The effect of pacing site on the echo zone in patients with concealed Wolff-Parkinson-White syndrome.

In 14 patients with the left-sided concealed Wolff-Parkinson-White syndrome, the effects of changing atrial pacing site on the echo zone were evaluated. In 12 patients, re-entrant tachycardia was induced by premature stimuli both in the coronary sinus (CS) and the high right atrium (HRA). In the remaining 2 patients, the tachycardia was induced by premature stimuli only in the CS. The lower limit of the echo zone was shifted to a longer coupling interval during CS pacing in 12 patients. The longer effective refractory period (ERP) of the CS was responsible for the shifting of the lower limit of the echo zone to a longer coupling interval. The upper limit of the echo zone was shifted to a longer coupling interval during CS pacing in 10 patients. The difference of atrial conduction times from the site of stimulation to the 2 conduction pathways (the normal conduction pathway and the accessory pathway) is thought to be responsible for the shifting of the upper limit of the echo zone.