Ventriculoatrial Conduction Time During Bundle Branch Reentrant Beat Initiating Orthodromic Tachycardia: A Simple and Reliable Method for Localization of Accessory Pathways

VA Interval Via Accessory Pathway During Bundle Branch Reentry . Bundle branch reentrant (BBR) complex is commonly induced during programmed ventricular stimulation with single ex‐trastimulus. In patients with atrioventricular accessory pathway, BBR beat frequently triggers orthodromic tachycardia. This study was designed to determine whether evaluation of the ventriculoatrial conduction time during BBR (VA BBR ) induced with right ventricular extrastimulation (i.e., left bundle branch block morphology) can separate left free‐wall (LFW) accessory pathways from left posteroseptal (LPS) or right‐sided pathways. Thirty‐eight patients with single atrioventricular accessory pathways were included. There were 28 men and 10 women with a mean age of 26 years. The accessory pathway was localized in LFW in 23 patients (group I) and LPS in seven (group ID. Eight patients (group III) had pathways located in the right side. In each patient, VA BBR was determined and compared with the following: (1) V 2 A 2 interval exclusively via accessory pathway; and (2) ventriculoatrial conduction time during orthodromic tachycardia with narrow QRS complex (VA NQ ), left bundle branch block plus normal axis (VA LB‐NA ) or left axis (VA LB‐LA ). In group I, VA BBR values (170–245 msec, mean 196.1 ± 20.5 msec) were 0–25 msec longer than V 2 A 2 (170–245 msec, mean 191.3 ± 19.1 msec) and 45–125 msec greater than VA NQ (100–155 msec, mean 125.6 ± 14.1 msec). VA BBR was identical to VA LB‐LA but 25–55 msec greater than VA, LB‐NA (140–205 msec, mean 160.9 ± 20.8 msec). In group II, VA BBR values (100–140 msec, mean 118.6 ± 14.3 msec) were 15–30 msec shorter than V 2 A 2 (125–165 msec, mean 140.7 ± 14.3 msec) and 15–25 msec longer than VA NQ (85–120 msec, mean 100.7 ± 12.0 msec). Comparing VA BBR with VA LB‐NA or VA LB‐LA did not show any statistically significant difference. In group III, VA BBR values were consistently shorter than V 2 A 2 and identical to VA NQ . Thus, assessment of VA BBR is a simple and useful method that can be reliably utilized to differentiate LFW pathways from LPS or right‐sided pathways. Furthermore, these data provide new insights into the electrophysiological characteristics of bundle branch reentry. ( J Cardiovasc Electrophysiol, Vol. 1, pp. 121–131, April 1990 )