On a standard 12-lead ECG, the delta wave and short PR interval characteristic of Wolff-Parkinson-White syndrome result from pre-excitation of the ventricles. The abnormal pathway responsible conducts impulses via:

• A Enhanced automaticity of the His bundle causing a shorter AV nodal refractory period
• B Mahaim fibers connecting the AV node to the right bundle branch only
• C Retrograde conduction through the normal His-Purkinje system
• D An accessory AV pathway (bundle of Kent) bypassing the AV node and its physiological delay ✓

Explanation

WPW syndrome is caused by an accessory atrioventricular pathway (bundle of Kent) that conducts impulses directly from atria to ventricles without the physiological delay imposed by the AV node. This pre-excites a region of ventricular myocardium, producing the slurred upstroke (delta wave) and shortening the PR interval. The delta wave represents initial slow cell-to-cell conduction in the pre-excited region before the normal His-Purkinje system activates the rest of the ventricles.

Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.

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Written and medically reviewed by the StethoPrep medical team.