What is the initial treatment for myocardial infarction (MI)?

Initial Treatment of Myocardial Infarction

The initial treatment for myocardial infarction (MI) should include immediate administration of aspirin 162-325 mg (chewed), anticoagulation, and rapid reperfusion therapy, with primary PCI being the preferred strategy when available within appropriate timeframes. 1

Immediate Pharmacological Management

Antiplatelet Therapy

• Aspirin

  • Administer 162-325 mg (non-enteric coated, chewed) immediately upon STEMI diagnosis 2, 1
  • Produces rapid antithrombotic effect through immediate inhibition of thromboxane A2 production 2
  • More rapid buccal absorption occurs with non-enteric-coated formulations 2
  • Lower initial dose (162 mg) may be as effective as and potentially safer than higher doses (325 mg) 3

• P2Y12 Inhibitor

  • Add a loading dose of a potent P2Y12 inhibitor 2, 1:
    • Preferred: Ticagrelor 180 mg or Prasugrel 60 mg
    • Alternative: Clopidogrel 600 mg (if ticagrelor or prasugrel unavailable)
  • Addition of clopidogrel to aspirin and fibrinolytic therapy reduces ischemic complications by 20% 4

Anticoagulation

• Start immediately with one of the following 1:
  • Unfractionated heparin (UFH): Weight-adjusted IV bolus followed by infusion
  • Enoxaparin: IV bolus followed by subcutaneous dosing
  • Bivalirudin (for primary PCI)
• Fondaparinux is contraindicated for primary PCI 2

Additional Medications

• Beta-blockers

  • Administer promptly in patients without contraindications 2, 1
  • IV beta-blockers are reasonable for patients with hypertension or tachyarrhythmias 2
  • Metoprolol can be initiated with three 5 mg IV boluses at 2-minute intervals, followed by oral therapy 5
  • Avoid in hypotensive patients or those with signs of heart failure 1

• Nitrates

  • For ongoing ischemic discomfort: Sublingual nitroglycerin (0.4 mg) every 5 minutes for up to 3 doses 2
  • IV nitroglycerin for ongoing ischemia, hypertension, or pulmonary congestion 2
  • Contraindicated with systolic BP <90 mmHg, severe bradycardia, tachycardia, RV infarction, or recent phosphodiesterase inhibitor use 2

Immediate Diagnostic Steps

• Obtain 12-lead ECG within 10 minutes of first medical contact 1
• Establish continuous ECG monitoring with defibrillator capacity immediately 1
• Determine reperfusion strategy based on ECG findings:
  • ST-segment elevation or new LBBB: Immediate reperfusion therapy 2
  • Non-ST-segment elevation: Medical management with risk stratification 2

Reperfusion Strategies

Primary PCI (Preferred Strategy)

• Goal: First medical contact-to-device time <90 minutes 1
• Indicated for STEMI patients with symptoms <12 hours 2, 1
• Direct transport to catheterization laboratory, bypassing emergency department when possible 2, 1
• For patients transferred to PCI-capable centers, bypass emergency department and go directly to cath lab 2

Fibrinolytic Therapy

• Indicated when primary PCI cannot be performed within 120 minutes of STEMI diagnosis 1
• Goal: Door-to-needle time <30 minutes 1
• Use fibrin-specific agents (tenecteplase, alteplase, or reteplase) 2, 1
• Continue anticoagulation after fibrinolysis 2
• Transfer to a PCI-capable center immediately after fibrinolysis 2

Common Pitfalls and Caveats

1. Delayed treatment: Every 30-minute delay in reperfusion increases mortality. Implement immediate treatment protocols.
2. Inappropriate reperfusion strategy selection: Consider local resources, time delays, and contraindications.
3. Inadequate antiplatelet therapy: Dual antiplatelet therapy is essential; aspirin alone is insufficient.
4. Contraindications overlooked: Screen for bleeding risks before anticoagulation and antiplatelet therapy.
5. Failure to recognize RV infarction: Presents with hypotension, clear lung fields, and elevated jugular venous pressure; avoid nitrates in these patients 1.

Monitoring After Initial Treatment

• Monitor for at least 24 hours after reperfusion therapy 1
• Perform routine echocardiography to assess ventricular function and detect complications 2, 1
• Watch for recurrent ischemia, heart failure, or serious arrhythmias 1

By following this algorithm for initial MI management, focusing on rapid diagnosis, antiplatelet/anticoagulant therapy, and timely reperfusion, patient outcomes regarding mortality and morbidity can be significantly improved.