ST-Elevation Myocardial Infarction (STEMI)

Definition and Pathophysiology

• Symptom to Diagnosis: An Evidence Based Guide, p. 174
• Fuster and Hurst's The Heart, 15th Ed., p. 599

Classification of MI (Universal Definition)

• STEMI: Transmural ischemia, typically from complete occlusion
• NSTEMI: Subendocardial injury, typically from incomplete occlusion; carries a higher subsequent risk for STEMI than vice versa

ECG Diagnostic Criteria

1. ST elevation at the J-point in ≥2 contiguous leads > 1 mm (in all leads except V2-V3)
2. In V2-V3: ≥2 mm in men <40 years, or ≥1.5 mm in women
3. New (or presumed new) left bundle branch block (LBBB)

• New ST elevation of 1 mm: ~80% probability of MI
• New ST depression or T-wave inversion: ~20% probability
• Symptom to Diagnosis: An Evidence Based Guide, pp. 173-174

Reperfusion - The Core of Management

Primary PCI (pPCI) - Preferred Strategy

• Superior to fibrinolysis for reducing death, reinfarction, and stroke (meta-analysis of 23 RCTs)
• Time target: Symptom onset to wire crossing (culprit artery) ≤120 minutes to choose pPCI over fibrinolysis
• AHA/ACC target: "First medical contact to device" time ≤90 min at a PCI-capable hospital, or ≤120 min if transfer is required
• Each 30-minute delay in treatment increases morbidity and mortality

Fibrinolytic Therapy - When PCI is Not Available in Time

• Give within 30 minutes of ED arrival if PCI cannot be accomplished within the time targets
• Administer within 10 minutes of STEMI diagnosis (prehospital administration is feasible and safe)
• Fibrin-specific agents (alteplase, tenecteplase, reteplase) are preferred over streptokinase
• Efficacy decreases as time from symptom onset elapses (thrombi "mature" and become harder to lyse)
• Reperfusion is recommended for presentations within 12 hours of symptom onset; benefit is limited beyond 48 hours

Fibrinolytic Dosing (Selected Agents)

• Tintinalli's Emergency Medicine, p. 385; Fuster and Hurst's The Heart, 15th Ed., p. 605

Pharmacotherapy

Antiplatelets (DAPT - Dual Antiplatelet Therapy)

Anticoagulants

Other Pharmacological Agents

• Beta-blockers: Start early unless risk for cardiogenic shock (heart failure signs, BP <120, HR >110 or <60, AV block, active asthma). Hold if any risk factors present.
• RAAS inhibition (ACE inhibitor or ARB): Initiate especially with reduced LVEF, anterior MI, or heart failure
• Statins (high-intensity): Initiate early for all STEMI patients
• Nitrates: Sublingual 0.4 mg q5 min x3 PRN pain; IV nitroglycerin for ongoing ischemia/hypertension
• Morphine: 2-5 mg IV q5-15 min PRN pain

Multivessel Disease

• In hemodynamically stable STEMI, complete revascularization of non-culprit lesions is recommended (though not necessarily at the time of primary PCI)
• In STEMI with cardiogenic shock, multivessel PCI at the time of the index procedure generally does not improve outcomes compared to culprit-only PCI

Complications

Pericarditis

• Early pericarditis: Pleuritic chest pain, pericardial rub, typical ECG changes after STEMI - treat with aspirin (650 mg QID) + colchicine
• Dressler syndrome (late, immune-mediated): Occurs 1-2 weeks post-STEMI; same treatment
• Anticoagulants should be avoided with active pericarditis (risk of tamponade)

Mechanical Complications (Free wall rupture, VSD, Papillary muscle rupture)

• Incidence ~0.27% in the pPCI era but 42% mortality
• Suspect with: sudden hypotension, recurrent chest pain, new systolic murmur, pulmonary congestion, JVD
• Require urgent surgical intervention

Electrical Complications

• Atrial fibrillation: Up to 21% of STEMI patients; treat with beta-blocker or amiodarone for rate/rhythm control + anticoagulation
• VT/VF: 6-8% of patients; treat with reperfusion, cardioversion/defibrillation, beta-blockers, amiodarone (or lidocaine if amiodarone contraindicated)
• VT/VF within 48 hours: low long-term arrhythmic risk
• VT/VF after 48 hours (without recurrent ischemia): worse prognosis, evaluate for ICD

Thromboembolism

• Clinically apparent in ~10% (silent in 20% at autopsy); contributes to ~25% of in-hospital deaths
• LV mural thrombus (common with large anterior MIs): anticoagulate for 3-6 months if demonstrated

LV Aneurysm

• Complications: HF, arterial embolism, ventricular arrhythmias
• Pseudoaneurysm (contained rupture) should be surgically repaired when recognized

Post-Discharge and Secondary Prevention

• Continue DAPT for 12 months; consider de-escalation or shortening based on bleeding vs ischemic risk
• Dual-pathway inhibition (aspirin + low-dose rivaroxaban) for chronic phase in selected patients
• Beta-blocker, statin, ACE inhibitor/ARB continued long-term
• Cardiac rehabilitation
• Smoking cessation, blood pressure and glycaemic control

2025 ACC/AHA Guideline update: The 2025 ACC/AHA/ACEP/NAEMSP/SCAI Guideline for the Management of ACS (PMID 40013746) was published in June 2025 and represents the most current evidence-based recommendations for STEMI. Key updates address antithrombotic strategies, timing of revascularization, and post-discharge care.