Abstract:
A tool for protecting a cardiac stimulating lead from damage upon passing through a hemostasis valve of a vascular introducer in the course of an implantation procedure comprises a splittable, peal-away sheath that is rendered sufficiently rigid by a tool dilator or placement of the lead body within the sheath so that the combination can be forced through a self-closing aperture formed through the hemostatic valve member. The use of the tubular sheath in breaching the self-closing aperture shields the lead electrodes and any covering that may be present from becoming distorted as well as from contamination by silicon oil commonly found in vascular introducers having a hemostasis valve.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    I. Field of the Invention  
           [0002]    This invention relates generally to implantable tissue stimulating apparatus of the type having a pulse generator and a medical lead for delivering electrical stimulation to target tissue, and more particularly to a tool to be used in facilitating the surgical implantation of a medical lead into a patient&#39;s body.  
           [0003]    II. Discussion of the Prior Art  
           [0004]    In implanting medical devices, such as pacemakers or pacemakers/defibrillators, a transvenous lead placement approach has found wide acceptance. Using the Seldinger technique, the right or left cephalic vein or the axillary vein is located and punctured with a relatively long, large-bore needle. A guidewire is then typically passed through the needle into the selected vein. The needle is then removed from the guidewire and replaced with an introducer incorporating a hemostasis valve to stem blood flow. Once the introducer is in place, the medical lead is forced through the hemostasis valve, the introducer&#39;s shaft, and thence, through the selected vein and ultimately into a selected chamber of the heart.  
           [0005]    An introducer that has found rather wide spread acceptance is the SafeSheath® manufactured and sold by Pressure Products of Rancho Palo Verdes, Calif. It incorporates a tear-away sheath having a break-away hemostasis valve assembly affixed to a proximal end of the sheath. The hemostasis valve assembly comprises a molded plastic housing containing an elastomeric disk having a self-closing aperture formed through its thickness dimension. The SafeSheath also includes a side entry port located distally of the housing containing the hemostasis valve whereby fluids containing an anti-coagulant may be infused through the lumen of the sheath and into the selected vein.  
           [0006]    Once the introducer is installed, a medical lead having one or more electrode surfaces at its distal end is passed through the hemostasis valve of the introducer and thence, through its sheath until the electrodes are positioned at a desired site within the heart. Once the distal end of the lead is appropriately placed, the introducer may be removed from the lead by splitting the break-away hemostasis valve assembly and the sheath.  
           [0007]    While introducers of the type described can be used with a variety of pacemaker/defibrillator leads, there are certain lead designs that can be damaged as the distal end portion bearing the electrodes is forced through the self-closing aperture of the hemostatic valve. The shocking electrodes on defibrillator leads are often in the form of an uninsulated wire coil supported by the lead&#39;s plastic body. As a lead of this type is forced through the hemostasis valve of an introducer, the excessive frictional forces tend to displace the turns of the coil so that they are no longer appropriately spaced.  
           [0008]    Other leads with which the SafeSheath introducer is incompatible are those in which a fabric covering is placed over the coil electrodes of defibrillator leads to inhibit tissue ingrowth into the coils of the shocking electrode. Because of the porosity of the fabric, electrical shocking currents readily pass through to surrounding tissue with very low impedance. However, it is found that the SafeSheath introducer incorporates a silicon oil as a lubricant on its hemostasis valve member and as such a fabric covered electrode of the lead is forced through the self-closing aperture, the silicon oil wipes off onto the fabric covering that tends to plug the pores in the fabric which adversely impacts the lead&#39;s electrical performance. Then, too, when attempting to pass this lead through the valve, frictional forces tend to displace the fabric covering, in effect, peeling it back. Another drawback of the hemostatic valve&#39;s direct engagement with the medical lead being implanted is that tactile feedback through the lead to the physician&#39;s fingers is severely dampened.  
           [0009]    From the foregoing discussion, those skilled in the art will appreciate that a need exists for a lead insertion tool that will obviate the cited drawbacks of state-of-the-art lead introducers incorporating a hemostasis valve. The present invention provides such a device.  
