Abstract:
A delivery system assembly includes an elongate inner member that extends distally through a lumen of an elongate outer tube of the assembly; the outer tube is moveable relative to the inner member between first and second positions to deploy an implantable medical device that is held within the outer tube lumen. The inner member may include a flared distal end that abuts, and preferably conforms to, the proximal end of the device, when the device is held within the outer tube lumen. The assembly further includes a stability sheath that surrounds a limited length of the outer tube, in proximity to the handle, to provide an interface for both an operator, who handles the assembly, and for an introducer sheath that provides passage for the assembly into the venous system, so that movement of the outer tube is not hindered by either during device deployment.

Description:
TECHNICAL FIELD 
       [0001]    The present invention pertains to delivery system assemblies for implantable medical devices, and more particularly to delivery system assemblies configured to facilitate percutaneous transvenous deployment of relatively compact implantable medical devices. 
       BACKGROUND 
       [0002]    The traditional implantable cardiac pacemaker includes a pulse generator device to which one or more flexible elongate lead wires are coupled. The device is typically implanted in a subcutaneous pocket, remote from the heart, and each of the one or more lead wires extends therefrom to a corresponding electrode, coupled thereto and positioned at a pacing site, either endocardial or epicardial. Mechanical complications and/or MRI compatibility issues, which are sometimes associated with elongate lead wires and well known to those skilled in the art, have motivated the development of cardiac pacing devices that are wholly contained within a relatively compact package for implant in close proximity to the pacing site, for example, within the right ventricle (RV) of the heart. With reference to  FIG. 1A , such a device  100  is illustrated, wherein pace/sense electrodes  111 ,  112  are formed on an exterior surface of an enclosure  101  that hermetically contains a pulse generator including pulse generator electronics and a power source.  FIG. 1A  further illustrates a fixation member  115  mounted to an end of enclosure  101 , in proximity to electrode  111 , in order to fix, or secure electrode  111  against the endocardial surface in the apex of the RV. Enclosure  101  is preferably formed from a biocompatible and biostable metal such as titanium overlaid with an insulative layer, for example, medical grade polyurethane or silicone, except where electrode  112  is formed as an exposed portion of capsule  101 . A hermetic feedthrough assembly (not shown), such as any known to those skilled in the art, couples electrode  111  to the pulse generator contained within enclosure  101 . 
         [0003]      FIG. 1B  illustrates a distal portion of a standard guiding catheter  150  having been maneuvered up through the inferior vena cava IVC and into the RV from the right atrium (RA), according to methods known in the art of interventional cardiology. Although device  100  may be delivered to the RV, for implant, through catheter  150 , improved delivery means are desirable to deploy device  100  at the implant site. 
       SUMMARY 
       [0004]    A delivery system assembly, according to embodiments of the present invention includes an elongate inner member that extends distally through a lumen of an elongate outer tube of the assembly; the outer tube is retractable relative to the inner member, from a first position to a second position, in order to deploy an implantable medical device that is held within the outer tube lumen in proximity to a distal end thereof. The inner member may include a flared distal end that abuts, and preferably conforms to, the proximal end of the device, when the device is held within the outer tube lumen. The assembly further includes a stability sheath that surrounds a limited length of the outer tube, in proximity to the handle, to provide an interface for both an operator, who handles the assembly, and for an introducer sheath, which may provide passage for the assembly into the venous system, so that retraction of the outer tube is not hindered by either during device deployment. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]    The following drawings are illustrative of particular embodiments of the present invention and therefore do not limit the scope 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. Embodiments will hereinafter be described in conjunction with the appended drawings wherein like numerals denote like elements, and 
           [0006]      FIG. 1A  is a schematic showing an example of an implanted cardiac stimulation device; 
           [0007]      FIG. 1B  is a schematic showing the implanted device along with a guiding catheter; 
           [0008]      FIG. 2A  is a plan view of a delivery system assembly, according to some embodiments; 
           [0009]      FIGS. 2B-C  are plan views of inner and outer subassemblies, respectively, of the system assembly shown in  FIG. 2A , according to some embodiments; 
           [0010]      FIG. 3A  is an enlarged plan view, including cut-away sections, of distal and proximal portions of the delivery system assembly; 
           [0011]      FIG. 3B  is another plan view of the system assembly; 
           [0012]      FIG. 4  is a plan view of the proximal portion of the delivery system assembly protruding from a proximal end of an introducer sheath; and 
           [0013]      FIG. 5  is another plan view of the delivery system assembly, according to some embodiments. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    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 practical examples, and those skilled in the art will recognize that some of the examples may have suitable alternatives. 
