What are the ST elevation criteria to diagnose Acute Coronary Syndrome (ACS) in a patient with suspected myocardial ischemia?

ST Elevation Criteria to Diagnose ACS

For STEMI diagnosis, you need new or presumed new ST-elevation ≥1 mm in ≥2 anatomically contiguous leads on a 12-lead ECG, with higher thresholds for leads V2-V3: ≥2 mm in men ≥40 years, ≥2.5 mm in men <40 years, and ≥1.5 mm in women regardless of age. 1, 2

Standard STEMI Electrocardiographic Criteria

The diagnostic threshold varies by lead location and patient demographics:

For all leads except V2-V3:

• ST-elevation ≥1 mm (0.1 mV) in ≥2 anatomically contiguous leads 1, 2

For leads V2-V3 (age and sex-specific):

• Men ≥40 years: ST-elevation ≥2 mm 1, 2
• Men <40 years: ST-elevation ≥2.5 mm 1, 2
• Women (all ages): ST-elevation ≥1.5 mm 1, 2

Measurement technique:

• Measure ST-elevation at the J-point (junction between QRS complex and ST segment) 1, 2
• ST-elevation must be present in at least 2 contiguous leads that represent the same anatomical territory 1, 2

Critical Timing Requirements

The 12-lead ECG must be obtained and interpreted within 10 minutes of first medical contact to identify STEMI patients requiring immediate reperfusion. 1, 2, 3 This rapid acquisition is associated with shorter reperfusion times and lower mortality rates. 1

Once STEMI is identified, immediate EMS transport to a PCI-capable hospital with early advance notification and cardiac catheterization team activation is required, targeting a first medical contact-to-device time ≤90 minutes. 1, 2

Additional ECG Patterns Requiring STEMI Activation

Posterior wall myocardial infarction:

• Obtain posterior leads V7-V9 when you see isolated ST-segment depression ≥0.5 mm in leads V1-V3, particularly with suspected left circumflex occlusion 1, 2
• ST-elevation ≥0.5 mm in posterior leads V7-V9 confirms posterior STEMI 1

Hyperacute T waves:

• Ongoing chest pain with hyperacute T waves (tall, peaked T waves) in a territorial distribution requires immediate STEMI protocol activation and emergency coronary angiography, even before ST-elevation develops 2

Non-ST-Elevation ACS Electrocardiographic Patterns

Patients without persistent ST-elevation may still have ACS (NSTE-ACS), with the following ECG findings:

• New or dynamic horizontal or down-sloping ST-segment depression ≥0.5 mm in ≥2 contiguous leads 1
• T-wave inversion >1 mm in ≥2 contiguous leads with prominent R wave or R/S ratio >1 1
• Transient ST-segment elevation (lasting <20 minutes) 1
• Flat T waves or pseudo-normalization of T waves 1
• Normal ECG (does not exclude ACS) 1

Many patients with NSTE-ACS have either nonspecific ST-segment or T-wave changes or a completely normal ECG—the absence of electrocardiographic evidence of ischemia does not exclude ACS. 1

Critical Pitfalls and Caveats

New left bundle branch block (LBBB) is NOT diagnostic of acute MI in isolation:

• A new or presumably new LBBB at presentation occurs infrequently and should NOT be considered diagnostic of STEMI without clinical correlation 1, 2
• A new LBBB in an asymptomatic patient does not constitute a STEMI equivalent 1

ST-segment elevation mimics that should NOT trigger STEMI activation without appropriate clinical context:

• Acute pericarditis 1, 2
• Left ventricular hypertrophy with strain pattern 1, 2
• Brugada syndrome 1, 2
• Right ventricular pacing 1, 2
• Takotsubo syndrome 1, 2
• Early repolarization 1, 2

Serial ECG Monitoring

When the initial ECG is nondiagnostic of STEMI but clinical suspicion remains high, perform serial ECGs to detect potential ischemic changes, especially when symptoms persist or the clinical condition deteriorates. 1 Repeat ECGs should be obtained if symptoms change or if troponins become positive. 1

Practical Algorithm for STEMI Activation

1. Obtain 12-lead ECG within 10 minutes of patient contact 1, 2, 3

2. Measure ST-elevation at the J-point in all leads 2

3. Apply sex- and age-specific criteria for V2-V3 leads 1, 2

4. If isolated ST-depression in V1-V3, obtain posterior leads V7-V9 1, 2

5. Activate catheterization laboratory immediately when STEMI criteria are met with compatible symptoms 2

6. Target door-to-balloon time ≤90 minutes for primary PCI 1, 2

The strength of this recommendation is based on the most recent 2025 ACC/AHA/ACEP/NAEMSP/SCAI guideline, which provides the most current and authoritative criteria for STEMI diagnosis and management. 1 These criteria are consistent across major international guidelines, including the 2021 ACC/AHA chest pain guideline 1 and the 2015 ESC guidelines. 1