Module 1
Topic 5
Lesson 18

Gap phenomenon in AV conduction

Laura Vitali Serdoz

What will you learn?

  • what is gap phenomenon
  • how to explain reappearing AV conduction
  • appreciation of interactions between supra- and infra-his conduction

About this scenario

  • The Gap phenomenon is observed during atrial extrastimulation in which AV block at longer coupling intervals is followed by restored AV conduction at shorter coupling intervals. Meaning that paradoxically a faster pace improves conduction.
  • It appears only when the initial site of block is in the distal conduction system (infra-his) and as the coupling interval is further decreased, a further (decremental) delay occurs in the proximal conducting site (supra-his). This "extra" time caused by the supra-his delay gives the distal site time to recover and conduct again
  • Key condition for occurrence of the gap phenomenon is that the effective refractory period of the distal site is longer than the functional refractory period of the proximal site