Figure 2.

Pacemaker leads and their inner conductor design. Pacemaker leads conductors are typically of a coaxial or coradial designs, surrounded by insulations layers (A,B). Coaxial design conductors have an inner conductor that extends down the length of the lead to the tip with another outer coil conductor that also runs down the lead to the ring electrode, the anode. Coradial conductors are composed of a single coil conductor which extends down the length of the lead and consists of two parallel, alternating conductor strands, one of which connects to the cathode and the other to the anode. Each conductor strand is individually coated with an inner insulation layer, which serves to insulate each strand from the other, despite being intertwined. The single two-component coil is surrounded by another outer insulation layer. A magnified scheme of the inner and outer insulation layers of a typical coaxial lead are shown (B). The conductors themselves are usually made of silver core alloy wires, consisting of a central core of relatively soft, low-resistance silver surrounded by a thick strong high-resistance MP-35N outer shell in the drawn filled tube design (C), or by few strands of high-resistance MP-35N shells in the drawn brazed strand design (D).