Which of the following is a key characteristic of Wolf-Parkinson-White syndrome?

Wolf-Parkinson-White syndrome is characterized primarily by the presence of an accessory conduction pathway in the heart, which leads to episodes of tachycardia. A key feature on an electrocardiogram (ECG) indicative of this syndrome is the presence of delta waves. These waves are seen due to the early activation of the ventricles as a result of the accessory pathway, known as the Bundle of Kent, which allows impulses to bypass the normal conduction route through the atrioventricular node. As a result, the QRS complex on the ECG is widened and has a distinctive slurred upstroke, which is referred to as a delta wave.

Other options presented, such as bradycardia during exercises, recurrent urinary tract infections, and increased respiratory rate, do not pertain to the hallmark features or typical manifestations of Wolf-Parkinson-White syndrome. Instead, they relate to entirely different clinical conditions or physiological responses, further reinforcing that delta waves on the ECG are the defining characteristic of this arrhythmia.