Understanding LOT-CRT: Current Insights, Limitations, and Our Center's Experience

Abstract

Cardiac resynchronization therapy (CRT) using biventricular (BiV) pacing is the standard treatment for heart failure (HF) patients with reduced left ventricular ejection fraction (LVEF) and electrical dyssynchrony. However, one in three patients remains a non-responder. Left bundle branch area pacing (LBBAP) could represent a more physiological alternative, but its effectiveness is limited in cases of atypical left bundle branch block (LBBB) or intraventricular conduction delay (IVCD). Left Bundle Branch Pacing Optimized cardiac resynchronization therapy (LOT-CRT) integrates LBBAP with coronary sinus (CS) lead pacing to improve electrical synchrony and clinical outcomes. This review evaluates the feasibility, advantages, disadvantages, and clinical outcomes of LOT-CRT. Additionally, we describe our center's experience and propose an evidence-based implantation algorithm. A review of published studies investigating LOT-CRT was conducted, comparing its effectiveness with BiV-CRT and LBBAP alone using QRS narrowing, LVEF improvement, left ventricular remodeling, New York Heart Association (NYHA) class changes and NT-proBNP levels. It was found that LOT-CRT outperforms BiV-CRT or LBBAP alone in selected populations, at the cost of higher clinical skills, longer procedural times, and specific device setups. Randomized trials are underway to further define its role in clinical practice.

Keywords: LOT-CRT; QRS narrowing; cardiac resynchronization therapy; electrophysiology; heart failure; intraventricular conduction delay; left bundle branch pacing.

Figure 1

Devices’ configurations and interventricular conduction pathways for LBBAP-CRT (P/D) and LOT-CRT(P/D). (a) LBBAP-CRT-P, (b) LOT-CRT-P, (c) LBBAP-CRT-D, (d) LOT-CRT-D. This schematic illustration depicts the conduction pathways involved in LBBAP- CRT and LOT-CRT. The green gradient line represents the electrical impulse generated by the LBBAP lead. LV depolarization originates solely from the LBBAP lead. In contrast, in LOT-CRT, the blue line illustrates the electrical impulse originating from the LV epicardial lead. In a LOT-CRT device, the LV is depolarized in a fusion mode, by an impulse propagating from the LBBAP lead (green gradient line) and the LV epicardial lead (blue gradient line). Figure created in BioRender. Bozika, M. (2025) https://BioRender.com/25t1kd2 (accessed on 12 April 2025).

Figure 2

A paradigm of the physiological criteria in a patient with intrinsic QRS 148 ms with LBBB morphology. The intrinsicoid deflection was recorded at 121 ms, corresponding to the left ventricular activation time. Upon advancing the LBBAP lead into the interventricular septum, the transsptal conduction time (TCT) was determined by measuring the interval from QRS onset to the maximum peak deflection recorded by the LBBAP lead (54 msec). Ideally, the paced SLVAT (left ventricular activation time during pacing) should equal the intrinsic activation time minus the TCT, as demonstrated in this case. This finding suggests the elimination of the abnormal right-to-left septal activation delay, supporting successful LBB capture. These observations are consistent with the physiological criteria for LBB capture in LBBB patients, as described by Jastrzębski et al. [25].

Figure 3

Visual representation of conduction block sites. In case of left Infrahisian block or LBBB, which are present in 46% and 18%, respectively, there is a high likelihood of LBBB correction. On the other hand, in 36% of cases with LBBB, Purkinje activation appears intact but slow. On this occasion, LBBB correction is not possible. Figure created in BioRender. Bozika, M. (2025) https://BioRender.com/kloieup (accessed on 12 April 2025).

Figure 4

This figure presents serial QRS narrowing, on our center, through different pacing modalities in a patient with a baseline QRS of 231 ms. (a) Baseline QRS of 231 ms (native conduction), (b) LBBAP only. QRS of 204 ms, (c) CRT LV-RV = 0 ms. QRS of 172 ms, (d) LOT-CRT. QRS of 143 ms.

Figure 5

Suggested implantation algorithm for LBBAP-CRT-D and LOT-CRT-D. This stepwise depiction aids clinical decision-making depending on the resynchronization or defibrillation requirements. Lead placement is illustrated in each modality. Subfigures (a–d) depict the final lead configurations for each approach: (a). LBBAP-CRT-P: Left bundle branch pacing with a pacemaker device, involving a single lead positioned for conduction system pacing. (b). LOT-CRT-P: Left bundle branch optimized CRT approach combining LBBAP with an additional pacing lead placed in the coronary sinus to enhance ventricular synchrony. (c). LBBAP-CRT-D: LBBAP in conjunction with a defibrillating lead positioned in the right ventricle, used in a CRT-D system. (d). LOT-CRT-D: Combination of LBBAP, coronary sinus pacing, and a right ventricular defibrillating lead, forming a comprehensive CRT-D approach. Figure created in BioRender. Bozika, M. (2025) https://BioRender.com/yu83hr4 (accessed on 12 April 2025). https://app.biorender.com/.