Wolff-Parkinson-White Syndrome (WPW) occurs when an accessory pathway is formed in birth due to incomplete separation of atria and ventricles during foetal development.
The extra accessory pathway bypasses the normal circuit, transmitting signals from the atria to the ventricles and vice versa (re-entry). This causes pre-excitation of the ventricles. It is then followed by normal depolarisation of the QRS complex. This gives you wide QRS complexes.
With WPW you will see: