What are the diagnostic criteria and treatment options for ST-Elevation Myocardial Infarction (STEMI)?

ST-Elevation Myocardial Infarction (STEMI): Diagnostic Criteria and Treatment

STEMI is diagnosed by characteristic symptoms of myocardial ischemia with persistent ECG ST elevation and requires immediate reperfusion therapy through either primary PCI or fibrinolysis to reduce mortality and morbidity. 1

Diagnostic Criteria

ECG Criteria

• ST-segment elevation at the J point in at least 2 contiguous leads:
  • ≥2 mm (0.2 mV) in men or ≥1.5 mm (0.15 mV) in women in leads V2–V3
  • ≥1 mm (0.1 mV) in other contiguous chest leads or limb leads 1

STEMI Equivalents (requiring same urgent treatment)

• ST depression in ≥2 precordial leads (V1–V4) indicating posterior MI
• Multilead ST depression with ST elevation in lead aVR (indicating left main or proximal LAD occlusion)
• Hyperacute T-wave changes in very early STEMI
• New or presumed new LBBB with appropriate clinical context (not in isolation) 1, 2

Clinical Presentation

• Characteristic chest pain/discomfort lasting ≥10 minutes (often described as pressure or heaviness)
• Pain may radiate to neck, jaw, or left arm
• Not fully responsive to nitroglycerin 1

Biomarkers

• Cardiac troponin is the preferred biomarker
• Not useful in initial diagnosis as they may be initially negative
• Should be measured at presentation and 6-12 hours after symptom onset if initially negative 1

Treatment Algorithm

Immediate Actions (First 10 minutes)

1. Obtain 12-lead ECG within 10 minutes of first medical contact 1
2. Administer aspirin 160-325 mg (chewed or crushed for rapid absorption) 1, 3
3. Establish IV access and cardiac monitoring
4. Determine reperfusion strategy within 10 minutes of STEMI diagnosis 1

Reperfusion Strategy Selection

• Primary PCI is preferred when:

  • Can be performed within 120 minutes of STEMI diagnosis
  • Skilled PCI facility with surgical backup available
  • Late presentation (>3 hours from symptom onset)
  • Contraindications to fibrinolysis exist
  • Diagnosis of STEMI is in doubt 1

• Fibrinolysis is preferred when:

  • Early presentation (<3 hours) and PCI cannot be performed within 120 minutes
  • No contraindications to fibrinolysis
  • Difficult vascular access anticipated 1

Adjunctive Pharmacotherapy

• Antiplatelet therapy:

  • For primary PCI: Aspirin plus prasugrel or ticagrelor
  • For fibrinolysis: Aspirin plus clopidogrel 1

• Anticoagulation:

  • For primary PCI: Unfractionated heparin (alternatives: enoxaparin or bivalirudin)
  • For fibrinolysis: Enoxaparin (alternative: unfractionated heparin) 1

• Analgesia: Morphine sulfate 4-8 mg IV initially, with 2-8 mg IV every 5-15 minutes as needed 3

• Other medications:

  • Nitroglycerin (sublingual or IV) unless hypotensive or contraindicated
  • Oxygen if oxygen saturation <90% or respiratory distress 3

Special Considerations

Cardiogenic Shock

• Perform immediate coronary angiography and revascularization
• Consider mechanical circulatory support (intra-aortic balloon pump)
• Provide inotropic support as needed 3

Right Ventricular Infarction

• Aggressive fluid resuscitation
• Avoid nitrates and other preload-reducing agents
• Consider inotropic support if hypotension persists despite fluid loading 3

Cardiac Arrest

• Patients with ST-elevation on post-resuscitation ECG should undergo primary PCI
• Without ST-elevation but high suspicion of ongoing ischemia, urgent angiography should be performed within 2 hours 1

Post-Reperfusion Care

Pharmacotherapy

• Continue DAPT (aspirin plus P2Y12 inhibitor) for 1 year
• Beta-blockers for all patients without contraindications
• ACE inhibitors/ARBs for patients with reduced ejection fraction, heart failure, or diabetes
• High-intensity statin therapy 1, 3

Secondary Prevention

• Cardiac rehabilitation
• Smoking cessation
• Blood pressure control
• Diabetes management
• Regular physical activity 3

Common Pitfalls to Avoid

• Delayed ECG interpretation - ECG should be obtained and interpreted within 10 minutes of arrival
• Waiting for biomarker results before initiating reperfusion therapy
• Misinterpreting STEMI equivalents (posterior MI, left main occlusion)
• Overlooking reperfusion in elderly patients who often present atypically
• Delaying transfer for primary PCI when indicated - "time is muscle" 1

The management of STEMI requires rapid diagnosis and immediate reperfusion to limit myocardial damage and improve outcomes. A well-coordinated system of care with clear protocols for ECG acquisition, interpretation, and rapid reperfusion decision-making is essential to reduce mortality and morbidity in these patients.