Here is a good example of an ECG showing the signs of Wolff-Parkinson-White syndrome during normal sinus rhythm. WPW is one of the “pre-excitation” syndromes caused by an accessory pathway between the atria and ventricles. Accessory pathways can bypass the AV node. These conduction pathways can conduct anterograde (forward toward the ventricles), retrograde (away from the ventricles), most commonly, in both directions. When the accessory pathway conducts in an anterograde fashion, it causes pre-excitation of the ventricles.