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NBME 20 Answers

nbme20/Block 2/Question#18

A 65-year-old man is brought to the emergency ...

ST-segment elevation

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submitted by hayayah(603),

This man is showing sxs of an MI.

Initial phase of myocardial infarction leads to subendocardial necrosis involving < 50% of the myocardial thickness (subendocardial infarction); EKG shows ST-segment depression.

Continued or severe ischemia (>20 minutes) leads to transmural necrosis involving most of the myocardial wall (transmural infarction); EKG shows ST-segment elevation.

charcot_bouchard  May i know where do u read this +1  
mbourne  @hayayah, Although this is a bit outside of the realm of Step 1, I want to clarify a point. Early MI does not typically lead to ST-depression. Early MI will typically present with hyperacute T-waves with straightening of the ST segment, and then evolve towards more familiar "STEMI" morphology. Great image representation of MI EKG changes: https://4.bp.blogspot.com/-_UbS4PvbTZE/Wr0M27TZhUI/AAAAAAAABB0/-M8FSuvTKeEGkx-7HrEd45Fl0phb2-T8gCLcBGAs/s1600/Progression%2Bof%2BACO%2Bfinal_diagram.png ST depression from subendocardial ischemia can occur with supply/demand mismatch --> ISCHEMIA, but not Myocardial INFARCTION. +  

ST will first decrease; however, after 20 min it will increase (elevate)