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

Objective: Pacing lead electrical delays and strict left bundle branch block (LBBB) criteria were assessed against cardiac resynchronization therapy (CRT) outcome.

Methods: Forty-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.

Results: Eighteen 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.

Conclusions: Interventricular electrical delay predicts left ventricular remodeling after CRT and new, strict ECG criteria of LBBB are superior in predicting remodeling.