12-lead electrocardiogram (ECG) of a right lateral accessory AV pathway

Electrocardiogram in sinus rhythm from a patient with Wolff-Parkinson-White syndrome shows classic preexcitation with a short PR interval, delta wave, and widened QRS complex with a left bundle branch block morphology. The delta wave is positive in the lateral leads 1, aVL, and V6, it is negative in lead III and isoelectric in lead aVF. The QRS axis of <30L distinguishes this pathway from an anteroseptal accessory AV pathway.