Anatomy - STEMI vs. non-STEMI

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It is important to distinguish between STEMI and non-STEMI because these two types of myocardial infarction have different treatments.

STEMI is characterized by the presence of ST deviation in two or more contiguous ECG leads. The presence of ST elevation in specific leads localizes the area of the myocardium at risk and aids in identifying which patients are candidates for coronary revascularization (PTCA or thrombolysis).

In some cases myocardial infarction manifests in the ECG leads as ST-depression and not ST elevation. In these cases, it is more appropriate to use the term “ST deviation myocardial infarction” rather than STEMI. Examples include:

  • Occlusion in the left main coronary artery before its bifurcation which presents with ST depression in most limb leads (and ST elevation in aVR)
  • RCx stenosis in a left dominant system
  • Posterior infarct which presents with ST depression in the anterior leads

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