Which CRT candidates may benefit from index-procedure LV lead availability during attempted LBBAP? Insights from an attempted LOT-CRT cohort

Background Conventional BiV-CRT achieves responder rates of approximately 60–70%; however, the response characteristics and optimal implementation strategy of left bundle branch area pacing–based CRT, including LOT-CRT, remain incompletely defined. In particular, it is unclear whether LV lead availability at the index procedure provides incremental benefit beyond LBBAP alone and whether certain phenotypes are predisposed to LBBAP failure. Methods We retrospectively screened 54 consecutive CRT-indicated patients. Eleven patients in whom an attempted LOT-CRT strategy was not selected upfront due to patient preference were excluded. The remaining 43 patients underwent attempted LOT-CRT and were categorized by procedural success into true LOT-CRT (n=34) and DSP-CRT (n=9). QRS duration was assessed at baseline, during LBBAP-only pacing, and after final CRT configuration. Six-month echocardiographic response was defined by LV end-systolic volume (LVESV) reduction (responder ≥15%, super-responder ≥30%). Results LBBAP was successful in 79.1% (34/43). QRS duration shortened stepwise from baseline to LBBAP-only and further after final CRT configuration (all p<0.001), demonstrating progressive electrical resynchronization. Even in successful LBBAP, LV lead addition resulted in additional QRS narrowing (median 7 ms, p<0.001), whereas in DSP-CRT the incremental reduction was larger (16 ms, p=0.039). Greater ΔQRS was significantly correlated with greater LV reverse remodeling at 6 months (Spearman ρ=0.44, p=0.003). The overall responder and super-responder rates were 81% (35/43) and 58% (25/43), respectively. Responder rates were 88% in true LOT-CRT versus 56% in DSP-CRT (p=0.046), and super-responder rates were 68% versus 22%, respectively (p=0.023). LBBAP failure clustered in a substrate- and severity-enriched phenotype characterized by universal LV scar, more frequent IVCD and diabetes, lower baseline LVEF, larger left ventricular end-diastolic dimension (LVDd) and end-diastolic volume (LVEDV), and higher BNP. Conclusions During attempted LBBAP in CRT candidates, LV pacing provides complementary electrical resynchronization irrespective of procedural success, with greater incremental benefit in substrate-complex patients prone to LBBAP failure and attenuated remodeling. These findings suggest that leaving CRT-indicated patients with failed LBBAP and incomplete resynchronization may be suboptimal. In an era where conventional BiV-CRT remains the established standard and CSP is an evolving alternative, maintaining index-procedure LV lead availability and promptly implementing LV pacing when effective LBBAP cannot be achieved should be considered as a pragmatic fail-safe strategy.