What is the management strategy for a patient with acute myocardial infarction (AMI)?

Management of Acute Myocardial Infarction

Immediate Actions Upon Arrival (Within 10 Minutes)

Administer aspirin 150-325 mg (chewed, not enteric-coated) immediately unless contraindicated, obtain a 12-lead ECG within 10 minutes, establish IV access, and initiate continuous cardiac monitoring. 1, 2

• Give supplemental oxygen if arterial oxygen saturation is <90% 1, 2
• Administer sublingual nitroglycerin (0.4 mg every 5 minutes up to 3 doses) for chest pain relief, but avoid if systolic BP <90 mmHg, heart rate <50 or >100 bpm, or suspected right ventricular infarction 1, 2
• Provide morphine 2-4 mg IV for pain not relieved by nitroglycerin 1
• Draw blood for cardiac biomarkers (troponin, CK-MB), complete blood count, metabolic panel, and lipid profile 1, 2

Reperfusion Strategy Selection (Goal: Door-to-Intervention <90-120 Minutes)

Primary percutaneous coronary intervention (PCI) is the preferred reperfusion strategy and must be performed within 90 minutes of first medical contact (or 60 minutes if presenting at a PCI-capable center). 1, 2

• Bypass the emergency department and transport directly to the catheterization laboratory if STEMI is confirmed 1, 2
• If primary PCI cannot be achieved within 90-120 minutes, administer fibrinolytic therapy immediately (goal: door-to-needle time <30 minutes) 1, 2
• Reperfusion therapy is indicated for all patients with symptom onset ≤12 hours and persistent ST-segment elevation or new left bundle branch block 1, 2

Fibrinolytic Therapy Contraindications

Absolute contraindications: Any prior hemorrhagic stroke, ischemic stroke within 6 months, known intracranial neoplasm, active internal bleeding (excluding menses), suspected aortic dissection 1

Relative contraindications: Severe uncontrolled hypertension (BP >180/110 mmHg), current therapeutic anticoagulation (INR >2-3), recent trauma or major surgery within 2-4 weeks, pregnancy 1

Antithrombotic Therapy for Primary PCI

Administer a loading dose of prasugrel 60 mg or ticagrelor 180 mg (preferred over clopidogrel 600 mg) before or at the time of PCI, combined with unfractionated heparin during the procedure. 1, 2

• Prasugrel and ticagrelor are superior to clopidogrel for reducing ischemic events 1, 2
• Enoxaparin or bivalirudin are acceptable alternatives to unfractionated heparin 1
• Avoid GP IIb/IIIa inhibitors routinely due to increased bleeding risk without mortality benefit 1
• Use radial artery access when the interventional cardiologist is experienced with this approach 1

Antithrombotic Therapy for Fibrinolysis

If fibrinolytic therapy is chosen, administer one of the following regimens with concurrent anticoagulation: 1, 2

• Tenecteplase (TNK-tPA): Single IV bolus weight-adjusted (30-50 mg based on body weight) with IV heparin for 24-48 hours 1

• Alteplase (tPA): 15 mg IV bolus, then 0.75 mg/kg over 30 minutes, then 0.5 mg/kg over 60 minutes (max 100 mg total) with IV heparin for 24-48 hours 1

• Streptokinase: 1.5 million units over 30-60 minutes (heparin optional, but do not re-administer streptokinase due to antibody formation) 1

• Add clopidogrel 75 mg daily to aspirin after fibrinolysis 2

• Continue anticoagulation until revascularization or for hospital stay up to 8 days 2

Beta-Blocker Therapy

Initiate IV metoprolol 5 mg every 2 minutes for 3 doses (total 15 mg) followed by oral metoprolol 50 mg every 6 hours starting 15 minutes after the last IV dose, if no contraindications exist. 1, 3

• Contraindications to IV beta-blockers: Systolic BP <100 mmHg, heart rate <60 bpm, signs of acute heart failure, second- or third-degree AV block, severe reactive airway disease 1, 3
• Oral beta-blockers should be continued indefinitely in all patients, particularly those with heart failure or LVEF <40% 1, 2
• Administer in a monitored setting with continuous ECG and blood pressure monitoring 3

ACE Inhibitor/ARB Therapy

Start an ACE inhibitor within the first 24 hours in patients with heart failure, LV systolic dysfunction (LVEF <40%), diabetes, or anterior infarction, provided systolic BP >100 mmHg. 1, 2

• An ARB (preferably valsartan) is an acceptable alternative in patients intolerant to ACE inhibitors 1
• ACE inhibitors should be considered in all patients without contraindications (hypotension, bilateral renal artery stenosis, hyperkalemia) 1

Mineralocorticoid Receptor Antagonist (MRA)

Add an MRA (spironolactone or eplerenone) in patients with LVEF <40% and heart failure or diabetes who are already receiving an ACE inhibitor and beta-blocker, provided serum creatinine is <2.5 mg/dL in men or <2.0 mg/dL in women and potassium is <5.0 mEq/L. 1

• Monitor serum potassium and renal function closely after initiation 1

High-Intensity Statin Therapy

Initiate high-intensity statin therapy (atorvastatin 40-80 mg or rosuvastatin 20-40 mg) as early as possible and continue indefinitely. 1, 2

Monitoring and Hospital Course

All STEMI patients require continuous ECG monitoring for a minimum of 24 hours in a coronary care unit (CCU) or intensive cardiac care unit (ICCU). 1, 2

• Patients with successful reperfusion and an uncomplicated course should remain in the CCU for at least 24 hours, then transfer to a step-down unit for an additional 24-48 hours 1
• Early discharge (48-72 hours) is appropriate for low-risk patients: age <70 years, LVEF >45%, successful PCI, no persistent arrhythmias 1

Pre-Discharge Assessment

Perform transthoracic echocardiography before discharge to assess LV and RV function, detect mechanical complications, and exclude LV thrombus. 2

• Conduct submaximal exercise testing at 4-7 days or symptom-limited testing at 10-14 days to assess functional capacity and stratify risk 2

Long-Term Dual Antiplatelet Therapy (DAPT)

Continue DAPT with aspirin 75-100 mg daily plus prasugrel 10 mg daily or ticagrelor 90 mg twice daily (or clopidogrel 75 mg daily if prasugrel/ticagrelor unavailable or contraindicated) for 12 months unless excessive bleeding risk exists. 1, 2

• After 12 months, continue aspirin monotherapy indefinitely 1, 2
• In patients requiring oral anticoagulation (e.g., atrial fibrillation), use triple therapy (oral anticoagulant + aspirin + clopidogrel) for 1-6 months depending on bleeding risk, then dual therapy (oral anticoagulant + single antiplatelet) for up to 12 months, followed by oral anticoagulant alone 1
• Clopidogrel is the P2Y12 inhibitor of choice in patients on oral anticoagulation; avoid prasugrel and ticagrelor 1
• Add a proton pump inhibitor for gastric protection in patients on triple therapy 1

Common Pitfalls to Avoid

• Do not delay reperfusion therapy while waiting for cardiac biomarker results; ECG findings are sufficient to initiate treatment 2
• Do not use NSAIDs other than aspirin post-MI, as they increase mortality and reinfarction risk 4
• Do not re-administer streptokinase if fibrinolysis fails or reocclusion occurs; use alteplase or proceed to rescue PCI 1
• Do not give IV beta-blockers to patients with signs of acute heart failure or cardiogenic shock 1, 3