Localization of the accessory pathway in the Wolff-Parkinson-White syndrome from the ventriculo-atrial conduction time of right ventricular apical extrasystoles.

In 18 consecutive patients with the Wolff-Parkinson-White syndrome undergoing electrophysiologic study, the ventriculo-atrial conduction time of right ventricular apical extrasystoles which advanced atrial activation during circus movement tachycardia was studied in relation to accessory pathway location. Accessory pathway location was determined by delta wave morphology during maximal pre-excitation, mapping of atrial activation during circus movement tachycardia and ventricular pacing, the effect of bundle branch block on ventriculo-atrial conduction time during circus movement tachycardia, and the effect of pacing from different sites in the atria on the stimulus-to-delta wave interval. In 7 patients with septal accessory pathways, ventriculo-atrial conduction time was similar during circus movement tachycardia and following right ventricular apical extrasystoles (mean difference 0 +/- 6 ms, range -5 to +10 ms). In contrast, in 11 patients with a left free wall accessory pathway, ventriculo-atrial conduction time increased by 46 +/- 15 ms (range 15 to 65 ms) following right ventricular apical extrasystoles. Therefore, measurement of the ventriculo-atrial conduction time of right ventricular extrasystoles during circus movement tachycardia provides an easy way to distinguish between septal and left free wall accessory pathways. This finding may be of particular use in determining the location of concealed bypass tracts.