MI. They begin to rise 4-6 hours after an MI, and remain elevated for 10 days. They have now become the primary biochemical tests used for the diagnosis of acute MI. They have also replaced LDH for the retrospective diagnosis of MI. But because of their persistent elevation for 10 days after an MI, they can™t be used to establish the diagnosis of re-infarction within 1-2 weeks after an MI.
LDH is present in cardiac muscle and other tissues like red cells, kidney, liver, and skeletal muscle. It begins to rise within 4-6 hours, reaches its peak in 24-48 hours and remains elevated for 6-7 days. Because of its low specificity and persistent elevation, it is not useful for the diagnosis of a re-infarction. It has also been replaced by cardiac troponins for the retrospective diagnosis of MIs as it lacks specificity.
Myoglobin is a heme-protein found in many tissues. It has a rapid rise and return to the baseline after an acute MI. It can be used to detect recurrent injury but because of lack of specificity, CK-MB is a better choice.
Educational Objective:
Emphasize the importance of CK-MB for the diagnosis of recurrent myocardial infarction
