Multimodal fatigue risk analysis of a stylet-driven lead design for left bundle branch area pacing

Left bundle branch area pacing (LBBAP) is an emerging approach in physiologic pacing. However, fatigue risk analysis of stylet driven leads (SDLs) at LBBAP locations has yet to be fully investigated.

This study evaluates the fatigue risk of an SDL when used for LBBAP and assesses the latest clinical performance based on product performance data.

Fatigue risk analysis of the SDL was conducted by calculating the safety factor (SF) of the commercially available lead when implanted in the deep septum for LBBAP, utilizing the workflow shown in Figure 1. Lower SF values indicate the stress on the lead is approaching fatigue limits, with risk of fracture increasing as the value approaches 1.0. Scenarios of lead curvatures were generated using in-silico simulations of leads implanted into a four-chamber beating heart model. The scenarios and implant variables (lead slack, tip angle, tip location, and depth into the septum) were informed by LBBAP publications. Additional modeling at non-LBBAP positions was performed for comparison. Expected stress on the lead was calculated using simulated curvatures, and the fatigue limit was established using both in-vitro bench tests and published data. Stress calculations were compared to the fatigue limit to calculate the SF for each implant scenario. Modeled lead curvatures were compared to fluoroscopic scans of in-vivo implants to verify representativeness, using the workflow shown in Figure 2. Lead fatigue testing was performed to verify durability expectations. Product performance data was analyzed from known LBBAP implants to assess in-vivo clinical performance relative to fatigue.

Safety factor (SF) values were calculated for a total of 8 LBBAP (SF=5.6 (4.6-8.1)), 5 right ventricular (apical, septal and right ventricular outflow tract, SF=5.1 (2.6-6.0)), 1 His bundle pacing (SF=3.7) and 1 right atrial (SF=4.9) in-silico implants. Curvatures of the LBBAP in-silico simulations in three views during the end systolic phase were found to have comparable curvatures (right anterior oblique, p=0.414; anteroposterior, p=0.897; left anterior oblique, p=0.777), vs. in-vivo LBBAP cases. Lead fatigue testing to 400 million cycles was successfully completed without failure, verifying durability by using a reduced SF (2.2±0.2) compared to all in-silico implant scenarios. A review of product performance data showed no known lead fracture events when used in LBBAP.

Safety factors of LBBAP implants were comparable to the other implant locations without introducing additional fatigue risk. Modeled scenarios were shown to be representative of in-vivo clinical cases. Successful bench testing at conditions beyond expected in-vivo conditions, along with product performance analysis, demonstrated long-term durability of the SDL lead when implanted for LBBAP.