Reliability of retrograde atrial activation patterns during ventricular pacing for localizing accessory pathways

Definitive localization of accessory pathways is based on atrial activation patterns during orthodromic supraventricular tachycardia when retrograde conduction occurs exclusively through the accessory pathway. In some patients, supraventricular tachycardia cannot be induced or is deleterious. To determine whether accessory pathway sites can be identified accurately during ventricular pacing, retrograde atrial activation was assessed during orthodromic supraventricular tachycardia and ventricular pacing at multiple cycle lengths in 41 patients with a single accessory pathway. To obviate retrograde fusion due to concomitant conduction through the normal atrioventricular (AV) conduction system that may obscure the location of the accessory pathway, the difference in conduction time from the site of earliest atrial activation to the His bundle atrial electrogram (ΔA-SVT) was measured during orthodromic supraventricular tachycardia and compared with values observed during ventricular pacing (ΔA-VP). Characteristic values for the ΔA-SVT interval were identified for left lateral (66 ± 17 ms), left posterior (50 ± 8 ms), posteroseptal (33 ± 7 ms), right free wall (22 ± 15 ms) and anteroseptal (0 ± 0 ms) accessory pathway sites. During ventricular pacing, the site with the earliest atrial electrogram was used to define the accessory pathway location only if the maximal value of the ΔA-VP interval over the range of cycle lengths assessed was comparable with the value of the ΔA-SVT interval characteristic of that region. Values of the ΔA-SVT interval correlated closely with the maximal values of the ΔA-VP interval (r = 0.91). With this approach, 40 (98%) of 41 accessory pathway sites were identified correctly during ventricular pacing. Thus, each accessory pathway region has a characteristic difference in conduction time from the site of earliest activation to the His bundle atrial electrogram (ΔA-SVT interval) and atrial activation pattern that, when reproduced during ventricular pacing, reliably identifies the accessory pathway location.