What amount of ST elevation on an electrocardiogram (ECG) is considered significant?

Significant ST Elevation Criteria on ECG

For STEMI diagnosis and reperfusion therapy, ST elevation is significant when measured at the J-point in at least two contiguous leads with the following thresholds: ≥2.5 mm in men <40 years, ≥2 mm in men ≥40 years, or ≥1.5 mm in women in leads V2-V3, and ≥1 mm in all other leads. 1

Standard Criteria by Lead Location

Precordial Leads (V1-V6)

• Men ≥40 years: ≥2 mm (0.2 mV) elevation in V2-V3 1
• Men <40 years: ≥2.5 mm (0.25 mV) elevation in V2-V3 1
• Women (all ages): ≥1.5 mm (0.15 mV) elevation in V2-V3 1
• All other precordial leads (V4-V6): ≥1 mm in all patients 1

The higher threshold in V2-V3 accounts for normal J-point elevation that is physiologically present in these leads, particularly in younger men. 1

Limb Leads (I, II, III, aVF, aVL)

• All patients: ≥1 mm (0.1 mV) elevation in at least two contiguous leads 1
• This applies to inferior leads (II, III, aVF) and lateral leads (I, aVL) 1

Critical Technical Points

Measurement Standards

• ST elevation is measured at the J-point (junction of QRS complex and ST segment) 1
• Standard ECG calibration is 10 mm/mV, so 1 mm = 0.1 mV 1
• Requires elevation in at least two anatomically contiguous leads 1

Contiguous Lead Groupings

• Anterior: V1-V6 (sequential) 1
• Inferior: II, III, aVF 1
• Lateral: I, aVL, V5-V6 1

Special Circumstances Requiring Additional Leads

Right Ventricular Infarction

• Record right precordial leads V3R-V4R in all inferior MI cases 1
• Significant elevation: ≥1 mm in right-sided leads 1
• Identifies concomitant RV infarction with higher risk of complications 1

Posterior MI (Circumflex Territory)

• ST depression ≥0.5 mm in V1-V3 with upright terminal T-waves suggests posterior MI 1
• Confirm with posterior leads V7-V9 showing ≥0.5 mm elevation 1
• These patients qualify for reperfusion therapy as STEMI-equivalents 1
• Research shows circumflex occlusions are frequently missed on standard 12-lead ECG 2

Important Clinical Caveats

Non-Diagnostic ST Elevation (<1 mm)

• ST elevation <1 mm in limb leads or <2 mm in precordial leads is considered non-specific 1
• These changes are less reliable and often seen in patients without acute coronary syndrome 1
• However, do not exclude ACS—repeat ECGs and monitor for dynamic changes 1

Confounding Patterns to Exclude

Before diagnosing STEMI, consider alternative causes of ST elevation: 1

• Left ventricular hypertrophy (LVH) with strain pattern
• Left bundle branch block (LBBB)—use modified Sgarbossa criteria if present 3
• Pacemaker rhythm—may prevent ST interpretation 1
• Left ventricular aneurysm—most commonly misdiagnosed as acute MI 4
• Benign early repolarization—second most commonly misdiagnosed 4
• Pericarditis, Takotsubo cardiomyopathy, Prinzmetal's angina 1

Dynamic ECG Changes

• Hyperacute T-waves may precede ST elevation in very early presentation 1
• Serial ECGs are essential if initial tracing is equivocal 1
• Approximately 5% of patients with normal ECGs ultimately have MI 1
• A completely normal ECG during chest pain should prompt consideration of alternative diagnoses 1

Prognostic Implications

ST Depression Patterns

• ST depression >1 mm in two contiguous leads indicates high-risk unstable angina or NSTEMI 1
• Do not give fibrinolytics for isolated ST depression (increased mortality risk) unless posterior MI suspected 1
• Deep symmetrical T-wave inversion in anterior leads suggests proximal LAD stenosis 1

Extent of ST Elevation

Research demonstrates a gradient of risk based on ECG abnormality severity, with ST elevation carrying higher mortality than ST depression or T-wave changes alone. 1 The amount and distribution of ST elevation correlates with infarct size. 2