Count to 10 - Anaesthetic Primary Podcast EP22 – Electrophysiology of the Heart | Anaesthetic Primary Topic | Cardiac Physiology | CT10
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Jun 25, 2024 Explore the fascinating world of cardiac electrophysiology, diving into the ionic basis of automaticity and the processes of cardiac excitation. Discover the intricacies of ECG interpretation and how electrical signals influence heart mechanics. Learn about the critical coupling between excitation and contraction, along with its pharmacological implications. The discussion also includes insights from recent exams, ensuring listeners are well-prepared. Tune in for an engaging deep dive into the electrical heartbeat that powers our lives!
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Potassium Sets Resting Potential
- Resting membrane potential in cardiac myocytes is largely set by potassium, with EK ≈ -94 mV matching RMP ≈ -90 mV.
- This explains why K+ permeability dominates baseline excitability and membrane voltage stability.
Five-Phase Fast Action Potential
- Fast-response cardiac action potentials (atria, ventricles, Purkinje) have five phases including a calcium-driven plateau (phase 2).
- Their long absolute refractory period (~250 ms) prevents tetany in cardiac muscle.
Pacemaker Cells Lack A True RMP
- Slow-response (SA/AV node) action potentials lack a stable RMP and show a pacemaker phase 4 with spontaneous depolarization.
- Phase 0 is mediated by L-type Ca2+ channels and threshold is ~ -40 mV, driven by funny (HCN) and T-type Ca2+ currents.