The Wolff-Parkinson-White syndrome is characterised by:
- episodes of tachycardia
- ECG signs of ventricular pre-excitation in between attacks
The phenomenon of ventricular pre-excitation results from abnormal atrio-ventricular conduction along a pathway termed the bundle of Kent. Such aberrant tissue rapidly conducts atrial depolarisations directly to the ventricular myocardium, so bypassing the slower AVN and the bundle of His. Often the QRS complex is normal during tachycardic episodes because the re-entry loop involves anterograde conduction along the AVN-His system and retrograde conduction along the bundle of Kent.
The abnormal wave of ventricular depolarisation results in a delta wave which appears as a slur to the upstroke of the otherwise normal QRS complex. The rapidity of the aberrant conduction pathway causes the PR interval to be shorter than normal.
About 50% of people with the ECG characteristics of WPW syndrome will experience re-entrant supraventricular tachycardias.