- Short PR interval (<120 ms during sinus rhythm in adults, <90 ms during sinus rhythm in children)
- Slurring of the initial portion of the QRS complex (delta wave), resulting in a prolonged QRS interval (≥120 ms in adults, >90 ms in children); wide QRS complex results from fusion of the two electrical impulses – one through the atrioventricular (AV) bypass tract and the other through the normal AV node
- Secondary ST-T wave changes may be present (i.e. ST-T segment deviation opposite in direction [discordant] to the main QRS deflection)
- Note: Wolff-Parkinson-White (WPW) syndrome exists due to an abnormal muscular network of conduction tissue that connects the atrium to the ventricle, thereby bypassing the AV node. Most patients do not have structural heart disease, but the syndrome is more common in patients with Ebstein’s anomaly (anomalous attachment and downward displacement of the tricuspid valve leaflets), mitral valve prolapse, hypertrophic cardiomyopathy, and dilated cardiomyopathy. Most tachyarrhythmias result from AV re-entry tachycardia and lead to a symptomatic narrow-complex tachycardia. A real concern is when WPW exists and a patient develop atrial fibrillation or flutter. In such cases, abnormal conduction down the AV bypass tract with retrograde conduction back up the AV node could result in a rapid, wide-complex and irregular tachycardia that can be life threatening.