What are the management options for Myocardial Infarction (MI)?

Management of Myocardial Infarction

For patients with acute MI presenting with ST-segment elevation or new left bundle branch block, immediate reperfusion with primary percutaneous coronary intervention (PCI) is the preferred strategy when it can be performed within 120 minutes by an experienced team; otherwise, fibrinolytic therapy should be initiated immediately. 1

Immediate Management (Emergency Department/First Hours)

Initial Interventions

• Administer aspirin 160-325 mg orally (chewed) immediately unless absolutely contraindicated—this is the single most critical antiplatelet intervention. 2, 3
• Provide oxygen by nasal prongs if oxygen saturation is less than 90%. 4
• Administer narcotic analgesia (morphine sulfate or meperidine) to minimize pain and anxiety—nitroglycerin should not substitute for adequate narcotic pain control. 2, 3
• Obtain a 12-lead ECG within 10 minutes of arrival to identify ST-segment elevation or new LBBB. 2, 4
• Establish continuous cardiac monitoring with defibrillation capacity immediately available. 3, 4

Reperfusion Strategy Decision Algorithm

For ST-elevation MI or new LBBB:

• If primary PCI can be performed within 120 minutes of diagnosis by skilled operators: Proceed directly to catheterization laboratory, bypassing the emergency department. 1, 4
• If primary PCI cannot be performed within 120 minutes: Initiate fibrinolytic therapy immediately—fibrin-specific agents are preferred over streptokinase. 1
• The greatest mortality benefit occurs when reperfusion is achieved within the first hour of symptom onset (35 lives saved per 1000 patients), compared to 16 lives saved per 1000 when given 7-12 hours after symptom onset. 2

For non-ST-elevation MI: Do not administer thrombolytic therapy; the benefit of primary PCI in these patients remains uncertain. 2

Antiplatelet Therapy

• Add a potent P2Y12 inhibitor before or during PCI, maintained for 12 months. 1
• Prasugrel 60 mg loading dose followed by 10 mg daily (5 mg daily if body weight <60 kg) is indicated for acute coronary syndrome managed with PCI. 5
• Clopidogrel 300 mg loading dose followed by 75 mg daily is an alternative, though less potent in patients who are not CYP2C19 poor metabolizers. 3, 6

Anticoagulation

• For primary PCI: Administer high-dose intravenous unfractionated heparin. 2, 3
• For fibrinolytic therapy with alteplase: Continue intravenous heparin for 48 hours after thrombolysis. 2
• For fibrinolytic therapy with streptokinase, APSAC, or urokinase: Limited evidence supports heparin benefit beyond aspirin and beta-blockers. 2
• Enoxaparin IV followed by subcutaneous administration is preferred over unfractionated heparin when fibrinolysis is used. 1

Management During First 24 Hours

Continuous Monitoring and Risk Stratification

• Monitor continuously for arrhythmias and conduction disturbances—reinfarction and death occur most frequently within the first 24 hours. 2
• Have emergency equipment immediately available: atropine, lidocaine, transcutaneous pacing patches, transvenous pacemaker, defibrillator, and epinephrine. 2, 3
• Limit physical activities for at least 12 hours. 2, 3
• Confirm diagnosis with serial ECGs and cardiac-specific troponin T or I measurements. 2

Pharmacological Management

• Intravenous nitroglycerin for 24-48 hours in patients without hypotension, bradycardia, or excessive tachycardia—this can be titrated successfully with frequent blood pressure monitoring. 2
• Early intravenous beta-blocker therapy followed by oral therapy should be initiated regardless of whether reperfusion was given, as beta-blockers diminish morbidity and mortality in both prethrombolytic and thrombolytic eras. 2
• Magnesium sulfate should be given as needed to replete magnesium deficits for 24 hours. 2
• Avoid calcium channel blockers—they have not been shown to reduce mortality and may be harmful in certain patients with cardiovascular disease. 2, 3

Special Considerations for Inferior MI with Right Ventricular Involvement

• Assess for right ventricular infarction (occurs in up to 50% of inferior MIs) by obtaining right-sided ECG leads, particularly V4R—ST elevation ≥1 mm is highly predictive. 3
• Look for the clinical triad: hypotension, clear lung fields, and elevated jugular venous pressure. 3
• Maintain RV preload through aggressive volume loading with IV normal saline for hypotension—this is critical. 2, 3
• Avoid nitrates and diuretics completely in RV involvement as they cause profound hypotension by reducing preload. 3
• Provide inotropic support with dobutamine if cardiac output fails to increase after volume loading. 3
• Record lead V4R early as ST elevation can resolve within 10 hours. 1, 3

