Cardiac Conduction System

Components of the Cardiac Conduction System

• Sinoatrial Node (SA Node):

  • Located in the right atrium near the entrance of the superior vena cava.
  • Acts as the natural pacemaker of the heart.
  • Initiates all heartbeats and determines heart rate.
  • Electrical impulses spread throughout both atria, causing them to contract.

• Atrioventricular Node (AV Node):

  • Located on the other side of the right atrium near the AV valve.
  • Serves as the electrical gateway to the ventricles.
  • Delays the passage of electrical impulses to ensure atria eject blood into ventricles before they contract.
  • Receives signals from the SA node.

• Atrioventricular Bundle (AV Bundle or Bundle of His):

  • Divides into right and left bundle branches.
  • Conducts impulses toward the apex of the heart.
  • Signals are passed onto Purkinje fibers, spreading throughout the ventricles.

Electrocardiogram (ECG/EKG)

• Composite recording of all action potentials produced by the nodes and heart cells.
• P Wave:
  • Represents atrial depolarization.
  • Atrial contraction (atrial systole) starts about 100ms after P wave begins.
• PR Interval:
  • Time between atrial depolarization and ventricular depolarization.
  • Reflects conduction through the AV node.
• QRS Complex:
  • Represents ventricular depolarization.
  • Q Wave: Depolarization of the interventricular septum.
  • R Wave: Depolarization of the main mass of ventricles.
  • S Wave: Last phase of ventricular depolarization toward the heart's base.
  • Atrial repolarization occurs here, but is obscured by QRS complex.
• ST Segment:
  • Reflects the plateau of action potentials in ventricles.
  • Indicates when ventricles contract and pump blood.
• T Wave:
  • Represents ventricular repolarization before ventricular relaxation (ventricular diastole).

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