• The fourth charactersitic of the heart muscle;
  • Specialised conducting systme to ensure that excitation travels to all the heart muscle fibres and in a certain pre-defined pattern.

Conducting Pathways include:

  • Anterior, Middle and Posterior Internodal Atrial bundles
  • A-V node - only pathway from atria to AV bundle; slow conduction and a long absolute refractory period
  • A-V bundle
  • Right and Left Bundle Branch
  • Purkinje Fibres
Heart Block
  • Failure of impulses arising at Atria to reach Ventricles
  • Blockage at AV node or Bundle
Two Main types of Heart Block
  • Partial - When some impulses fail to pass, This can be divide into : Regular - ratio between atrial and ventricular rhythm is constant; Irregular - no fixed ratio.
  • Complete - when all atrial impulses fail to reach the ventricles; atria and ventricles beat at their own rhythm and ther is no co-ordination.

Another classification for heart block divides into three:

  • 1st degree: delay in conduction
  • 2nd degree: partial block
  • 3rd degree: complete block