What is the pathognomonic EKG finding at rest with WPW syndrome?

In Wolff-Parkinson-White (WPW) syndrome, the characteristic electrocardiogram (EKG) finding is the presence of a delta wave. This delta wave is caused by pre-excitation of the ventricles due to an accessory pathway, also known as the bundle of Kent, which bypasses the normal conduction delay at the atrioventricular node.

On the EKG, the delta wave appears as a slurred upstroke at the beginning of the QRS complex, reflecting the early activation of ventricular myocardium. This finding is key to the diagnosis of WPW syndrome. The QRS complex may also be wide due to this pre-excitation, further emphasizing the abnormal conduction pattern that is characteristic of the syndrome.

In contrast, other findings listed in the options do not have specific associations with WPW syndrome. Prolonged QT interval is associated with various other conditions and electrolyte imbalances, ST segment elevation typically indicates myocardial ischemia or infarction, and inverted T waves are nonspecific and can be seen in multiple cardiovascular or pulmonary conditions. Thus, the delta wave is the signature finding for WPW syndrome at rest on an EKG.