Final answer:
The key EKG finding in WPW syndrome is the delta wave, along with a short PR interval and a broadened QRS complex, indicative of an abnormal electrical pathway in the heart.
Step-by-step explanation:
The pathognomonic EKG finding at rest associated with Wolff-Parkinson-White (WPW) syndrome is the presence of a delta wave. This occurs due to pre-excitation of the ventricles from an accessory pathway, which bypasses the normal conduction system.
The EKG will also typically show a short PR interval and a broadened QRS complex due to the premature ventricular depolarization. Unlike other cardiac abnormalities such as atrial fibrillation, ventricular tachycardia, and third-degree block, the WPW syndrome has this unique delta wave that suggests electrical impulses are following an abnormal pathway through the heart.