How does an external cardiac Defibrillator terminate life-threatening ventricular fibrillation? (Hard)
Answer and explanation
Correct answer: D. Simultaneous high-energy depolarization of all myocardium extinguishing wavelets
- Step 1: Defibrillation delivers a synchronized or asynchronous direct current electrical pulse (typically 120-200 Joules biphasic) across the chest. Step 2. This depolarizes the entire myocardium simultaneously, creating a refractory period that extinguishes re-entrant circuits and lets the SA node restart sinus rhythm. Answer: Delivers a high-energy DC electric shock that simultaneously depolarizes all myocardium, allowing the SA node to resume pacing. Why not the others: A defibrillator does not mechanically pump blood; vagal stimulation does not stop VF; calcium injection is not electrical defibrillation.
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