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Understanding the Cardiac Conduction System

Oct 24, 2024

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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