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

Electrocardiogram in sinus rhythm from a patient with Wolff-Parkinson-White syndrome shows a widened QRS complex which is not maximally preexcited. Although the delta wave and QRS are positive in lead I, the negative delta wave in lead aVL and the right bundle branch block morphology localize the accessory pathway to the left lateral mitral annulus.