Longer right to left ventricular activation delay at cardiac resynchronization therapy implantation is associated with improved clinical outcome in left bundle branch block patients.

AIMS Data on longer right to left ventricular activation delay (RV-LV AD) predicting clinical outcome after cardiac resynchronization therapy (CRT) by left bundle branch block (LBBB) are limited. We aimed to evaluate the impact of RV-LV AD on N-terminal pro-B-type natriuretic peptide (NT-proBNP), ejection fraction (EF), and clinical outcome in patients implanted with CRT, stratified by LBBB at baseline. METHODS AND RESULTS Heart failure (HF) patients undergoing CRT implantation with EF ≤ 35% and QRS ≥ 120 ms were evaluated based on their RV-LV AD at implantation. Baseline and 6-month clinical parameters, EF, and NT-proBNP values were assessed. The primary endpoint was HF or death, the secondary endpoint was all-cause mortality. A total of 125 patients with CRT were studied, 62% had LBBB. During the median follow-up of 2.2 years, 44 (35%) patients had HF/death, 36 (29%) patients died. Patients with RV-LV AD ≥ 86 ms (lower quartile) had significantly lower risk of HF/death [hazard ratio (HR): 0.44; 95% confidence interval (95% CI): 0.23-0.82; P = 0.001] and all-cause mortality (HR: 0.48; 95% CI: 0.23-1.00; P = 0.05), compared with those with RV-LV AD < 86 ms. Patients with RV-LV AD ≥ 86 ms and LBBB showed the greatest improvement in EF (28-36%; P<0.001), NT-proBNP (2771-1216 ng/mL; P < 0.001), and they had better HF-free survival (HR: 0.23, 95% CI: 0.11-0.49, P < 0.001) and overall survival (HR: 0.35, 95% CI: 0.16-0.75; P = 0.007). There was no difference in outcome by RV-LV AD in non-LBBB patients. CONCLUSION Left bundle branch block patients with longer RV-LV activation delay at CRT implantation had greater improvement in NT-proBNP, EF, and significantly better clinical outcome.