Construction of the lumenless lead
The currently available 3830 pacing lead and the investigational Medtronic Next Generation Defibrillation Lead have a unique design. By eliminating the central lumen, which contributes about 40% of the diameter of a standard 7 French pacemaker lead, the 3830 lead is only 4.1 French diameter[10]. Traditional coaxial leads employ a coiled inner conductor with a central lumen, allowing for the insertion of shapeable stylets to facilitate steering and placement. This inner coiled conductor and lumen has two adverse effects: first it requires space necessitating a larger lead diameter and second the central lumen creates susceptibility to kinking with flexion when under tight bending conditions. This kinking can lead to a point of repetitive localized stress causing metal fatigue, potentially resulting in conductor fracture. The two lumenless leads described contain a flexible, high tensile strength cable as the inner conductor which is intended to avoid this issue by reducing stress in high bending conditions. One difference with lumenless leads is the method of extraction when needed. During extraction, locking stylets are typically placed into the inner lumen of coaxial leads that expand to grip the inner coil surface to allow for traction on a high tensile strength structure. This is not possible with lumenless leads. Rather, the central cable may be used itself for traction. This cable does not stretch during traction compared to a coiled conductor and allows for traction directly to the lead tip appropriate for small diameter lead use conditions. In addition, since the lead helix is not retractable, it is designed to straighten with about 2 Kg of force reducing the potential of myocardial avulsion[11].