         SUMMARY OF THE INVENTION  
         [0010]    The present invention comprises a lead insertion tool adapted for use with a lead introducer having an elastomeric hemostasis valve with a self-closing aperture. The tool comprises a tubular sheath having a relatively thin wall with at least one longitudinal groove formed inwardly thereof to facilitate rupture of the sheath along the groove. The lumen of the tubular sheath is sized to receive a medical lead therethrough with a predetermined clearance fit. A tool dilator that has a generally rigid shaft is insertable through the lumen of the tubular sheath and when so inserted renders the sheath sufficiently rigid to allow insertion of the sheath and dilator through the self-closing aperture of the lead introducer. Once inserted through the aperture, the tool dilator is removed from the tubular sheath and the distal end of the medical lead is then advanced through the lumen of the sheath which holds the aperture in the hemostasis valve open while shielding the lead from exposure to contaminating silicon oil and minimizing friction that distorts the lead electrodes and/or fabric covering. Once the lead has made its way past the hemostasis valve, provision is made for rupturing the tubular sheath of the insertion tool along its length, allowing it to be pealed off from the lead body.  
           [0011]    In accordance with a further feature of the invention, the tool dilator may be dispensed with when the lead insertion tool is assembled onto the distal end portion of the lead to be installed and then the lead with the tubular sheath surrounding its distal end are passed through the hemostasis valve as a unit. 
       
    
    
     DESCRIPTION OF THE DRAWINGS  
       [0012]    The foregoing features and objects, as well as others, will become apparent to those skilled in the art from the following detailed description of a preferred embodiment, especially when considered in conjunction with the accompanying drawings in which:  
         [0013]    [0013]FIG. 1 is an exploded side elevational view of the lead insertion tool comprising a preferred embodiment of the present invention;  
         [0014]    [0014]FIG. 2 is an enlarged view of the hub portion of a lead introducer showing the hemostasis valve;  
         [0015]    [0015]FIG. 3 is a top plan view of the tubular sheath component shown in FIG. 1; and  
         [0016]    [0016]FIG. 4 is a greatly enlarged, cut-away view of the lead insertion tool when used to pass a distal end of a medical lead through a hemostasis valve of an introducer.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0017]    Certain terminology will be used in the following description for convenience in reference only and will not be limiting. The words “upwardly”, “downwardly”, “rightwardly” and “leftwardly” will refer to directions in the drawings to which reference is made. The words “inwardly” and “outwardly” will refer to directions toward and away from, respectively, the geometric center of the device and associated parts thereof. Said terminology will include the words above specifically mentioned, derivatives thereof and words of similar import.  
         [0018]    Referring initially to FIG. 1, there is indicated generally by numeral  10  a conventional introducer set of a type used in implanting medical leads for an implantable pacemaker or pacemaker defibrillator. It is seen to comprise a flexible, tubular sheath  12  having a proximal end  14  and a distal end  16  and with a lumen extending therebetween. Completing the set is a dilator (not shown). Affixed to the proximal end  14  of the sheath  12  is a hub member  18  that is molded from a suitable plastic. Contained within the hub  18  is an elastomeric disk  20  (FIG. 2) having a self-closing aperture  22  formed through the thickness dimension thereof. The hub  18  further includes a side port  24  having a bore, not shown, that is in fluid communication with the lumen of the sheath  12 . A length of tubing  26  may be connected to the side port  24  and affixed to the other end of the tubing  26  is a stop cock member  28 . This stop cock is also a conventional component and has provision for controlling the flow of a flushing fluid, such as saline or saline mixed with an anti-coagulant to inhibit plugging or clogging of the sheath  12  by blood.  
         [0019]    For illustrative purposes only, the introducer set  10  may comprise a SafeSheath introducer of Pressure Products, Inc. or another introducer set incorporating a hemostatic valve.  
         [0020]    In accordance with a first embodiment of the invention, the lead insertion tool consists of a two-piece assembly including a tubular sheath member  30  and a tool dilator  32 . The sheath member  30  has a relatively thin-walled, extruded plastic, tubular sheath  34 . Affixed to a proximal end  36  thereof is a hub  38  having a Luer fitting  40  on its proximal end. Wings  42  and  44  project laterally from the hub. The hub  38  has longitudinally extending grooves  46  formed inwardly from the outer surface thereof at diametrically located positions. These grooves are not so deep as to intersect with the lumen  48  formed through the hub (FIG. 3). The tubular sheath portion  34  also includes diametrically opposed score lines, as at  50 , that are vertically aligned with the grooves  46  and  48 .  
         [0021]    With the described arrangement, a medical professional is able to split the sheath member  30  into two halves along the grooves  46  and score lines  50  by applying a downward bending force to the wing members  42  and  44 .  