         [0015]      FIG. 2A  is a plan view of a delivery system assembly  200 , according to some embodiments.  FIG. 2A  illustrates system assembly including a handle  210  from which an elongate outer subassembly extends; the outer subassembly, which is also shown in  FIG. 2C , includes an elongate outer tube  230  and a stability sheath  250  surrounding a length L of outer tube  230 . With reference to  FIGS. 2A and 2C , outer tube  230  is coupled to a first control member  211  of handle  210 , for example, by a UV cure adhesive, and a proximal end  251  of stability sheath  250  is fixed to handle  210 , distal to control member  211 .  FIG. 2B  is a plan view of an inner subassembly that extends within the outer subassembly.  FIG. 2B  illustrates the inner subassembly including an elongate inner member  220 , which extends from a proximal end  221  thereof to a flared distal end  222  thereof; proximal end  221  of inner member  220  is fixed within handle  210  and may be coupled to a luer fitting (not shown) to which a stop cock  260  is shown coupled in  FIG. 2A . With reference to the cut-away section shown in  FIG. 3A , flared distal end  222  is contained within a distal-most portion of outer tube  230 , just proximal to a distal end  232  of outer tube  230 , according to some embodiments. According to the illustrated embodiment, first control member  211  is slidable along handle  210  to move/retract outer tube  230  longitudinally, relative to inner member  220 , from a first position  31 , which is illustrated in  FIG. 3A , to a second position  32 , for example, where distal end  232  of outer tube  230  is approximately aligned with flared distal end  222  of inner member  220 , which is illustrated in  FIG. 3B . Alternately, second position  32  may be located more proximally, such that more of inner member is exposed distal to distal end  232  of outer tube  230 , or more distally, such that only fixation member  115  of device  100  is exposed. According to some embodiments, an O-ring type seal member (i.e. silicone; not shown), which may be lubricated, for example, with silicone oil, forms a dynamic sealing interface between outer tube  230  and inner member  220  within handle  210 , in proximity to first control member  211 . 
         [0016]    With further reference to  FIG. 3A , device  100  is shown held within the distal-most portion of outer tube  230 , just proximal to distal end  232 .  FIG. 3A  further illustrates a proximal end  121  of device  100  abutting flared distal end  222  of inner member  220 , which, preferably conforms to proximal end  121  of device  100 . With reference back to  FIG. 1B , it may be appreciated that delivery system assembly  200  is preferably employed in place of the illustrated guiding catheter  150 , to deliver device  100  through the venous system and into proximity with a target implant site, for example, in the RV, when outer tube  230  is in first position  31  shown in  FIG. 3A . According to an exemplary embodiment, a distal-most portion of outer tube  230 , which contains device  100 , has an inner diameter of approximately 0.275 inch (˜0.7 cm) and an outer diameter of approximately 0.3 inch (˜0.8 cm). Although  FIG. 3A  illustrates the distal-most portion of outer tube  230  being enlarged from a remainder of outer tube  230 , for example, over a length of approximately 3.5 cm (˜1.4 inch), according to alternate embodiments, an outer diameter along a more significant length up to an entire length of outer tube  230  may be the same as that of the distal-most portion. With reference to  FIG. 3B , once delivery system assembly  200 , with device  100  held therein, is positioned with distal end  232  of outer tube  230  adjacent to the target implant site, outer tube  230  is retracted, per arrow R ( FIG. 3A ), by means of first control member  211 , to second position  32  ( FIG. 3B ), so that fixation member  115  of device  100  is exposed to secure electrode  111  to tissue at the implant site. According to  FIG. 3B , almost an entirety of device  100  exposed when outer  230  is in second position  32 ; thus, a distance between first position  31  and second position  32  may be as small as approximately 2 cm up to approximately 6 cm, depending on the length of device  100 . Alternately, second position  32 , as mentioned above, may be located to only expose enough of fixation member  115  to secure device  100  at the implant site, in which case, the distance between the first and second positions may be as small as approximately 0.5 cm to 1 cm. According to some preferred embodiments, flared distal end  222  of inner member  220  is radiopaque and distal end  232  of outer tube  230  is fitted with a radiopaque marker, so that the retraction of outer tube  230 , relative to flared distal end  222 , for the deployment of device  100 , can be observed via fluoroscopy. According to an exemplary embodiment, flared distal end  222  is formed from a polyether block amide, for example, PEBAX® 7033, with a radiopaque Barium sulfate filler; and the distal-most portion of outer tube  230  is formed from a polyether block amide, for example, PEBAX® 7233, which, at distal end  232 , includes a radiopaque band of 75% Tungsten and 25% PEBAX® 6033 sandwiched between layers of the PEBAX® 7233. 
