Abstract:
A medical device having retention means extending along a length of an elongate body of the medical device including a plurality of projections adapted to interfere with a wall of a generally tubular vessel to retain the body within the vessel.

Description:
TECHNICAL FIELD 
   The present invention relates to medical devices and more particularly to means for retaining or preventing dislodgement of a lead positioned within a body. 
   BACKGROUND 
   Medical devices often include a therapy generator and one or more elongate leads, coupled thereto, which are positioned within a patient&#39;s body to deliver therapy from the generator. Such therapy may be in the form of electrical stimulation, delivered via electrical conductors extending through a lead body, or fluid infusion, delivered via a lumen extending through a lead body. Some examples of electrical stimulation include pacing and defibrillation; some examples of fluids, which may be infused, include drugs, nutrients, and genetic materials. In many applications, leads are inserted through one or more blood vessels and are ultimately positioned within a blood vessel where the lead must be retained for a period of time in order to deliver the therapy. Therefore it is desirable to provide lead retention means allowing insertion or forward motion of lead, to position the lead within a vessel, while preventing retraction or rearward motion of the lead during therapy delivery. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The following drawings are illustrative of particular embodiments of the invention and therefore do not limit its scope, but are presented to assist in providing a proper understanding of the invention. The drawings are not to scale (unless so stated) and are intended for use in conjunction with the explanations in the following detailed description. The present invention will hereinafter be described in conjunction with the appended drawings, wherein like numerals denote like elements, and: 
       FIG. 1  is a plan view with a partial section of a lead including means for retention according to one embodiment of the present invention; 
       FIG. 2A  is an enlarged plan view of a retention means according to one embodiment of the present invention; 
       FIG. 2B  is an enlarged partial section view of means for retention according to an alternate embodiment; 
       FIG. 2C  is an enlarged plan view of means for retention according to another embodiment; 
       FIG. 2D  is an enlarged partial section view of means for retention according to yet another embodiment of the present invention; 
       FIG. 3  is a plan view of a lead which may incorporate retention means according to embodiments of the present invention; 
       FIGS. 4A–B  are plan views of a portion of a lead body including retention means according to an alternate embodiment of the present invention; 
       FIGS. 5A–B  are schematic views of a portion of a lead body including retention means according to yet another embodiment of the present invention; and 
       FIG. 6  is a schematic view of a medical device, which may incorporate retention means according to embodiments of the present invention. 
   

   DETAILED DESCRIPTION 
   The following detailed description is exemplary in nature and is not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the following description provides a practical illustration for implementing exemplary embodiments of the invention. 
     FIG. 1  is a plan view with a partial section of a lead  10  including means for retention  15  according to one embodiment of the present invention.  FIG. 1  illustrates lead  10  including a lead body  12 , a connector  16  coupled to a proximal end  121  of the lead body  12  and an electrode  14  coupled to a distal end  122  of the lead body  12 ; a conductor  13 , extending within an outer sheath  11 , couples electrode  14  to connector  16 , in order to deliver electrical stimulation, and forms a lumen for slideably engaging a stylet  18 . Means and materials for constructing such a lead are well known to those skilled in the art. 
     FIG. 1  further illustrates retention means  15  formed along an outer surface of lead body  12  in proximity to distal end  122 . According to embodiments of the present invention, retention means  15  allows insertion of lead body  12  through a vessel, for example a vessel  607  as illustrated in  FIG. 6 , while preventing retraction of lead body  12  within the vessel due to an interference of retention means  15  along a wall of the vessel that contacts lead body  12 . Retention means according to some embodiments of the present invention extends along a length greater than or equal to approximately 1 mm and may be implemented along any portion of a lead body alone or in conjunction with other retention means; further, retention means  15  may be an integral part of outer sheath  11  or may be formed on a separate collar fitted about lead body  12 , either in-line with or about outer sheath  11 . Suitable materials for outer sheath  11  and retention means  15  include those that are biocompatible, examples of which include, but are not limited to, silicone and polyurethane. 
