AVNRT

• reentry in AV node—this is the example of reentry that we used above

• 40% of individuals have two pathways in their AV node, a slow and a fast pathway

• in most patients, physiologically, the slow pathway doesn’t do anything. we know that because after ablation, people do fine the rest of their lives

• mechanism: one impulse goes down both pathways, but F pathway transmits this to ventricles first. this blocks the transmission in S pathway

• a second, early impulse occurs, and it can’t go down the fast pathway because it is blocked (it’s repolarizing). so instead the impulse goes down the slow pathway

• by the time it finishes the slow pathway, the fast pathway is again ready to accept depolarization, which it gets from the early signal wrapping around the slow pathway. this starts a wave of reentrant activity

• ECG
  

  • narrow-complex arrhythmia

  • conduction is going down and QRS looks normal

  • quite fast, characteristically about 150 bpm

  • relationship between atria and ventricles firing is VA VA instead of AV AV

  • the ventricle is being activated in reverse, so this is pseudo R’ wave

  • you see these little R’ waves and this is indicative

• rx

  • class II β-blockers or class IV Ca-channel blockers

  • however, catheter ablation of slow pathway is > 95% successful and the procedure is assoc with very few complications

Category: Pathology Notes