New strict left bundle branch block criteria reflect left ventricular activation differences

•Interventricular electrical delay predicts cardiac remodeling after CRT•New, strict ECG criteria for LBBB are better at predicting response to CRT•Patients with IHD have more heterogeneous interventricular electrical delays•Patients with IHD have lower response-rates to CRT than patients with DCM

AimsPacing lead electrical delays and strict left bundle branch block (LBBB) criteria were assessed against cardiac resynchronization therapy (CRT) outcome.MethodsForty-nine patients with LBBB and QRS duration > 130 milliseconds underwent CRT-implantation. Sensed right ventricular to left ventricular electrical delay (RV-LV-IED) was measured. Response to CRT was defined as ≥ 15% decrease in left ventricular end-systolic volume.ResultsEighteen of 20 (90%) patients with non-ischemic dilated cardiomyopathy (DCM) and 18 of 29 (62%) with ischemic heart disease (IHD) responded to CRT, p < 0.01. When applying new strict ECG criteria subsequent rates of response in DCM were 18/19 (95%) and in IHD of 18/23 (78%) respectively, p < 0.05 between IHD groups. Correspondingly, RV-LV-IED was longer in DCM compared to IHD patients and in responders compared to non-responders, p = 0.017 and p < 0.001, respectively.ConclusionInterventricular electrical delay predicts left ventricular remodeling after CRT and new, strict ECG criteria of LBBB are superior in predicting remodeling.