   Various embodiments of retention means include projections formed along retaining segments as illustrated in FIGS.  2 A–D and  4 A– 5 B. It should be noted that alternate embodiments include, but are not limited to, retaining segments extending around an entire circumference of a lead body and segments extending only about a portion of the circumference of the lead body. For example, a plurality of projections may lie in a line, single file, along a length of a retaining segment, as illustrated in  FIG. 2A , or each individual projection may extend circumferentially about all or a portion of a retaining segment, as illustrated in  FIG. 2C , or a plurality of projections may lie approximately side-by-side about all or a portion of a circumference, as illustrated in  FIG. 2D . 
   In some embodiments, retaining segments as a whole or just the projections may be formed of a bioadsorbable material, examples of which include those taught in lines  10 – 24  of U.S. Pat. No. 6,173,206. According to these embodiments, if a lead body is chronically implanted, the retaining segment or projections would remain intact long enough to hold the body in place for a period of time up to tissue encapsulation of the body; this may facilitate extraction of a chronically implanted lead. One example of an appropriate bioadsorbable material, polydioxanone is described along with means for molding the material in U.S. Pat. No. 4,490,326, the teachings of which are incorporated by reference herein. 
     FIG. 2A  is an enlarged plan view of means for retention according to one embodiment of the present invention.  FIG. 2A  illustrates a retaining segment  380  including a plurality of barb-like projections  385  positioned in a single-file line along a length of the segment  380 ; each of the plurality of projections  385  include a length L and extend laterally from a lead body  312  toward a proximal end  321  at an angle  33 , which, according to some embodiments, is less than approximately 45 degrees. According to this embodiment of the present invention and various other embodiments illustrated herein length L is greater than approximately 100 microns.  FIG. 2A  further illustrates projections  385  as portions of a wall  387  forming retaining segment, having been lifted out of wall  387  according to one embodiment of the present invention.  FIG. 2B  illustrates an alternate retaining segment  30  extending along a length of lead body  312  and including tread-like projections  31  extending laterally from lead body  312  to form a textured surface adapted to engage a vessel wall, similar to, for example, a sole of a shoe designed to facilitate traction. According to some embodiments of the present invention, projections, i.e.  385 ,  31 , are directly formed in outer surfaces, being integral with a bulk material underlying the surfaces, but, according to alternate embodiments, the projections are formed of separate materials either embedded in or adhered to these surfaces. Alternative methods of forming examples of these embodiments will be described herein below. 
     FIG. 2B  further illustrates retaining segment  30  including a coating  36 , which is soluble in body fluids; according to this embodiment, coating  36  fills in around projections  31  and remains intact temporarily, during positioning of lead body  312 , so that lead body  312  may be moved back and forth through a vessel if repositioning is necessary. Suitable materials forming coating  36  are soluble in body fluids (within a temperature range encompassing normal body temperature), non-toxic, biocompatible and non-pyrogenic; examples of such a material include sugar derivatives, such as mannitol and dextrose, salts, such as sodium chloride and potassium chloride, and polyvinylpyrrolidone (PVP). Portions of U.S. Pat. No. 4,827,940 teaching methods for forming and applying a mannitol solution are incorporated by reference herein. According to an alternate embodiment, a covering in the form of a thin wall tube may be deployed over retaining segment  30  in place of coating  36 . It should be noted that any of the embodiments described herein may include such a coating or a covering facilitating positioning of lead bodies. 
     FIG. 2C  is an enlarged plan view of means for retention according to another embodiment.  FIG. 2C  illustrates a retaining segment  300  coupled to a portion of lead body  312  and including a proximal end  3210  and a plurality of projections  310 , each of which extend around all or a portion of a circumference of lead body  312  and extend laterally from lead body  312  at angle  33  with terminal ends  311  of projections  310  directed toward proximal end  3210 . 
