Cardiac resynchroniation therapy for non-LBBB and mid-range QRS: clinical value or questionable benefit?

Abstract Introduction The clinical benefit of cardiac resynchronization therapy (CRT) in patients with non-left bundle branch block (non-LBBB) morphology and QRS mid-range remains uncertain and controversial. Aim To assess the impact of QRS morphology and duration in echocardiographic response to CRT and clinical outcomes in our population. Methods Single center retrospective analysis of pts admitted to CRT implantation between 2017-2024. Inclusion criteria: QRS duration ≥130 ms, left ventricular ejection fraction (LVEF) ≤35% and echocardiogram performed 6-12months post-implantation. Patients were classified into LBBB and non-LBBB groups and further stratified by QRS duration (130-149 ms and ≥150 ms). Echocardiographic response was defined as an improvement in LVEF≥10%/reduction in left ventricular end systolic volume ≥ 15% at 6-12 months post-implantation. The primary endpoint was a composite of all-cause death and heart failure hospitalizations (HFH). Results We included 128 pts (70±10 years, 66% males, LVEF 28±6%, 34% ischemic cardiomyopathy), 77% in the LBBB group. The non-LBBB group had a higher proportion of males (97% vs. 56%, p0.005), atrial fibrillation (50% vs 30%, p=0,039) and less use of beta-blocker (87% vs 67%, p=0,012). Non-LBBB patients had a shorter baseline QRS duration (158±20 ms vs. 165±17 ms, p=0,04) and larger left atrial volumes (51 mL IQR 42–64 vs. 41 mL IQR 36–49, p=0,002). No differences in the rate of ICD implantations between groups (73% vs 64%, p=0,36). During the first year, there was a trend to higher echocardiographic response in the LBBB group (83% vs 65%, p=0,057) (Fig.1) with comparable rates of NYHA improvement (63% vs 58%, p=0,62). During a median follow-up of 34 IQR 16–53 months, there were no statistically significant differences in the primary endpoint between groups (40% vs 27%, p=0,18), with similar rates of HFH (p=0,34) and all-cause death (p=0,13). However, the non-LBBB group experienced more ventricular arrhythmias (23,3% vs 8,2%, p=0,014). When we stratified the groups according to the QRS duration (LBBB+QRS≥150 ms, LBBB+QRS 130-149ms, Non-LBBB≥150 ms, Non-LBBB+QRS 130-149ms), it was noticeable that, despite the absence of significant differences in the rates of echocardiographic response (p=0,20), there was a clear significant difference in the rates of the primary endpoint, with worse outcomes in the non-LBBB+ QRS 130-149 ms group (p0,005) (Fig.3), mainly driven by all-cause death (Fig.2). Conclusion In our cohort, pts with non-LBBB benefit for CRT, with notable echocardiographic and clinical improvements. Those with QRS≥150 ms have clinical outcomes comparable to LBBB group, with worse prognosis of the ones with mid-range QRS. This underscores the importance of careful patient selection, particularly within the non-LBBB subgroup.