The Concept Behind ST Segment Depression in SubEndocardial Infarction - USMLE Forums
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Old 05-04-2011
qurat21's Avatar
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EKG The Concept Behind ST Segment Depression in SubEndocardial Infarction

I don't understand the concept of ST segment depression in sub-endocardial MI and ST segment elevation in transmural MI. can anyone help?
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Old 05-04-2011
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In case of subendocardial infarct the sub endocardial tissue is injured while the epicardial tissue is normal. As the injured tissue attains negative charge the direction vector would go from positive epicardium to negative endocardium. i.e away from the electrode.So we get a negative period and hence ST segment depression

In transmural infarct the entire area of myocardium because injured leading to negativity..So direction vector then goes from adjacent positive (normal) tissue to the damaged tissue.i.e. towards the surface electrode..Hence a positive period which corresponds to St segment elevation.

Hope this helps.
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Old 05-04-2011
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Probably this can help
Origin of QRS complex on ECG!

Also StepTaker talked about this issue here
ST changes in MI
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Cardiovascular-, Physiology-

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