Management of Bradycardia and Conduction Disturbances

• Treat symptomatic sinus bradycardia (common in inferior MI) with IV atropine 0.5 mg, repeated up to 2.0 mg total. 3
• Consider temporary pacing for symptomatic high-degree AV block, especially if unresponsive to atropine. 3

Management After First 24 Hours

Maintenance Antiplatelet Therapy

• Continue aspirin 75-100 mg daily indefinitely—this lower maintenance dose (compared to the initial 160-325 mg) is as effective and associated with less bleeding. 2, 1, 7
• Maintain dual antiplatelet therapy for 12 months after PCI with aspirin plus P2Y12 inhibitor. 1

Beta-Blocker Therapy

• Continue oral beta-blocker therapy for at least 6 weeks in all patients. 2
• Initiate beta-blockers specifically in patients with heart failure and/or left ventricular ejection fraction <40% for long-term mortality benefit. 1

ACE Inhibitor Therapy

• Initiate ACE inhibitors within the first 24 hours in patients with evidence of heart failure, LV systolic dysfunction, diabetes, or anterior infarction. 2, 1
• Continue ACE inhibitors indefinitely for long-term benefit. 2

Statin Therapy

• Initiate high-intensity statin therapy as early as possible and maintain long-term with goal of reducing LDL to less than 100 mg/dL. 2, 1

Nitroglycerin

• Continue intravenous nitroglycerin for 24-48 hours, then transition to oral nitrates as needed—avoid oral nitrates in the acute phase due to inability to titrate dose in evolving hemodynamic situations. 2

Management of Complications

Recurrent Chest Pain

• If due to pericarditis: Administer high-dose aspirin 650 mg every 4-6 hours. 2
• If due to recurrent ischemia: Treat with intravenous nitroglycerin, analgesics, and antithrombotic medications (aspirin, heparin); consider coronary angiography with revascularization. 2

Heart Failure

• Administer diuretics (usually intravenous furosemide) and afterload-reducing agents. 2

Cardiogenic Shock

• Consider insertion of intra-aortic balloon pump for hemodynamic support. 2
• Perform emergency coronary angiography followed by PTCA or CABG. 2

Thromboembolism Prevention

• Patients with large anterior MI or LV mural thrombus on echocardiography are at high risk for embolic stroke—administer intravenous heparin early to reduce this risk. 2

Preparation for Discharge (4-14 Days)

Risk Stratification

• Perform standard exercise testing: submaximal at 4-7 days or symptom-limited at 10-14 days to assess functional capacity, evaluate medical regimen efficacy, and stratify risk for subsequent cardiac events. 2
• Perform routine echocardiography during hospitalization to evaluate LV and RV function. 1

Discharge Medications

• Aspirin 75-100 mg daily indefinitely 2, 1
• Beta-blocker indefinitely 2
• ACE inhibitor indefinitely 2
• High-intensity statin indefinitely 2, 1
• P2Y12 inhibitor for 12 months 1

Long-Term Management

Lifestyle Modifications

• Smoking cessation is essential—provide support, nicotine replacement therapy, varenicline, and bupropion. 2, 1
• Achieve ideal body weight through diet low in saturated fat and cholesterol. 2
• Engage in formal cardiac rehabilitation program with goal of 20 minutes of exercise at brisk walking level at least three times weekly. 2

Critical Pitfalls to Avoid

• Never administer nitrates in right ventricular infarction—this causes profound hypotension. 1, 3
• Do not use calcium channel blockers in acute MI—they do not reduce mortality and may be harmful. 2, 3
• Do not discontinue aspirin or P2Y12 inhibitors prematurely—stopping increases risk of stent thrombosis, MI, and death. 5
• Avoid prophylactic antiarrhythmic agents in the first 24 hours—they are not recommended. 2
• Do not administer beta-blockers to patients in low-output state due to pump failure. 3
• Discontinue NSAIDs (except aspirin) due to increased risks of mortality, reinfarction, and complications. 3
• Avoid omeprazole or esomeprazole with clopidogrel—they significantly reduce antiplatelet activity. 6