What is the medical treatment for myocardial infarction (MI)?

Medical Treatment of Myocardial Infarction

Immediately administer aspirin 160-325 mg, oxygen via nasal prongs, sublingual nitroglycerin (unless systolic BP <90 mmHg or HR <50 or >100 bpm), and morphine for pain control upon arrival to the emergency department. 1, 2

Initial Emergency Department Management (First 10-20 Minutes)

• Perform a 12-lead ECG within 10 minutes of arrival to identify ST-segment elevation (≥1 mV in contiguous leads), which indicates thrombotic coronary occlusion and makes the patient a candidate for immediate reperfusion therapy 1, 2

• Establish continuous cardiac monitoring with emergency resuscitation equipment (atropine, lidocaine, transcutaneous pacing patches, defibrillator, epinephrine) immediately available 1, 2

• Administer aspirin 160-325 mg orally (or 300 mg per alternative protocols) immediately and continue indefinitely 1

• Give sublingual nitroglycerin unless contraindicated by hypotension (systolic BP <90 mmHg) or heart rate abnormalities (<50 or >100 bpm) 1, 2

• Provide adequate analgesia with morphine sulfate or meperidine to relieve chest pain and anxiety 1

• Administer oxygen by nasal prongs to all patients 1, 2

Reperfusion Strategy Decision (Time-Critical)

The choice between primary PCI and thrombolytic therapy depends on time to treatment and facility capabilities:

Primary PCI (Preferred if Available)

• Choose primary PCI if it can be performed within 90-120 minutes by skilled personnel with access to emergency CABG surgery 1, 2, 3
• Primary PCI has superior outcomes compared to thrombolysis, with lower rates of reinfarction (8.5% vs 16.8% at 6 months) and intracranial hemorrhage (0% vs 2.0%) 4
• The success rate for immediate PTCA is 97% when performed by experienced operators 4

Thrombolytic Therapy (If PCI Not Available)

• Administer thrombolytic therapy within 30 minutes of arrival if primary PCI cannot be performed within 120 minutes 1, 3
• Greatest benefit occurs when thrombolysis is initiated within the first hour of symptom onset (35 lives saved per 1,000 patients treated vs 16 lives saved per 1,000 when given 7-12 hours after onset) 1, 2
• Thrombolytic therapy provides a 21% proportional reduction in 35-day mortality (21 deaths prevented per 1,000 patients treated) 1
• Tissue plasminogen activator (tPA/alteplase) is preferred over streptokinase or urokinase due to fibrin specificity 1, 3
• Do NOT give thrombolytic therapy to patients without ST-segment elevation - it provides no benefit and increases bleeding risk 1

Critical pitfall: Thrombolytic therapy increases risk of intracranial hemorrhage, particularly in patients >65 years, body weight <70 kg, systemic hypertension, or receiving tPA 1

Pharmacological Management: First 24 Hours

Beta-Blockers (Mortality Benefit)

• Administer early intravenous beta-blocker therapy followed by oral therapy unless contraindicated 1, 2
• For metoprolol: give three 5 mg IV bolus injections at 2-minute intervals, then start 50 mg orally every 6 hours for 48 hours, followed by 100 mg twice daily 5
• Beta-blockers reduce morbidity and mortality regardless of whether reperfusion therapy was given 1
• Monitor blood pressure, heart rate, and ECG during IV administration 5

Anticoagulation

• Administer intravenous heparin 5,000 IU initially for patients receiving thrombolytic therapy or at high risk for embolic stroke 1
• For patients with large anterior MI or LV mural thrombus on echocardiography, give IV heparin to reduce embolic stroke risk (9.0% vs 3.7% without anticoagulation) 1, 2
• If alteplase (tPA) was given, continue IV heparin for 48 hours 1, 2
• For streptokinase, evidence for additional heparin benefit beyond aspirin is limited 1

Nitroglycerin

• Begin intravenous nitroglycerin for 24-48 hours if no hypotension, bradycardia, or excessive tachycardia 1, 2
• IV nitroglycerin allows proper dose titration with frequent BP and heart rate monitoring 1
• Do NOT use oral nitrates in the acute phase - inability to titrate dose in evolving hemodynamic situations is dangerous 1
• Nitroglycerin should not substitute for narcotic analgesics 1

