ST-Segment Elevation Myocardial Infarction (STEMI) Diagnosis

Definition and Criteria

The European Society of Cardiology and American College of Cardiology define significant ST elevation as ≥2 mm (0.2 mV) in men or ≥1.5 mm (0.15 mV) in women in leads V2-V3, and/or ≥1 mm (0.1 mV) in other contiguous chest leads or limb leads, occurring in at least 2 contiguous leads 1, 2
Significant ST elevation varies based on specific factors, including leads V2-V3, where men ≥40 years should have ≥2 mm (0.2 mV), men <40 years should have ≥2.5 mm (0.25 mV), and women should have ≥1.5 mm (0.15 mV) 1, 2
Other chest leads (V1, V4-V6) and limb leads (I, II, III, aVL, aVF) require ≥1 mm (0.1 mV) for significant ST elevation 1, 2
Posterior leads (V7-V9) require ≥0.5 mm for significant ST elevation, suggesting posterior (inferobasal) MI 1, 2
Right ventricular leads (V3R-V6R) with ≥1 mm ST elevation indicate right ventricular involvement, especially in inferior MI 3

ST elevation should be measured at the J-point (where the QRS complex ends and the ST segment begins) 1, 4
ST elevation must be present in at least two contiguous leads to be considered significant 1, 4
The elevation should be new or presumed new, and comparison with previous ECGs is valuable when available 5, 6
ST elevation should be persistent rather than transient 6
A normal ECG does not exclude acute coronary syndrome (ACS), with approximately 5% of patients with normal ECGs ultimately found to have acute myocardial infarction or unstable angina 5, 6

New or presumably new Left Bundle Branch Block (LBBB) is no longer considered a standalone STEMI equivalent due to its infrequent occurrence and potential to interfere with ST-elevation analysis 4, 2
ST depression >1 mm in two or more contiguous leads can indicate non-ST elevation ACS and should not be overlooked 5, 6
Conditions that can mimic STEMI ECG patterns include Brugada syndrome 4
ST depression in leads V1-V3 may represent posterior wall MI and should prompt consideration of additional posterior leads (V7-V9) 1, 7

Compare with previous ECGs when available 5, 6
Perform serial ECGs at 10-minute intervals during the first hour if clinical suspicion is high but initial ECG is non-diagnostic 7
Consider additional leads (right-sided and posterior) in appropriate clinical scenarios 1, 7, 2, 3
The diagnosis of STEMI requires both appropriate ECG findings and a clinical presentation consistent with acute myocardial ischemia, according to the American College of Emergency Physicians 8
ST elevation criteria are most useful when applied in the appropriate clinical context, as they help identify patients who would benefit from urgent reperfusion therapy, as stated by the American College of Emergency Physicians 8