What are the high-, intermediate-, and low-probability ECG features of myocardial infarction (MI, heart attack)?

Updated: May 07, 2019
  • Author: A Maziar Zafari, MD, PhD, FACC, FAHA; Chief Editor: Eric H Yang, MD  more...
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High-probability ECG features of MI are the following:

  • ST-segment elevation greater than 1 mm in two anatomically contiguous leads
  • The presence of new Q waves

Intermediate-probability ECG features of MI are the following:

  • ST-segment depression
  • T-wave inversion
  • Other nonspecific ST-T wave abnormalities

Low-probability ECG features of MI are normal ECG findings. However, normal or nonspecific findings on ECGs do not exclude the possibility of MI.

Special attention should be made if there is diffuse ST depression in the precordial and extremity leads associated with more than 1 mm ST elevation in lead aVR, as this may indicate stenosis of the left main coronary artery or the proximal section of the left anterior descending coronary artery. [2, 4, 41]

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