Why does the QRS interval widen 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

The QRS interval is widened because the ventricles are initially activated via the AP, which lies outside the normal conducting system, producing an early, albeit relatively slow, initial propagation of depolarization forces through the ventricular tissue. This produces the delta wave. The delta wave makes the QRS appear wider than expected and the PR interval somewhat shortened. This is known as a manifest AP because it is easily identifiable on ECG.


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