Electrophysiologic characteristics of ventricular extrastimulation-induceddissipation of functional bundle branch block associated with supraventricular tachycardia

introduction: Linking-related anterograde functional bundle branch block du ring supraventricular tachycardia (SVT) is due to repetitive concealed retr ograde conduction of impulses from the contralateral bundle branch and can be eliminated by a critically timed premature ventricular beat (PVB). We as sessed the electrophysiologic characteristics of PVB-induced dissipation of functional bundle branch block during SVT. Methods and Results: During SVT with functional bundle branch block, PVB wa s delivered from the right ventricular apex, scanning the tachycardia cycle length (CL) with 10-msec decrements in the coupling interval in 14 patient s (3 AV nodal reentrant tachycardia and 11 orthodromic AV reciprocating tac hycardia). Dissipation was achieved in group 1: functional right bundle bra nch block (RBBB) in 4, functional left bundle branch block (LBBB) in 4, and both functional RBBB and LBBB in I with a dissipation zone occupying 4% to 13% (mean 8.5%) of the tachycardia CL. The outer limits were 22 +/- 16 mse c and 68 +/- 14 msec < tachycardia CL; the inner limits were 56 +/- 18 msec and 90 +/- 24 msec < tachycardia CL for RBBB and LBBB, respectively (both P < 0.05). Dissipation could not be achieved in group 2 (4 RBBB and I LBBB) due to CL-dependent bundle branch block and/or local ventricular refractor iness. Conclusion: During SVT, functional bundle branch block due to "linking" oft en can be dissipated by timely PVB delivered from the right ventricular ape x within a narrow zone of the tachycardia CL. Our findings suggest that the dissipation zone is affected by the pattern of functional bundle branch bl ock relative to the site of PVB delivery.