Internal MedicineCardiologyAcute ST‑Elevation Myocardial Infarction (STEMI)

Acute ST‑Elevation Myocardial Infarction (STEMI)

Must-Not-Miss / Red Flags

  • Cardiogenic shock – cold, clammy, systolic BP < 90 mmHg, pulmonary edema
  • Free wall rupture – sudden electrical dissociation, tamponade
  • Ventricular septal defect – new holosystolic murmur, acute CHF
Patient Explanation
“A heart attack happens when a blood clot suddenly blocks one of the heart’s arteries. We need to open it quickly with a balloon to save the heart muscle.”
Board Fact
“ST‑segment elevation ≥1 mm in two contiguous leads or new LBBB → STEMI until proven otherwise.”
ICD-10
I21.3

Definition & Core Concept

ST‑Elevation Myocardial Infarction (STEMI) is the transmural necrosis of myocardial tissue caused by prolonged, complete occlusion of an epicardial coronary artery, usually from thrombus formation after atherosclerotic plaque rupture.

Epidemiology & Risk Factors

  • Leading cause of death worldwide; 1 in 5 deaths is from CAD
  • Risk factors: Age >45♂ / >55♀, HTN, DM, smoking, family history, obesity
  • Peak incidence between 6 AM and noon (circadian surge in catecholamines)

Pathophysiology (Rule of 3)

  1. Endothelial injury & plaque formation – LDL oxidation → foam cells → fatty streak
  2. Plaque rupture – fibrous cap degradation by MMPs → exposure of thrombogenic core
  3. Thrombotic occlusion – platelet adhesion, aggregation, fibrin clot → 100% occlusion → STEMI

Clinical Presentation

  • Classic: Substernal crushing chest pain radiating to left arm/jaw, diaphoresis, dyspnea, nausea/vomiting
  • Atypical (women, elderly, diabetics): Fatigue, syncope, epigastric pain, isolated dyspnea

Diagnostic Workup

ECG within 10 minutes – ST‑elevation ≥1 mm in ≥2 contiguous leads or new LBBB.

High‑sensitivity Troponin I – rising/falling pattern.

Chest X‑ray – rule out aortic dissection, pneumothorax.

Management Protocol

  1. MONA: Morphine 2‑4 mg IV, Oxygen if SpO₂ <90%, Nitroglycerin 0.4 mg SL, Aspirin 324 mg chewed
  2. P2Y₁₂ inhibitor: Ticagrelor 180 mg or Clopidogrel 600 mg
  3. Anticoagulation: Heparin or Enoxaparin
  4. Primary PCI – door‑to‑balloon < 90 minutes; if unavailable, fibrinolytic therapy within 30 minutes

Complications & Prognosis

  • Arrhythmias: VF/VT (common cause of pre‑hospital death)
  • Heart failure / cardiogenic shock
  • Mechanical complications: Papillary muscle rupture (1‑5 days), VSD, free wall rupture (5‑10 days)
  • Dressler syndrome (autoimmune pericarditis 2‑6 weeks post‑MI)

ICU Criteria

CCU/ICU admission if: cardiogenic shock (Killip IV), persistent chest pain despite medical therapy, malignant arrhythmias, or mechanical complications.

Clinical Vignette

Mr. J., 58‑year‑old smoker, develops crushing chest pain while shovelling snow. Pain radiates to left jaw, he becomes diaphoretic and short of breath. EMS records ST‑elevation in leads V1‑V4. Cath lab is activated.

Pearls & Pitfalls

  • Always obtain a right‑sided ECG (V₄R) in inferior STEMI to rule out RV infarction – if present, nitrates are contraindicated.
  • Don’t rely on a single negative troponin; repeat after 3‑6 hours.

Discharge & Follow-Up

Discharge medications: Dual antiplatelet therapy (aspirin + ticagrelor) for 12 months, high‑intensity statin (atorvastatin 80 mg), beta‑blocker, ACE inhibitor/ARB, aldosterone antagonist if LVEF ≤40%. Refer to cardiac rehabilitation.

Literature & Guidelines

2023 ESC STEMI Guidelines. O’Gara PT et al., 2013 ACCF/AHA STEMI Guideline. PMID: 23256913.

Personal Clinical Notes