What is the initial treatment approach for patients presenting with ST-Elevation Myocardial Infarction (STEMI) or Non-ST-Elevation Myocardial Infarction (NSTEMI)?

Initial Treatment of Myocardial Infarction (STEMI and NSTEMI)

All patients presenting with either STEMI or NSTEMI should receive immediate aspirin (162-325 mg loading dose, then 75-162 mg daily indefinitely) and a second antiplatelet agent (P2Y12 inhibitor), combined with anticoagulation, followed by risk-based decisions regarding timing of coronary angiography. 1, 2

Immediate Medical Therapy (Applies to Both STEMI and NSTEMI)

Antiplatelet Therapy

• Aspirin 162-325 mg loading dose should be administered immediately upon presentation and continued indefinitely at 75-162 mg daily. 1, 2, 3
• Add a P2Y12 inhibitor as dual antiplatelet therapy on presentation. 1, 2
  • For NSTEMI patients with planned invasive strategy: Clopidogrel (300-600 mg loading dose, then 75 mg daily), ticagrelor (180 mg loading dose, then 90 mg twice daily), or prasugrel (60 mg loading dose, then 10 mg daily) can be initiated. 1, 4
  • For STEMI patients: The same P2Y12 inhibitors apply, with prasugrel administered at time of PCI once coronary anatomy is known. 4
  • Critical timing consideration: In UA/NSTEMI patients, prasugrel loading should not be given until coronary anatomy is established to avoid excessive bleeding risk if urgent CABG is needed. 4

Anticoagulation

• Parenteral anticoagulation must be initiated immediately with unfractionated heparin, enoxaparin, fondaparinux, or bivalirudin, continuing for at least 48 hours or until revascularization. 2, 3

Adjunctive Medical Therapy

• Beta-blockers should be administered unless contraindicated (heart failure, hypotension, bradycardia). 2
• Nitrates should be used for symptom relief and ongoing ischemia. 2
• Morphine sulfate intravenously for pain control, though be aware it may delay absorption of oral P2Y12 inhibitors by up to 2 hours. 4, 5
• Oxygen 2-4 L/min if hypoxemic. 5

Risk Stratification and Invasive Strategy Selection

STEMI Management

STEMI patients require immediate reperfusion therapy—primary PCI is superior to fibrinolysis when performed within 90 minutes of first medical contact at experienced centers. 6, 7

• Primary PCI should be performed within 90 minutes of first medical contact. 6, 8
• If PCI cannot be achieved within 90-120 minutes and patient presents within 3 hours of symptom onset, fibrinolytic therapy is equally effective as delayed PCI. 5
• Fibrinolysis is contraindicated in NSTEMI patients—multiple trials (TIMI 11B, ISIS-2, GISSI 1) demonstrated no benefit and increased risk of MI. 1, 2

NSTEMI Management: Timing of Invasive Strategy

High-risk NSTEMI patients should undergo early invasive strategy (coronary angiography with intent to revascularize) within 12-24 hours of presentation. 1, 2

High-Risk Features Requiring Early Invasive Strategy (within 12-24 hours):

• Refractory angina despite maximal medical therapy 1, 2
• Hemodynamic instability or cardiogenic shock 1, 2
• Life-threatening ventricular arrhythmias or electrical instability 1, 2
• Elevated troponin (troponin T >0.01 ng/mL or troponin I >0.1 ng/mL) 2
• Dynamic ST-segment or T-wave changes 2
• TIMI risk score ≥3 or GRACE score >140 1, 2
• LVEF <40% 2
• Diabetes mellitus 2
• Prior PCI or CABG 2

Immediate Catheterization Laboratory (No Delay):

Patients with refractory angina despite maximal medical therapy, hemodynamic instability, cardiogenic shock, life-threatening ventricular arrhythmias, or mechanical complications should proceed directly to the catheterization laboratory without delay. 2, 3

Conservative Strategy Acceptable For:

Low- to intermediate-risk NSTEMI patients without high-risk features may be managed with an initial conservative (selectively invasive) strategy, with angiography performed only if medical therapy fails or objective ischemia develops. 1

Glycoprotein IIb/IIIa Inhibitors

• Intravenous GP IIb/IIIa inhibitors (eptifibatide or tirofiban preferred) can be added before PCI in high-risk patients, particularly those receiving clopidogrel rather than newer P2Y12 inhibitors. 1, 2
• Routine upstream (pre-catheterization) GP IIb/IIIa inhibitor use is not recommended—administration at time of PCI is preferred. 2

Duration of Dual Antiplatelet Therapy

Continue dual antiplatelet therapy (aspirin plus P2Y12 inhibitor) for at least 12 months after ACS, regardless of whether stent was placed or stent type. 1, 2, 3

Critical Pitfalls to Avoid

Timing Errors

• Do not delay invasive strategy in truly high-risk NSTEMI patients—the ISAR-COOL trial demonstrated that delayed invasive strategy (86 hours) had significantly worse outcomes than very early strategy (2.4 hours). 2
• Do not administer prasugrel loading dose in UA/NSTEMI patients before coronary anatomy is known—this substantially increases bleeding risk if urgent CABG is required. 4

Drug Interactions

• Avoid combining clopidogrel with omeprazole or esomeprazole, as these proton pump inhibitors significantly reduce clopidogrel's antiplatelet efficacy. 2

Inappropriate Patient Selection

• Do not perform early invasive strategy in patients with extensive comorbidities (liver failure, pulmonary failure, cancer) where risks outweigh benefits. 1, 2
• Do not perform early invasive strategy in patients with low likelihood of ACS or those who refuse revascularization. 1, 2

Fibrinolysis Misuse

• Never administer fibrinolytic therapy to NSTEMI patients—this increases MI risk without benefit. 1, 2

Weight-Based Dosing

• Consider reducing prasugrel maintenance dose to 5 mg daily in patients weighing <60 kg due to increased bleeding risk from higher drug exposure. 4

Age Considerations

• Prasugrel is generally not recommended in patients ≥75 years due to increased fatal and intracranial bleeding risk, except in high-risk situations (diabetes or prior MI) where benefit may outweigh risk. 4

Secondary Prevention Initiated Before Discharge

• High-intensity statin therapy should be started before discharge regardless of baseline LDL levels. 2, 3
• ACE inhibitor should be initiated within 24 hours for patients with pulmonary congestion, LVEF ≤0.40, hypertension, or diabetes. 3
• Beta-blockers should be continued indefinitely with careful titration. 2, 3