What is the appropriate acute treatment for a patient with suspected acute myocardial infarction?

Acute Treatment for Suspected Myocardial Infarction

For suspected acute MI, immediately administer oxygen (if SaO2 <90%), aspirin 160-325 mg orally, sublingual nitroglycerin (unless contraindicated), and morphine 4-8 mg IV for pain control, while obtaining a 12-lead ECG within 10 minutes to determine if ST-elevation is present and guide reperfusion strategy. 1, 2

Immediate Emergency Department Management (Within 10-20 Minutes)

Upon arrival, the following must be initiated simultaneously:

• Oxygen: Administer by nasal prongs only if oxygen saturation <90% (routine oxygen is not recommended, Class III evidence) 2
• Aspirin: 160-325 mg orally or IV if unable to swallow (Class I, Level B recommendation) 1, 2
• Nitroglycerin: Sublingual unless systolic BP <90 mmHg, heart rate <50 or >100 bpm, or patient has taken phosphodiesterase-5 inhibitors (tadalafil) within 48 hours 1, 3
• Morphine sulfate: 4-8 mg IV with additional 2 mg doses at 5-15 minute intervals for pain control and anxiety reduction 1, 4, 2
• 12-lead ECG: Must be performed and interpreted within 10 minutes of arrival 1, 2

Critical Contraindication Alert

Nitrates are absolutely contraindicated for at least 48 hours after phosphodiesterase-5 inhibitor use (e.g., tadalafil) due to risk of severe, potentially fatal hypotension. 3 In these patients, use morphine exclusively for pain control. 3

Reperfusion Strategy Based on ECG Findings

ST-Elevation MI (STEMI) or New LBBB

Primary PCI is the definitive reperfusion strategy and must be performed within 90-120 minutes of first medical contact (Class I, Level A recommendation). 3, 2

If primary PCI cannot be performed within 120 minutes of diagnosis, initiate fibrinolytic therapy immediately with a fibrin-specific agent (preferably tenecteplase), ideally within 10 minutes of decision. 2

The mortality benefit is highly time-dependent:

• Within first hour: 35 lives saved per 1000 patients treated 1
• 7-12 hours after onset: 16 lives saved per 1000 patients treated 1
• Greatest benefit occurs within 6 hours, but definite benefit exists up to 12 hours 1

Non-ST-Elevation MI

Do not administer thrombolytic therapy to patients without ST-elevation; the benefit of primary PCI in these patients remains uncertain. 1

Antithrombotic Regimen

Antiplatelet Therapy

• Aspirin: Continue 160-325 mg daily indefinitely after initial dose 1
• P2Y12 inhibitor: Administer potent agent (prasugrel 60 mg or ticagrelor 180 mg loading dose) before or at time of PCI, preferred over clopidogrel (Class I, Level A recommendation) 3, 2
• Dual antiplatelet therapy (DAPT): Continue aspirin 75-100 mg plus ticagrelor or prasugrel for 12 months post-MI (Class I, Level A recommendation) 2

Anticoagulation

• For primary PCI: Unfractionated heparin as weight-adjusted IV bolus followed by infusion 1, 3, 2
• For fibrinolytic therapy: Enoxaparin IV followed by subcutaneous dosing 3
• For alteplase (tPA) specifically: Continue IV heparin for additional 48 hours 1
• For large anterior MI or LV mural thrombus: Early IV heparin reduces embolic stroke risk 1

First 24 Hours of Hospitalization

Monitoring and Activity

• Continuous cardiac monitoring for arrhythmias and hemodynamic instability 1, 4, 2
• Limit physical activities for at least 12 hours 1
• Serial ECGs and cardiac markers (troponin T/I or CK-MB) to confirm diagnosis 1
• Emergency equipment immediately available: Atropine, lidocaine, transcutaneous pacing patches/transvenous pacemaker, defibrillator, epinephrine 1

Beta-Blocker Therapy

Administer early IV beta-blocker (e.g., metoprolol) in hemodynamically stable patients, followed by oral therapy, regardless of whether reperfusion therapy was given (reduces morbidity and mortality in both prethrombolytic and thrombolytic eras). 1, 5

Contraindications include hypotension, bradycardia, or excessive tachycardia. 1

Nitroglycerin

Infuse IV nitroglycerin for 24-48 hours in patients without hypotension, bradycardia, or excessive tachycardia. 1 This allows dose titration based on hemodynamics, unlike oral nitrates which cannot be adjusted in acute evolving situations. 1 Nitroglycerin should not substitute for narcotic analgesics. 1

Medications to Avoid

• Prophylactic antiarrhythmic agents: Not recommended in first 24 hours 1
• Calcium channel blockers: Have not reduced mortality and may be harmful in certain patients 1
• NSAIDs for pain: Prohibited due to prothrombotic effects 2
• Benzodiazepines: Not mentioned in ESC guidelines; can cause respiratory depression, hypotension, and may obscure clinical signs of complications 4

Post-Reperfusion Management

After Fibrinolytic Therapy

• Transfer immediately to PCI-capable center (Class I, Level A recommendation) 2
• Coronary angiography within 2-24 hours after successful fibrinolysis 3, 2
• Emergency angiography and PCI immediately if heart failure or shock develops 3, 2

Routine Post-MI Care

• Echocardiography during hospital stay to assess LV/RV function, detect mechanical complications, and exclude LV thrombus 3
• ACE inhibitors: Initiate early, particularly for large anterior MI or heart failure 1
• High-intensity statin therapy: For all STEMI patients 3
• Proton pump inhibitor: For patients at high GI bleeding risk on DAPT (Class I, Level B recommendation) 2

Management of Complications

Recurrent Ischemic Chest Pain

Treat with IV nitroglycerin, analgesics, and antithrombotic medications (aspirin, heparin); consider coronary angiography with revascularization. 1

Pericarditis

Administer high-dose aspirin 650 mg every 4-6 hours. 1

Heart Failure

Administer IV diuretic (usually furosemide) and afterload-reducing agent. 1

Cardiogenic Shock

Consider intra-aortic balloon pump insertion and emergency coronary angiography, followed by PCI or CABG. 1

Right Ventricular Infarction with Hypotension

Treat vigorously with intravascular volume expansion using normal saline and inotropic agents if hypotension persists. 1

Key Pitfalls to Avoid

• Do not delay reperfusion therapy waiting for troponin results; ECG diagnosis is sufficient 2
• Do not perform routine thrombus aspiration during primary PCI (Class III recommendation) 2
• Do not treat non-culprit vessels during index PCI unless patient is in cardiogenic shock 2
• Do not use oral nitrates in acute phase due to inability to titrate; use IV nitroglycerin instead 1
• Do not overlook atypical presentations: ST-elevation without chest pain still requires immediate STEMI protocol activation 2