A preexcitation syndrome, such as Wolff-Parkinson-White syndrome, results from which conduction pattern?

• A. Atrial impulses are delayed by the AV node.
• B. Conduction is normal through the AV node.
• C. Ventricular impulses fail to depolarize atria.
• D. Atrial impulses bypass the typical electrical pathway and activate the ventricular myocardium directly.

Answer: (D)

Preexcitation occurs when an accessory pathway allows atrial impulses to bypass the AV node and activate the ventricles directly. In Wolff-Parkinson-White, this means ventricular activation begins earlier than usual because the impulse doesn’t go through the normal AV nodal delay. This direct ventricular activation shortens the PR interval and creates a delta wave, often with a widened QRS from fusion of the two activation paths. So the pattern is atrial impulses bypassing the typical electrical pathway and activating the ventricular myocardium directly. This differs from normal conduction, where the AV node provides the delay before ventricular activation.