Medical Emergencies: Myocardial Infarction

Myocardial infarction (MI), commonly called a heart attack, occurs when blood flow to part of the heart muscle is blocked, causing tissue death. Rapid intervention is critical - "Time is muscle."

Pathophysiology

1. Atherosclerotic plaque ruptures in coronary artery
2. Platelets aggregate at the rupture site
3. Thrombus (clot) forms, blocking blood flow
4. Cardiac muscle distal to blockage becomes ischemic
5. Without reperfusion, ischemia progresses to infarction (cell death)

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Types of Myocardial Infarction

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Classic Signs and Symptoms

Typical Presentation:

• Chest pain - Crushing, squeezing, pressure-like
  • Substernal location
  • Radiates to left arm, jaw, neck, back, or epigastrium
  • Not relieved by rest or nitroglycerin (distinguishes from angina)
  • Lasts longer than 20 minutes
• Diaphoresis - Cold, clammy, profuse sweating
• Nausea and vomiting
• Shortness of breath
• Anxiety - Feeling of impending doom
• Pale, cool skin

Atypical Presentations

Important: Women, elderly, and diabetic patients often present WITHOUT classic chest pain!

Atypical Symptoms (More Common in Women/Diabetics):

• Fatigue, weakness
• Back pain
• Jaw pain
• Indigestion or epigastric discomfort
• Shortness of breath without chest pain
• Flu-like symptoms
• Nausea only

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MONA Protocol

The MONA mnemonic guides initial MI treatment:

M - Morphine

• Dose: 2-4 mg IV; may repeat every 5-15 minutes
• Purpose: Pain relief, reduces anxiety, decreases oxygen demand
• Caution: Use only if pain not controlled by nitroglycerin
• Monitor for respiratory depression, hypotension
• Current guidelines recommend using with caution (may mask symptoms)

O - Oxygen

• Indication: Administer if SpO2 < 94% or patient is in respiratory distress
• Note: Routine oxygen is NOT recommended for normoxic patients
• Start at 2-4 L/min via nasal cannula; titrate to maintain SpO2 > 94%

N - Nitroglycerin

• Dose: 0.4 mg sublingual every 5 minutes x 3 doses maximum
• Purpose: Vasodilation decreases preload and myocardial oxygen demand
• Contraindications:
  • SBP < 90 mmHg
  • Severe bradycardia (< 50) or tachycardia (> 100)
  • Right ventricular infarction
  • Phosphodiesterase inhibitor use within 24-48 hours (sildenafil, tadalafil)

A - Aspirin

• Dose: 162-325 mg chewed immediately
• Purpose: Antiplatelet effect prevents further clot formation
• Priority: Often considered the MOST important initial intervention
• Chewing provides faster absorption than swallowing whole

Exam Tip: While MONA is the classic mnemonic, current guidelines prioritize Aspirin as the first medication given. Some sources use MOAN (Morphine, Oxygen, Aspirin, Nitroglycerin) to emphasize aspirin's priority.

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Diagnostic Tests

12-Lead ECG

• Obtain within 10 minutes of arrival
• STEMI shows ST-segment elevation in leads corresponding to affected area:
  • Leads II, III, aVF = Inferior MI
  • Leads V1-V4 = Anterior MI
  • Leads I, aVL, V5-V6 = Lateral MI

Cardiac Biomarkers

Troponin is the most specific marker for myocardial damage. Serial troponins are drawn at presentation and 3-6 hours later.

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Reperfusion Therapy

Goal: Restore blood flow to save heart muscle

Percutaneous Coronary Intervention (PCI)

• First-line treatment for STEMI
• Catheter-based balloon angioplasty with stent placement
• Door-to-balloon time goal: < 90 minutes
• Preferred over thrombolytics when available

Thrombolytic Therapy

• Used when PCI not available within 120 minutes
• Door-to-needle time goal: < 30 minutes
• Contraindications similar to stroke tPA:
  • Active bleeding
  • Recent surgery
  • History of hemorrhagic stroke
  • Uncontrolled hypertension

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Nursing Care During Acute MI

Immediate Actions

1. Activate emergency response
2. Obtain 12-lead ECG within 10 minutes
3. Establish IV access
4. Administer aspirin (chewed)
5. Apply oxygen if indicated
6. Continuous cardiac monitoring
7. Draw cardiac biomarkers

Ongoing Monitoring

• Vital signs every 5-15 minutes during acute phase
• Continuous telemetry for arrhythmias
• Pain assessment using 0-10 scale
• Monitor for complications:
  • Arrhythmias (especially V-fib)
  • Heart failure
  • Cardiogenic shock
  • Mechanical complications (septal rupture, papillary muscle rupture)

Patient Education Post-MI

• Cardiac rehabilitation
• Medication adherence (aspirin, beta-blockers, statins, ACE inhibitors)
• Lifestyle modifications (smoking cessation, diet, exercise)
• When to seek emergency care

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Complications of MI

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Key Points for the NCLEX

• Aspirin is priority - chew 162-325 mg immediately
• Troponin is the most specific cardiac biomarker
• STEMI requires emergent reperfusion (PCI or thrombolytics)
• Door-to-balloon time goal: < 90 minutes
• Do NOT give nitroglycerin if:
  • SBP < 90 mmHg
  • Patient took phosphodiesterase inhibitor (Viagra) recently
  • Right ventricular infarction suspected
• Women and diabetics may present atypically - maintain high suspicion
• Most dangerous arrhythmia post-MI is ventricular fibrillation