A cardiac pacemaker, other CRT device or neurostimulator has one or more
fine wire leads. Formed of a glass, silica, sapphire or crystalline
quartz fiber with a metal buffer cladding, a unipolar lead can have an
outer diameter as small as about 300 microns or even smaller. The
buffered fibers are extremely durable, can be bent through small radii
and will not fatigue even from millions of iterations of flexing. Bipolar
leads can include several conductors side by side within a glass/silica
fiber, or can be concentric metal coatings in a structure including
several fiber layers. An outer protective sheath of a flexible polymer
material can be included.