         [0017]    According to embodiments of the present invention, stability sheath  250  is relatively rigid and allows for the above-described relative movement of outer tube  230  therein, so that, for example, an operator, who is handling delivery system assembly  200 , cannot inadvertently, by applying a force around outer tube  230  in proximity to handle  210 , impede the retraction of outer tube  230 , during device deployment, which may cause inner member  220  to apply a push force against device  100  that may injure tissue at the implant site. With reference to  FIG. 4 , stability sheath  250  further prevents similar forces from being applied to outer tube  230  within an introducer sheath  450 . Introducer sheath  450 , such as the typical type known to those skilled in the art, provides percutaneous venous access for delivery system assembly  200  and has a relatively flexible shaft wall  154  that may collapse about system assembly  200  at the entry site into the venous system; furthermore, sheath  450  may include a valve  152  (designated with dashed lines) within a proximal hub thereof, which, to prevent blood backflow around the inserted system assembly  200 , is compressed thereabout. 
         [0018]    Stability sheath  250  preferably has an inner surface spaced apart from the outer tube by a radial gap, for example, being approximately 0.002 inch and approximately 0.01 inch; however, if the inner surface of stability sheath  250  is highly lubricious, the gap may be smaller. According to an exemplary embodiment, stability sheath  250  includes an inner polymer layer adhered to an outer polymer layer, for example, by a compatible extrudable tie-layer resin like PLEXAR®, wherein the inner polymer layer is formed from a high density polyethylene (HDPE), for lubricity, the outer layer is formed from a Nylon, for example, AESNO® Nylon 12, for relatively high radial strength; a wall thickness of each of the inner and outer layers is between approximately 0.005 inch (˜0.13 mm) and approximately 0.025 inch (˜0.65 mm), preferably approximately 0.012 inch. With reference back to  FIG. 2C , length L of outer tube  230  which is surrounded by stability sheath  250  is preferably shorter than a length of introducer sheath  450 , for example, between approximately 15 cm and approximately 53 cm, preferably between approximately 46 cm and approximately 53 cm, when an overall length of outer tube  203  between handle  210  and distal end  232 , in first position  31 , is approximately 103 to 107 cm. Thus, the relative rigidity of stability sheath  250  does not impact the flexibility of delivery system assembly  200 , over that length which extends distally beyond introducer sheath  450 , to hinder system maneuverability in advancing distal end  232  to the target implant site. With reference back to  FIG. 2B , when introducer sheath  450  is between approximately 55 cm to 65 cm long, it may just reach into RA from a femoral venous access site. 
         [0019]    With further reference to  FIGS. 2A and 4 , delivery system assembly  200  further includes an optional overlay  275 , which is shown surrounding stability sheath  250 , in proximity to handle  210 . Optional overlay  275  provides an enhanced interface between system assembly  200  and valve  152  of introducer sheath  450 , for example, for improved sealing and/or with additional radial strength to counteract a compressive force of valve  152 , which, if valve  152  is a Tuohy Borst type, can be tightened down to different degrees depending upon the operator. Optional overlay  275  is preferably slidable over stability sheath  250  so that overlay  275  may be repositioned with respect to handle  210  in order to coincide with valve  152  of introducer sheath  450 , following the introduction and advancement of system assembly  200  into proximity with the target implant site for deployment of device  100 . Optional overlay  275 , according to some embodiments, may also be temporarily positioned around outer tube  230 , between a distal end of stability sheath  250  and the above-described enlarged distal-most portion of outer tube  230 , to provide additional support as delivery system assembly  200  is being introduced into introducer sheath  450 . According to an exemplary embodiment, optional valve interface overlay  275  is formed from a polyether block amide, for example, PEBAX® 7030, which may include a titanium oxide filler. 
