Treatment of Myocardial Infarction
For ST-elevation myocardial infarction (STEMI), immediate primary percutaneous coronary intervention (PCI) within 90-120 minutes of first medical contact is the definitive treatment, combined with dual antiplatelet therapy (aspirin plus a potent P2Y12 inhibitor), anticoagulation, and guideline-directed medical therapy including beta-blockers, ACE inhibitors, and high-intensity statins. 1
Immediate Reperfusion Strategy
Primary PCI is the preferred reperfusion method for all STEMI patients presenting within 12 hours of symptom onset with persistent ST-segment elevation. 1 Patients should bypass the emergency department and transfer directly to the catheterization laboratory when possible. 1
If primary PCI cannot be performed within 120 minutes of diagnosis, fibrinolytic therapy is recommended within 12 hours of symptom onset in patients without contraindications. 1 Use fibrin-specific agents (tenecteplase, alteplase, or reteplase). 1 After fibrinolysis, all patients require immediate transfer to a PCI-capable center, with angiography and PCI of the infarct-related artery performed between 2-24 hours after successful fibrinolysis. 1
Rescue PCI must be performed immediately when fibrinolysis fails (less than 50% ST-segment resolution at 60-90 minutes) or with hemodynamic/electrical instability. 1
Antithrombotic Therapy
Antiplatelet Regimen
Aspirin should be administered immediately (oral 150-300 mg chewed or 75-250 mg IV) to all patients without contraindications. 1 For acute MI, use a loading dose of 160-325 mg, then maintain with 75-100 mg daily indefinitely. 1 Research shows 162 mg may be as effective as 325 mg with potentially less bleeding risk. 2
Add a potent P2Y12 inhibitor immediately: prasugrel or ticagrelor preferred over clopidogrel, given before or at the time of PCI and maintained for 12 months unless excessive bleeding risk exists. 1 For fibrinolysis patients, use clopidogrel 300 mg loading dose (75 mg if age ≥75 years), then 75 mg daily. 1
Anticoagulation
For primary PCI: Use unfractionated heparin as weight-adjusted IV bolus followed by infusion. 1
For fibrinolytic therapy: Enoxaparin IV followed by subcutaneous (preferred over UFH) or UFH as weight-adjusted IV bolus with infusion, continued until revascularization or for hospital duration up to 8 days. 1 Fondaparinux is contraindicated for primary PCI. 1
Acute Medical Management
Pain Control
Morphine sulfate 4-8 mg IV with additional 2 mg doses at 5-15 minute intervals for pain control and anxiety reduction. 1, 3 Morphine reduces sympathetic drive and myocardial oxygen demand. 3
Nitroglycerin IV should be infused for 24-48 hours in hemodynamically stable patients to treat ongoing ischemia and reduce preload. 1 Critical contraindication: Avoid nitrates if patient has used phosphodiesterase-5 inhibitors (contraindicated for at least 48 hours after tadalafil due to risk of severe hypotension). 4
Beta-Blockers
Intravenous beta-blocker therapy (metoprolol 5 mg IV every 2 minutes for three doses) should be initiated early in hemodynamically stable patients without contraindications (no hypotension, acute heart failure, AV block, or severe bradycardia). 1, 5 Follow with oral metoprolol 50 mg every 6 hours for 48 hours, then 100 mg twice daily. 5
Oral beta-blockers are mandatory for all patients with heart failure and/or LVEF <40% after stabilization to reduce death, recurrent MI, and heart failure hospitalization. 1
Oxygen Therapy
Administer oxygen only if SaO2 <90% or PaO2 <60 mmHg, targeting saturation >95%. 1
Heart Failure and Cardiogenic Shock Management
For pulmonary congestion: IV loop diuretics (furosemide 20-40 mg IV with repeated doses as needed) and IV nitrates if blood pressure allows. 1
For cardiogenic shock: Immediate PCI is indicated; if anatomy unsuitable or PCI fails, emergency CABG is recommended. 1 Intra-aortic balloon pump may be considered but is not routinely indicated. 1
Long-Term Medical Therapy
ACE Inhibitors
ACE inhibitors should be started within 24 hours for all patients with heart failure, LVEF <40%, diabetes, or anterior infarct. 1 For acute MI, begin lisinopril 5 mg within 24 hours, then 5 mg after 24 hours, then 10 mg daily (reduce to 2.5 mg if systolic BP <120 mmHg). 6 Continue indefinitely for patients with LVEF <40% and/or heart failure. 1
ARBs (preferably valsartan) are alternatives for ACE inhibitor-intolerant patients with heart failure and/or LV systolic dysfunction. 1
Mineralocorticoid Receptor Antagonists
MRAs are recommended for patients with heart failure and LVEF <40% without severe renal failure or hyperkalemia, already receiving ACE inhibitor and beta-blocker. 1
Statin Therapy
High-intensity statin therapy must be initiated as early as possible and maintained 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. 1
Proton Pump Inhibitors
PPIs in combination with dual antiplatelet therapy are recommended for patients at high gastrointestinal bleeding risk. 1
Post-Acute Management
Routine echocardiography during hospitalization is recommended to assess LV and RV function, detect mechanical complications, and exclude LV thrombus. 1
Cardiac rehabilitation participation is strongly recommended. 1
Smoking cessation interventions with repeated advice, follow-up support, and pharmacotherapy (nicotine replacement, varenicline, or bupropion) should be provided. 1
Critical Pitfalls to Avoid
Time is myocardium: Every minute of delay increases myocardial necrosis with greatest mortality benefit occurring within first 3 hours of symptom onset. 4 Do not delay reperfusion for any reason.
Avoid IV beta-blockers in patients with hypotension, acute heart failure, AV block, or severe bradycardia. 1
Do not perform routine PCI of occluded infarct-related artery >48 hours after STEMI onset in asymptomatic patients. 1
Monitor closely for complications: persistent hypotension (9% with lisinopril vs 3.7% without) and renal dysfunction (2.4% vs 1.1%) are more common with ACE inhibitors in acute MI. 6