What is the hallmark EKG finding of Wolff-Parkinson-White syndrome?

The hallmark electrocardiogram (EKG) finding of Wolff-Parkinson-White (WPW) syndrome is the presence of a delta wave. A delta wave manifests as a slurred initial phase of the QRS complex and is indicative of the accessory pathway that characterizes this syndrome. In WPW, there is an additional electrical conduction pathway, known as the bypass tract, that can lead to rapid heart rates due to reentrant circuits.

The presence of the delta wave is critical because it highlights the abnormal conduction that occurs when the electrical impulse travels through both the normal AV node and the accessory pathway, causing a pre-excitation effect. This results in a distinctive W-shaped QRS complex morphology on the EKG.

Understanding the delta wave is essential for recognizing WPW, as it informs both diagnosis and treatment. The other options, while they represent different conditions or aspects of cardiac conduction, do not specifically indicate Wolff-Parkinson-White syndrome and are therefore not the defining characteristic in this context.