Complications of MI

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MI Complications - Timeline of Trouble

  • Acute (0-48 hours)

    • Arrhythmias (esp. V-fib): #1 cause of early death.
    • Cardiogenic shock.
    • Acute congestive heart failure.
  • Subacute (3-14 days)

    • Free wall rupture → Cardiac tamponade.
    • Papillary muscle rupture → Acute severe mitral regurgitation.
    • Interventricular septal rupture → VSD.
    • Fibrinous pericarditis.
  • Chronic (>2 weeks)

    • Dressler syndrome (autoimmune pericarditis).
    • True ventricular aneurysm → Mural thrombus.
    • Chronic heart failure.

Post-MI Mechanical Complications: Ruptures & Defects

⭐ A new, harsh holosystolic murmur 5-7 days post-MI strongly suggests a ventricular septal rupture, typically heard best at the left sternal border.

Electrical Instability - Faulty Wiring Fiascos

  • Arrhythmias are the most common cause of death in the first 48 hours post-MI.
  • Ventricular Fibrillation (VFib):
    • Most frequent cause of sudden cardiac death, especially in the first 24 hours.
    • Requires immediate defibrillation.
  • Ventricular Tachycardia (VTach):
    • Can be sustained or non-sustained; may lead to VFib.
    • Treat with amiodarone or synchronized cardioversion if hemodynamically unstable.
  • AV Block:
    • Commonly associated with inferior wall MIs (RCA occlusion).
    • Often transient; treat symptomatic bradycardia with atropine or temporary pacing.

⭐ Post-inferior MI, new-onset heart block (especially complete heart block) is a major concern due to ischemia of the AV node, which is typically supplied by the RCA.

ECG: Ventricular Fibrillation to Sinus Rhythm Conversion

Mechanical Ruptures - Structural Catastrophes

*Occur subacutely (3-14 days) post-MI as macrophages degrade structural collagen, leading to catastrophic failure. Presents with sudden, severe hypotension and shock.

RuptureOnset (days)MurmurVesselKey Finding
Papillary Muscle3-5New holosystolic (mitral regurg)RCAGiant V-waves in PCWP
Interventricular Septum3-5New harsh holosystolic + thrillLAD↑ O₂ step-up (RA → RV)
Free Wall5-14Muffled heart soundsLADPericardial tamponade, PEA

📌 Mnemonic: Remember the timeline: Inflammation (1-3 days) → Softening/Rupture (3-14 days) → Scarring (>2 weeks).

Pump & Pericardial Problems - Powerless & Pained

  • Cardiogenic Shock (Killip IV): Severe LV dysfunction causing hypotension (SBP <90 mmHg), ↓ cardiac index (<2.2 L/min/m²), and pulmonary congestion (PCWP >18 mmHg).

  • Pericardial Inflammation: Two distinct forms based on timing.

-   **Early Post-Infarction Pericarditis:** Occurs **1-3** days post-MI. Treat with high-dose Aspirin.
-   **Dressler Syndrome:** Autoimmune-mediated, weeks to months later. Treat with NSAIDs/Colchicine.

⭐ The friction rub in early pericarditis is often transient; in Dressler's, it's more persistent.

Chronic Remodeling - Scars and Stretches

  • True Ventricular Aneurysm: A late complication, occurring >2 weeks to months post-MI. The infarcted wall is replaced by a thin, non-contractile fibrous scar that bulges paradoxically during systole.
    • Key Feature: Persistent ST-segment elevation in the leads of the prior infarction.
    • Major Risks: Formation of a mural thrombus leading to systemic embolization, and progressive heart failure.

⭐ Unlike a pseudoaneurysm, a true ventricular aneurysm has a low risk of rupture because it is composed of fibrous scar tissue.

ECG: Left Ventricular Aneurysm with ST Elevation & Q Waves

High‑Yield Points - ⚡ Biggest Takeaways

  • Ventricular fibrillation is the most common cause of death within 24 hours post-MI.
  • Papillary muscle rupture (2-7 days) causes acute, severe mitral regurgitation.
  • Ventricular free wall rupture (5-14 days) leads to cardiac tamponade and sudden death.
  • Interventricular septal rupture (3-5 days) creates a VSD with a new holosystolic murmur.
  • Ventricular aneurysm (weeks later) causes persistent ST elevation and risk of mural thrombus.
  • Dressler syndrome is an autoimmune pericarditis occurring weeks to months post-MI.

Practice Questions: Complications of MI

Test your understanding with these related questions

A 28-year-old male presents with sharp, stabbing chest pain that worsens when lying flat and improves when sitting forward. He reports a recent viral upper respiratory infection 2 weeks ago. On examination, a friction rub is heard on auscultation. His vital signs are stable. An ECG is most likely to show which of the following findings in this patient?

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Flashcards: Complications of MI

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Unstable angina has a high risk of progression to _____

TAP TO REVEAL ANSWER

Unstable angina has a high risk of progression to _____

myocardial infarction

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