How is orthodromic tachycardia differentiated from AV nodal reentrant tachycardia (AVNRT) 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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Answer

This type of SVT may be difficult to distinguish from the usual AV nodal reentrant tachycardia (AVNRT) on a standard surface ECG. In adults, if the heart rate is higher than 200 bpm or a retrograde P wave is visible in the ST segment (long R-P tachycardia), a concealed AP-mediated orthodromic reentrant tachycardia (ORT) may be the diagnosis. However, this determination is most accurately made with electrophysiologic studies (EPS), or if SVT terminates with a single PVC. Other differentiating factors include the following [10] :

  • Anterior AVNRT: Presence of pseudo r' wave in lead V1, or a pseudo S wave in leads II, III, and aVF
  • Posterior AVNRT: Presence of a more than 20-ms difference in R-P interval between leads I and III
  • AVNRT: Presence of an AV block or AV dissociation (uncommon and of short duration) excludes the presence of an AP; development of a bundle branch block with an unchanged atrial-atrial (AA) or His-His (HH) interval
  • Orthodromic AVRT: Development of a bundle branch block in the presence of a significant change in the ventriculoatrial (VA) interval (diagnostic), with localization of the AP to the same side as the block.

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