an implantable defibrillator lead comprises a flexible core onto which is wound helically wound coils to form an electrode . these electrode coils are partially encapsulated by a flexible matrix which holds them in their wrapped position around the core . due to its coiled coil structure , this electrode provides improved flexibility , and can be used endocardially , intravascularly , epicardially , or subcutaneously . the electrode may function alternately as a defibrillation electrode and as a sensing electrode in a lead with a separate pacing electrode .