Perspective:

Patients in the present study had higher rates of LVAD implantation, cardiac transplantation, and all-cause mortality (32%) than in previous randomized clinical trials. The clinical endpoint did not include heart failure hospitalizations or other heart failure events, which are usually included in cardiac resynchronization studies. Instead, the authors focused on the most adverse events, seeking to find the most discriminating LBBB morphology for the survival analysis. The main difference among the four LBBB definitions is the presence of notching or slurring of the QRS complex, which are required in the AHA and Strauss et al. definitions. All but the Strauss et al. LBBB definition dictate that the initial Q wave in the lateral leads should be absent. It is striking that only 14% of patients had LBBB pattern according to all four LBBB definitions. The AHA and Strauss et al. definitions classified the lowest proportion of patients as LBBB. Regardless of the definition used, the risk reduction in adverse events was similar. Despite much having been published in the literature on this topic of patient selection for CRT, time and time again the most powerful discriminating criterion is LBBB, and the present study shows that is true regardless of how LBBB is defined.