Biomedical Engineering Reference
In-Depth Information
creep, and good electrical insulation performance are required for this component
of the leads.
Conducting wires
Lead wires do not directly contact tissue, but they do perform the most important
function: they carry the electric signals. The two major types of conductor
designs in pacing leads are coils and cables (Fig. 4.5).
The coil, first suggested by Chardack, has been greatly attributed to reducing
incidents of conductor fracture. Initially, wire used in coils was stainless steel,
which occasionally corroded. Platinum and platinum alloys were used to reduce
corrosion, but they were very expensive and wire fracture remained an issue.
These materials were eventually replaced by the super-alloy MP35N, which has
excellent corrosion properties and mechanical properties, making it ideal for use
in coils. MP35N coils were improved upon by using multiple smaller diameter
wires. Multiple smaller diameter wires allowed the electrical resistance to drop
and extended the life of the coil. To further reduce the electrical resistance, a
4.5 Cross-section of a defibrillator lead body showing the small cable
conductors and one larger coil conductor. Outside tubing insulates the
conductors. The conductors themselves are mounted in a multilumen tubing
that separates and further insulates the individual conductors (courtesy of
Medtronic, Inc.).
