Double ventricular response to an extrastimulus in a patient with triple atrioventricular pathways

A patient with the Wolff-Parkinson-White Syndrome was studied through recordings of the intracardiac potentials and programmed atrial stimulation. During programmed atrial stimulation at progressively shorter coupling intervals (A1-A2 intervals), the His deflection was always recorded after the ventricular complex. Thus, at coupling intervals between 295 and 250 msec, there was a double ventricular response, one through the accessory pathway (QRS complex of the Wolff-Parkinson-White morphologic pattern) and the other by the normal atrioventricular pathway (normal QRS complex or with pattern of left bundle-branch block). At a coupling interval of 295 msec, the atrio-His (A-H) interval increased from 200 to 350 msec. This fact and the presence of two distinct A2-H2 intervals are suggestive of the existence of dual atrioventricular pathways, coexisting functionally with a lateral accessory bypass (Kent's bundle).