How does shortened pr interval lead to svt?

Short pr: The short pr in WPW implies an accessory pathway for av conduction. Having multiple pathways for impulse conduction allows multiple reentry circuits for stimuli and tachycardia is much easier to sustain.

Short pr: The PR interval represents the time it takes for electricity to pass from the top to the bottom heart chambers. Normally, there's a delay in this passage, of up to 1/5th of a second; however, if the passage is too fast, or less than ~1/8th of a second, a short circuiting "bypass" tract may be present, which can lead to a SVT. Catheter ablation can cure these, so speak with a heart rhythm doctor.