referring to fig5 a preferred form of the invention basically includes an implantable lead 10 having a body 12 around which is wrapped a wire 30 . an outer covering 90 is located around the body and wire . referring to fig1 - 3 , body 12 comprises a generally cylindrical core 14 defining an inner surface 16 that forms a lumen in the shape of a cylinder having a central axis 18 . alternatively , core 14 may be solid . core 14 also includes support members in the form of beads 21 - 24 that are aligned parallel to axis 18 and which form semicircles in cross - section . beads 21 - 24 are integrally formed with core 14 which is fabricated from a solvent , heat or adhesive compatible material , such as polyethylene , various fluorocarbons , such as teflon pfa ( perfluoroalkoxy ), urethanes , etc ., that are considered acceptable for long - term implantable use . drugs may be infused into a patient &# 39 ; s body through the lumen . a stylet may be inserted into the lumen to add stiffness useful during implantation . referring to fig4 core 14 and beads 21 - 24 form an uneven outer surface 26 on which a wire 30 is wound to form convolutions , such as 31 - 35 . referring to fig5 convolutions 31 - 35 each have portions , such as 41 - 44 , displaced from surface 26 . the convolutions make contact with beads 21 - 24 forming nodal intersection points 51 - 54 . wire 30 is preferably fabricated from multistrand wire cable coated with an insulation fabricated from a material compatible with bonding to core 14 . for example , both the core 14 and the coating of wire 30 could be fabricated from a fluorocarbon , such as teflon pfa . wire 30 is coiled around core 14 with insufficient tension to cause the wire material to exceed its yield point , yet is held in intimate contact with beads 21 - 24 of core 14 . this is an important feature which substantially adds to the flex fatigue life of the lead and also allows for high pitch coils to be fabricated . the embodiments shown in fig1 - 5 resist stretching in the direction of axis 18 . for some applications this is an important feature . as shown in fig5 body 12 and wire 30 are covered by a conventional jacket 90 fabricated from materials generally considered acceptable for long term implantable use , typically polyurethane or silicone rubber . the diameter of wire 30 is approximately in the range of 0 . 002 inch to 0 . 012 inch . the pitch angle 38 ( fig4 ) of the convolutions shown in fig4 is in the range of 10 degrees to approaching 90 degrees . at 10 degrees the helical coil approaches a straight or linear wire whereas when it approaches 90 degrees the helical coil would be considered tight or close wound . typically , wire 30 is connected to one electrode to provide electrical stimulation of tissue after the lead is implanted in the patient , but multiple wires could be utilized to connect to multiple electrodes forming independent circuits , i . e ., multiconductor leads . in order to fabricate the emodiments shown in fig1 - 5 , the wire is bonded to beads 21 - 24 at each intersection of the wire insulation and beads forming nodal connections . the point of attachment holds wire 30 in the desired shape and acts as a hinge to allow the wire to move when in tension , compression , or bending . this is an important feature which facilitates implantation of lead 10 in a patient . the bonding of the joints can be accomplished by methods compatible with the base materials used for the coating on wire 30 and the core 14 . one method would be heat bonding where the heat application zone may include the entire length of the body 12 or be in specific areas . the heat application may be by convection in an oven or by infrared heating . similar methodologies could be used for solvent or adhesive bonding of the joints . those skilled in the art can select the relationship between the number of beads and the pitch of wire 30 . generally , the greater the pitch of wire 30 , the fewer beads are required . very long pitches may require more beads to give sufficient attachment points to properly support wire 30 . after the insulation of wire 30 is successfully bonded to body 12 , jacket 90 is placed over coil 30 by conventional methods . referring to fig6 an alternative embodiment of the invention comprises body 12 in the form of convolutions 61 - 67 that are formed in a clockwise direction . convolutions 61 - 67 are shown mounted on a mandrel 70 that defines a cylinder having a central axis 72 . mandrel 70 is used to form convolutions 61 - 67 in a conventional manner . the mandrel is withdrawn after the fabrication process is complete , thereby forming a hollow lumen in body 12 . a stylet may be inserted in the lumen , and drugs may be infused through the lumen . alternatively , a thin walled tube could replace the forming mandrel allowing a closed conduit from proximal to distal ends of body 12 . the core convolutions would &# 34 ; float &# 34 ; on the inner conduit formed by the thin walled tube . drugs may be infused through the thin walled tube . convolutions 61 - 67 are shown with a triangular cross section . however , convolutions with a circular , rectangular or elliptical cross section also can be used . the pitch of convolutions 61 - 67 preferably is in the range described previously . convolutions 81 - 85 of wire 30 are wound around the outside of convolutions 61 - 67 in a counterclockwise direction opposite the clockwise direction of convolutions 61 - 67 . heat treating fuses the points of contact of convolutions 61 - 67 and 81 - 85 in the same manner described in connection with fig1 - 5 . convolutions 81 - 85 preferably have a pitch approximately equal to that of core 12 convolutions 61 - 67 . an outer covering can be placed over convolutions 61 - 67 and 81 - 85 in the same manner as covering 90 shown in fig5 . the embodiment shown in fig6 enables stretching in the direction of axis 72 . for some applications where lead elongation could be a factor , this embodiment provides the necessary lead compliance to eliminate failures due to tensile mode breaks and / or reduces the lead movement at the electrodes , eliminating the need to reposition the lead due to dislodgement . those skilled in the art will recognize that the preferred embodiments may be altered or amended without departing from the true spirit and scope of the invention , as defined in the accompanying claims .
an implantable lead having a body defining an uneven outer surface and a wire carried by the outer surface to form convolutions arranged so that portions of each convolution are displaced from the outer surface . the body may include a hollow core which carries beads so that stretching in the direction of a central axis is inhibited and drug infusion is facilitated . alternatively , the body may take the form of a helix so that stretching of the lead in the direction of the central axis is facilitated .