What defines Wolff-Parkinson-White (WPW) syndrome?

Wolff-Parkinson-White (WPW) syndrome is characterized by the presence of an accessory pathway that connects the atria to the ventricles, bypassing the normal conduction system. This abnormal conduction pathway allows for a quicker electrical connection, which can lead to a re-entrant tachycardia, a rapid heart rhythm.

The accessory pathway can cause the heart to beat faster than normal, and this can be seen on an electrocardiogram (ECG) as a shortened PR interval and a characteristic delta wave, suggesting that the electrical signal is transmitted through this pathway rather than solely through the AV node. Therefore, the defining feature of WPW syndrome is indeed the presence of this accessory pathway.

While a short PR interval can be observed in WPW due to the early activation of the ventricles, it is not the defining characteristic on its own. Additionally, prolonged QRS duration may occur when there is fusion of the normal and accessory pathways during arrhythmic episodes, but it is not consistent in all cases. Elevated ST segments are not characteristic of WPW syndrome and are more associated with other cardiac conditions such as myocardial injury. Thus, the identification of the accessory pathway is what fundamentally defines WPW syndrome.