What do example ECGs (electrocardiograms) of STEMI (ST-Elevation Myocardial Infarction) look like?

STEMI ECG Examples and Characteristics

STEMI ECGs demonstrate ST-segment elevation ≥1 mm in ≥2 contiguous leads, with specific voltage criteria in precordial leads V2-V3: ≥2.5 mm in men <40 years, ≥2 mm in men ≥40 years, and ≥1.5 mm in women. 1

Classic STEMI Patterns by Location

Anterior STEMI (LAD Occlusion)

• ST-segment elevation centered on leads V1-V4, with involvement of leads I and aVL 1
• Precordial leads show progressive ST elevation, typically maximal in V2-V3 1
• May present with reciprocal ST depression in inferior leads 1

Inferior STEMI

• ST-segment elevation ≥1 mm in leads II, III, and aVF 1
• Should prompt recording of right precordial leads (V3R-V4R) to identify concomitant right ventricular infarction 1
• Reciprocal ST depression often visible in anterior leads 1

Posterior STEMI (Often Missed)

• Isolated ST-depression ≥0.5 mm in leads V1-V3 with positive terminal T-waves represents the dominant finding 1
• Additional posterior leads V7-V9 should show ST elevation ≥0.5 mm (≥1.0 mm in men ≥40 years) 1, 2
• This pattern qualifies for STEMI reperfusion therapy despite appearing as "ST depression" on standard 12-lead ECG 2

STEMI Equivalents (Critical Patterns Without Classic ST Elevation)

Takotsubo Syndrome vs. Anterior STEMI

• Takotsubo shows ST elevation centered on V2-V5 and leads II and aVR, while anterior STEMI centers on V1-V4 and leads I and aVL 1
• ST elevation in lead V1 is less pronounced in Takotsubo than anterior STEMI 1
• Both demonstrate temporal evolution with progressive T-wave inversion and QT prolongation over days 1

Left Main or Multivessel Disease

• ST-depression ≥1 mm in ≥8 surface leads coupled with ST elevation in aVR and/or V1 suggests left main or multivessel obstruction 1
• Often presents with hemodynamic compromise 1
• Requires emergency angiography despite lack of classic STEMI pattern 1

Hyperacute T-Waves

• Tall, peaked T-waves may precede ST-segment elevation in very early presentation 1, 3
• Requires serial ECGs at 10-minute intervals if initial ECG is nondiagnostic but clinical suspicion remains high 1, 3

Confounding Patterns Requiring Special Consideration

Left Bundle Branch Block (LBBB)

• LBBB obscures ST-segment interpretation and represents highest-risk ECG pattern for mortality 1
• Requires urgent angiography when persistent ischemic symptoms occur with LBBB of uncertain age 1
• Point-of-care troponin testing 1-2 hours after symptom onset may help guide decision for emergency catheterization 1

Ventricular Paced Rhythm

• Pacemaker rhythm prevents ST-segment interpretation and may require urgent angiography 1
• Consider reprogramming pacemaker to allow evaluation of intrinsic rhythm in non-pacemaker-dependent patients, without delaying invasive investigation 1

Critical Pitfalls to Avoid

Approximately 4% of acute MI patients show ST elevation isolated to posterior leads V7-V9, "hidden" from standard 12-lead ECG 1. This represents circumflex occlusion and qualifies for acute reperfusion therapy 1.

A completely normal ECG does not exclude ACS—1-6% of such patients ultimately have NSTEMI and ≥4% have unstable angina 1. Serial ECGs are mandatory when clinical suspicion persists 3.

Marked symmetrical T-wave inversion ≥2 mm in precordial leads strongly suggests critical LAD stenosis 1, often with anterior wall hypokinesis and high risk if treated medically alone 1.

Temporal Evolution Pattern

The ECG demonstrates predictable evolution over hours to weeks 1:

• Initial: ST-segment elevation (if present) with hyperacute T-waves 1, 3
• Hours to days: Progressive T-wave inversion and QT prolongation 1
• Days to weeks: Gradual resolution of T-wave inversion and QT prolongation 1
• Evolution influenced by ballooning pattern, time from symptom onset, myocardial edema, and recovery rate 1