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

Initial Treatment for Myocardial Infarction

Immediately administer aspirin 160-325 mg orally, initiate continuous cardiac monitoring, obtain a 12-lead ECG within 10 minutes, and give sublingual nitroglycerin (unless systolic BP <90 mmHg), followed by reperfusion therapy within 90 minutes if ST-elevation is present. 1

Immediate Actions (First 10 Minutes)

Time-critical interventions must begin the moment MI is suspected:

• Aspirin 160-325 mg orally should be given immediately upon arrival—this is the single most important initial medication 2, 1
• Continuous cardiac monitoring must be initiated immediately to detect life-threatening arrhythmias 2, 1
• 12-lead ECG must be obtained within 10 minutes to identify ST-segment elevation ≥1 mm in contiguous leads or new left bundle branch block 1, 3
• Oxygen therapy should only be administered if oxygen saturation is <90% or PaO₂ <60 mmHg—routine oxygen is not recommended when SaO₂ ≥90% 1

Critical pitfall: Do not delay treatment for insurance verification or administrative procedures 2. Do not wait for cardiac biomarker results when ECG shows ST-elevation 1, 3.

Pain Management and Hemodynamic Support

Adequate analgesia is essential and should not be delayed:

• Sublingual nitroglycerin should be given unless systolic blood pressure is <90 mmHg or heart rate is <50 or >100 beats per minute 2, 1
• Intravenous morphine sulfate should be administered for pain control, though be aware this may delay oral antiplatelet absorption 2, 3
• Intravenous diamorphine with an antiemetic is the analgesic of choice in some protocols 2

Critical pitfall: Avoid nitrates in patients with inferior STEMI and suspected right ventricular involvement, as they can cause profound hypotension 1. Nitroglycerin should also be avoided in the presence of marked bradycardia or tachycardia with relative hypotension 2.

Antiplatelet Therapy

Dual antiplatelet therapy should be initiated immediately:

• Aspirin 160-325 mg is mandatory unless contraindicated 2, 1
• P2Y12 inhibitor (ticagrelor or prasugrel preferred over clopidogrel) should be administered if there are no contraindications 1, 3

Reperfusion Strategy (Within 90-120 Minutes)

The choice between primary PCI and fibrinolytic therapy depends on time to treatment:

• Primary PCI is preferred when available within 90 minutes of first medical contact 1, 3
• Fibrinolytic therapy should be initiated if PCI cannot be performed within 120 minutes, with door-to-needle time ≤30 minutes 3
• Thrombolytic therapy should be started by emergency department physicians when clinical presentation and ECG are characteristic of acute MI 2
• In rural settings, protocols for initiating thrombolytic therapy before transfer to tertiary centers are appropriate and have been shown to be safe and effective 2, 1

Time-dependent benefit: Treatment within the first hour ("golden hour") saves 65 lives per 1,000 patients treated, compared to 25 lives per 1,000 when treated between 4-6 hours 2. Maximum benefit occurs within 12 hours of symptom onset 3.

Critical pitfall: Do not delay reperfusion therapy while consulting with the patient's private physician if this causes significant delay 2.

Beta-Blocker Therapy (Early Phase)

For hemodynamically stable patients, early beta-blocker therapy reduces mortality:

• Metoprolol tartrate 5 mg IV should be given as three bolus injections at 2-minute intervals during the early phase 4
• After tolerating the full IV dose (15 mg), initiate metoprolol tartrate 50 mg orally every 6 hours starting 15 minutes after the last IV dose, continued for 48 hours 4
• Maintenance dosage is 100 mg orally twice daily thereafter 4

Critical pitfall: Beta-blockers should be used with caution in patients with conduction abnormalities, as they may worsen bradycardia or heart block 1. Discontinue in patients with severe intolerance 4.

ACE Inhibitor Therapy (Within 24 Hours)

ACE inhibitors reduce mortality when started early:

• Lisinopril 5 mg orally should be given within 24 hours of symptom onset in hemodynamically stable patients 5
• Follow with 5 mg after 24 hours, 10 mg after 48 hours, then 10 mg once daily for at least 6 weeks 5
• In patients with low systolic blood pressure (≤120 mmHg and >100 mmHg), initiate with 2.5 mg 5

Critical pitfall: If systolic blood pressure falls to ≤100 mmHg, reduce to 5 mg daily; if <90 mmHg for more than 1 hour, withdraw lisinopril 5.

Management of Specific Complications

Bradyarrhythmias and conduction disturbances require immediate attention:

• Transcutaneous pacing capabilities should be immediately available 1
• For symptomatic bradycardia, administer atropine 0.5-1.0 mg IV (may repeat to maximum 3 mg) 2
• Patients with inferior wall MI require close monitoring for conduction abnormalities and right ventricular involvement 1

Severe hypoxemia despite supplemental oxygen:

• Endotracheal intubation and mechanical ventilation should not be unnecessarily delayed in patients with severe congestive heart failure, pulmonary edema, or mechanical complications 2

Critical Time Targets

Door-to-treatment times directly impact mortality:

• ECG within 10 minutes of arrival 1, 3
• Complete initial assessment within 20 minutes 1
• Door-to-balloon time ≤90 minutes for primary PCI 3
• Door-to-needle time ≤30 minutes for fibrinolysis 3
• Call-to-needle time ≤90 minutes for overall system performance 2

Critical pitfall: Critically ill patients (cardiac arrest, repetitive ventricular tachyarrhythmias, severe bradycardia, or shock) should be taken directly to hospitals with cardiac catheterization and cardiac surgery facilities if this does not require excessive transport time 2.