What is the management protocol for myocardial infarction (MI) according to the latest edition of Harrison's?

Management Protocol for Myocardial Infarction

For STEMI patients, immediate reperfusion with primary PCI is the preferred strategy when it can be performed within 120 minutes of diagnosis; if this timeframe cannot be met, fibrinolytic therapy should be initiated immediately, preferably in the pre-hospital setting. 1

Initial Assessment and Diagnosis

• Obtain a 12-lead ECG within 10 minutes of first medical contact to identify ST-segment elevation or new left bundle branch block 2
• Initiate continuous ECG monitoring with defibrillator capacity immediately 2
• Do not administer routine oxygen therapy unless oxygen saturation is <90% 2
• Assess for contraindications to reperfusion therapy, particularly active bleeding or prior stroke/TIA 3, 4

Immediate Pharmacological Therapy

Aspirin

• Administer aspirin 150-325 mg orally (or 250-500 mg IV if unable to swallow) as soon as possible 1, 5
• Continue aspirin 75-100 mg daily indefinitely 1, 5
• Research suggests 162 mg is rapidly absorbed and may be as effective as 325 mg with potentially less bleeding risk 6, 7

P2Y12 Inhibitor

• Administer a potent P2Y12 inhibitor (prasugrel or ticagrelor) before or at the time of PCI; use clopidogrel only if these are unavailable or contraindicated 1
• Prasugrel: 60 mg loading dose, then 10 mg daily (reduce to 5 mg daily if body weight <60 kg) 4
• Avoid prasugrel in patients ≥75 years unless high-risk features (diabetes or prior MI) are present 4
• Continue dual antiplatelet therapy (DAPT) for 12 months unless excessive bleeding risk 1

Reperfusion Strategy Selection

Primary PCI (Preferred)

• Transfer patients directly to the catheterization laboratory, bypassing the emergency department 1, 2
• Administer unfractionated heparin 100 U/kg IV bolus (60 U/kg if GPIIb/IIIa inhibitors used) 2
• Do not use fondaparinux for primary PCI 1
• Perform radial access and drug-eluting stent implantation as standard of care 2
• Do not perform routine thrombus aspiration or deferred stenting 2

Fibrinolytic Therapy (When PCI Cannot Be Performed Within 120 Minutes)

Inclusion criteria: 3

• Symptoms ≤12 hours from onset
• Persistent ST-segment elevation or new LBBB
• No contraindications (active bleeding, prior stroke/TIA)

Fibrinolytic agent selection: 1, 3

• Use a fibrin-specific agent: tenecteplase (preferred), alteplase, or reteplase
• Tenecteplase: 30-50 mg (0.53 mg/kg) as single IV bolus 2
• Reduce tenecteplase dose by 50% in patients ≥75 years to minimize stroke risk 3

Adjunctive therapy with fibrinolysis: 1, 3

• Aspirin 150-325 mg orally or IV
• Clopidogrel loading dose plus maintenance
• Anticoagulation with enoxaparin IV followed by subcutaneous (preferred over UFH) or weight-adjusted UFH bolus followed by infusion
• Continue anticoagulation until revascularization or up to 8 days of hospitalization

Post-fibrinolysis management: 1, 3

• Transfer all patients to a PCI-capable center immediately after fibrinolysis
• Assess ST-segment resolution at 60-90 minutes in the lead with greatest initial elevation
• Perform rescue PCI immediately if <50% ST-segment resolution (failed fibrinolysis) 1, 3
• Perform rescue PCI for hemodynamic instability, electrical instability, worsening ischemia, or cardiogenic shock 1, 3
• In successful fibrinolysis, perform angiography and PCI of the infarct-related artery between 2-24 hours 1, 3

Beta-Blocker Therapy

Early IV beta-blocker administration: 8

• Once hemodynamic stability is confirmed, administer metoprolol 5 mg IV bolus at 2-minute intervals for three doses (total 15 mg)
• Monitor blood pressure, heart rate, and ECG continuously during IV administration
• Avoid IV beta-blockers in patients with hypotension, acute heart failure, AV block, or severe bradycardia 1

Oral beta-blocker therapy: 8

• If full IV dose tolerated: start metoprolol 50 mg orally every 6 hours, beginning 15 minutes after last IV dose, continue for 48 hours
• Maintenance: metoprolol 100 mg orally twice daily
• Oral beta-blockers are indicated in patients with heart failure and/or LVEF <40% unless contraindicated 1

ACE Inhibitor Therapy

• Start ACE inhibitors within the first 24 hours in patients with heart failure, LV systolic dysfunction, diabetes, or anterior infarction 1, 5
• Use ARB (preferably valsartan) if ACE inhibitor intolerant 1
• Add mineralocorticoid receptor antagonist if ejection fraction <40% with heart failure or diabetes, provided no renal failure or hyperkalemia 1

Statin Therapy

• Initiate high-intensity statin therapy as early as possible and maintain long-term 1, 5
• Target LDL-C <1.8 mmol/L (70 mg/dL) or ≥50% reduction if baseline LDL-C is 1.8-3.5 mmol/L (70-135 mg/dL) 1

Gastrointestinal Protection

• Administer a proton pump inhibitor in combination with DAPT for patients at high risk of gastrointestinal bleeding 1, 2

In-Hospital Monitoring and Assessment

• Perform routine echocardiography during hospitalization to assess LV and RV function, detect mechanical complications, and exclude LV thrombus 1, 5
• Manage heart failure with diuretics (IV furosemide) and afterload reduction 5
• For cardiogenic shock, consider intra-aortic balloon counterpulsation and emergency angiography with revascularization 5, 2

Pre-Discharge and Long-Term Management

Antiplatelet therapy: 1, 5, 2

• Continue aspirin 75-100 mg daily indefinitely
• Continue DAPT for 12 months after PCI unless contraindicated

Risk factor modification: 1, 5

• Provide intensive smoking cessation counseling with nicotine replacement, varenicline, or bupropion
• Recommend participation in cardiac rehabilitation program
• Advise diet low in saturated fat and cholesterol, weight management, and regular exercise (at least 20 minutes of brisk walking three times weekly)

Critical Pitfalls to Avoid

• Never routinely perform PCI of an occluded infarct-related artery >48 hours after STEMI onset in asymptomatic patients 1, 2
• Do not combine fibrinolysis with planned immediate PCI, as this increases mortality 3
• Do not discontinue antiplatelet therapy prematurely, as this increases risk of stent thrombosis, MI, and death 5, 2
• When surgery is needed, discontinue prasugrel at least 7 days prior if possible 4
• Recognize atypical presentations, especially in women, elderly, and diabetic patients, to avoid delayed diagnosis 2