Figure 94-20

Wolff-Parkinson-White syndrome in a patient with free-wall accessory pathway.
A. Sinus rhythm with fusion beats showing different degrees of pre excitation.
B.Maximal preexcitation during atrial fibrillation. Note marked change in QRS duration and electrical axis.

Reference:Castellanos,A. and others,Hurst's The Heart 8th Edition,The Resting,321-356.