Nursing Pharmacology Chapter 8:   Antiarrhythmic Agents

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Cardiac Electrophysiology

 

 

Cardiac Cell Phase 0 and Sodium Current

  • Note the rapid "upstroke" characteristic of Phase 0 depolarization.

  • This abrupt change in membrane potential is caused by rapid, synchronous opening of Na+ channels.

  • Note the relationships between the the ECG tracing and phase 0

 

Ca2+:  Channel Activation Sequence similar to sodium; but occurring at more positive membrane potentials (phases 1 and 2)

  • Following intense inward Na+ current (phase 0), Ca2+currents:

  • Phases 1 and 2, are slowly inactivated.   (Ca2+channel activation occurred later than for Na+)

 

Channel Inactivation, Re-establishing the Resting Membrane Potential

  • Final repolarization (phase 3):

    • Complete Na+ and Ca2+ channel inactivation

  • Increased potassium permeability

  • Membrane potential approaches K+ equilibrium potential, which approximates the normal resting membrane potential.

Hondeghem, L.M. and Roden, D.M., "Agents Used in Cardiac Arrhythmias", in Basic and Clinical Pharmacology, Katzung, B.G., editor, Appleton and Lange, 1998, pp 216-241.

 

 
 

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