Date: 29 Jul 2009

Supernormal conduction and linking in an accessory AV pathway

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Introduction

Spontaneous intermittent block over an accessory pathway manifested as alternating QRS complexes of pre-excited and normally conducted beats suggests a prolonged antegrade refractory period [1]. Similarly, sudden loss of the delta wave during exercise [2] is also considered evidence of prolonged refractoriness over an accessory A–V pathway. However, the antegrade refractory period of an accessory A–V pathway is not the only determinant of conduction over bypass tracts. Two other important but frequently overlooked electrophysiologic mechanisms modulate conduction over accessory A–V pathways: supernormal conduction [3] and linking [4] between the normal conduction system and the accessory A–V pathway.

We present a patient that, despite intermittent preexcitation at rest and loss of preexcitation during exercise, had an accessory A–V pathway able to conduct at fast rates as demonstrated during the electrophysiology study. Both supernormal conduction and the linking phenomenon