The characteristic features demonstrated here include: a short PR interval . Delta waves , or slurring of the initial portion of the QRS; prolongation of the QRS; and secondary ST-T wave changes. These findings are the result of an accessory pathway that bypasses the A-V node and produces aberrant activation of the ventricle, as seen in the Wolff-Parkinson-White syndrome. The tall R wave in V1 in this type of Wolff-Parkinson-White is due to posteroanterior activation of the ventricle.