What is the initial management of myocardial infarction (MI) in the emergency department?

Initial Management of Myocardial Infarction in the Emergency Department

Patients with suspected acute MI should receive immediate aspirin 160-325 mg orally, continuous cardiac monitoring, a 12-lead ECG within 10 minutes, and rapid assessment for reperfusion therapy based on ST-segment elevation or new left bundle branch block. 1

Immediate Assessment and Stabilization (First 10-20 Minutes)

• Obtain a 12-lead ECG within 10 minutes of arrival to identify ST-segment elevation ≥1 mm in contiguous leads or new LBBB, which indicates need for immediate reperfusion therapy 2, 1
• Complete the entire initial assessment within 20 minutes of arrival 1
• Initiate continuous cardiac monitoring immediately to detect life-threatening arrhythmias 1
• Ensure transcutaneous pacing patches, defibrillator, atropine, lidocaine, and epinephrine are immediately available 2
• Administer oxygen only if arterial oxygen saturation is <90% or PaO₂ <60 mmHg—routine oxygen therapy when SaO₂ ≥90% is not recommended 1

Immediate Pharmacological Interventions

Antiplatelet Therapy

• Administer aspirin 160-325 mg orally immediately upon suspicion of MI, even before ECG confirmation 2, 1
• Pre-hospital aspirin administration improves survival and should not be delayed 3
• Add a P2Y12 inhibitor (ticagrelor or prasugrel preferred over clopidogrel) as dual antiplatelet therapy 1, 4
• Clopidogrel 75 mg daily reduces death, reinfarction, or stroke by 9% when added to aspirin 5

Pain Management and Hemodynamic Control

• Administer sublingual nitroglycerin unless systolic blood pressure is <90 mmHg or heart rate is <50 or >100 beats per minute 1
• Intravenous nitroglycerin should be used for 24-48 hours in patients without hypotension, bradycardia, or excessive tachycardia, as it can be titrated to hemodynamic response 2
• Provide adequate analgesia with morphine sulfate or meperidine—nitroglycerin should not substitute for narcotic analgesics 2
• Avoid nitrates in patients with inferior STEMI and suspected right ventricular involvement, as they can cause profound hypotension 1

Beta-Blocker Therapy

• Initiate early intravenous β-adrenergic blocker therapy followed by oral therapy in patients with evolving acute MI, provided there are no contraindications 2
• β-blockers should be given regardless of whether reperfusion therapy was administered, as they reduce morbidity and mortality 2

Anticoagulation

• Administer parenteral anticoagulation with unfractionated heparin, low-molecular-weight heparin, bivalirudin, or fondaparinux 4
• For patients receiving thrombolytic therapy, heparin administration recommendations vary by specific agent used 2

Reperfusion Strategy Decision-Making

ST-Elevation MI or New LBBB

• Primary PCI is the preferred reperfusion strategy when it can be performed within 90 minutes of first medical contact 1
• If the anticipated time from STEMI diagnosis to PCI-mediated reperfusion is >120 minutes, initiate fibrinolytic therapy immediately (within 10 minutes of STEMI diagnosis) 2
• The greatest mortality benefit occurs when reperfusion is initiated within the first hour ("golden hour"), with 35 lives saved per 1000 patients treated within the first hour versus 16 lives saved per 1000 when given 7-12 hours after symptom onset 2, 6
• Reperfusion therapy should be initiated within 12 hours of symptom onset, with progressively diminishing benefit after 6 hours 6

Non-ST-Elevation MI

• Patients without ST-segment elevation should not receive thrombolytic therapy 2
• PCI is recommended for non-ST-elevation ACS; fibrinolytic therapy is typically not indicated 4

Management of Cardiac Rhythm Disturbances

• For symptomatic or hemodynamically significant bradycardia, administer atropine 0.5-1.0 mg IV (may repeat to maximum of 3 mg) 1
• Transcutaneous pacing capabilities must be immediately available 1
• Patients with inferior wall MI require close monitoring for conduction abnormalities and right ventricular involvement 1
• Prophylactic antiarrhythmic agents are not recommended in the first 24 hours 2

Special Considerations and Complications

Right Ventricular Infarction

• Treat vigorously with intravascular volume expansion using normal saline 2
• Administer inotropic agents if hypotension persists despite volume expansion 2

Heart Failure and Cardiogenic Shock

• Administer intravenous diuretic (usually furosemide) and an afterload-reducing agent for heart failure 2
• Consider intra-aortic balloon pump and emergency coronary angiography followed by PTCA or CABG for cardiogenic shock 2

Recurrent Chest Pain

• Treat recurrent ischemic chest pain with intravenous nitroglycerin, analgesics, and antithrombotic medications (aspirin, heparin) 2
• Consider coronary angiography with subsequent revascularization 2
• For chest pain believed to be pericarditis, administer high-dose aspirin 650 mg every 4-6 hours 2

Medications to Avoid

• Calcium channel blockers have not been shown to reduce mortality in acute MI and may be harmful in certain patients 2
• Avoid oral nitrate preparations in the acute setting due to inability to titrate dose in evolving hemodynamic situations 2

Common Pitfalls to Avoid

• Do not delay reperfusion therapy while waiting for cardiac biomarker results when ECG shows ST-segment elevation or new LBBB 1, 6
• Do not administer excessive fluids to patients without right ventricular involvement, as this may worsen left ventricular failure 1
• Do not use beta-blockers or calcium channel blockers in patients with conduction abnormalities, as they may worsen bradycardia or heart block 1
• Do not substitute nitroglycerin for adequate narcotic analgesia 2
• Do not perform routine catheterization within 2-3 hours of fibrinolytic administration unless rescue PCI is needed due to increased bleeding risk 6