Lesson 1: Cardiac Conduction

Lesson 1: Cardiac Conduction System

  • Components of the Cardiac Conduction System:

    • Sinoatrial (SA) node

    • Atrioventricular (AV) node

    • Bundle of His

    • Bundle branches

    • Purkinje fibers

  • Internodal Tracts:

    1. Anterior internodal tract (Bachmann bundle)

    2. Middle internodal tract (Wenckebach tract)

    3. Posterior internodal tract (Thorel tract)

  • Conduction Velocities:

    • Slowest to Fastest: AV node < SA node < Myocardial muscle cells < His Bundle < Bundle branches < Purkinje fibers

  • Electrical Isolation:

    • Connective tissue isolates atria from ventricles; AV node acts as a gatekeeper for impulses.

Conduction Velocity

  • Velocity Values:

    • SA and AV nodes: 0.02−0.10extm/sec0.02 - 0.10 ext{ m/sec} (slow)

    • Myocardial muscle cells: 0.3−1extm/sec0.3 - 1 ext{ m/sec} (intermediate)

    • His bundle, bundle branches, Purkinje fibers: 1−4extm/sec1 - 4 ext{ m/sec} (fast)

  • Factors Affecting Velocity:

    1. Resting membrane potential

    2. Amplitude of action potential

    3. Rate of change in membrane potential during phase 0

    • ANS tone

    • Hyperkalemia

    • Ischemia

    • Acidosis

    • Antiarrhythmic drugs

Accessory Pathways

  • Function of AV Node:

    • Only electrical pathway between atria and ventricles; maintains synchrony.

  • Accessory Pathways:

    • Bypass normal conduction pathways; can cause dysrhythmias (e.g., Wolff-Parkinson-White syndrome).

    • Examples:

    • James fiber

    • Atrio-hisian fiber

    • Kent's bundle

    • Mahaim bundle

    • Connections:

    • Atria to AV node

    • Atria to His bundle

    • Atria to ventricle

    • AV node to ventricle