Strain-based staging classification of left bundle branch block-induced cardiac remodeling predicts reverse remodeling after cardiac resynchronization therapy

Abstract

Abstract Background Left bundle branch block (LBBB)-induced adverse remodeling is a gradual but largely unknown process, causing a variable degree of left ventricular (LV) dysfunction and response to cardiac resynchronization therapy (CRT). In LBBB patients with septal flash (SF), an electro-mechanical continuum of different speckle-tracking strain patterns was observed, with each pattern tightly correlating with the degree of LV remodeling and dysfunction (1) (Figure 1). Purpose In this study, we investigated the relationship between the staged LBBB strain patterns in CRT-eligible patients and their prediction with respect to reverse remodeling and clinical outcome. Methods This study enrolled CRT patients from the PREDICT-CRT study population (2). Inclusion criteria were LV ejection fraction (LVEF) ≤35%, QRS duration ≥120 ms, NYHA class II–IV, absence of right ventricular pacing and availability of speckle tracking strain imaging. All patients underwent an echocardiographic examination before and 12 months after CRT implant. LV volumes, strain and dyssynchrony were assessed. Mid-septal longitudinal strain curves were classified into 5 patterns (LBBB-0 through LBBB-4; Figure 1). Primary endpoint was all-cause mortality. Results The study involved 250 patients (mean age 64±10 years; 79% men) with a mean LVEF of 26±7%. LBBB was present in 220 (89%) patients and 206 (82%) patients had SF. Prior to CRT implant, a LBBB-0 pattern was observed in 33 (13%), LBBB-1 in 33 (13%), LBBB-2 in 39 (16%), LBBB-3 in 44 (18%) and LBBB-4 in 101 (40%) patients. Patients with LBBB-3 and -4 patterns more frequently had LBBB, lower LVEF, increased mechanical dyssynchrony and more prominent SF (p<0.001 for all) compared with patients with LBBB-0, -1 and -2 patterns. Across the stages, CRT resulted in a gradual volumetric response, ranging from no response in stage LBBB-0 patients (ΔLV end-systolic volume +7±33%; ΔLVEF −2±9%) to super-response in stage LBBB-4 patients (ΔLV end-systolic volume −40±29%; ΔLVEF +15±13%) (p<0.001 for all). Interestingly, following reverse remodeling, the LV function of stage LBBB-2, -3 and -4 patients improved to a similar LVEF of 38% (p=1.000) in this cohort. Patients in stage LBBB-0 had a significantly less favorable five-year outcome compared to those in stage LBBB≥1 (log-rank p=0.003). There was no difference in long-term outcome between stage LBBB-1 to −4 patients (log-rank p=0.510). Conclusion Strain-based LBBB staging predicts the extent of LV reverse remodeling in CRT patients. CRT did not translate into improved absolute survival in the more advanced stages, but the observed gradual volumetric response suggests that CRT corrects the LBBB-induced mortality. Funding Acknowledgement Type of funding sources: None. Figure 1