Electrophysiology Unit (EPU) 26.19 Practice Test

Manifest WPW on ECG reflects pre-excitation of the ventricles via an accessory pathway that bypasses part of the AV node delay. This makes ventricular activation occur earlier, shortening the PR interval. The early activation produces a delta wave at the start of the QRS, giving a slurred upstroke. Because part of the ventricle is activated early (via the pathway) and the rest through the normal conduction system, the QRS appears widened. So the characteristic pattern is a short PR interval, a delta wave, and a widened QRS. Other patterns—like a prolonged PR interval, or normal PR and QRS—don’t show this pre-excitation feature.