ST-Elevation Myocardial Infarction (STEMI)

Definition & Pathophysiology

• Incidence: ~50–133/100,000/year (declining in the US/Europe with improved prevention)
• Average age at first MI: 65.6 years (males), 72.0 years (females)
• More common in men; female incidence rises post-menopause
• Estimated ~500,000 STEMI events annually in the United States

ECG Diagnosis

Diagnostic Criteria (ST Elevation)

• ≥2 contiguous leads with ST elevation ≥1 mm (≥2 mm in V1–V3 in men; ≥1.5 mm in women)
• New LBBB with ischemic symptoms (treated as STEMI equivalent)

ECG Localization of Culprit Artery

Tip: ST depression in anterior leads V1–V3 with early precordial transition may indicate posterior wall MI, especially if associated with inferior ST elevation (inferoposterior MI). Right-sided leads (V3R–V4R) are essential when inferior STEMI is suspected — to detect right ventricular involvement.

Management Overview

Time-Sensitive Goals

Reperfusion Strategy

• PCI cannot be achieved within 120 minutes of first medical contact
• No contraindications exist
• Symptom onset <12 hours

Fibrinolytic Agents

• Clot-specific (preferred in US): Alteplase (tPA), reteplase (rPA), tenecteplase (TNK-tPA)
• Non-clot-specific: Streptokinase, urokinase — act via systemic fibrinogenolysis

Absolute Contraindications to Fibrinolysis

• Prior intracranial hemorrhage (any time) or stroke of unknown origin
• Ischemic stroke within 6 months (or 3 months per some guidelines)
• Known intracranial neoplasm or vascular lesion
• Active or suspected aortic dissection
• Active bleeding or known bleeding disorder (excluding menses)
• Significant head/facial trauma within 3 months

Relative Contraindications

• Uncontrolled severe hypertension (>180/110 mmHg)
• Prolonged CPR (>10 min), recent surgery (<3 weeks), noncompressible puncture
• Pregnancy; active peptic ulcer; high INR on anticoagulation
• Prior streptokinase use (if re-using SK — allergic reaction risk)

Pharmacological Therapy (Acute Phase)

Antiplatelets

Anticoagulants (Antithrombins)

Glycoprotein IIb/IIIa Inhibitors

• Abciximab, eptifibatide, tirofiban — adjunct to PCI, especially in high-thrombus burden
• No dose adjustment needed for CKD with abciximab

β-Blockers

• Oral β-blockers within 24 hours of STEMI (if no contraindications: HR <60, SBP <100, signs of HF, >1st-degree AVB, active bronchospasm)
• IV β-blockers reserved for severe hypertension or ongoing ischemia
• Contraindications: PR >0.24 sec, 2nd/3rd-degree heart block, active asthma, cardiogenic shock risk factors

ACE Inhibitors / ARBs

• Start as soon as possible post-STEMI, especially:
  • LVEF <40%
  • Anterior MI
  • Clinical heart failure
• ARB if ACE inhibitor-intolerant

Aldosterone Antagonist (e.g., Eplerenone)

• Indicated when: already on ACE inhibitor + β-blocker AND LVEF <40% AND HF symptoms or diabetes

Statins

• High-intensity statin (atorvastatin 40–80 mg or rosuvastatin 20–40 mg) initiated acutely

Multivessel Disease in STEMI

• Culprit-only PCI at time of primary PCI is standard
• Complete revascularization of non-culprit vessels: recommended during the index hospitalization or staged early (within days to weeks) for hemodynamically stable patients — trials (COMPLETE, PRAMI, CvLPRIT) demonstrate reduction in major adverse CV events
• Exception: Cardiogenic shock — routine multivessel PCI at index procedure is NOT recommended (CULPRIT-SHOCK trial showed harm)

Dual Antiplatelet Therapy (DAPT) Duration

Complications of STEMI

Electrical

• Ventricular fibrillation/tachycardia (highest risk first 24–48 hours)
• Accelerated idioventricular rhythm (reperfusion arrhythmia — usually benign)
• Heart block (especially with inferior MI — RCA supplies AV node in 90%)
• Atrial fibrillation

Mechanical

• Papillary muscle rupture → acute mitral regurgitation (harsh systolic murmur, flash pulmonary edema, 2–7 days post-MI)
• Free wall rupture → cardiac tamponade (rapid hemodynamic collapse, usually fatal without surgery)
• Ventricular septal defect (VSD) → new harsh pansystolic murmur + right heart failure (2–5 days post-MI)
• LV aneurysm → persistent ST elevation, thrombus, refractory HF, arrhythmia (weeks to months)
• LV pseudoaneurysm → contained free wall rupture — urgent surgical repair needed

Pericarditis (Dressler Syndrome)

• Early (1–3 days): pericarditis from transmural necrosis
• Late (Dressler, weeks–months): autoimmune pericarditis
• Treatment: high-dose aspirin preferred; colchicine or narcotic analgesics if not tolerated. Avoid NSAIDs and glucocorticoids (impair myocardial healing)

Cardiogenic Shock

• Occurs in ~5–10% of STEMI
• Defined by hypotension + signs of organ hypoperfusion
• Mortality remains ~40–50% despite modern therapy
• Immediate pPCI is lifesaving; IABP does not reduce mortality (IABP-SHOCK II); consider Impella or ECMO in refractory cases

Post-STEMI Secondary Prevention

Infarct Size & Prognosis

1. Rapid reperfusion (every 30-minute delay increases mortality)
2. Ischemic preconditioning
3. Cardioprotective adjuncts (under investigation: cyclosporine, hypothermia — results mixed)

Recent evidence note: A 2025 systematic review/meta-analysis (PMID 40854299) examined the impact of smartphone apps on reperfusion times in STEMI, suggesting digital health tools may help reduce door-to-balloon times — an emerging area of evidence.