Electrode
BACKGROUND OF THE INVENTION 
     This invention relates to electrodes, and most particularly to electrodes that may usefully be lodged in, for example, the human heart, for cooperation with a pacemaker. There has long been need for such a device characterized by improved ease of implantment and reliability of performance. 
     Two prior art electrode patents that are of interest are Bolduc U.S. Pat. No. 3,844,292 (which discloses a form of barbed electrode, in an intravascular device) and Chardack U.S. Pat. No. 3,216,424 (which discloses a plastic flat &#34;[b]ase 4 [that] can be sutured in place, through openings 11&#34;.) 
     SUMMARY OF THE INVENTION 
     The invention features an electrode having a longitudinally extending barb shaft with a barb sharp at one end and not at the other and a placement element extending alongside said barb shaft. In preferred embodiments the placement element is of silicone rubber, has a flat surface parallel with the barb shaft, and has small holes extending through it. 
     The invention has numerous advantages. It permits lodging the electrode in the thin atrium wall. Alternatively, still through an easily tolerated single small access portal in the pericardium, it can be lodged in a thin right ventricular wall. Lodging is positive and reliable. Axial rotation is prevented. Good electrical contact exists. The electrode moves complexly with the heart, millions of times per year, resisting both dislodgment and formation of impaired tissue (as results from relative movement). Positioning is extremely precise, with the barb along a path generally parallel to the heart wall. Use of very flexible leads is permitted. 
     PREFERRED EMBODIMENT 
     We turn now to drawings and description of a preferred embodiment of the invention. 
    
    
     DRAWINGS 
     FIG. 1 is a perspective view, partially broken away, of a preferred embodiment of electrode according to the invention; 
     FIG. 2 is a view, partly in side elevation, partly broken away (within the dashed line, and toward its connector end), and partly in section, of said embodiment; 
     FIG. 3 is a side elevation view, partially broken away, thereof; 
     FIG. 4 is a front elevation view, partially broken away, thereof; 
     FIG. 5 is a cross-sectional view of a set of crimping tools for use in making said embodiment; 
     FIG. 6 is a cross-sectional view of another set of crimping tools for use in making said embodiment; and 
     FIG. 7 is an end view, partially broken away, of the barb end of said embodiment being held in a holding clamp, for implantation in a heart wall. 
    
    
     DESCRIPTION 
     The presently preferred embodiment of the electrode is indicated generally at 10. 
     A barb element, indicated generally at 12, is secured, through sleeve 14 (at 14a), inside the wrappings of lead 16, which in turn is secured in crimped connections to the sleeve at 14b and (not shown) to connector tip 18. Lead 16 is surrounded by silicone rubber covering 20, which is enlarged and shaped toward the barb end of the electrode to provide a placement element 22. 
     Lead 16 is formed of flat ribbons of platinum: iridium alloy, wound around a central non-conductive core, of the general character described in Bolduc U.S. Pat. No. 3,572,344, &#34;Electrode Apparatus with Novel Lead Construction&#34;, granted Mar. 23, 1971. Barb element 12 and sleeve 14 are formed from the same alloy as lead 16. 
     The barb element 12 includes barb shaft 24, mounting shaft 26, and spacing shaft 28; the latter shaft extends generally perpendicularly to the two other shafts. Barb 30 is carried by barb shaft 24, and terminates in sharpened point 32 facing longitudinally of the electrode toward its connector tip end and flat surface 34 facing in a generally opposite direction. 
     Thin sleeves of silicone rubber (not shown) are provided (applied while xylene-soft) over the straight portions of shaft 28, to reduce the threshold current. 
     In assembling the lead to the barb element, the non-conductive center of lead 16 was removed far enough longitudinally to make room for the end of mounting shaft 26 of the barb element. It was then inserted into the end of the lead, and sleeve 14 secured thereover at crimped portion 14a with the crimping tool shown in FIG. 6; the crimp 14b of sleeve to lead was by the crimping tool shown in FIG. 5. In making the barb element, the point was initially formed by heating together two rods, one bent at 20°, until a ball was formed at the tip; the point was then formed, and the flat surface 34. 
     In the embodiment shown, spacing shaft 28 was about 7/32 inches in length; its distance from surface 44 was about 5/32 inches. 
     In operation, a surgeon makes a small, easily tolerated incision, exposing the pericardium. The barb end of an electrode is held, at its rounded portion 36 adjacent its placement element 22, in the two rounded jaw portions 38 carried by the two legs 40 of the scissors-like (with clamping ratchet adjacent thumb and finger holes) holding clamp indicated generally at 42. Barb 30 may then be inserted into an atrial of ventricular wall in an angular way, until placement surface 44 of placement element 22 engages the heart wall; the device may then be pushed to &#34;ski&#34; along on surface 44 until spacing shaft 28 stops movement. The portion of the barb element outside the dotted lines of FIG. 2 is then firmly implanted in the heart wall, without perforation, with precise positioning. Not only blunt portion 34 but surface 44 as well helps hold the barb in its inserted position from the start; surface 44 prevents axial rotation; and within a short time, further, tissue grows around the electrode and into holes 46 to further assist in anchoring the electrode. 
     OTHER EMBODIMENTS 
     Other embodiments within the invention will occur to those skilled in the art. For example, the barb may be formed entirely of suitable plastic, secured onto a metal barb shaft by any suitable means; it may even be that this will be the most preferred means.