an implantable cardioversion or defibrillation lead provided with a large surface , carbon fiber electrode . the lead takes the form of an elongated tubular braid of carbon fiber , provided with a central core of insulating plastic . over the majority of the braid &# 39 ; s length , it is covered by an outer sheath of insulating plastic as well , serving as a lead conductor . at its distal end , the braid is not covered , and the exposed portion of the braid serves as the electrode .