Body implantable lead with stiffening stylet

#This invention relates to a body implantable lead bearing an electrode for connecting a living body organ to an electrical device, and more particularly to the combination of such a lead with an improved stiffening stylet. Notwithstanding its various uses, this invention will be described as an endocardial pacing and sensing lead for connecting a pacemaker pulse generator to cardiac tissue.

#Endocardial pacing and sensing leads of the types shown in U.S. Pat. No. 3,128,418 for example, comprise one or more lengths of hollow, coiled wire conductor encased within a suitable insulating material, such as silicone rubber, that is substantially inert to body fluids and tissues, a hollow connector pin attached to the proximal end of each conductor, and an electrically conductive electrode at the distal end of the conductor adapted to be placed in contact with the endocardium of a patient. A lumen extends through each pin and the corresponding length of coiled wire conductor to the electrode at the distal end thereof and receives a stiffening stylet of cylindrical stainless steel wire for imparting stiffness to the lead to facilitate its advancement through the venous system of the patient and into the apex of the right ventricle. With the stylet removed from the lead, the lead is very flexible and difficult to so advance. Further details of the construction and utility of such an endocardial pacing lead may be obtained by reference to the aforementioned U.S. Pat. No. 3,348,548.

#The conventional endocardial pacing lead employs a relatively blunt tip electrode at its distal end that is adapted to be lodged in the trabeculae at the apex of the right ventricle. An improved endocardial pacing lead employing a rigid, electrically conductive helix with a sharp tip at the distal end of the lead adapted to be screwed into the endocardium is disclosed in copending U.S. Pat. No. 3,974,834 issued Aug. 17, 1976 entitled BODY IMPLANTABLE LEAD and assigned to Medtronic, Inc. The improved lead can be lodged in and permanently secured to or removed from body tissue without the use of complex electrode advancement mechanisms or bulky sleeves or catheter introducers to protect the patient's veins and tricuspid valve from snagging on the sharp tip of the helix. Placement of this improved body implantable lead is effected through the employment of a shroud of resilient non-conductive material extending from the silicon rubber casing of the lead through the length of the helix that is adapted to retract upon contact with tissue as the helical electrode is screwed therein. One or more conventional stylets of stainless steel wire are employed to stiffen the improved body implantable lead during the introduction and placement thereof.

#FIG. 1 shows a view of a preferred embodiment of the body implantable, intravascular lead of the present invention including in part and in side elevation partly on longitudinal section of the distal portion of the lead and including a depiction of the improved stiffening stylets partly inserted in the lumens of the lead;

#FIG. 2 shows the lead of FIG. 1 being lodged in and permanently secured to the tissue forming the apex of the right ventricle of the heart;

#FIG. 3 is a detail drawing, partly in longitudinal section, of the knob and a portion of the wire of the improved stiffening stylet; and

#Referring now to the preferred embodiment of the invention depicted in FIG. 1, there is shown the improved intravascular endocardial lead fully described in the aforementioned U.S. patent application Ser. No. 570,917 comprising an elongated lead portion 10, a distal electrode end portion 12 and a proximal terminal end portion 13. The lead, in bipolar configuration, comprises a pair of closely wound, coiled conductors 14, 15 each in the form of a spring spirally wound about and along the axis of the conductor. The spring coil conductors 14, 15 extend through the length of the lead 10 in separate lumens of a jacket or sleeve 16 of electrically insulating material, the coils 14, 15 having the capability of stretching and flexing independently of one another and the sleeve 16.

#Each spiral conductor 14,15 is formed of electrically conductive material offering low electrical resistance and also resistent to corrosion by body fluids. A platinum-iridium alloy is an example of a suitable material. Sleeve 16 is formed of an electrically insulating material, and preferably a silicone rubber such as clean room grade Silastic available from Dow Corning Corporation. This material is additionally suitable because it is inert and well tolerated by body tissue.

#At the proximal end 13 of the lead 10, the conductors 14 and 15 are received in and crimped to tubular terminal pins 17 and 18, respectively. A bifurcated boot 19 of the same material as jacket 16 is molded about the terminal pins 17,18 and the terminal ends of coils 14 and 15 and jacket 16, with the pins 17 and 18 projecting therebeyond. These pins are adapted for insertion in receptacles provided on the pulse generator, which can comprise any suitable implantable pulse generator such as that shown, for example, in U.S. Pat. No. 3,057,356.