Myocardial Infarction (MI) for NCLEX, HESI & ATI

Myocardial infarction (MI) is one of the highest-yield cardiovascular topics on NCLEX, HESI, and ATI exams. This note distills the key concepts — types, immediate treatment, reperfusion timing, complications, medications, and nursing priorities — into a rapid-revision format.

Definition

Myocardial infarction (MI) is the death of heart muscle tissue caused by a sudden loss of blood supply, usually from a blood clot blocking a coronary artery. Without oxygen, heart muscle cells begin to die within 20 minutes — "time is muscle."

Types of MI

• STEMI → full-thickness damage of the heart muscle.
• NSTEMI → damage limited to the inner layer.
• Troponin is elevated in both STEMI and NSTEMI, but normal in unstable angina.

Killip Classification

A clinical grading system used to assess the severity of heart failure in a patient having an acute MI.

Signs and Symptoms

• Chest pain: crushing, squeezing, pressure, or heaviness behind the breastbone.
• Pain may radiate to the left arm, jaw, shoulder, back, or upper abdomen.
• Shortness of breath, with or without chest pain.
• Diaphoresis (sweating), nausea, vomiting, lightheadedness.
• Sense of impending doom or extreme fatigue.
• Atypical presentations:
  • Women: indigestion, extreme fatigue, back pain — often without chest pain.
  • Elderly: confusion or sudden shortness of breath.
  • Diabetics: "silent" MI with no pain at all.

Diagnostic Tests

• 12-lead ECG within 10 minutes of arrival.
  • ST elevation = STEMI → immediate reperfusion.
• Troponin: the gold-standard marker for muscle death.
  • Rises 3–6 hours after symptoms start.
  • Stays elevated up to 2 weeks.
  • A normal troponin 6 hours after chest pain onset rules out MI.
• Chest X-ray — checks for pulmonary edema.
• Echocardiogram — assesses pumping function and damaged areas.

Immediate Treatment — MONA

Key rules:

• Aspirin 325 mg chewed immediately for faster absorption.
• Nitroglycerin SL every 5 minutes for up to 3 doses.
• Never give nitroglycerin if SBP < 90 or patient took Viagra/PDE-5 inhibitor in the last 24–48 hours.
• Morphine for severe pain unrelieved by nitroglycerin — watch for hypotension.
• Oxygen only if SpO₂ < 90%.

Reperfusion Therapy (Opening the Artery)

Primary PCI (Percutaneous Coronary Intervention)

• Angioplasty with stent placement.
• Door-to-balloon time < 90 minutes.
• Best option when available quickly.

Fibrinolytic (Clot-Busting) Therapy

• IV clot-dissolving medication.
• Door-to-needle time < 30 minutes.
• Most effective within 3 hours of symptom onset.
• Monitor closely for bleeding.

Contraindications to Fibrinolytics

• Active bleeding
• Recent stroke or head injury
• Recent major surgery
• Severe hypertension (>180/110)
• History of intracranial hemorrhage

Complications

Early (First 48 Hours)

• Arrhythmias — most common cause of death in the first hours.
• Ventricular fibrillation — requires immediate defibrillation.
• Heart block — may require a pacemaker.
• Cardiogenic shock — low BP, cold/clammy skin, confusion, low urine output.

Heart Failure

• Fluid in the lungs → crackles and dyspnea.
• Severity assessed by Killip class.

Mechanical (Days 2–7)

• Papillary muscle rupture — sudden loud murmur, pulmonary edema.
• Ventricular septal rupture — harsh murmur from a hole between ventricles.
• Free wall rupture — blood leaks into the pericardial sac; often fatal.

Late (Weeks to Months)

• Pericarditis — sharp chest pain that improves when sitting up.
• Dressler's syndrome — autoimmune pericarditis weeks after MI.
• Left ventricular thrombus — clot can embolize and cause stroke.

Long-Term Medications

• Aspirin — lifelong to prevent another MI.
• Second antiplatelet (e.g., clopidogrel) with aspirin for at least 12 months — known as dual antiplatelet therapy (DAPT); prevents stent thrombosis.
• Beta-blockers — reduce heart rate and workload.
• ACE inhibitors — vasodilation and prevention of cardiac remodeling.
• Statins — stabilize plaque and lower cholesterol (even if levels are normal).
• Aldosterone antagonists (e.g., spironolactone) — given if the heart is weak.

Watch for: bleeding with antiplatelets; hyperkalemia with ACE inhibitors and spironolactone.

Nursing Care After MI

• Continuous cardiac monitoring for arrhythmias.
• Frequent vital signs: BP, HR, SpO₂.
• Assess and treat chest pain.
• Monitor for bleeding from anticoagulants/antiplatelets.
• Auscultate lungs and check for edema (signs of heart failure).
• Provide oxygen only if needed.
• Promote rest to reduce cardiac workload.
• Stool softeners to prevent straining (Valsalva stresses the heart).
• Progress activity gradually as ordered.
• Provide thorough discharge teaching on medications.

Patient Teaching

• Take antiplatelets exactly as prescribed; never stop without consulting the provider.
• Report bleeding: dark/tarry stools, coffee-ground emesis, unusual bruising.
• Nitroglycerin 3-5-3 rule: take 1 tablet → wait 5 min → if no relief, take another → wait 5 min → take a 3rd. If no relief after 3 doses in 15 minutes, call 911. Do not drive yourself.
• Quit smoking — the single most important lifestyle change.
• Heart-healthy diet: low in salt, saturated fat, and processed foods.
• Attend cardiac rehabilitation for safe, supervised exercise.
• Recognize MI symptoms and seek help quickly.
• Keep all follow-up appointments.

Common NCLEX Traps

• Confusing STEMI (ST up) with NSTEMI (ST down).
• Forgetting that troponin is elevated in both STEMI and NSTEMI, but normal in unstable angina.
• Giving oxygen to everyone — it's only indicated if SpO₂ < 90%.
• Giving nitroglycerin when BP is low or after recent Viagra/PDE-5 inhibitor use.
• Forgetting aspirin must be chewed, not swallowed.
• Not knowing door-to-balloon < 90 min and door-to-needle < 30 min.
• Missing fibrinolytic contraindications.
• Failing to recognize cardiogenic shock or Killip class.
• Assuming all post-MI chest pain is new ischemia — could be pericarditis.
• Forgetting the 3-5-3 rule for nitroglycerin.

Key Takeaways

• STEMI = full blockage + ST elevation; NSTEMI = partial blockage + ST depression; both have elevated troponin.
• MONA = Morphine, Oxygen (only if SpO₂ < 90%), Nitroglycerin, Aspirin (chewed).
• Reperfusion timing: PCI < 90 minutes, fibrinolytics < 30 minutes (best within 3 hours).
• Complications progress over time: early arrhythmias → days 2–7 mechanical ruptures → later pericarditis/Dressler's.
• Long-term meds: aspirin + clopidogrel (DAPT), beta-blocker, ACE inhibitor, statin — and teach the 3-5-3 nitroglycerin rule.
• Time is muscle — faster reperfusion saves more myocardium.