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].