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

Initial Treatment Protocol for Acute Myocardial Infarction

For patients presenting with acute MI, immediately administer aspirin 160-325 mg (chewed or IV), oxygen, sublingual nitroglycerin (if hemodynamically stable), and morphine for pain control, followed by urgent reperfusion via primary PCI within 90-120 minutes or fibrinolytic therapy if PCI is unavailable, combined with potent P2Y12 inhibitors and anticoagulation. 1, 2

Immediate Actions Upon Arrival (Within 10 Minutes)

Initial Medications - Administer Simultaneously:

• Aspirin 160-325 mg orally (chewed) or IV if patient cannot swallow - this is the single most critical intervention 1, 2
• Oxygen by nasal cannula for all patients 1, 2
• Sublingual nitroglycerin - withhold only if systolic BP <90 mmHg OR heart rate <50 or >100 bpm 1, 2
• Morphine sulfate or meperidine for adequate analgesia 1
• Obtain 12-lead ECG within 10 minutes to guide reperfusion strategy 1, 2

Reperfusion Strategy Decision Tree

If ST-Segment Elevation or New LBBB Present:

Primary PCI is strongly preferred if available within 90-120 minutes of first medical contact 1, 2:

• Transfer patient directly to catheterization laboratory, bypassing emergency department 1, 2
• Requires 24/7 PCI-capable center 1
• Reperfusion therapy indicated for all patients with symptoms ≤12 hours duration 1, 2

Fibrinolytic therapy if PCI unavailable within appropriate timeframe 1, 2:

• Initiate as soon as possible, preferably pre-hospital 1
• Use fibrin-specific agents: tenecteplase, alteplase, or reteplase 1
• Greatest mortality benefit when given within first 6 hours (35 lives saved per 1000 patients), still beneficial up to 12 hours (16 lives saved per 1000 patients) 1
• All patients require immediate transfer to PCI-capable center after fibrinolysis 1

If No ST-Elevation:

• Do not administer thrombolytic therapy 1
• Proceed with medical management and risk stratification

Antithrombotic Therapy Based on Reperfusion Strategy

For Primary PCI:

P2Y12 Inhibitor - administer before or at time of PCI 1, 2:

• Prasugrel or ticagrelor preferred over clopidogrel 1, 2
• Continue for 12 months unless excessive bleeding risk 1, 2
• Clopidogrel acceptable if prasugrel/ticagrelor unavailable or contraindicated 1, 2

Anticoagulation during PCI 1:

• High-dose IV heparin weight-adjusted bolus followed by infusion 2
• Fondaparinux is contraindicated for primary PCI 1

For Fibrinolytic Therapy:

Antiplatelet therapy 1:

• Aspirin (already given) 1
• Clopidogrel 75 mg daily in addition to aspirin 1, 2

Anticoagulation - choose one 1, 2:

• Enoxaparin IV followed by subcutaneous (preferred over UFH) 1
• UFH as weight-adjusted IV bolus followed by infusion 1
• Continue until revascularization or hospital stay up to 8 days 1, 2

Post-fibrinolysis management 1:

• Rescue PCI immediately if <50% ST-segment resolution at 60-90 minutes 1
• Routine angiography and PCI of infarct-related artery between 2-24 hours after successful fibrinolysis 1
• Emergency angiography for heart failure/shock, hemodynamic instability, or recurrent ischemia 1

Beta-Blocker Therapy

Early IV beta-blocker followed by oral therapy in hemodynamically stable patients 2, 3:

• Metoprolol 5 mg IV every 2 minutes for 3 doses 2
• Begin oral metoprolol 50 mg every 6 hours starting 15 minutes after last IV dose, continue for 48 hours 3
• Maintenance dose 100 mg orally twice daily thereafter 3

Contraindications to IV beta-blockers 2:

• Hypotension
• Acute heart failure
• AV block
• Severe bradycardia

ACE Inhibitor Therapy

Initiate within first 24 hours in appropriate patients 2, 4:

• Heart failure present
• LV systolic dysfunction
• Diabetes mellitus
• Anterior infarct

Dosing for acute MI 4:

• Lisinopril 5 mg orally initially in hemodynamically stable patients 4
• Follow with 5 mg after 24 hours, 10 mg after 48 hours, then 10 mg daily 4
• Start with 2.5 mg if systolic BP ≤120 mmHg and >100 mmHg during first 3 days 4
• Continue for at least 6 weeks 4

Critical Timing Considerations

Time-dependent mortality benefit 1:

• Within 1 hour: 35 lives saved per 1000 patients treated
• 7-12 hours: 16 lives saved per 1000 patients treated
• Overall 21% proportional mortality reduction with reperfusion therapy 1

Pre-Discharge Assessment

Routine echocardiography during hospital stay 1, 2:

• Assess LV and RV function
• Detect mechanical complications
• Exclude LV thrombus

Long-Term Management (Discharge to 12 Months)

Dual antiplatelet therapy (DAPT) 1, 2:

• Low-dose aspirin 75-100 mg daily 1, 2
• Plus ticagrelor or prasugrel (or clopidogrel if unavailable/contraindicated) 1, 2
• Continue for 12 months unless excessive bleeding risk 1, 2

Beta-blockers 2:

• Continue indefinitely in patients with heart failure and/or LVEF <40% 2

High-intensity statin therapy 2:

• Start as early as possible and maintain long-term 2

Cardiac rehabilitation 1:

• Participation strongly recommended 1

Smoking cessation 1:

• Repeated counseling with pharmacotherapy (nicotine replacement, varenicline, or bupropion) 1

Common Pitfalls to Avoid

• Do not delay aspirin administration - this is the most time-sensitive intervention after oxygen 1
• Do not give thrombolytics to patients without ST-elevation - increases bleeding risk without mortality benefit 1
• Do not use fondaparinux for primary PCI - it is contraindicated 1
• Do not give IV beta-blockers to hemodynamically unstable patients - assess for heart failure, hypotension, and bradycardia first 2
• Do not bypass the catheterization laboratory - patients should go directly there, not through ED 1, 2
• Do not use clopidogrel as first-line P2Y12 inhibitor when prasugrel or ticagrelor are available - the latter are more potent 1, 2