intrinsic conduction system

• SA Node


  • Located in upper right atrium
  • Initiates the depolarization impulse which, in turn, generates an action potential that spreads throughout the atria to the AV node
  • Sets the overall pace of the heartbeat
• Internodal Pathway


  • Located in the walls of the atria
  • Links the SA node to the AV node
  • Distributes the action potential to the contractile cells of the atria
• AV Node


  • Located in the inferior interatrial septum
  • The action potential is delayed here briefly, while the atria contract, before being transmitted to the AV bundle
• AV Bundle


  • The only electrical connection between the atria and the ventricles
  • Allows the action potential to move from the interatrial septum to the interventricular septum, connecting the AV node to the Bundle Branches
• Bundle Branches


  Convey the action potential down the interventricular septum
• Purkinje Fibers


  • Begin at the lower interventricular septum to the apex of the heart, then continue superiorly through the myocardium of the ventricles
  • The Purkinje fibers convey the action potential to the contractile cells of the ventricle
• Action potentials, which spread from the autorhythmic cells of the intrinsic conduction system to the contractile cells are electrical events
• Subsequent contraction of the contractile cells is a mechanical event that causes a heartbeat
• P Wave


  • Small upward wave
  • Indicates atrial depolarization
• QRS Wave


  • Downward deflection, then a large upward peak, ending as a downward deflection
  • Represents ventricular depolarization
• T Wave


  • Dome-shaped wave
  • Represents ventricular repolarization
• In a normal ECG tracing, atrial repolarization is hidden by the QRS complex
• The contraction of the ventricle begins at the apex of the heart and moves superiorly, forcing the blood upward toward the arteries. This is important because the large arteries are located superiorly. So blood has to be rung from the bottom of the heart up
• P wave


  Indicates atrial depolarization which is followed by atrial contraction
• QRS complex


  Represents ventricular depolarization which is followed by ventricular contraction
• T wave


  Represents ventricular repolarization which is followed by ventricular relaxation