Effect of Lead Body and Helix Design Variables on Implantation Success, Insertion Depth, and Muscle Torque in Left...

Lumenless and stylet-driven leads used for left bundle branch area pacing differ in design and have a significant implantation learning curve. While prior studies examined longer helices for deep septal pacing, the influence of other design variables remains unclear.

To evaluate how helix design and axial force affect interventricular septum insertion efficacy.

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. Axial force simulating lumenless (30g) or stylet-driven (60g) leads was applied, and a fixed number of rotations were delivered at a constant rate. Each helix design (n=8) was tested 3x per axial force at three septal sites. Insertion depth, muscle-torque and visual feedback were recorded. Insertion was successful if depth exceeded coil length without surface entanglement. Effects of design factors were compared.

At 30g, more helix turns significantly improved insertion success (P=0.04), while fewer turns frequently produced entangled failure (P=0.04) marked by high torque variability (P<0.001). Smaller-pitch helices trended toward higher torque and success, whereas larger pitch achieved greater depth (P=0.05). 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 than at 30g.

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 is helpful for optimizing lead design.