Initiation of AV node reentry (AVNRT)

• about 40% of the population has two pathways in AV node—fast pathway F and slow pathway S

• these two pathways have all the requirements for reentry

  • fast pathway has fast conduction but very slow repolarization (criterion 1)

  • slow pathway has slow conduction (criterion 3)

  • unidirectional conduction block (criterion 2)

  • SA node fires. AP goes through fast pathway straight to ventricles. it is blocked in the slow pathway because the AP propagates so slowly through S

  • F then takes a long time to repolarize (criterion 1); the next SA node beat, which is early, can’t go down F because F is still repolarizing. so, the early beat goes down S

  • by the time F has finished repolarizing, the early beat has passed through S and now “wraps around,” retrograde, to activate F from “below”

Category: Pathology Notes