Effect of lead body and helix design variables on implantation success, insertion depth, and muscle torque in the left bundle branch area: Insights from an ex vivo porcine model

BACKGROUND: Lumenless and stylet-driven leads used for left bundle branch area pacing differ in design and have a significant implantation learning curve. Although previous studies examined longer helices for deep-septal pacing, the influence of other design variables remains unclear. OBJECTIVE: This study aimed to evaluate how helix design and axial force affect interventricular septum insertion efficacy. METHODS: Rigid leads were developed using helical coils with variable outer diameter, number of turns, and pitch. Porcine septa (n = 16) were clamped perpendicularly for insertion using an optimized rotation-response system. Leads were tested under low (30g) and high (60g) axial force conditions to represent lumenless and stylet-driven leads, respectively, and a fixed number of rotations were delivered at a constant rate. Each helix design (n = 8) was tested 3× per axial force at 3 septal sites. Insertion depth, muscle torque, and visual feedback were recorded. Insertion was successful if the depth exceeded coil length without surface entanglement. Effects of design factors were compared. RESULTS: At 30g, more helix turns significantly improved insertion success (P = .04), whereas fewer turns frequently produced entangled failure (P = .04) marked by high torque variability (P < .001). Smaller-pitch helices trended toward higher torque and success, whereas a larger pitch achieved greater depth (P = .05). Larger outer diameters also trended toward higher torque and improved success at 30g. At 60g, the influence of helix design variable diminished and consistently yielded higher values than at 30g. CONCLUSION: An optimized lead rotation-to-translation system elucidates how helix geometry and axial force interact during septal insertion. These interactions are explainable using an intuitive mechanical framework, which helps optimize lead design.