In Wolff-Parkinson-White (WPW) syndrome there is an extra connection (an accessory pathway) between the atria and ventricles. This means that as well as electrical impulses passing normally between the atria and the ventricles at the AV node, electrical impulses can also pass abnormally along the accessory pathway.
This is a companion discussion topic for the original article at https://patient.info/heart-health/palpitations-leaflet/wolff-parkinson-white-syndrome