Limitations
It should be noted that our findings, based on a subanalysis of the MADIT-CRT trial, should be considered as hypothesis generating since other unmeasured variables in the MADIT CRT data set may have further contributed to the observed outcomes. Accordingly, the present findings need to be further validated in prospective studies that will be appropriately design to identify LBBB patients who may derive benefit vs. harm from CRT implantation. At present, we believe that our data can be used to enhance decision support in this high-risk and understudied population. Furthermore, the current analysis utilizes patient data from MADIT-CRT cohort, with specific enrollment selection criteria. Thus, the findings of the present study are applicable only to patients with mild heart failure symptoms enrolled in the trial.