9.4 Medical Emergencies: Myocardial Infarction (MONA)
Key Takeaways
MONA mnemonic: Morphine (if pain unrelieved), Oxygen (if SpO2 < 94%), Nitroglycerin, Aspirin (priority)
Classic MI symptoms: crushing substernal chest pain radiating to jaw/arm, diaphoresis, nausea, shortness of breath
Women and diabetics may present atypically with fatigue, back pain, or indigestion rather than chest pain
Troponin is the most specific cardiac biomarker; elevates 3-6 hours post-MI and remains elevated 10-14 days
12-lead ECG should be obtained within 10 minutes; STEMI requires immediate reperfusion (PCI or thrombolytics)
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
- Atherosclerotic plaque ruptures in coronary artery
- Platelets aggregate at the rupture site
- Thrombus (clot) forms, blocking blood flow
- Cardiac muscle distal to blockage becomes ischemic
- Without reperfusion, ischemia progresses to infarction (cell death)
Types of Myocardial Infarction
| Type | ECG Finding | Treatment Priority |
|---|---|---|
| STEMI | ST-segment elevation | Emergent reperfusion (PCI < 90 min or thrombolytics < 30 min) |
| NSTEMI | ST depression or T-wave inversion | Medical management, possible PCI |
| Unstable Angina | May be normal or show ST changes | Medical management, risk stratification |
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
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.
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
| Marker | Onset | Peak | Return to Normal |
|---|---|---|---|
| Troponin I/T | 3-6 hours | 12-24 hours | 10-14 days |
| CK-MB | 3-6 hours | 12-24 hours | 2-3 days |
| Myoglobin | 1-2 hours | 6-9 hours | 24 hours |
Troponin is the most specific marker for myocardial damage. Serial troponins are drawn at presentation and 3-6 hours later.
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
Nursing Care During Acute MI
Immediate Actions
- Activate emergency response
- Obtain 12-lead ECG within 10 minutes
- Establish IV access
- Administer aspirin (chewed)
- Apply oxygen if indicated
- Continuous cardiac monitoring
- 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
Complications of MI
| Complication | Timing | Signs |
|---|---|---|
| Arrhythmias | First 24-48 hours | Irregular rhythm, palpitations |
| Heart Failure | Days to weeks | Crackles, JVD, edema |
| Cardiogenic Shock | Hours to days | Hypotension, cool skin, altered mental status |
| Pericarditis | 2-3 days post-MI | Friction rub, chest pain worse with breathing |
| Ventricular Rupture | 3-5 days | Sudden death, JVD, pulseless electrical activity |
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
A patient with chest pain is prescribed sublingual nitroglycerin. Which assessment finding would cause the nurse to withhold this medication?
Heart rate of 72 bpm
Blood pressure of 82/56 mmHg
Respiratory rate of 18
Oxygen saturation of 96%
Which medication in the MONA protocol should be administered first to a patient experiencing an acute MI?
Morphine
Oxygen
Nitroglycerin
Aspirin
A 62-year-old woman with diabetes presents with fatigue, nausea, and jaw pain. Her ECG shows ST elevation. What should the nurse suspect?
Anxiety attack
Gastroesophageal reflux
Acute myocardial infarction
Dental abscess
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