Pacemaker electrode

An extractable endocardial tip for an electrode of an electrical stimulator has a tip body with a front end for positioning the electrode within a desired area and a back end for connecting to an electrical source. A fin protrudes from the tip body and has an anterior leading edge and a posterior receding edge wherein the posterior receding edge is serrated to form a cutting surface. The tip body also has an internally threaded bore for engaging a mating externally threaded stylet. When the tip body is pulled by pulling on the mating stylet, the serrated edge cuts through any fibrous scar tissue or any other material that surrounds the electrode to facilitate the relatively easy withdrawal of the electrode from the heart.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 5 , an existing electrical stimulator such as a pacemaker 11 consists of a power source and electronic circuitry which together constitute a pulse generator housed within the pacemaker 11 . The pacemaker 11 is arranged to be inserted within a patients body normally near one of the pectoral muscles. An insulated lead 13 or electrical wire having a proximal end connected into a receiving port of the pacemaker 11 and a distal end connected to one or more extractable endocardial electrode tips 15 (shown in isolated fashion as 15 in FIG. 1 ). Tip 15 is located inside the patients heart 17 (see FIG. 5 ) and provides a direct connection with the pacemaker 11 and the heart 17 . Generally, the electrode tip 15 is implanted for sensing cardiac activity and providing pacing pulses. The electrode tip 15 may be substantially flush with the surface of the heart 17 to contact heart tissue to provide epicardial stimulation/sensing functions. Alternatively, the body of the electrode tip 15 may include an attachment means such as a helical screw tip, barb, or some other device for fixation to the heart or any other desired organ or area. The attachment means maybe on the anterior end of the electrode tip 15 . The electrode tip 15 preferably enables stimulation and sensing of cardiac tissue from the pacemaker via the lead 13 . Typically, electrode 15 is positioned in the right ventricle 19 near the apex 21 of the heart 17 where the free walls of the right ventricle meet the intraventricular septum. By being positioned in the right ventricle 19 near the apex 21 of the heart 17 , the electrodes 15 are in contact with the apical area of the heart 17 and can deliver stimulating impulses to the endocardium for pacing the apical area. As shown in FIG. 5 , the lead 13 to the electrode tip 15 may have a curve imparted to it to aid in positioning the electrode against a desired area such as the intraventricular septum. The desired area for placement of the electrode tip 15 could also include any other area of the body where an organ needs a stimulator point or an electrical stimulator is needed. Referring to FIG. 1 , the lead body 25 of the electrode tip 15 has a general cylindrical shape and an anterior end 27 for positioning within a desired area and a posterior end 29 for connecting to an insulated lead 13 . The lead body 25 is made of physically compatible conductive material, for example micro porous platinum black or any other suitable conductive material may be deposited upon the outside surface 31 . In the first embodiment, the outer surface 31 of the body 25 is smooth. However, the exterior surface of the body and fin may have irregularities as shown in FIGS. 6 and 7 . The electrode tip 15 contains at least one fin 33 protruding from the body 25 , to aid in fixation as well as extraction of the electrode tip 15 . The fin 33 generally has an anterior leading edge 35 and a posterior receding edge 37 . The anterior leading edge 35 inclines rearward and at an acute angle of generally 20 degrees relative to the longitudinal axis of the lead body 25 . The anterior leading edge 35 is slightly curved outward. Leading edge 35 begins a selected distance from tip 41 and posterior edge 37 terminates a selected distance from end 43 . The total length of fin 33 is about 60% the total length of the electrode tip 15 . As shown in FIGS. 2, 3 and 4 , fin 33 is on a radial line 34 which intersects the longitudinal axis 36 of electrode tip 15 . The radial extent of fin 33 (represented by the length of line 34 passing through tip 33 in FIG. 2 ) is less than the radius of the body 25 . As shown in FIG. 4 , the posterior edge 37 is curved in shape in a radius about a center point 45 . Center point 45 is located exterior of body 25 and forward from edge 37 . This provides a generally convex shape to edge 37 with the central portion being farther rearward than the inner and outer termination of edge 37 . At least a portion of the posterior receding edge 37 is serrated to form a cutting edge 47 for the extraction of the electrode. The serrations may be cut at opposite angles to enhance the sharpness of the edge 47 . Any general fin shape that would provide a cutting edge 47 suitable for cutting tissue surrounding the electrode tip 15 can be used. The cutting edge 47 is relatively sharp and is able to cut through any tissue or obstruction that may cover the electrode tip 15 simply by pulling on the lead 13 . The electrode tip 15 may be inserted into the heart 17 or any other organ through a venous access. The electrode tip 15 may also be inserted by cutting into the desired organ and inserting the electrode tip 15 or the electrode tip 15 may be attached to the organ by attachment means such as a screw 49 or a barb 51 . During implant, the lead ( 13 in FIG. 1 ) is stiffened with a stylet, straightening the curve for insertion through an introducer sheath and through a vein. Upon removal of the stylet, or insertion of a less stiff stylet, the lead body resumes its curved shape to guide the electrode tip 15 toward the desired area. Pulling on one arm of the stylet and pushing on the other arm causes the pair to bow a sufficient amount to position the electrode tip 15 . Use of this technique for steerable guide wires is known in the art. The reinsertion of the same or a similar stylet will provide the necessary strength and stiffness to actively extract the inventive lead 13 by simply pulling on the lead 13 with relatively little force. Another technique for achieving a desired insulated lead 13 curvature is disclosed in U.S. Pat. No. 4,677,990 to Neubauer, and the patent is incorporated herein by reference. When it is time for the electrode to be withdrawn from the heart 17 , a stylet is reinserted into the insulated lead 13 to stiffen the insulated lead 13 and light pressure is applied to the insulated lead 13 such that the cutting edge 47 of the fin 33 cuts through any fibrous scar tissue or any other inhibiting material that surrounds the electrode tip 15 to facilitate the relatively easy withdraw of the electrode tip 15 from the heart 17 . Once the electrode tip 15 is free from the tissue or material holding it in place, the electrode tip 15 is withdrawn from the organ by simply continuing the light pressure on the insulated lead 13 until it is totally withdrawn from the patient's body. When the electrode tip 15 is coming out towards the surface, the fin 33 will cut any fibrotic tissue surrounding the insertion opening made when the electrode tip 15 was first inserted. Because the tissue surrounding the insertion opening is cut, the same hole maybe used for access to the subclavian for the implantation of a new pacemaker lead 13 . While the electrode may generally be withdrawn from the heart by simple pulling force applied to the insulated lead 13 , FIGS. 11 - 14 illustrate another aspect of the invention in which a specially designed stylet ( 61 in FIG. 14 ) is used to assist in retracting the electrode tip. Stylet 61 is typically formed of metal and has a proximal end 63 and a distal end 65 which is externally threaded. As shown in FIG. 12 , the electrode tip 67 has an inner threaded core 69 which matingly engages the externally threaded end 65 of stylet 61 . The pacemaker conducting wire 71 forms a spiral or coil which passes through an inner diameter 73 of the threaded core 69 (see FIG. 13 ). A portion of the outer body 75 of the electrode tip is shown broken away in FIGS. 11 and 12 to better illustrate the bore leading to the inner threaded core of the electrode tip. Stylet 61 can be fed into position so that tip 65 engages threaded core 69 . This allows an additional pulling or pushing force to be applied to the electrode tip 67 . This added pulling ability is a significant improvement and forms an important further aspect of the invention. FIGS. 6 and 7 show embodiments of the electrode tip having convexities 53 and concavities 55 on the external surface thereof. The convexities 53 and concavities 55 provide an increased contact area that improves the conductivity of electrical stimuli to the heart or any other desired organ. The outer surface 31 may be covered by a biocompatible material to help facilitate tissue growth. The electrode tip 15 may be used as a subcutaneous (SQ) patch electrode or defibrillator electrode. In addition to or instead of the SQ electrode, a superior vena cava (SVC) electrode may be used, and may be located on the body or may be on a separate electrode tip 15 . A septal pacing electrode may be used to pace the ventricles as needed, and may provide improved hemodynamics as compared with the typical method of pacing at the apex 21 . Two sensing electrodes may be positioned to provide optimum clinical pacing and/or sensing. As another alternative, pairs of electrodes 15 may be used to discriminate between various arrhythmias, using the techniques of one or more of the following U.S. Patents, which are incorporated herein by reference in their entirety: U.S. Pat. Nos. 4,354,497 to Kahn; 4,790,317 to Davies; and 4,799,493 to DuFault. Referring to FIGS. 8 - 10 the body 25 may have one, two, three or four fins 33 . An extra fin increases the surface area to sense and stimulate the organ in need as well as aid in fixation and extraction. The fins 33 maybe placed any distance from each other but preferably are equal distance from each other. Fibrotic scar tissue and endothelium make it particularly difficult to free the electrode tip 15 and are a common problem when trying to remove the electrode tip 15 . However the present invention is able to cut through the fibrotic scar tissue for a relatively easy extraction. The fin 33 is an intrinsic part of the electrode tip 15 and provides an increased contact area to sense and stimulate the organ in need. It should be understood that various alternatives to the embodiments of the invention described herein may be employed in practicing the invention. For example the tip 15 may have 4 or 5 fins 33 (see FIG. 10 with 4 fins 33 ). Also, the fin 33 maybe the same length or less than about 60% the total length of the electrode tip 15 . It is intended that the following claims define the scope of the invention and that structures and methods within the scope of these claims and their equivalents be covered thereby.