What is the initial treatment for a myocardial infarction (heart attack)?

Initial Treatment for Myocardial Infarction

Immediately administer aspirin 160-325 mg orally, establish continuous cardiac monitoring, obtain a 12-lead ECG within 10 minutes, and give sublingual nitroglycerin (unless systolic BP <90 mmHg or heart rate <50 or >100 bpm), followed by urgent reperfusion therapy with primary PCI or fibrinolysis depending on availability and timing. 1

Immediate Actions Upon Patient Arrival (First 10 Minutes)

Critical Initial Steps

• Establish continuous cardiac monitoring immediately upon patient entry to detect life-threatening arrhythmias 2, 1
• Obtain 12-lead ECG within 10 minutes of arrival to identify ST-segment elevation ≥1 mm in contiguous leads or new left bundle branch block 2, 1, 3
• Administer aspirin 160-325 mg orally immediately—this is the single most important initial pharmacological intervention 2, 1
• Assess oxygen saturation and provide supplemental oxygen only if SaO₂ <90% or PaO₂ <60 mmHg; routine oxygen therapy when SaO₂ ≥90% is not recommended 1, 3

Immediate Pharmacological Management

• Give sublingual nitroglycerin unless systolic blood pressure is <90 mmHg or heart rate is <50 or >100 beats per minute 2, 1
• Administer intravenous morphine sulfate for adequate analgesia, titrated to pain relief 2, 1
• Provide antiemetic with morphine administration (such as with diamorphine) 2

Reperfusion Strategy Decision (Within 90-120 Minutes)

For ST-Elevation MI or New LBBB

• Primary PCI is the preferred reperfusion strategy if it can be performed within 90 minutes of first medical contact by experienced personnel 1, 4
• Administer fibrinolytic therapy if PCI cannot be performed within 120 minutes of first medical contact, with door-to-needle time ≤30 minutes 1, 3
• Greatest benefit occurs within the first hour ("golden hour"), with 35 lives saved per 1,000 patients treated, progressively diminishing thereafter 3, 4
• Reperfusion therapy should be initiated within 12 hours of symptom onset; beyond 12 hours offers little benefit in most patients 3

Additional Antiplatelet Therapy

• Administer a P2Y12 inhibitor (ticagrelor or prasugrel preferred over clopidogrel) if no contraindications exist 1, 3

Adjunctive Pharmacological Therapy (First 24-48 Hours)

Beta-Blocker Therapy

• For early intravenous beta-blocker administration: Give three bolus injections of metoprolol 5 mg each at approximately 2-minute intervals during the early phase after hemodynamic stabilization 5
• Follow with oral metoprolol 50 mg every 6 hours starting 15 minutes after the last intravenous dose, continued for 48 hours, then 100 mg twice daily 5
• Avoid in patients with bradycardia, heart block, or hypotension as beta-blockers may worsen these conditions 1

Nitroglycerin Infusion

• Begin intravenous nitroglycerin for 24-48 hours if no hypotension, bradycardia (<50 bpm), or excessive tachycardia (>100 bpm) is present 2, 4
• Avoid nitrates in inferior STEMI with suspected right ventricular involvement as they can cause profound hypotension 1

ACE Inhibitor Therapy

• Initiate lisinopril 5 mg orally within 24 hours of symptom onset in hemodynamically stable patients, followed by 5 mg after 24 hours, 10 mg after 48 hours, then 10 mg once daily 6
• Start with 2.5 mg in patients with low systolic blood pressure (≤120 mmHg and >100 mmHg) during the first 3 days after infarction 6
• Continue therapy for at least 6 weeks to reduce mortality 6

Anticoagulation

• Consider intravenous heparin, particularly for patients with large anterior MI who are at high risk for left ventricular mural thrombus and embolic stroke 4

Critical Time Targets

• Complete initial assessment within 10 minutes of arrival 1, 3
• Total evaluation should not exceed 20 minutes 1, 3
• Door-to-balloon time for primary PCI: ≤90 minutes 1, 3
• Door-to-needle time for fibrinolysis: ≤30 minutes 1, 3
• Call-to-needle time (from symptom recognition to treatment): ≤90 minutes 2

Special Triage Considerations

High-Risk Patients Requiring Tertiary Care

• Patients with cardiac arrest, repetitive ventricular tachyarrhythmias, severe bradycardia, or shock should be transported directly to hospitals with cardiac catheterization and cardiac surgery facilities if this does not require excessive transport time 2
• Patients with signs of shock, pulmonary congestion, heart rate >100 bpm, and systolic blood pressure <100 mmHg should ideally be triaged to facilities capable of cardiac catheterization and revascularization 2

Rural Community Protocols

• Initiate thrombolytic therapy in rural hospitals before transfer when appropriate, as this has been shown to be safe and effective 2, 1
• Develop protocols for rapid telephone consultation with nearby medical centers for appropriate patient transfer 2

Common Pitfalls and Caveats

• Do not delay reperfusion therapy while waiting for cardiac biomarker results when ECG shows clear ST-segment elevation—ECG findings alone warrant immediate treatment 1, 3
• Do not withhold treatment due to administrative procedures such as establishing insurance coverage 2
• Avoid excessive fluid administration in patients without right ventricular involvement as it may worsen left ventricular failure 1
• Do not use long-acting oral nitrate preparations in early acute MI management; intravenous nitroglycerin allows more precise control 2
• Monitor closely for hypotension after initial nitroglycerin dose, as inadvertent systemic hypotension can worsen myocardial ischemia 2
• Recognize atypical presentations: chest tightness, acute epigastric distress, and other symptoms suggestive of acute MI must trigger immediate evaluation 2, 3
• For inferior wall MI, monitor closely for conduction abnormalities and right ventricular involvement 1

Monitoring Requirements

• Continuous ECG monitoring from time of entry through the acute phase 2
• Frequent vital signs during initial evaluation and after medication administration 2
• Careful observation for several minutes after initial nitroglycerin dose 2
• Emergency resuscitation equipment must be readily available 4