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 persistent ST-segment elevation at the J point in at least 2 contiguous leads (with specific voltage thresholds of ≥1 mm in all leads except V2-V3, where thresholds are ≥2.5 mm for men <40 years, ≥2 mm for men ≥40 years, and ≥1.5 mm for women) in the setting of characteristic chest pain, and requires immediate reperfusion therapy within 120 minutes of diagnosis to reduce mortality and morbidity. 1

Diagnostic Criteria

ECG Criteria

• ST-segment elevation at the J point in at least 2 contiguous leads
• Specific voltage thresholds:
  • ≥1 mm in all leads except V2-V3
  • For leads V2-V3:
    • ≥2.5 mm for men <40 years
    • ≥2 mm for men ≥40 years
    • ≥1.5 mm for women 1

Clinical Presentation

• Characteristic chest pain/discomfort lasting ≥10 minutes
• Pain typically described as pressure or heaviness
• May radiate to the neck, jaw, or left arm 1

Laboratory Testing

• Cardiac troponin is the preferred biomarker
• Important: Troponin may be initially negative and should not delay reperfusion therapy
• Should be measured at presentation and 6-12 hours after symptom onset if initially negative 1

STEMI Equivalents

Up to 30% of patients with acute coronary occlusion may not meet classic STEMI criteria. Important STEMI equivalents to recognize include:

• De Winter T-waves (upsloping ST depression with tall symmetric T waves in precordial leads)
• Wellens syndrome (deep T-wave inversions in anterior leads)
• Posterior MI (ST depression in V1-V3 with tall R waves)
• New left bundle branch block with appropriate clinical context
• Hyperacute T-waves 2

Initial Management

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) immediately 1
3. Establish IV access and cardiac monitoring
4. Determine reperfusion strategy within 10 minutes of STEMI diagnosis 1

Reperfusion Strategy

Primary PCI

• Preferred when it can be performed within 120 minutes of STEMI diagnosis
• Requires skilled PCI facility with surgical backup 1
• Antiplatelet therapy:
  • Aspirin plus prasugrel or ticagrelor 1
• Anticoagulation:
  • Unfractionated heparin (alternatives: enoxaparin or bivalirudin) 1

Fibrinolysis

• Preferred when:
  • Early presentation (<3 hours)
  • PCI cannot be performed within 120 minutes
  • No contraindications to fibrinolysis exist 1
• Antiplatelet therapy:
  • Aspirin plus clopidogrel 1
• Anticoagulation:
  • Enoxaparin (alternative: unfractionated heparin) 1
• Transfer to PCI-capable facility after fibrinolysis for routine early angiography (3-24 hours)

Post-STEMI Care

Medication Therapy

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

Secondary Prevention

• Cardiac rehabilitation
• Smoking cessation
• Blood pressure control
• Diabetes management
• Regular physical activity 1

Common Pitfalls to Avoid

1. Delaying ECG interpretation or waiting for biomarker results before initiating reperfusion therapy
2. Misinterpreting STEMI equivalents
3. Overlooking reperfusion in elderly patients
4. Delaying transfer for primary PCI when indicated 1
5. Failing to recognize symptoms promptly, leading to delayed presentation 3
6. Insufficient public awareness about STEMI symptoms and the "time is muscle" concept 3

Special Considerations

In resource-limited settings, challenges may include:

• Limited access to ECG or cardiac biomarker testing
• Delayed access to medical services
• Lack of PCI-capable facilities within appropriate timeframes 3

In these cases:

• Clinical judgment becomes crucial
• Fibrinolysis may be the more accessible reperfusion strategy
• Development of STEMI networks and standardized protocols can help improve outcomes 3, 4

Remember that early diagnosis and immediate reperfusion are the most effective ways to limit myocardial ischemia, reduce infarct size, and improve survival outcomes 4, 5.