     FIG. 2D  is an enlarged partial section view of means for retention according to yet another embodiment of the present invention.  FIG. 2D  illustrates a retaining segment  350  including a plurality of fish scale-like projections  355  positioned side-by-side about a circumference of lead body  312  and along a length of segment  350  and including terminal ends  351  directed toward a proximal end  3215 .  FIG. 2D  further illustrates projections  355  as discrete elements embedded in an underlying surface  375  of segment  350  according to one embodiment of the present invention.  FIG. 2D  also illustrates, by way of a dashed line connecting projections  355  around a circumference, another embodiment in which embedded elements forming projections may be rings or portions of a coil circling a portion of or the entire circumference of segment  350  creating projections similar to projections  310  illustrated in  FIG. 2C . 
   According to further alternate embodiments, some or all projections of a retaining segment, for example projections  385 ,  31 ,  310  and  355  ( FIGS. 2A–D ), each include micro-features further enhancing engagement of the projections with the vessel wall. In  FIG. 2A  such a feature is illustrated on one of projections  385  as a hole or indentation  25 ; in  FIG. 2B  such a feature is illustrated as a modified surface  26  on one of projections  31  wherein surface  26  includes texture, adhesive spots, or some material promoting thrombotic adhesion to vessel wall. 
   Methods for forming various embodiments of retaining segments, for example those depicted in  FIGS. 2A–D , include, but are not limited to, molding, extrusion, cutting, laser ablation, and coating. These methods may form projections directly in outer surfaces, such that they are integral with a bulk material underlying the surfaces, or may integrate the projections with the surface by embedding or adhering. 
   According to some embodiments of the present invention, transfer or injection molding, using methods known to those skilled in the art, are used to form a retaining segment including projections, examples of which include those depicted in  FIGS. 2B–C . According to other embodiments, a cutting process may be used to create projections on a retaining segment, for example segment  380  illustrated in  FIG. 2A ; a blade may be used to nick the surface or to cut all the way through a wall of the retaining segment. 
   Alternatively, laser ablation may be used to create projections from a bulk material of a retaining segment, i.e.  FIGS. 2B–C , or by exposing, at a surface of the segment, portions of materials which have been embedded within the bulk material underlying the surface during, for example, a molding or extrusion process, i.e.  FIG. 2D . U.S. Pat. No. 5,580,699 describes a suitable laser ablation process, which may be used to form retaining segments and the pertinent teachings of the &#39;699 patent are incorporated by reference herein. U.S. Pat. No. 4,272,577 describes an extrusion process for forming ski bases having direction-dependent friction coefficients wherein harder particles, within a plastic matrix flowing through a slit nozzle, become obliquely oriented relative to the surface of the base; in one case, by means of a temperature gradient across the nozzle. We contemplate that similar methods may be developed by those skilled in the art, according to the teachings of the &#39;577 patent, in order to extrude retaining segments according to the present invention, and incorporate by reference the pertinent teachings of the &#39;577 patent herein. Some composite materials suitable for embodiments of the present invention include but are not limited to polyamide and polyimide particles, polyester fibers, carbon fibers or particles and any combination thereof blended with silicone. 
   According to further alternate embodiments a coating applied to a surface of a retaining segment may form projections and or micro-features on projections, for example similar to those illustrated in  FIGS. 2B–C . Stewart et al. describe an example of a suitable coating process via plasma deposition in commonly assigned U.S. Pat. No. 6,549,811, which is incorporated by reference in its entirety herein. Furthermore coatings including particles blended within, for example a silicone medical adhesive including biocompatible metal particles or hard plastic particles may form an embodiment of the present invention for example similar to those illustrated in  FIGS. 2B and 2D . 
     FIG. 3  is a plan view of a lead  40 , which may incorporate retention means according to embodiments of the present invention.  FIG. 3  illustrates lead  40  including a proximal portion  43 , a first preformed bend  41  extending from proximal portion  43  to an intermediate segment  45  and a second preformed bend  42  extending from intermediate segment  45  to distal segment  46 , which is terminated by a tip  44 . Such a lead is fully described in commonly assigned U.S. Pat. No. 5,999,858, which is herein incorporated by reference in its entirety. According to embodiments of the present invention, first and second bends  41  and  42  acting as means for retention of lead body in a coronary vessel, for example a coronary sinus  605  or a branch vessel  607  thereof illustrated in  FIG. 6 , are supplemented by any of the retaining segments described herein, which may be formed along the lead body surface at first bend  41 , intermediate segment  45 , second bend  42 , distal segment  46 , or any combination thereof. Any other combination of bends within a lead body is within the scope of the present invention. 
