Phase 0 Sodium Influx — FRCA Primary MCQ
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Correct answer: A — Rapid sodium influx through voltage-gated sodium channels
Phase 0 (rapid depolarisation) of the ventricular action potential is caused by rapid influx of Na+ through voltage-gated sodium channels. This produces the sharp upstroke of the action potential reaching approximately +30 mV. The speed of Phase 0 determines conduction velocity. SA and AV node Phase 0 is slower because it depends on Ca2+ (not Na+) influx.
Reference: Power Kam 2018 Principles of Physiology for the Anaesthetist