Myocardial Infarction Clinical Guide

Introduction

Myocardial infarction (MI), commonly known as a heart attack, results from acute ischemic necrosis of myocardial tissue due to obstruction of a coronary artery. It remains a leading cause of mortality and morbidity worldwide. Rapid recognition, prompt reperfusion, and evidence-based medical therapy are critical to salvaging myocardium, preventing complications, and improving patient outcomes.

Epidemiology and Risk Factors

• Incidence: Approximately 805,000 MIs occur annually in the United States; over 20 million worldwide.
• Age and Sex: Risk increases with age; men present earlier (average age 66) than women (average age 72).
• Modifiable Risks:
• Hypertension, dyslipidemia, smoking, diabetes mellitus, obesity, physical inactivity, and diet high in saturated fats.
• Psychosocial stress and poor adherence to preventive measures.
• Nonmodifiable Risks: Family history, age, male sex (or postmenopausal status in women), and genetic predisposition.

Pathophysiology

• Atherosclerotic Plaque Rupture: Inflammation destabilizes atheromatous plaques, exposing subendothelial collagen and lipids.
• Thrombus Formation: Platelet aggregation and fibrin deposition occlude the vessel, causing ischemia.
• Myocardial Necrosis: Prolonged ischemia leads to irreversible cardiomyocyte death, beginning subendocardially and extending transmurally if untreated.

Classification

• STEMI (ST-elevation MI): Complete occlusion of a major coronary artery; diagnostic ECG shows new ST elevations in at least two contiguous leads.
• NSTEMI (Non–ST-elevation MI): Partial or transient occlusion; ECG may show ST depression or T-wave inversion; cardiac biomarkers (troponin) are elevated.
• Unstable Angina: Clinical syndrome of ischemia without biomarker elevation or persistent ECG changes; managed similarly to NSTEMI.

Clinical Presentation and Diagnosis

Presentation

• Typical Symptoms: Central chest pain or pressure, radiating to left arm, neck, or jaw; diaphoresis; dyspnea; nausea.
• Atypical Symptoms: Elderly, women, and diabetics may present with fatigue, syncope, or epigastric discomfort without chest pain.

Diagnostic Evaluation

1. Electrocardiogram (ECG): Obtain within 10 minutes of presentation; differentiate STEMI from NSTEMI/unstable angina.
2. Cardiac Biomarkers: Serial troponin measurements confirm myocardial injury; CK-MB may be adjunct.
3. Imaging: Echocardiography assesses wall motion abnormalities and mechanical complications (ventricular septal rupture, pericardial effusion).
4. Coronary Angiography: Gold standard for lesion localization and guides revascularization strategy.

Acute Management

Initial Stabilization (MONA-B)

• Morphine: Analgesia and preload reduction.
• Oxygen: If SpO₂ < 90%.
• Nitrates: Sublingual or IV to relieve ischemia.
• Aspirin: 162–325 mg chewable immediately.
• Beta-Blockers: IV or oral within 24 hours unless contraindicated.

Reperfusion Therapy

• STEMI: Primary percutaneous coronary intervention (PCI) within 90 minutes of first medical contact is preferred.
• If PCI not available within guideline-recommended window, administer fibrinolysis (e.g., tenecteplase) within 30 minutes.
• NSTEMI/Unstable Angina: Early invasive strategy (PCI or CABG) guided by risk stratification (TIMI, GRACE scores).

Adjunctive Pharmacotherapy

• Antiplatelet Agents: P2Y₁₂ inhibitor (clopidogrel, prasugrel, or ticagrelor) in addition to aspirin.
• Anticoagulation: Unfractionated heparin or bivalirudin during PCI; consider enoxaparin for medical management.
• High-Intensity Statin: Initiate or continue high-dose statin regardless of baseline LDL.
• ACE Inhibitors or ARBs: Start within 24 hours to reduce remodeling and improve survival.
• Aldosterone Antagonists: Eplerenone or spironolactone in patients with reduced ejection fraction and heart failure or diabetes.

Secondary Prevention and Long-Term Management

• Lifestyle Modification: Smoking cessation, dietary counseling (Mediterranean diet), weight management, and regular aerobic exercise.
• Risk Factor Control: Tight blood pressure (<130/80 mm Hg) and glycemic control (HbA₁c <7%).
• Medication Adherence: Dual antiplatelet therapy for at least 12 months post-PCI; statins, beta-blockers, ACE inhibitors continued indefinitely.
• Cardiac Rehabilitation: Supervised, multidisciplinary program including exercise training, education, nutritional guidance, and psychological support.

Monitoring and Follow-Up

• Serial Ejection Fraction Assessment: Echocardiography at 4–6 weeks post-MI to guide device therapy (ICD) in left ventricular dysfunction.
• Surveillance for Complications: Monitor for arrhythmias, heart failure, mechanical complications, and depression.
• Regular Clinic Visits: Evaluate functional status, adherence, and adjust therapy.

Patient Education and Self-Care

• Teach recognition of angina symptoms and activation of emergency services.
• Provide a written action plan (medications, contact information, lifestyle goals).
• Encourage participation in peer support groups to enhance adherence and psychosocial well-being.

Conclusion

Effective management of myocardial infarction hinges on rapid identification, timely reperfusion, evidence-based pharmacotherapy, and comprehensive secondary prevention. Multidisciplinary collaboration among emergency medicine, cardiology, nursing, rehabilitation, and primary care teams is vital to optimize recovery and reduce recurrent events.