Bundle-branch reentry and the postpacing interval after entrainment by right ventricular apex stimulation - A new approach to elucidate the mechanismof wide-QRS-complex tachycardia with atrioventricular dissociation

Background-Diagnosis of bundle-branch reentry ventricular tachycardia (BBR- VT) by the standard approach is challenging, and this may lead to nonrecogn ition of this tachycardia mechanism. Because the postpacing interval (PPI) after entrainment has been correlated with the distance from the pacing sit e to the reentrant circuit, BBR-VT entrainment by pacing from the right ven tricular apex (RVA) should result in a PPI similar to the tachycardia cycle length (TCL). This factor may differentiate BBR-VT from other mechanisms o f wide-QRS-complex tachycardia with AV dissociation, such as myocardial ree ntrant VT (MR-VT) or AV nodal reentrant tachycardia (AVNRT), in which the c ircuit is usually located away from the RVA. Methods and Results-Transient entrainment by RVA pacing was attempted in 18 consecutive BBR-VTs and finally achieved in 13. Results were compared with those found in 59 consecutive MR-VTs and 50 consecutive AVNRTs. The mean P PI-TCL difference was significantly (P<0.0001) shorter in the BBR-VT group (9+/-11 ms) than in the MR-VT (109+/-48 ms) and the AVNRT (150+/-29 ms) gro ups. No BBR-VT showed a PPI-TCL >30 ms (range -12 to 24 ms). Except for 2 M R-VTs, no MR-VT (range 21 to 211 ms) or AVNRT (range 100 to 215 ms) showed a PPI-TCL <30 ms. Conclusions-A PPI-TCL >30 ms, after entrainment by RVA stimulation, makes B BR-VT unlikely. Conversely, a PPI-TCL <30 ms is suggestive of BBR-VT but sh ould lead to further investigation by use of conventional criteria.