PO-05-138 A NEW CRITERION FOR LEFT BUNDLE BRANCH BLOCK (LBBB)—INSIGHTS FROM LEFT SEPTAL RECORDINGS

Abstract

Standard definitions for LBBB were based on early animal experiments or on mathematical modeling of action potentials, and they may incorrectly classify patients. Our aim was to utilize intracardiac analysis of human LBBB to establish a new criterion for surface LBBB, and then to validate these criteria in an independent data set. Multielectrode recordings of left ventricular (LV) septal activation were obtained in 75 patients who met standard ACC/AHA/HRS criteria for LBBB based on their surface ECGs and divided into two groups: those in which complete conduction block (CCB) was present (48 patients) and those where intact Purkinje activation (IPA) was noted (27 patients). The ECGs of these patients were then analyzed to identify criteria most predictive of CCB versus IPA. Next, this criterion was validated using a set of 46 patients who developed new LBBB (mechanistically due to proximal CCB) after undergoing transcatheter aortic valve replacement (TAVR) implant at our institution. Any patient who met standard LBBB criteria prior to a clear new LBBB at implant was considered to have proven IVCD prior to implant. Intracardiac analysis identified that presence of late notching in the septal and lateral leads was the most predictive feature of CCB. Based on ROC curves for the time from QRS onset to the latest notch in each of these leads, we found that lead I had the best performance, with an area under the ROC curve of 0.77 and an optimal criterion of time-to-notch of greater than 75 ms (see FIGURE). When added to conventional criteria, the novel criterion demonstrated a sensitivity of 71% and a specificity of 74% in this population. In our independent validation population, our criterion was found to have a sensitivity of 87%. In the patients with IVCD pre-implant, our criterion had a specificity of 100%, albeit with a small sample size. Time-to-notch in Lead I occurring more than 75 ms after QRS onset is a simple ECG criterion for LBBB which can be used to improve specificity to identify patients with CCB. Correct classification of patients may better identify candidates for cardiac resynchronization therapy (CRT) and conduction system pacing (CSP).