How are accessory pathways (APs) diagnosed in Wolff-Parkinson-White (WPW) syndrome?

Updated: Jan 08, 2017
  • Author: Christopher R Ellis, MD, FACC, FHRS; Chief Editor: Mikhael F El-Chami, MD  more...
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Diagnosis of accessory pathways (APs) is indicated. During ventricular pacing, premature ventricular stimulation activates the atria before retrograde depolarization of the His bundle. This indicates that the impulse reached the atria before it depolarized the His bundle and must have traveled via a different pathway (bypass tract).

If the ventricles can be stimulated prematurely during tachycardia at a time when the His bundle is refractory and the impulse still conducts to the atrium (His-refractory or His-synchronous premature ventricular complex [PVC]), this indicates that retrograde propagation traveled to the atrium over a pathway other than the bundle of His, representing the usual inferior input to the AV node.

In addition, if a PVC, delivered at a time when the His bundle is refractory, terminates the tachycardia without retrograde activation of the atria, it most likely invaded, and blocked in, an AP. If repeatable, this is diagnostic of orthodromic reentrant tachycardia (ORT).

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