What is the immediate assessment and treatment protocol for an adult presenting with an acute myocardial infarction (STEMI or NSTEMI)?

Immediate Assessment and Treatment Protocol for Acute Myocardial Infarction

Initial Diagnostic Actions (First 10 Minutes)

Obtain a 12-lead ECG within 10 minutes of first medical contact and interpret it immediately to distinguish STEMI from NSTEMI. 1 This single test determines your entire management pathway and must not be delayed for troponin results or other testing. 2

• Initiate continuous cardiac monitoring with defibrillator capability for all suspected MI patients 1
• Recognize STEMI equivalents beyond classic ST-elevation: new bundle-branch block, ventricular pacing, hyperacute T-waves, isolated anterior ST-depression, or diffuse ST-depression with ST-elevation in aVR 1
• Administer supplemental oxygen only when peripheral oxygen saturation is <90%; routine oxygen in normoxic patients provides no benefit 1, 2
• Draw high-sensitivity cardiac troponin using a 0-hour/1-hour protocol if available, with additional testing at 3-6 hours if initial results are inconclusive 3
• Perform echocardiography during the hospital stay to assess left and right ventricular function, detect mechanical complications, and exclude left ventricular thrombus 3

---

STEMI Management Protocol

Reperfusion Strategy Selection (Time-Critical Decision)

Primary PCI is the definitive reperfusion strategy when door-to-balloon time can be achieved within 90-120 minutes of first medical contact. 3, 1, 2 This approach reduces mortality, reinfarction, and stroke compared to fibrinolysis when performed by experienced operators. 2

If primary PCI cannot be performed within 120 minutes of STEMI diagnosis, initiate fibrinolytic therapy within 10 minutes of diagnosis, preferably in the pre-hospital setting. 3, 1, 2 Target door-to-needle time ≤30 minutes. 3

• Transfer patients directly to the catheterization laboratory, bypassing the emergency department when primary PCI is the chosen strategy 1
• Reperfusion therapy is mandatory for all patients with ischemic symptoms <12 hours and persistent ST-segment elevation 3, 1
• Consider reperfusion beyond 12 hours when clinical or electrocardiographic evidence of ongoing ischemia persists 1
• Patients with cardiogenic shock or severe heart failure should be transported immediately to a facility capable of cardiac catheterization and rapid revascularization 3

Antithrombotic Therapy for Primary PCI

Administer aspirin 150-325 mg (oral or IV if unable to swallow) immediately upon presentation. 3, 1, 2

Give a potent P2Y12 inhibitor—prasugrel 60 mg or ticagrelor 180 mg—before or at the time of PCI; use clopidogrel only if these agents are unavailable or contraindicated. 3, 1, 2 Prasugrel and ticagrelor are superior to clopidogrel for reducing ischemic events. 3

• Administer weight-adjusted unfractionated heparin as IV bolus followed by infusion; enoxaparin or bivalirudin are acceptable alternatives 3, 1
• Avoid fondaparinux in patients undergoing primary PCI due to high risk of catheter thrombosis 3, 1
• Continue dual antiplatelet therapy (aspirin plus P2Y12 inhibitor) for 12 months unless excessive bleeding risk exists 3, 1, 2

Antithrombotic Therapy for Fibrinolytic Strategy

Use a fibrin-specific thrombolytic agent (tenecteplase, alteplase, or reteplase) administered as a single IV bolus over 5 seconds. 3, 1, 4 Tenecteplase is preferred for ease of administration. 4

• Give aspirin loading dose (oral or IV) 3, 1
• Add clopidogrel to aspirin for dual antiplatelet therapy 3, 1
• Prefer enoxaparin (IV bolus followed by subcutaneous dosing) over unfractionated heparin for anticoagulation 3, 1
• Transfer the patient immediately to a PCI-capable center after fibrinolysis, regardless of apparent reperfusion success 3, 1, 2

Post-Fibrinolysis Management

Perform rescue PCI immediately if fibrinolysis fails, defined as <50% ST-segment resolution at 60-90 minutes. 3, 1, 2 Failed reperfusion indicates ongoing coronary occlusion and mandates urgent mechanical intervention. 2

• Proceed to emergency angiography and PCI for hemodynamic instability, electrical instability, or worsening ischemia at any time 3, 1
• In patients with successful fibrinolysis, schedule angiography and PCI of the infarct-related artery within 2-24 hours 3, 1, 2
• Emergency angiography is indicated for patients who develop heart failure or cardiogenic shock after fibrinolysis 3, 1

Primary PCI Technical Details

• Use radial arterial access as the standard approach 1, 2
• Implant drug-eluting stents routinely 1, 2
• Do not perform routine thrombus aspiration (contraindicated, Class III) 1, 2
• Treat only the infarct-related artery during the acute procedure unless the patient is in cardiogenic shock 2

