Contractile Asymmetry and Survival in Patients with Left Bundle Branch Block Treated with Cardiac Resynchronization Therapy

Abstract

Currently, electrical rather than mechanical parameters of delayed left ventricular (LV) activation are used for patient selection for cardiac resynchronization therapy (CRT). However, despite adhering to current guideline-based criteria, about one-third of heart failure (HF) patients fail to derive benefit from CRT. This study sought to investigate the prognostic survival significance of a recently introduced index of contractile asymmetry (ICA) based on deformation of entire opposing LV walls in the context of selecting patients with HF and left bundle branch block (LBBB) for CRT. We analyzed 367 patients with HF and LBBB undergoing CRT (31.6% females, 69±9 years, ischemic etiology in 50.7%, LV ejection fraction 27±6%). ICA was calculated using LV strain rate values from curved anatomical M-mode plots of apical 2D-echocardiography images. The predictive value of ICA was assessed using Kaplan-Meier analysis and Cox proportional hazards models. During a median follow-up time of 5.54 years, death or cardiac transplantation occurred in 105 (28.6%) cases. Higher baseline ICA values in all apical views, particularly in the 2-chamber view (ICA-2ch), were associated with increased event-free survival, unadjusted hazard ratio was 0.28 (95% confidence interval 0.18-0.46). Higher ICA-2ch (>0.319 s-1) consistently predicted survival across clinical subgroups and remained significant after covariate adjustment, while the event rate sharply increased in low ICA-2ch cases. Additionally, including ICA-2ch improved the predictive value of the multivariate risk model containing the typical LBBB pattern. Pre-implant ICA suggests a quantitative prognostic threshold for both long-term survival and adverse outcomes following CRT implantation.