Provocative Cases -> Teaching Case Reports D-PO01 - Featured Poster Session (ID 11) Poster

D-PO01-091 - Antidromic And Orthodromic Tachycardia Via Nodofascicular Accessory Pathway Connecting Av Node To Left Septal Fascicle (ID 84)


Background: Ortho and antidromic tachycardia (ORT, ART) via nodofascicular pathway (NFP) to right bundle branch (RBB) has been described.
Objective: We describe a NFP to left septal fascicle (LSF).
Results: 69 yo M prior radiofrequency ablation (RFA) for posterior fascicle (PF) VT and AT from coronary sinus os, with recurrent verapamil sensitive T, cycle length (TCL) 350 ms, incomplete right bundle branch block (iRBBB) morphology, left superior axis. Sinus QRS (Fig) had small r/s V1, prominent R V2, normal PR and QRS axis, HV 42 ms. Clinical T induced with atrial burst pacing and S1S2; VA dissociation, HV 14 ms, retrograde His activation. Right ventricle septum (VS) entrainment (E) near distal His (Fig) produced concealed fusion (CF), orthodromic (retro) capture of His, stim-QRS 326 ms suggesting selective capture of NFP. Post-pacing interval (PPI)-TCL = 12 ms. E at adjacent left VS showed same with stim-QRS 270 ms. Proximal LBB potential here preceded QRS by 24 ms. Pressure induced RBBB without change in TCL. RFA mid PF terminated T. 2nd T occurred spontaneously; CL 350ms, HV 52 ms, antegrade His activation, VA dissociation. QRS right axis, rS V1-3. RBBB did not alter TCL, LBBB increased TCL and VH interval. RVS E showed CF, orthodromic His capture and PPI-TCL = 12 ms. E of a fascicular potential at inferior LV posterior process (Fig) showed same. 5W RFA terminated ORT, titrated to 25W. No further T could be induced.
Conclusion: Sinus QRS prior to RFA was mildly preexcited based on V2 R that normalized after. CF from RVS/LVS, as well as same TCL with retro- and antegrade His activation confirms ART and ORT via NFP. This case demonstrates that NFP can obliquely cross septum from AVN to LSF.