Special Circumstances in STEMI

• In patients with cardiac arrest and ST-elevation, proceed with primary PCI 1
• In cardiac arrest without ST-elevation but high suspicion of coronary ischemia, perform urgent angiography within 2 hours after excluding non-coronary causes 3, 1
• Severe hypertension (systolic >180 mmHg or diastolic >110 mmHg) is a relative contraindication to fibrinolysis; rapidly lower blood pressure below these thresholds before administering thrombolytics 1
• IV beta-blockers can be used acutely to reduce blood pressure to <180/110 mmHg before thrombolysis in patients without cardiogenic shock, severe heart failure, or bradycardia 1, 5

---

NSTEMI Management Protocol

Risk Stratification and Timing of Invasive Strategy

An immediate invasive strategy (<2 hours) is mandatory for patients with very-high-risk criteria: 3

• Hemodynamic instability or cardiogenic shock
• Recurrent or ongoing chest pain refractory to medical treatment
• Life-threatening arrhythmias or cardiac arrest
• Mechanical complications of MI
• Acute heart failure with refractory angina or ST deviation
• Recurrent dynamic ST- or T-wave changes, particularly with intermittent ST elevation

An early invasive strategy (<24 hours) is recommended for patients with high-risk criteria: 3

• Rise or fall in cardiac troponin compatible with MI
• Dynamic ST- or T-wave changes (symptomatic or silent)
• GRACE score >140

An invasive strategy (<72 hours) is recommended for patients with intermediate-risk criteria: 3

• Diabetes mellitus
• Renal insufficiency (eGFR <60 mL/min/1.73 m²)
• LVEF <40% or congestive heart failure
• Early post-infarction angina
• Recent PCI or prior CABG
• GRACE risk score >109 and <140, or recurrent symptoms or known ischemia on non-invasive testing

Antithrombotic Therapy for NSTEMI

Administer aspirin 75-100 mg immediately upon presentation. 3

Ticagrelor (180 mg loading dose, 90 mg twice daily) is recommended for all patients at moderate to high risk of ischemic events (e.g., elevated cardiac troponins), regardless of initial treatment strategy. 3 Ticagrelor should be started even in patients pretreated with clopidogrel, which should be discontinued. 3

• Prasugrel (60 mg loading dose, 10 mg daily) is recommended in patients proceeding to PCI who are not at high bleeding risk and have no history of stroke or TIA 3
• Use clopidogrel only if ticagrelor or prasugrel are unavailable or contraindicated 3
• Continue P2Y12 inhibitor in addition to aspirin for 12 months unless excessive bleeding risk exists 3
• Administer parenteral anticoagulation with unfractionated heparin, low-molecular-weight heparin, bivalirudin, or fondaparinux 6

---

Long-Term Medical Therapy (Both STEMI and NSTEMI)

Initiate high-intensity statin therapy as early as possible and maintain long-term, targeting LDL-C <1.8 mmol/L (70 mg/dL) or ≥50% reduction if baseline LDL-C is 1.8-3.5 mmol/L. 3, 2

Start ACE inhibitors within the first 24 hours of MI in patients with heart failure, left ventricular dysfunction, diabetes, or anterior infarction. 3

Oral beta-blockers are indicated in patients with heart failure and/or LVEF <40% unless contraindicated. 3, 2 However, avoid IV beta-blockers in patients with hypotension, acute heart failure, AV block, or severe bradycardia (Class III). 3, 5

• Prescribe a proton pump inhibitor in combination with dual antiplatelet therapy for patients at high risk of gastrointestinal bleeding 3, 2
• Administer morphine 4-8 mg IV with additional 2 mg doses at 5-15 minute intervals for pain control and anxiety reduction 2
• Provide nitroglycerin for ongoing chest pain unless contraindicated by hypotension, right ventricular infarction, or recent phosphodiesterase-5 inhibitor use 6

---

Cardiac Rehabilitation and Secondary Prevention

Participation in a cardiac rehabilitation program is recommended for all post-MI patients. 3

Identify smokers and provide repeated advice on stopping, with offers of follow-up support, nicotine replacement therapies, varenicline, and bupropion individually or in combination. 3

---

Common Pitfalls to Avoid

• Do not delay reperfusion therapy to wait for troponin results; ECG diagnosis is sufficient to proceed with STEMI management 2
• Do not use NSAIDs for pain relief due to pro-thrombotic effects 2
• Do not perform routine PCI of an occluded infarct-related artery >48 hours after onset of STEMI in asymptomatic patients (Class III) 3
• Do not use facilitated PCI (full-dose fibrinolysis followed by immediate PCI) as this strategy may be harmful 3
• Do not administer prasugrel within 24 hours of fibrin-specific fibrinolytic therapy or to patients with prior stroke/TIA (Class III: Harm) 2
• Do not give IV beta-blockers to patients presenting with signs of heart failure, low cardiac output, or increased risk for cardiogenic shock 3, 5