What are the ST elevation criteria for myocardial infarction (MI)?

ST Elevation Criteria for Myocardial Infarction

ST-segment elevation (measured at the J-point) is considered diagnostic of myocardial infarction when there are at least two contiguous leads with ST-segment elevation of ≥2.5 mm in men <40 years, ≥2 mm in men ≥40 years, or ≥1.5 mm in women in leads V2-V3 and/or ≥1 mm in all other leads. 1

Standard ST Elevation Criteria

• ST elevation should be measured at the J-point (where the QRS complex meets the ST segment) 1
• Standard calibration of ECG is 10mm/mV, so 0.1 mV equals 1 mm on the vertical axis 1
• ST elevation must be present in at least two contiguous leads 1
• Lead-specific ST elevation thresholds:
  • Precordial leads V2-V3:
    • ≥2.5 mm (0.25 mV) in men under 40 years 1
    • ≥2 mm (0.2 mV) in men 40 years and older 1
    • ≥1.5 mm (0.15 mV) in women 1
  • All other leads (including limb leads and remaining precordial leads):
    • ≥1 mm (0.1 mV) 1

Special Considerations

• For inferior MI, it is recommended to record right precordial leads (V3R and V4R) to identify concomitant right ventricular infarction 1
• For suspected posterior MI:
  • ST depression in leads V1-V3 may indicate posterior MI, especially when the terminal T-wave is positive (ST elevation equivalent) 1
  • Confirmation by ST elevation ≥0.5 mm in posterior leads V7-V9 should be considered 1
• Isolated posterior MI may present with ST depression ≥0.5 mm in leads V1-V3 as the dominant finding and should be managed as a STEMI 1

Important Caveats and Pitfalls

• Left bundle branch block (LBBB) may interfere with ST-segment analysis and should not be considered diagnostic of acute MI in isolation 1

  • The 2013 ACCF/AHA guidelines removed new LBBB as a STEMI equivalent due to its infrequent occurrence 1
  • Modified Sgarbossa criteria may help identify STEMI in the presence of LBBB 2

• Non-diagnostic ECGs:

  • Some patients with acute coronary occlusion may present without diagnostic ST elevation 1
  • Early presentation may show hyperacute T-waves before ST elevation develops 1
  • Occlusion of the circumflex coronary artery, vein graft, or left main disease may present without classic ST elevation 1

• ST elevation in lead aVR with multilead ST depression was previously thought to indicate left main or proximal LAD occlusion, but recent research shows acute coronary occlusion in only 10% of such cases 3

• Subtle ST elevation in inferior leads that doesn't meet the 1 mm threshold may still represent occlusion MI, especially when accompanied by ST depression in lead aVL 4

Clinical Application

• When STEMI is suspected, a 12-lead ECG must be acquired and interpreted as soon as possible to facilitate early diagnosis and triage 1
• If the initial ECG is equivocal but clinical suspicion remains high, serial ECGs should be performed to detect dynamic changes 1
• The sensitivity of standard ECG for diagnosing MI can be increased by using additional leads (right precordial and posterior leads) in specific clinical scenarios 5
• In patients with suspected posterior MI, extending the standard 12-lead ECG with leads V7-V9 may identify patients who would otherwise be missed 1

Remember that these criteria are meant to guide reperfusion therapy decisions, and clinical judgment remains essential, particularly in cases with atypical presentations or non-diagnostic ECGs with high clinical suspicion for acute coronary occlusion 1.