Abstract 14513: An Aberrant Friend - Using Bundle Branch Block for Septal Accessory Pathway Localization

Introduction: While changes in the ventriculoatrial (VA) time with RBBB or LBBB during ORT utilizing a free wall accessory pathway (AP) is well described, such a change in VA time can also be helpful in identifying the location of a septal AP. Objectives: To demonstrate the effect of RBBB and LBBB aberrancy on the VA time for ORT involving septal AP and thereby assist in identifying a posteroseptal AP. Results: A 51-year-old man with WPW syndrome was referred for EP study and ablation due to palpitations. With programmed atrial extrastimulation, an atypical echo beat was noted. While attempting to induce tachycardia, double atrial extrastimuli resulted in non-sustained ORT both with RBBB and LBBB aberrancies (Figure). Measurement of the VA time during non-sustained ORT demonstrated a VA time that was longer in the presence of LBBB aberrancy (110ms) than RBBB aberrancy (97ms) compared to narrow QRS (95ms). Electroanatomic mapping identified the earliest atrial activation of the echo beat on the right posteroseptum. Radiofrequency ablation at this site resulted in immediate loss of ventricular pre-excitation. Conclusions: Changes in the VA interval during AP-mediated SVT are especially important for pathway localization. As demonstrated in prior studies, for free wall APs, the difference between sinus and bundle branch block time (ΔVA) is usually >35ms compared to <35ms for septal APs. Furthermore, studies described that for septal APs, posteroseptal APs have a greater VA time with LBBB, anteroseptal APs with RBBB and no significant change in VA time with midseptal APs. By demonstrating both RBBB and LBBB aberrancy in this patient, this case uniquely validates the concept that the VA time with LBBB aberrancy is greater with posteroseptal APs.