Cardiac Arrhythmias: Difference between revisions

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===Phase 1: Early Rapid Repolarization===
===Phase 1: Early Rapid Repolarization===
Immediately following rapid depolarization, the inactivation of the Na<sup>+</sup> channel (I<sub>Na</sub>) and subsequent activation of the outward K<sup>+</sup> channel (I<sub>TO</sub>) and the Na<sup>+</sup>/Ca<sup>2+</sup> exchanger produce a early rapid repolarization. Due to the absence of I<sub>Na</sub> in the upstroke of sinus node and AV node cells and the subsequent slower depolarization, this rapid repolarisation is not visible in their action potentials.
Immediately following rapid depolarization, the inactivation of the Na<sup>+</sup> channel (I<sub>Na</sub>) and subsequent activation of the outward K<sup>+</sup> channel (I<sub>TO</sub>) and the Na<sup>+</sup>/Ca<sup>2+</sup> exchanger produce a early rapid repolarization. Due to the limited role of the Na<sup>+</sup> channel in the upstroke of sinus node and AV node cells and the subsequent slower depolarization, this rapid repolarisation is not visible in their action potentials.


===Phase 2: Plateau===
===Phase 2: Plateau===
The plateau phase represents an equal influx and efflux of ions producing a stable membrane potential. The influx is mediated by Ca<sup>2+</sup> through the open L-type Ca<sup>2+</sup> channels and the exchange of Na<sup>+</sup> for internal Ca<sup>2+</sup> by the Na<sup>+</sup>/Ca<sup>2+</sup> exchanger. The efflux is the result of outward current carried by K<sup>+</sup> and Cl<sup>-</sup> ions.
The plateau phase represents an equal influx and efflux of ions producing a stable membrane potential. The influx is mediated by Ca<sup>2+</sup> through the open L-type Ca<sup>2+</sup> channels (I<sub>Ca-L</sub>)and the exchange of Na<sup>+</sup> for internal Ca<sup>2+</sup> by the Na<sup>+</sup>/Ca<sup>2+</sup> exchanger. The efflux is the result of outward current carried by K<sup>+</sup> (I<sub>Kr</sub> and Cl<sup>-</sup> ions.


===Phase 3: Final Rapid Repolarization===
===Phase 3: Final Rapid Repolarization===
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