A cardiac pacemaker or other implantable electrostimulation device has one or more durable fine wire leads to the heart or other electrostimulation site. The lead is formed of a core of silica or glass fiber or similar material, with a protective coating preferably including a metal buffer for conduction. The lead can be unipolar or bipolar (or even with three or more conductors), of small diameter and preferably with an anchoring configuration at the distal end of the lead. The anchor feature can take any of several nonlinear forms such that once implanted in a constrained configuration, the anchor can be released to the expanded, nonlinear configuration. The electrostimulation leads of the invention are extremely durable, can be bent through small radii and can exhibit long life without fatigue failure.
