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.