What is the management of acute myocardial infarction (AMI)?

Management of Acute Myocardial Infarction

Immediate reperfusion therapy—either primary PCI within 90-120 minutes or fibrinolysis within 30 minutes of diagnosis—combined with aspirin, anticoagulation, and adjunctive pharmacotherapy represents the cornerstone of AMI management and directly reduces mortality. 1, 2

Pre-Hospital and Emergency Department Management (First 10 Minutes)

Immediate Actions Upon Arrival

• Obtain a 12-lead ECG within 10 minutes of arrival to identify ST-segment elevation (≥1 mm in contiguous leads) or new left bundle branch block 1, 3
• Administer aspirin 160-325 mg orally (chewed and swallowed) immediately unless contraindicated 1, 2
• Give sublingual nitroglycerin unless systolic blood pressure <90 mmHg, heart rate <50 or >100 bpm 1
• Provide oxygen 2-4 L/min via nasal prongs to maintain saturation >90%, especially if breathless, heart failure, or shock present 1, 2
• Administer morphine sulfate 4-8 mg IV with additional 2 mg doses every 5 minutes until pain relieved (avoid intramuscular injections) 1, 3
• Establish continuous cardiac monitoring with defibrillator immediately available 1, 3

Critical Diagnostic Steps

• Draw blood for cardiac markers (troponin, CK-MB), complete blood count, chemistry panel, and lipid profile—but do not wait for results before initiating reperfusion therapy 1
• Obtain portable chest X-ray to exclude other causes (aortic dissection, pneumothorax) 1
• Perform focused examination looking for: pallor, sweating, hypotension, narrow pulse pressure, third heart sound, basal rales, irregular pulse 1

Reperfusion Strategy Selection (Time Zero = ECG Diagnosis)

Primary PCI Strategy (Preferred)

Primary PCI is the preferred reperfusion method if it can be performed within 90 minutes of first medical contact (or 120 minutes from STEMI diagnosis) by experienced operators at high-volume centers with 24/7 capability 1, 2

• Use radial artery access as standard approach during primary PCI 1
• Implant drug-eluting stents routinely; avoid routine thrombus aspiration or deferred stenting 1
• Treat severe non-infarct-related artery stenoses before hospital discharge (either during index procedure or staged) 1
• In cardiogenic shock, consider immediate PCI of non-culprit vessels during index procedure 1

Fibrinolytic Therapy Strategy

Administer fibrinolysis within 10 minutes of STEMI diagnosis if anticipated time to PCI exceeds 120 minutes 1, 2

• Greatest benefit occurs within first hour of symptom onset (35 lives saved per 1000 patients) compared to 16 lives saved per 1000 when given 7-12 hours after onset 1, 3
• Use fibrin-specific agents: tenecteplase, alteplase, or reteplase 2
• Transfer all fibrinolysis patients to PCI-capable center immediately after treatment, regardless of apparent success 1

Absolute Contraindications to Fibrinolysis

• Any prior intracranial hemorrhage or known intracranial neoplasm 1
• Active internal bleeding (excluding menses) 1
• Suspected aortic dissection 1
• Ischemic stroke within 3 months or any hemorrhagic stroke 1

Relative Contraindications Requiring Careful Assessment

• Severe uncontrolled hypertension (>180/110 mmHg) 1
• Current therapeutic anticoagulation (INR >2-3) 1
• Recent trauma or major surgery within 2-4 weeks 1
• Recent internal bleeding within 2-4 weeks 1
• Pregnancy 1

Acute Pharmacological Management (First 24-48 Hours)

Antiplatelet Therapy

• Continue aspirin 75-325 mg daily indefinitely 1, 2, 4
• For primary PCI: administer loading dose of prasugrel 60 mg or ticagrelor 180 mg at time of PCI 1, 5
• For fibrinolysis: administer clopidogrel 300 mg loading dose 1
• Continue dual antiplatelet therapy (aspirin plus P2Y12 inhibitor) for 12 months 1, 2
• For prasugrel: reduce maintenance dose to 5 mg daily if body weight <60 kg due to increased bleeding risk 5

Anticoagulation

• Primary PCI: administer unfractionated heparin (enoxaparin or bivalirudin are alternatives) 1, 2
• Fibrinolysis: administer enoxaparin (unfractionated heparin is alternative) 1, 2
• Continue anticoagulation particularly for large anterior MI to prevent left ventricular mural thrombus and embolic stroke 3

Beta-Blocker Therapy

Initiate intravenous beta-blocker therapy within first 24 hours followed by oral therapy unless contraindicated 1, 2

• Contraindications include: signs of heart failure, low cardiac output, increased risk of cardiogenic shock, heart block, active asthma 1
• Continue beta-blockers indefinitely as they reduce mortality and reinfarction 1, 2

