Electrocardiograms from patients presenting with WPW demonstrate a group of characteristic findings frequently associated with paroxysmal tachycardias and atrial fibrillation. In WPW, accessory pathways of accelerated ventricular impulse formation lead to the development of delta waves. These waves resemble pathological Q waves and represent initial slurring of the QRS complex as a result of early ventricular depolarization through this accessory pathway (see lead II, V1 and V6 - arrow below). As a result, the PR interval is shortened to less than 0.12 seconds and the QRS direction is altered (lead III), while its duration is extended to greater than 0.10 seconds. Secondary T wave anomalies resulting from abnormal ventricular repolarization are often demonstrated (leads II, III, V2, V3 and V4).