R-R' interval in the left bundle branch block predicts long-term outcomes after cardiac resynchronization therapy by estimating greater mechanical dyssynchrony and viable myocardium.

Background: Typical left bundle branch block (LBBB) shows 2 peaks of the R wave, which reflect activation reaching the interventricular septum (R) and posterolateral wall (R') sequentially.

Objective: The purpose of this study was to investigate the relationship among R-R' interval (RR'), mechanical dyssynchrony, extent of viable myocardium, and long-term outcomes in cardiac resynchronization therapy (CRT) candidates.

Methods: The study enrolled 49 patients (34 men; mean age: 69 ± 11 years) with LBBB who received CRT.