         [0022]    The lumen  48  of the device is sized to receive the distal end portion of a medical lead  52  through it.  
         [0023]    In that the wall thickness of the sheath  34  is only about 0.010 in., it may lack sufficient rigidity to allow it to be passed through the self-closing aperture  22  of the hemostatic valve member  20  of the introducer  10 . There is, therefore, provided the tool dilator  32  having a generally rigid shaft  54  which, when inserted through the lumen  48  of the tubular sheath member  30 , provides sufficient support to permit the sheath  34  containing the shaft  54  to pass through the self-closing aperture  22 . Affixed to the proximal end  56  of the shaft  54  is a Luer lock member  58  for cooperating with the Luer fitting  40  of the sheath member  30 . A swivel  60  is rotationally joined to an upper surface of the Luer lock  58 . The swivel  60  includes a central bore that tapers to a lesser diameter of a bore formed longitudinally through the generally rigid shaft  54 . The diameter of the bore extending through the shaft  54  is of a size to accommodate a conventional guidewire that can be inserted through the tool dilator  32 , the sheath member  30  and the introducer set  10  if desired.  
         [0024]    In use, the person involved with implanting the lead  52  may pass a guidewire (not shown) through a hollow trocar used to pierce the selected vein. Leaving the guidewire in place, the needle may then be stripped off from the guidewire and replaced with the introducer set  10  which would be passed over the guidewire and into the puncture wound until the distal end  16  of the introducer set  10  is located within the lumen of the selected vein in which the lead  52  is to be routed in reaching the heart. Once the introducer is in place, its dilator is withdrawn and the combination of the sheath member  30  and the tool dilator  54  that are now locked together by engagement of the Luer lock  58  with the Luer fitting  40  is used to penetrate through the self-closing aperture  22  of the hemostasis valve  20  contained within the hub  18  of the introducer. The wings  42  prevent the sheath member  30  from passing completely through the hemostasis valve and into the blood vessel. Next, the tool dilator  32  is removed from the sheath member  30  and, at this point, a cap (not shown) may be screwed onto the Luer fitting  40  to maintain hemostasis. When the physician is ready to insert the medical lead and advance it into the heart, the cap is removed and the distal end of the lead  52  is inserted through the lumen  48  which is now holding the self-closing aperture open. In that the elastomeric, self-closing hemostasis valve is not acting on the lead, tactile feedback is maintained. Once the lead has been advanced into the heart, the sheath member  30  can be slipped rearward in the proximal direction until the sheath  34  is free of the hub  18  of the introducer. Now, the attending physician may apply finger pressure to the wings  42  and  44  to thereby split the hub  38  along the grooves  46  and  48  and tear the thin-walled sheath  34  along its score line  50 . Thus, the sheath member  30  can be completely removed from the lead.  
         [0025]    The introducer  10  employed is also designed to be split and pealed free from the lead.  
         [0026]    In accordance with an alternate embodiment, the tool dilator  32  can be dispensed with and only the sheath member  30  employed to aid in breaching the self-closing aperture  22  of the hemostatic valve member  20 . Here, after the introducer  10  has been placed and its dilator removed, the distal end of the lead  52  may be inserted directly through the bore of the hub  30  and into the lumen of the thin-walled tube  34 , but not so far as to project out the distal end of the tubular sheath  34 . The combination of the lead  52  filling the lumen of the thin-walled sheath  34  can render the sheath  34  sufficiently rigid to allow it to be passed through the hemostasis valve. Once the assembly has been mated with the hub  18  of the introducer, the lead  52  can be further advanced through the sheath  12  of the introducer and the selected vein into the heart. Again, because the sheath member  30  is splittable, it can readily be removed from the lead once the lead has been positioned.  
         [0027]    It should also be mentioned that the length of the tubular sheath  34  is such that when inserted into the hub  18  of the introducer, it will pass through the self-closing aperture  22  but not extend so far as to occlude or block the flow of fluid that may be injected through the side port  24 , via the stop cock  28  and the tubing  26 .  
         [0028]    This invention has been described herein in considerable detail in order to comply with the patent statutes and to provide those skilled in the art with the information needed to apply the novel principles and to construct and use such specialized components as are required. However, it is to be understood that the invention can be carried out by specifically different equipment and devices, and that various modifications, both as to the equipment and operating procedures, can be accomplished without departing from the scope of the invention itself.