Nitrate Therapy

• Administer intravenous nitroglycerin for 24-48 hours for anti-ischemic or antihypertensive effects if no hypotension, bradycardia, or excessive tachycardia 1, 3
• Avoid nitrates if systolic blood pressure <90 mmHg or suspected right ventricular infarction 1

ACE Inhibitor Therapy

Start ACE inhibitors within first 24 hours in patients with anterior MI, heart failure, left ventricular ejection fraction <40%, or diabetes 1, 2, 4

• Ensure systolic blood pressure >100 mmHg before initiation 3
• Continue indefinitely for mortality reduction 1, 2

Statin Therapy

Initiate high-intensity statin therapy as early as possible and continue long-term 2

• Target LDL cholesterol <100 mg/dL (preferably <70 mg/dL) 1
• Start treatment even with normal baseline lipid levels based on HPS study findings 1

Management of Specific Complications

Heart Failure and Pulmonary Congestion

• Administer intravenous furosemide for volume overload 1, 4
• Provide oxygen to maintain saturation >90% 4
• Give morphine sulfate for pulmonary congestion 4
• Use afterload-reducing agents (ACE inhibitors) 1

Cardiogenic Shock

• Consider intra-aortic balloon pump for hemodynamic support 1
• Perform emergency coronary angiography followed by PCI or CABG 1, 2
• Administer inotropic agents if hypotension persists 1

Right Ventricular Infarction

• Treat with aggressive intravascular volume expansion using normal saline 1
• Add inotropic agents if hypotension persists after volume loading 1
• Avoid nitrates and diuretics which reduce preload 1

Recurrent Ischemia

• Administer intravenous nitroglycerin, analgesics, and antithrombotic medications (aspirin, heparin) 1
• Perform urgent coronary angiography with subsequent revascularization 1

Monitoring and In-Hospital Care (24-72 Hours)

Continuous Monitoring Requirements

• Monitor in CCU/ICCU for minimum 24 hours with continuous ECG monitoring 4
• Continue monitoring for 24-48 hours in step-down unit 4
• Watch for life-threatening arrhythmias, hemodynamic instability, ongoing ischemia, or heart failure 1, 4

Diagnostic Evaluation

• Perform routine echocardiography during hospital stay to assess left and right ventricular function, detect mechanical complications, and exclude left ventricular thrombus 2, 4
• For anterior MI specifically, echocardiography identifies high-risk features including left ventricular dysfunction and potential mural thrombus 3

Pre-Discharge Risk Stratification

Exercise Testing

Perform submaximal exercise testing at 4-7 days post-MI or symptom-limited testing at 10-14 days 1, 4

• Assess functional capacity and ability to perform activities at home and work 1
• Evaluate efficacy of current medical regimen 1
• Stratify risk for subsequent cardiac events 1

Early Discharge Criteria (48-72 Hours)

Low-risk patients eligible for early discharge must meet ALL criteria: 4

• Age <70 years
• Left ventricular ejection fraction >45%
• One- or two-vessel disease with successful PCI
• No persistent arrhythmias
• No signs or symptoms of ongoing myocardial ischemia

Discharge Medications (Mandatory)

All patients must be discharged on the following unless specific contraindications exist: 4

• Aspirin 75-325 mg daily indefinitely 2, 4
• P2Y12 inhibitor (clopidogrel 75 mg daily, prasugrel 10 mg daily, or ticagrelor 90 mg twice daily) for 12 months 2, 4
• High-intensity statin therapy 4
• Beta-blocker 4
• ACE inhibitor (especially if anterior MI, heart failure, LVEF <40%, or diabetes) 4
• Sublingual nitroglycerin with clear instructions on use 4

Long-Term Secondary Prevention

Lifestyle Modifications

• Mandatory smoking cessation with nicotine replacement, varenicline, or bupropion 2, 4
• Target blood pressure <140/90 mmHg 4
• Achieve ideal body weight 1, 4
• Follow diet low in saturated fat and cholesterol 1, 2
• Engage in cardiac rehabilitation program 1, 2
• Exercise at least 20 minutes of brisk walking three times weekly 1, 2

Follow-Up Structure

• Schedule outpatient appointments within 1-2 weeks for higher-risk patients and 2-6 weeks for low-risk patients 4
• Implement weekly telephone calls for first 4 weeks to reinforce education, monitor recovery, and assess risk factor modification 4

Critical Pitfalls to Avoid

• Never delay reperfusion therapy waiting for cardiac marker results 1
• Never administer thrombolytics to patients without ST-elevation or new LBBB (except equivalent patterns like true posterior MI) 1
• Never discharge without written medication instructions in understandable, culturally sensitive language 4
• Never omit ACE inhibitors in patients with reduced ejection fraction, heart failure, anterior MI, or diabetes 4
• Never discharge without sublingual nitroglycerin and explicit instructions 4
• Never use calcium channel blockers routinely as they do not reduce mortality and may be harmful 1
• Never use routine Class I antiarrhythmic agents as they have not shown benefit 6