Wolff-Parkinson-White Syndrome is a type of pre-excitation syndrome which can cause reentrant tachyarrhythmias via an accessory pathway. The pathway, called the Bundle of Kent, aberrantly connects the atria to the ventricles, providing a second pathway for conduction between the two other than the atrio-ventricular node. This causes recognizable changes in a patients ECG, and can lead to wide and narrow QRS changes.