What is the evidence‑based initial and early management of an adult presenting with an acute myocardial infarction (ST‑segment elevation myocardial infarction or high‑risk non‑ST‑segment elevation myocardial infarction)?

Management of Acute Myocardial Infarction

Immediate Actions (First 10 Minutes)

Obtain a 12-lead ECG within 10 minutes of first medical contact and immediately administer aspirin 150–325 mg orally (or 250–500 mg IV if the patient cannot swallow). 1, 2

• Initiate continuous ECG monitoring with defibrillator capacity immediately in all patients with suspected acute MI 1, 2
• Do not provide routine supplemental oxygen unless oxygen saturation falls below 90% 1, 2
• Administer morphine 4–8 mg IV for pain control, with additional 2 mg doses every 5–15 minutes as needed 3

Reperfusion Strategy Selection: The 120-Minute Rule

Primary percutaneous coronary intervention (PCI) is the definitive reperfusion strategy when it can be performed within 120 minutes of STEMI diagnosis; if this timeline cannot be met, initiate fibrinolytic therapy within 10 minutes. 1, 2, 3

For Patients Presenting Directly to a PCI-Capable Hospital:

• Perform primary PCI within 90 minutes of first medical contact 2, 3
• Transfer the patient directly to the catheterization laboratory, bypassing the emergency department 1, 2
• PCI-capable centers must provide 24/7 service without delay, even during off-hours 2

For Patients at Non-PCI-Capable Facilities:

• Transfer immediately for primary PCI if first-medical-contact-to-device time will be ≤120 minutes 2
• Maintain a door-in-door-out time of ≤30 minutes to achieve the 120-minute goal 2
• If primary PCI will exceed 120 minutes, administer fibrinolytic therapy within 10–30 minutes of diagnosis 2, 4

Mandatory Primary PCI Regardless of Time Delay:

• Cardiogenic shock or acute severe heart failure at any time after symptom onset 1, 2
• Contraindications to fibrinolytic therapy (active bleeding, recent stroke, terminal illness) 2
• Cardiac arrest with ST-elevation on post-resuscitation ECG 1, 2

Antithrombotic Regimen for Primary PCI

P2Y12 Inhibitor Loading:

Administer prasugrel 60 mg or ticagrelor 180 mg loading dose before or at the time of PCI; use clopidogrel 600 mg only if prasugrel or ticagrelor are unavailable. 1, 2, 5

• For patients weighing <60 kg, consider reducing prasugrel maintenance dose to 5 mg daily due to increased bleeding risk 5
• In STEMI patients presenting within 12 hours of symptom onset, the loading dose may be administered at the time of diagnosis, though most receive it at the time of PCI 5
• A 2023 meta-analysis demonstrated that pretreatment with P2Y12 inhibitors reduces definite stent thrombosis (OR 0.61), all-cause death (OR 0.77), and cardiogenic shock (OR 0.60) without increasing major bleeding 6

Anticoagulation:

• Administer unfractionated heparin 100 U/kg IV bolus (reduce to 60 U/kg if GPIIb/IIIa inhibitor is used) 1, 2
• Enoxaparin or bivalirudin are acceptable alternatives 1
• Fondaparinux is contraindicated for primary PCI 1, 2

Technical Standards During Primary PCI

Use routine radial arterial access and implant drug-eluting stents as the default strategy. 1, 2

• Routine thrombus aspiration is contraindicated (Class III recommendation) 1, 2
• Deferred stenting is contraindicated 1, 2
• Treat only the infarct-related artery during the index procedure unless the patient is in cardiogenic shock 1, 2
• For severe non-infarct-related artery stenoses, consider revascularization before hospital discharge (either during index PCI or staged) 1, 2

Fibrinolytic Strategy (When PCI Delay >120 Minutes)

Administer a fibrin-specific agent (tenecteplase, alteplase, or reteplase) within 10–30 minutes of diagnosis, preferably in the pre-hospital setting. 1, 2, 4

Mandatory Adjunctive Therapy with Fibrinolysis:

• Continue aspirin (oral or IV) 2, 4
• Add clopidogrel (not prasugrel or ticagrelor initially) 2, 4
• Provide anticoagulation with enoxaparin (preferred) or unfractionated heparin until revascularization or up to 8 days of hospitalization 2, 4
• For patients ≥75 years old receiving tenecteplase, use a 50% dose reduction to reduce stroke risk 2

Post-Fibrinolysis Management Algorithm:

All patients receiving fibrinolysis must be transferred immediately to a PCI-capable center regardless of apparent success. 4, 3

