Review of Conduction

Review the graphics below: On the left is a description of normal cardiac conduction. On the right is one example of abnormal cardiac conduction. In this example, the result is a *tachyarrhythmia.

Be prepared to answer the following questions from these diagrams.

In normal conduction, what is the only normal gateway of impulse conduction to the ventricles?

If conduction follows an abnormal or "accessory" pathway back toward the AV node, what is the usual result?

Normal Cardiac Conduction in Relation to EKG Diagram
Abnormal Cardiac Conduction: Supraventricular Tachycardia

Normal cardiac conduction occurs as:

  • an impulse is generated at the SA node and spreads across both atria, causing them to contract. Note that the atrial impulse correlates with the P wave in the EKG diagram above.
  • The Fibro-fatty atrioventricular groove insulates the ventricles from the atrial impulse. The AV node is the only normal gateway of conduction to the ventricles.
  • The impulse is delayed at the AV node, travels down the AV bundle and it's branches and reaches the Purkinje fibers. The ventricles are stimulated to contract. Follow the red dots and note correlation with the QRS wave in the EKG diagram above.
  • The T wave correlates with repolarization of the ventricles.

Abnormal cardiac conduction can occur in many ways. For example, in this diagram:

  • The red dots follow the normal conduction pathway.
  • The yellow dot represents conduction via an abnormal "accessory" pathway back toward the AV node. Typically, impulses travelling these abnormal pathways restimulate the atria and/or ventricles and cause arrythmias.
  • The abnormal EKG tracing shown here represents a supraventricular tachycardia.