How does the immediate management differ for a patient with ST‑segment elevation myocardial infarction (STEMI) versus non‑ST‑segment elevation myocardial infarction (NSTEMI)?

STEMI versus NSTEMI Management: Critical Differences

The fundamental difference is that STEMI requires immediate reperfusion (primary PCI within 90-120 minutes or fibrinolysis within 10 minutes), whereas NSTEMI management is risk-stratified with invasive intervention timed according to clinical stability—high-risk NSTEMI within 24 hours, very high-risk within 2 hours. 1, 2

Time-Zero Definition and ECG Interpretation

STEMI Management:

• Time zero begins the moment ST-segment elevation (or equivalent) is identified on ECG; this starts the reperfusion clock 1
• Obtain 12-lead ECG within 10 minutes of first medical contact 1, 2, 3
• Recognize STEMI equivalents that mandate the same urgent approach: new left bundle branch block, hyperacute T-waves, isolated anterior ST-depression with ST-elevation in aVR, or universal ST-depression with aVR elevation 1, 2

NSTEMI Management:

• ECG shows ST-segment depression (31%), T-wave inversions (12%), both (16%), or neither (41%) 1, 4
• Obtain ECG within 10 minutes, but this triggers risk stratification rather than immediate reperfusion 1, 2
• Measure high-sensitivity troponin immediately and repeat at 6-12 hours to distinguish NSTEMI from unstable angina 1

Reperfusion Strategy: The 120-Minute Rule

STEMI—Immediate Reperfusion:

• Primary PCI is mandatory within 90 minutes at PCI-capable centers or 120 minutes with transfer 1, 2, 3
• If anticipated PCI time exceeds 120 minutes, initiate fibrinolysis within 10 minutes of STEMI diagnosis 1, 3
• Transfer patients directly to the catheterization laboratory, bypassing the emergency department entirely 1, 2, 3
• PCI-capable centers must provide 24/7 no-delay service 1, 3
• Perform primary PCI regardless of time delay in cardiogenic shock, acute severe heart failure, or contraindications to fibrinolysis 1, 2, 3

NSTEMI—Risk-Stratified Timing:

• Very high-risk patients (refractory angina, hemodynamic instability, cardiogenic shock, life-threatening arrhythmias, acute heart failure) require immediate invasive strategy within 2 hours 1, 2
• High-risk patients (GRACE score >140, TIMI risk score >4, elevated troponin, dynamic ST-changes) undergo early invasive strategy within 24 hours 1, 2
• Low-risk patients may be managed conservatively with stress testing before discharge 1
• There is no absolute time window; stable NSTEMI patients can safely wait for angiography during regular working hours 1

Antithrombotic Therapy Differences

STEMI—Potent Agents Before PCI:

• Aspirin 150-325 mg orally (or 250-500 mg IV) immediately at first medical contact 1, 2, 3
• Potent P2Y12 inhibitor before or at the time of PCI: prasugrel 60 mg loading dose or ticagrelor 180 mg loading dose (clopidogrel only if unavailable) 1, 2, 3
• Unfractionated heparin 100 U/kg IV bolus (60 U/kg if GPIIb/IIIa inhibitor used); enoxaparin or bivalirudin are alternatives 1, 2
• Fondaparinux is contraindicated for primary PCI 1, 3

STEMI with Fibrinolysis:

• Aspirin plus clopidogrel (prasugrel/ticagrelor not recommended with fibrinolysis) 1
• Enoxaparin preferred over unfractionated heparin 1

NSTEMI—Defer P2Y12 Until Anatomy Known:

• Aspirin 75-150 mg immediately 1
• Defer P2Y12 inhibitor loading until coronary anatomy is defined at angiography, especially if CABG is likely within 5 days 1
• Anticoagulation with unfractionated heparin or low-molecular-weight heparin 1, 2
• Once PCI is performed, use same potent P2Y12 inhibitors as STEMI (prasugrel, ticagrelor, or clopidogrel) 1, 2

Technical PCI Standards

Both STEMI and NSTEMI:

• Routine radial arterial access to minimize bleeding 1, 3
• Routine drug-eluting stent implantation 1, 3
• Routine thrombus aspiration is contraindicated 1, 3
• Deferred stenting is contraindicated 1, 3

Post-Procedure Monitoring and Discharge

STEMI:

• Monitor for at least 24 hours after reperfusion 1
• Early ambulation and early discharge are optimal in uncomplicated patients 1
• Dual antiplatelet therapy (aspirin plus prasugrel/ticagrelor) for 12 months 1, 2, 3

NSTEMI:

• Observational period includes multi-lead ECG ischemia monitoring 1
• Repeat troponin at 6-12 hours 1
• Dual antiplatelet therapy for 12 months after PCI 1, 2
• Consider treatment of non-infarct-related artery stenoses before discharge 1

Critical Pitfalls Specific to Each

STEMI Pitfalls:

• Never delay ECG beyond 10 minutes of first medical contact 2, 3
• Do not miss STEMI equivalents (bundle branch block, hyperacute T-waves, posterior MI, aVR elevation patterns) that require the same urgent PCI approach 1, 2
• Do not postpone PCI to "stabilize" other conditions (e.g., active GI bleeding); the mortality risk from untreated STEMI exceeds procedural bleeding risk 3
• Atypical presentations (especially women, elderly, diabetics) may lack chest pain 2

NSTEMI Pitfalls:

• Do not overlook very high-risk features requiring immediate invasive management within 2 hours (refractory ischemia, hemodynamic instability, arrhythmias, acute heart failure) 1, 2
• Do not rush low-risk NSTEMI patients to the catheterization laboratory; risk stratification prevents unnecessary urgent procedures 1
• Avoid early invasive strategy in Type 2 NSTEMI (supply-demand mismatch from anemia, tachyarrhythmia, hypotension) unless concurrent Type 1 MI is suspected 5
• Do not give clopidogrel prematurely if CABG is likely; defer P2Y12 inhibitor until anatomy is known 1

Special Populations

Cardiogenic Shock (Both STEMI and NSTEMI):

• Emergency angiography and PCI immediately regardless of time from symptom onset 1, 2, 3
• Consider non-infarct-related artery PCI during the index procedure in shock 1

Cardiac Arrest:

• STEMI with post-resuscitation ST-elevation: immediate primary PCI 1, 2
• No ST-elevation but high suspicion of ischemia: urgent angiography within 2 hours 1

Contraindications to Fibrinolysis:

• Primary PCI is mandatory for STEMI regardless of anticipated delay 2, 3

Shared Long-Term Management

Both STEMI and NSTEMI require identical secondary prevention:

• High-intensity statin therapy initiated early 1, 2, 3
• Beta-blockers in patients with heart failure or LVEF <40% 1, 2, 3
• ACE inhibitors within 24 hours for heart failure, LV dysfunction, diabetes, or anterior infarction 1, 3
• Cardiac rehabilitation participation 3