• Perform routine angiography and PCI between 2–24 hours after fibrinolysis (Class I, Level A) 4
• Perform immediate rescue PCI if <50% ST-segment resolution at 60–90 minutes, hemodynamic instability, or refractory ischemia 2, 4, 3
• Monitor for successful reperfusion by assessing symptom relief, hemodynamic stability, and ≥50% reduction in ST-segment elevation on follow-up ECG 60–90 minutes after administration 2

Special Clinical Scenarios

Patients Taking Oral Anticoagulation:

Triage these patients for primary PCI regardless of anticipated time to reperfusion, as oral anticoagulation is a relative contraindication for fibrinolysis. 1

• Administer additional parenteral anticoagulation regardless of timing of last oral anticoagulant dose 1
• Use clopidogrel 600 mg loading dose (prasugrel and ticagrelor are not recommended) 1
• Avoid GPIIb/IIIa inhibitors 1
• Continue chronic anticoagulation during admission and provide gastric protection with a proton pump inhibitor 1

Cardiac Arrest with STEMI:

• Perform primary PCI immediately in patients with resuscitated cardiac arrest and ST-elevation on post-resuscitation ECG 1, 2
• If ST-elevation is absent but high suspicion of ongoing ischemia exists, perform urgent angiography within 2 hours 1, 2
• Initiate targeted temperature management early in unresponsive patients after cardiac arrest 1, 2
• Do not use pre-hospital cooling with large volumes of cold IV fluid immediately after return of spontaneous circulation 1, 2

Late Presentation (>12 Hours):

• Routine PCI of an occluded infarct-related artery >48 hours after symptom onset is not indicated in asymptomatic patients (Class III, Level A) 2, 4
• PCI is warranted in patients with hemodynamic or electrical instability, or persistent symptoms, regardless of time delay 2

In-Hospital Management

Monitoring:

Monitor all STEMI patients for a minimum of 24 hours in a coronary care unit or intensive cardiac care unit. 1, 2

• Patients with successful reperfusion and uncomplicated course should remain in CCU/ICCU for 24 hours, then move to a step-down monitored bed for an additional 24–48 hours 1
• Early discharge (within 48–72 hours) is appropriate in selected low-risk patients (age <70 years, LVEF >45%, one- or two-vessel disease, successful PCI, no persistent arrhythmias) if early rehabilitation and adequate follow-up are arranged 1

Dual Antiplatelet Therapy (DAPT):

Continue aspirin 75–100 mg daily plus prasugrel 10 mg daily or ticagrelor 90 mg twice daily for 12 months after PCI. 2, 3

• For patients <60 kg on prasugrel, consider reducing maintenance dose to 5 mg daily 5
• Add a proton pump inhibitor in patients at high risk of gastrointestinal bleeding 2, 3

Additional Evidence-Based Medications:

• Initiate high-intensity statin therapy as early as possible 2
• Start beta-blockers orally in patients with heart failure and/or LVEF <40% unless contraindicated 2, 7
• For IV metoprolol in the early phase: administer three bolus injections of 5 mg each at approximately 2-minute intervals, monitoring blood pressure, heart rate, and ECG during administration 7
• Initiate ACE inhibitors within 24 hours in patients with heart failure, LV systolic dysfunction, diabetes, or anterior infarction 2, 3

Post-Discharge Management

• Continue aspirin 75–100 mg daily indefinitely 2
• Maintain DAPT for 12 months unless excessive bleeding risk exists 2, 3
• Target LDL-C <1.8 mmol/L (70 mg/dL) or reduce by at least 50% if baseline is 1.8–3.5 mmol/L 2
• Provide smoking cessation counseling with pharmacological support 2
• Enroll patients in a cardiac rehabilitation program (either in-hospital or outpatient) 1, 2
• Schedule early post-discharge consultations with a cardiologist, primary care physician, or specialized nurse 1

Critical Pitfalls to Avoid

• Do not delay reperfusion therapy to wait for troponin results; ECG diagnosis is sufficient 2
• Do not treat non-culprit vessels during index PCI unless the patient is in cardiogenic shock 1, 2
• Do not use NSAIDs for pain relief due to pro-thrombotic effects 2
• Do not administer prasugrel within 24 hours of fibrin-specific fibrinolysis or in patients with prior stroke/TIA (Class III: Harm) 3
• Do not re-administer fibrinolytic agents for persistent ST-elevation; proceed directly to rescue PCI 3
• Do not use fondaparinux as the sole anticoagulant during PCI due to high risk of catheter thrombosis 3