In WPW, the accessory pathway acts as a bypass tract connecting the atria to the ventricles,
‘short-circuiting’ the AV node.
This leads to much earlier activation of the ventricles compared to normal (called pre-excitation). This is results in the classical ‘delta-wave’ on the ECG (purple). The rest of the ventricle is activated via the slower conducting AV node.
Slide 4 of 7