     FIGS. 4A–B  are partial plan views of one embodiment of lead  40  showing only a portion at first bend  41 , which includes a retaining segment formed by projections  51 . According to some embodiments of the present invention a retaining segment may be activated by a bending of a lead body as illustrated in  FIGS. 4A–B . If a stylet, for example stylet  18  shown in  FIG. 1 , is inserted into lead  40  to straighten preformed bend  41 , projections  51  become approximately parallel with an outer surface of lead  40 , as illustrated in  FIG. 4A . Once the stylet is removed preformed bend  41  reforms such that projections  51  protrude laterally and are thus activated to prevent rearward motion of lead  40  within a vessel. If it becomes necessary to reposition lead  40 , the stylet may be reinserted to straighten bend  41  thus bringing projections into approximate alignment with the surface of lead  40 . It should be noted that the embodiment illustrated in  FIG. 2D  may be of the type illustrated in  FIGS. 4A–B . 
     FIG. 3  further illustrates lead  40  including an anchoring sleeve  48  positioned about proximal portion  43  thereof. According to an additional embodiment of the present invention, means for retention as illustrated herein, may be formed along an outer surface of proximal portion to provide frictional forces complementing anchoring sleeve  48  at a venous entry point. The means for retention may either engage an inner surface of anchoring sleeve  48  or engage a vein wall in proximity to the entry point. 
     FIGS. 5A–B  schematic views of a portion of a lead body including retention means according to yet another embodiment.  FIGS. 5A–B  illustrate a lead body  20  including a plurality of hair-like projections or fibers  205  each attached at one end to lead body  20  and directed by their attachment points  23  to extend out from and along a length of body  20  toward a proximal end  221  of body  20 . According to the illustrated embodiment, as lead body  20  is advanced distally in a vessel  207  per arrow A, as in  FIG. 5A , projections  205  are suspended proximally; when lead body  20  is retracted proximally per arrow B, as in  FIG. 5B , projections  205  are forced toward a distal end  222  of body  20  to become bunched up and wedged between body  20  and a wall of vessel  207 , thereby providing retention means for lead body  20 . Projections may be formed from a bioadsorbable polymer, for example polyglyocolic acid or polylactic acid. Alternately projections  205  may be formed from polyester fibers or some other material promoting thrombotic adhesion with the vessel wall to enhance retention within vessel  207 ; such thrombotic projections may include a non-thrombogenic coating adapted to dissolve after the lead is positioned per  FIG. 5B , examples of which include a benzalkonium chloride-heparin solution and polyvinylpyrrolidone. Projections  205  may be attached at attachment points  23  by embedment within lead body  20  or by adhesive attachment, for example by means of silicone medical adhesive. 
     FIG. 6  is a schematic view of an exemplary medical device, which may incorporate retention means according to embodiments of the present invention.  FIG. 6  illustrates the medical device including a therapy generator  600  coupled to a lead  60  implanted within branch vessel  607  emanating from coronary sinus  605 . Lead  60  including a connector terminating a proximal portion  62 , an electrode in proximity to a distal end  66  and a conductor extending through an outer insulative sheath (similar to lead  10  illustrated in  FIG. 1 ) may deliver electrical therapy, or may deliver infusions of therapeutic fluids from generator  600  through a central lumen.  FIG. 6  further illustrates potential retention segment sites  65 ,  61 , and  63  along lead  60  where projections of retention segments according to embodiments of the present invention would engage a wall of vessels  605  and  607  to prevent rearward dislodgment of lead  60  from vessel  607 . 
   Although embodiments of the present invention are described in the context of therapy delivery, diagnostic devices adapted for insertion within a blood vessel may also incorporate retention means described herein and thus fall within the scope of the present invention. In the foregoing detailed description, the invention has been described with reference to specific embodiments. However, it may be appreciated that various modifications and changes can be made without departing from the scope of the invention as set forth in the appended claims.