A Strain-Based Staging Classification of Left Bundle Branch Block-Induced Cardiac Remodeling

Abstract

Objectives: This study speculated that longitudinal strain curves in left bundle branch block (LBBB) could be shaped by the degree of LBBB-induced cardiac remodeling.

Background: LBBB independently affects left ventricular (LV) structure and function, but large individual variability may exist in LBBB-induced adverse remodeling.

Methods: Consecutive patients with LBBB with septal flash (LBBB-SF) underwent thorough echocardiographic assessment, including speckle tracking-based strain analysis. Four major septal longitudinal strain patterns (LBBB-1 through LBBB-4) were discerned and staged on the basis of: 1) correlation analysis with echocardiographic indexes of cardiac remodeling, including the extent of SF; 2) strain pattern analysis in cardiac resynchronization therapy (CRT) super-responders; and 3) strain pattern analysis in patients with acute procedural-induced LBBB.

Results: The study enrolled 237 patients with LBBB-SF (mean age: 67 ± 13 years; 57% men). LBBB-1 was observed in 60 (26%), LBBB-2 in 118 (50%), LBBB-3 in 29 (12%), and LBBB-4 in 26 (11%) patients. Patients at higher LBBB stages had larger end-diastolic volumes, lower LV ejection fractions, longer QRS duration, increased mechanical dyssynchrony, and more prominent SF compared with less advanced stages (p < 0.001 for all). Among CRT super-responders (n = 30; mean age: 63 ± 10 years), an inverse transition from stages LBBB-3 and -4 (pre-implant) to stages LBBB-1 and -2 (pace-off, median follow-up of 66 months [interquartile range: 32 to 78 months]) was observed (p < 0.001). Patients with acute LBBB (n = 27; mean age: 83 ± 5.1 years) only presented with a stage LBBB-1 (72%) or -2 pattern (24%).

Conclusions: The proposed classification suggests a pathophysiological continuum of LBBB-induced LV remodeling and may be valuable to assess the attribution of LBBB to the extent of LV remodeling and dysfunction.

Keywords: cardiac remodeling; cardiac resynchronization therapy; left bundle branch block; septal flash; speckle-tracking strain.