EKG
STEMI — localization by leads
EKG

STEMI — localization by leads

Map the ST-elevation pattern to the infarct territory and the culprit artery.

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◆Recognize a STEMI

  • •ST elevation ≥1 mm in 2 contiguous limb leads OR ≥2 mm in V2–V3 (men ≥40), ≥2.5 mm (men <40), ≥1.5 mm (women)
  • •New LBBB with chest pain = STEMI equivalent (use Sgarbossa criteria)
  • •Reciprocal ST depression in opposite leads CONFIRMS true STEMI vs early repolarization
  • •Hyperacute T waves precede ST elevation — broad, peaked, symmetric

◆Territory by ST-elevation pattern

  • •Anterior (V1–V4) → LAD; proximal LAD if also lateral V5–V6 + reciprocal in II/III/aVF
  • •Inferior (II, III, aVF) → RCA (80%) or LCx; check V4R for RV involvement
  • •Lateral (I, aVL, V5–V6) → LCx
  • •Posterior (ST depression V1–V3 + tall R V1–V2) → LCx or distal RCA
  • •RV infarct (V4R ST elevation) → proximal RCA — preload-dependent, AVOID nitrates, GIVE fluids
  • •Left main / 3-vessel: ST elevation in aVR > 1 mm with widespread ST depression

◆Management (door-to-needle / door-to-balloon)

  • •PCI within 90 min if PCI-capable center; transfer to PCI center if within 120 min total
  • •Fibrinolytics if PCI not available within 120 min and no contraindications; within 30 min of door
  • •MONA-BASH: O2 if hypoxic, ASA 325 chewed, nitrates (NOT in RV/severe AS/sildenafil), morphine, β-blocker (delay if CHF/shock), ACE-i, statin, heparin

STEMI lead-to-artery map

Lead patternLikely culprit artery
V1–V4 (anterior)LAD
I, aVL, V5–V6 (lateral)LCx
II, III, aVF (inferior)RCA (or LCx)
V1–V3 ST depression + tall R V1 (posterior)LCx / distal RCA
V4R elevation (right ventricular)Proximal RCA
aVR > 1 mm + diffuse ST depressionLeft main / severe 3-vessel

High-yield pearls

  • ◆Inferior STEMI + bradycardia + hypotension → think RV infarct → fluids first, AVOID nitrates
  • ◆New LBBB + chest pain = treat as STEMI
  • ◆aVR elevation with diffuse ST depression → left main occlusion, get to cath lab
  • ◆Posterior STEMI hides as ST depression in V1–V3 with tall R waves — get posterior leads
  • ◆Wellens' syndrome: biphasic or deep symmetric T inversion V2–V3 → critical LAD stenosis, even if asymptomatic
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