What is the recommended immediate management for an adult presenting with acute chest pain and a new ST‑segment elevation myocardial infarction (STEMI) diagnosed within 12 hours?

Immediate Management of STEMI

For adults with acute STEMI diagnosed within 12 hours of symptom onset, immediately administer aspirin 150–325 mg (chewable) or 250–500 mg IV, initiate anticoagulation, and transfer for primary PCI if it can be performed within 120 minutes of first medical contact; if PCI will be delayed beyond 120 minutes, administer fibrinolytic therapy immediately, preferably in the pre-hospital setting. 1, 2, 3

Initial Assessment & Immediate Interventions

Within the first 10 minutes:

• Obtain and interpret a 12-lead ECG within 10 minutes of first medical contact to confirm STEMI and establish "time zero" 4
• Administer aspirin 150–325 mg orally (chewable preferred) or 250–500 mg IV if the patient cannot swallow 2, 3
• Start anticoagulation with unfractionated heparin (weight-adjusted IV bolus then infusion) or enoxaparin (IV bolus followed by subcutaneous dosing, which is preferred) 2, 4, 3
• Provide supplemental oxygen only if oxygen saturation is <90%—routine oxygen in normoxic patients provides no benefit 3
• Initiate continuous ECG monitoring with defibrillator capacity 3

Reperfusion Strategy Decision Algorithm

The critical decision point is whether primary PCI can be achieved within 120 minutes of first medical contact:

If PCI Available Within 120 Minutes:

• Transfer immediately to a PCI-capable facility for primary percutaneous coronary intervention 1, 2, 3
• This is the preferred reperfusion strategy when door-to-balloon time can be achieved in <90 minutes by an experienced operator (>75 PCIs/year) at a high-volume center (>200 PCIs annually, including ≥36 primary PCIs for STEMI) 1
• Do not administer fibrinolytic therapy if PCI can be performed within this timeframe 2, 4
• For patients presenting to non-PCI-capable hospitals, arrange immediate transfer without fibrinolysis 3

If PCI Will Be Delayed Beyond 120 Minutes:

Initiate fibrinolytic therapy immediately (within 10 minutes of STEMI diagnosis), preferably in the pre-hospital setting: 2, 4

Fibrinolytic agent selection:

• Use a fibrin-specific thrombolytic: tenecteplase (preferred for single-bolus administration), alteplase, or reteplase 2, 4
• For symptom duration <6 hours, alteplase or tenecteplase are superior to streptokinase 5

Mandatory adjunctive medications with fibrinolysis:

• Aspirin: Already administered as above 2
• Clopidogrel: 300–600 mg loading dose immediately (clopidogrel is the only P2Y12 inhibitor recommended with fibrinolysis—do not use prasugrel or ticagrelor initially) 1, 2, 4
• Anticoagulation: Continue enoxaparin or UFH until revascularization or for up to 8 days of hospitalization 2, 4

Post-fibrinolysis management (pharmacoinvasive strategy):

• Transfer all patients to a PCI-capable center immediately after fibrinolysis—do not wait to assess reperfusion success 2, 4
• Notify the receiving PCI center during transport so the catheterization lab can be prepared 4
• Assess ST-segment resolution at 60–90 minutes post-fibrinolysis 2, 4
• Perform routine angiography 2–24 hours after successful fibrinolysis (≥50% ST-segment resolution) in hemodynamically stable patients 2, 4
• Perform immediate (rescue) PCI if <50% ST-segment resolution at 60–90 minutes, or if the patient develops heart failure, cardiogenic shock, hemodynamic/electrical instability, or recurrent ischemia 2, 4
• At the time of angiography/PCI, switch from clopidogrel to prasugrel (60 mg loading) or ticagrelor (180 mg loading), and continue dual antiplatelet therapy for 12 months 4

Timing Considerations & Evidence Strength

The benefit of reperfusion is time-dependent:

• Greatest benefit occurs within the first 3 hours of symptom onset 4
• Fibrinolytic therapy is generally not recommended for patients presenting 12–24 hours after symptom onset unless continuing ischemic pain with persistent ST-elevation is present 1
• Fibrinolytic therapy is contraindicated (Class III) for patients presenting >24 hours after symptom onset 1
• Every minute of delay increases myocardial necrosis 6

Special Populations & Scenarios

Post-cardiac arrest with ROSC:

• Perform emergent coronary angiography immediately rather than delaying, even if the patient is unconscious 1, 3
• Angiography/PCI should not preclude or delay therapeutic hypothermia 1

Patients with contraindications to fibrinolysis:

• PCI is recommended despite delay, rather than foregoing reperfusion therapy entirely 1

STEMI patients presenting >12 hours after symptom onset:

• In the TRITON-TIMI 38 trial, the prasugrel loading dose was not administered until coronary anatomy was established in these patients 7
• Most received the loading dose at the time of PCI 7

Critical Pitfalls to Avoid

• Do not combine fibrinolytic therapy with immediate PCI—this is harmful (Class III: Harm) 3
• Do not use prasugrel or ticagrelor as the initial P2Y12 inhibitor with fibrinolysis—clopidogrel is specifically indicated in this setting 2, 4
• Do not delay transfer to a PCI-capable center after fibrinolysis—all patients require angiography regardless of apparent clinical success 2, 4
• Do not miss the 2–24 hour window for routine angiography after successful fibrinolysis—adherence improves outcomes 2, 4
• Do not administer routine supplemental oxygen to normoxic patients—it provides no benefit 3
• Do not use fondaparinux for primary PCI—it is contraindicated (Class III) 4
• Do not delay reperfusion beyond 120 minutes when attempting primary PCI—fibrinolysis followed by transfer yields better outcomes 4

Antiplatelet Therapy Dosing Specifics

For patients undergoing primary PCI:

• Prasugrel 60 mg loading dose may be administered after coronary anatomy is established, followed by 10 mg daily 7
• Consider reducing maintenance dose to 5 mg daily in patients <60 kg due to increased bleeding risk 7
• Prasugrel is contraindicated in patients with prior TIA or stroke due to increased risk of intracranial hemorrhage 7
• Prasugrel is generally not recommended in patients ≥75 years except in high-risk situations (diabetes or prior MI) 7

For patients receiving fibrinolysis:

• Clopidogrel 300 mg loading dose for patients up to 75 years of age 1
• Switch to prasugrel or ticagrelor at the time of subsequent PCI 4