How do atriofascicular tracts help differentiate Wolff-Parkinson-White (WPW) syndrome from preexcited tachycardia caused by Mahaim fibers?

Updated: Jan 08, 2017
  • Author: Christopher R Ellis, MD, FACC, FHRS; Chief Editor: Mikhael F El-Chami, MD  more...
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In the presence of atriofascicular tracts, preexcited tachycardia has a left bundle-branch block (LBBB) pattern, a long AV interval (due to the long conduction time over the accessory pathway), and short ventriculoatrial (VA) intervals. If right bundle-branch block (RBBB) develops, it may prolong the tachycardia cycle length (slow the AV reentrant tachycardia [AVRT]). Any right free wall bypass tract-mediated SVT will be prolonged with RBBB but should be unaffected by LBBB aberrancy.

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