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

Initial Treatment for Myocardial Infarction

Upon arrival, immediately administer aspirin 160-325 mg orally, obtain a 12-lead ECG within 10 minutes, initiate continuous cardiac monitoring, give sublingual nitroglycerin (unless systolic BP <90 mmHg or heart rate <50 or >100 bpm), and provide supplemental oxygen only if oxygen saturation is <90%. 1, 2, 3

Immediate Actions (Within 10 Minutes of Arrival)

Time-Critical Assessment:

• Place patient on continuous cardiac monitoring immediately with defibrillator nearby 1, 2, 4
• Obtain 12-lead ECG within 10 minutes of emergency department arrival 1, 2, 3
• Complete initial assessment within 10 minutes; total evaluation should not exceed 20 minutes 2

First-Line Medications:

• Aspirin 160-325 mg orally - administer immediately unless contraindicated 1, 2, 3, 4
• Sublingual nitroglycerin - give unless systolic blood pressure <90 mmHg or heart rate <50 or >100 bpm 1, 2, 3
• Supplemental oxygen - provide only if oxygen saturation <90% or PaO₂ <60 mmHg; routine oxygen in non-hypoxemic patients may increase myocardial injury 2, 3, 4
• Morphine sulfate or meperidine - administer titrated intravenous opioids for adequate analgesia and anxiety relief, though be aware this may delay oral antiplatelet absorption 1, 2, 4

ECG-Based Reperfusion Strategy

For ST-Elevation MI (≥1 mm in contiguous leads or new left bundle branch block):

The distinction between ST-elevation and non-ST-elevation MI is critical, as these represent different pathoanatomies requiring different therapeutic approaches. 1

• Primary PCI preferred if available within 90 minutes of first medical contact (door-to-balloon time ≤90 minutes) 2, 3
• Fibrinolytic therapy if PCI cannot be performed within 120 minutes; door-to-needle time should be ≤30 minutes 2, 3
• Thrombolytic therapy provides 21% proportional reduction in 35-day mortality, saving 35 lives per 1000 patients when given within the first hour versus 16 lives per 1000 when given 7-12 hours after symptom onset 1
• Administer P2Y12 inhibitor (ticagrelor or prasugrel preferred over clopidogrel) 2

For Non-ST-Elevation MI:

• Do not administer thrombolytic therapy - these patients should not receive fibrinolysis 1
• The benefit of primary PCI in non-ST-elevation patients remains uncertain 1

Critical Pitfalls to Avoid

Medication Contraindications:

• Do not give nitrates to patients with right ventricular involvement, as this reduces preload and worsens hemodynamics 4
• Do not administer beta-blockers to patients with signs of heart failure, low-output state, or risk factors for cardiogenic shock 4
• Avoid nonsteroidal anti-inflammatory drugs (except aspirin) due to increased mortality risk 4

Time-Dependent Errors:

• Do not delay treatment for administrative procedures such as establishing insurance coverage 1
• Do not wait for cardiac biomarker results before initiating reperfusion therapy 3
• Do not attempt prolonged consultation with the patient's private physician if this delays specific therapy 1

Transport and Triage Considerations

Prehospital Management:

• Patients should call 911 and be transported by ambulance rather than private vehicle, as approximately 1 in 300 patients transported by private vehicle experiences cardiac arrest en route 1
• Critically ill patients (cardiac arrest, repetitive ventricular tachyarrhythmias, severe bradycardia, or shock) should be taken to hospitals with cardiac catheterization and surgical capabilities if transport time is not excessive 1, 3

Recognition of Atypical Presentations:

• Epigastric pain, severe indigestion, fatigue, dyspnea, faintness, or syncope (especially in elderly patients) should trigger immediate MI protocol activation 2, 3
• Chest discomfort may present as pressure rather than pain and can radiate to arm, throat, or lower jaw 1