A time to notch in lead I longer than 75 milliseconds has been proposed as a new ECG criterion for left bundle branch block (LBBB). The derivation cohort was from a prospective study of patients undergoing electrophysiological study from March 2016 through November 2019 and a validation cohort was assembled retrospectively for patients from the same center from October 2015 through May 2022. A total of 75 patients (median age 63 years; 21 female) with baseline LBBB on 12-lead ECG underwent intracardiac recording of the left ventricular septum with 48 complete conduction block (CCB) and 27 intact Purkinje activation (IPA). Analysis of surface ECGs revealed that late notches in the QRS complexes of lateral leads were associated with CCB (83.3% with CCB vs 48.1% with IPA had a notch or slur in lead I; P = .003). Receiver operating characteristic curves for all septal and lateral leads showed lead I as the best with a time to notch longer than 75 milliseconds. Used in conjunction with the criteria for LBBB, this criterion had a sensitivity of 71% and specificity of 74% in the derivation population, contrasting with a sensitivity of 96% and specificity of 33% for the Strauss criteria. In an independent validation cohort of 46 patients (median age 78.5 years, 21 female) undergoing transcatheter aortic valve replacement with interval development of new LBBB, the time-to-notch criterion demonstrated a sensitivity of 87%. In the subset of 10 patients with preprocedural intraventricular conduction delay (IVCD), the criterion correctly distinguished IVCD from LBBB in all cases. The Strauss criteria performed similarly in the validation cohort. The new simple ECG criterion may improve the specificity for LBBB criteria (such as QRS duration ≥ 120ms, dominant S wave in V1, and broad monophasic R wave in lateral leads, etc.) to identify patients with conduction block and aid in clinical decision-making. Source: https://jamanetwork.com/
