Acute Coronary Syndromes & STEMI Equivalents
Emergency management of ischemic chest pain: ECG diagnosis of subtle STEMI equivalents, right ventricular infarction precautions, antiplatelet/anticoagulation dosing, and cath lab activation pathways.
Resuscitation Quick Ribbon (First 2 Minutes)
Aspirin:324 mg chewable PO immediately (non-enteric coated)
P2Y12 Inhibitor:Ticagrelor 180 mg PO OR Clopidogrel 600 mg PO loading dose
Anticoagulation:Heparin bolus 60 units/kg IV (max 4,000 U), then infusion 12 units/kg/h (max 1,000 U/h)
Door-to-Balloon Time:< 90 minutes for primary PCI; < 120 minutes if transferred
Right Ventricular Infarct:Avoid nitrates/diuretics; administer 500–1000 mL crystalloid bolus for hypotension
Bottom-Line Clinical Pearl
Time is myocardium. Do NOT wait for troponin results to activate the cardiac catheterization laboratory for STEMI or STEMI equivalents (Wellens syndrome, de Winter T-waves, Sgarbossa-positive LBBB/paced rhythm, posterior MI). In inferior wall myocardial infarctions (leads II, III, aVF), always obtain right-sided leads (V4R); if ST elevation is present in V4R, nitrates and morphine are ABSOLUTELY CONTRAINDICATED due to preload dependence.
1. Classic STEMI Diagnostic Criteria & Anatomical Localizations
| Infarct Territory | Leads with ST Elevation | Reciprocal Depression | Culprit Coronary Artery |
|---|---|---|---|
| Anteroseptal | V1, V2, V3, V4 | II, III, aVF | Left Anterior Descending (LAD) |
| Lateral | I, aVL, V5, V6 | II, III, aVF | Left Circumflex (LCx) or Diagonal of LAD |
| Inferior | II, III, aVF | I, aVL | Right Coronary Artery (RCA) > LCx |
| Right Ventricle | V4R (right-sided lead) | I, aVL | Proximal RCA (preload dependent!) |
| Posterior | V7, V8, V9 (or tall R + ST dep in V1–V3) | None (primary ST dep V1–V3) | Posterior Descending Artery (PDA from RCA) |
2. High-Yield STEMI Equivalents (Cath Lab Activation Triggers)
- Wellens Syndrome: Deeply inverted or biphasic T-waves in V2–V3 in a pain-free patient with history of anginal chest pain. Signifies critical high-grade proximal LAD stenosis; stress testing is strictly contraindicated due to risk of transmural infarction.
- de Winter T-Waves: 1–3 mm ST depression at J-point with tall, prominent, symmetric T-waves in V1–V6, plus ST elevation in aVR. Represents acute LAD occlusion presenting without classic ST elevation; requires immediate emergent PCI.
- Modified Sgarbossa Criteria (LBBB or Ventricular Paced Rhythm): 1) Concordant ST elevation >= 1 mm in any lead with positive QRS (5 points); 2) Concordant ST depression >= 1 mm in V1, V2, or V3 (3 points); 3) Excessively discordant ST elevation / S-wave ratio <= -0.25 (Modified Smith-Sgarbossa rule). Any positive criterion warrants immediate cath lab activation.
- aVR Elevation with Multilead Depression: ST elevation >= 1 mm in aVR with diffuse ST depression across 6+ leads (I, II, aVF, V4–V6). Indicates severe left main coronary artery occlusion or triple-vessel disease.
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