Antiplatelet Therapy Beyond Aspirin

• Add clopidogrel 600 mg loading dose followed by daily maintenance (or consider prasugrel/ticagrelor if no bleeding risk) 1

Medications to AVOID

• Do NOT give prophylactic antiarrhythmic agents in the first 24 hours 1, 2
• Do NOT use calcium channel blockers - they have not reduced mortality and may be harmful 1

Management After First 24 Hours

Continue Core Medications

• Aspirin 160-325 mg daily indefinitely 1, 2
• Beta-blocker therapy for at least 6 weeks (continue indefinitely for long-term benefit) 1, 2
• IV nitroglycerin for 24-48 hours total, then transition to oral if needed 1, 2
• Magnesium sulfate as needed to replete deficits for 24 hours 1, 2

ACE Inhibitors (Mortality Benefit)

• Start ACE inhibitor therapy (e.g., lisinopril 5 mg within 24 hours, then 5 mg after 24 hours, then 10 mg daily) for patients with anterior MI or left ventricular dysfunction 1, 2, 6
• Reduce dose to 2.5 mg if systolic BP <120 mmHg at baseline 6
• ACE inhibitors reduce 6-week mortality by 11% (6.4% vs 7.2%) 6
• Monitor for hypotension and renal dysfunction (increased creatinine >3 mg/dL or doubling of baseline) 6

Activity Restrictions

• Limit physical activities for at least 12 hours after admission 1, 2
• Continuously monitor by electrocardiography as reinfarction and death occur most frequently within first 24 hours 1

Management of Complications

Recurrent Chest Pain

• If due to pericarditis: high-dose aspirin 650 mg every 4-6 hours 1
• If due to myocardial ischemia: IV nitroglycerin, analgesics, antithrombotic medications (aspirin, heparin), and consider coronary angiography with revascularization 1

Heart Failure

• Administer IV furosemide (diuretic) and an afterload-reducing agent 1

Cardiogenic Shock

• Insert intra-aortic balloon pump for hemodynamic support 1
• Perform emergency coronary angiography followed by PTCA or CABG 1

Right Ventricular Infarction

• Treat with vigorous intravascular volume expansion using normal saline and inotropic agents if hypotension persists 1

Special Considerations for Anterior MI

Anterior MI carries higher risk than inferior MI and requires heightened vigilance:

• Higher risk for left ventricular dysfunction and heart failure 2, 3
• Higher risk for LV mural thrombus formation leading to embolic stroke 2, 3
• Higher risk for conduction disturbances and arrhythmias 2, 3
• Perform echocardiography to evaluate LV function and detect mural thrombus 2, 3

Pre-Discharge Risk Stratification (Days 4-14)

• Perform submaximal exercise testing at 4-7 days or symptom-limited testing at 10-14 days 1
• This assesses functional capacity, evaluates medical regimen efficacy, and stratifies risk for subsequent cardiac events 1

Long-Term Management (Indefinite)

Medications

• Continue aspirin indefinitely 1
• Continue beta-blocker indefinitely 1
• Continue ACE inhibitor at selected dose 1

Lipid Management

• If LDL cholesterol >130 mg/dL despite diet, initiate drug therapy with goal of reducing LDL to <100 mg/dL 1

Lifestyle Modifications

• Mandatory smoking cessation 1
• Achieve ideal body weight 1
• Diet low in saturated fat and cholesterol 1
• Exercise at level of brisk walking for 20 minutes at least three times weekly 1
• Participate in formal cardiac rehabilitation program 1

Critical Pitfalls to Avoid

• Delaying reperfusion beyond the first hour dramatically reduces effectiveness (35 lives saved per 1,000 in first hour vs 16 lives saved per 1,000 at 7-12 hours) 1, 2, 3
• Using oral nitrates instead of IV nitroglycerin in acute phase prevents proper dose titration 1, 2
• Giving thrombolytics to patients without ST-elevation - no benefit and increased bleeding risk 1
• Not having emergency equipment immediately available (atropine, lidocaine, pacing, defibrillator, epinephrine) 1, 2
• Administering calcium channel blockers - no mortality benefit and potential harm 1, 2
• Failing to transfer patients to PCI-capable center after fibrinolysis - all patients need angiography within 2-24 hours 3
• Missing failed fibrinolysis - arrange rescue PCI immediately if reperfusion unsuccessful 3