         [0020]      FIG. 5  is another plan view of delivery system assembly  200 , according to some embodiments, wherein a distal portion of outer tube  230  is shown deflected, per arrow D. Deflection of the distal portion of outer tube  230  may be useful in maneuvering delivery system assembly  200  to the target implant site, for example, into the RV through the tricuspid valve, from the RA, as shown in  FIG. 1B . With reference back to  FIG. 2B , according to some preferred embodiments, inner member  220  includes a pull wire  225 , which extends along a length of inner member  220 , preferably within a lumen (not shown) of inner member  220 , to affect the deflection shown in  FIG. 5 . According to the illustrated embodiment, a proximal end  51  of pull wire  225  is coupled to a second control member  212  of handle  210  ( FIG. 2A ), and a distal end  52  of pull wire  225  is anchored in proximity to flared distal end  222  of inner member  220 . A flexibility of a shaft that forms inner member  220 , as well as that which forms outer tube  230 , is preferably graduated from a relatively stiff proximal segment to a relatively flexible distal segment to facilitate the deflection illustrated in  FIG. 5 . With reference to  FIG. 3A , when second control member  212  is moved, per arrow P, in a proximal direction, distal end  52  of pull wire  225  is pulled, per arrow P, to deflect the relatively flexible distal segment(s) of inner member, just proximal to flared distal end  222 , and, thereby, cause deflection of the relatively flexible distal segment(s) of outer tube  230 , for example, like that shown in  FIG. 5 . According to the illustrated embodiment, a shoulder  233  is formed at the transition from a lumen LD of the enlarged distal-most portion, which contains device  100 , to a smaller diameter lumen LP that extends proximally within tube  230 , such that flared distal end  222  may seat against shoulder  233  to enhance the deflection, in some instances. 
         [0021]    The construction of shafts for inner member  220  and outer tube  230  may be any suitable type known in the art to achieve suitable graduated flexibility for the necessary maneuverability thereof, which includes pushability and torque transfer, as well as the above described deflection. According to an exemplary embodiment, the shaft of inner member  220  extends over a length of approximately 118 cm, from proximal end  221  to the site where distal end  52  of pull wire  225  is anchored, just proximal to flared distal end  222 , and includes a stainless steel braid (0.0012″×0.003″×70 PPI) surrounding a PEBAX® 7033 liner, a proximal layer of Trogamid® polyamide overlaying the braid, along a length of approximately 108 cm, and a distal layer of Vestamid® polyamide overlaying the braid, along a length of approximately 10 cm; a proximal segment of the shaft is further overlaid with AESNO® Nylon 12 along a length of approximately 100 cm; an intermediary segment of the shaft, which extends distally from the proximal segment over a length of approximately 11 cm, is further overlaid with PEBAX® 55; and a distal segment of the shaft, which extends distally from the intermediary segment to the site where pull wire  225  is anchored, over a length of approximately 7 cm, is further overlaid with PEBAX® 3533. Furthermore, according to the exemplary embodiment, outer tube  230  includes a braid reinforced liner, for example, PEBAX® 6333 with a stainless steel braid (i.e. 0.0018″×0.008″×45 PPI) extending from proximal end  231  to just proximal to the above-described enlarged distal-most portion of outer tube  230 ; a proximal segment of the shaft is overlaid with PEBAX® 7033 and extends over a length of approximately 92 cm (a proximal portion of which length is always contained within handle  210 ); an intermediary segment of the shaft is overlaid with PEBAX®4033 and extends distally from the proximal segment over a length of approximately 10 cm; and a distal segment of the shaft is overlaid with PEBAX® 3533 and extends distally from the intermediary segment, over a length of approximately 3 cm, to just proximal to the distal-most portion. Outer and inner diameters of outer tube  230 , along the above-described segments, may be approximately 0.187 inch (˜4.75 mm) and approximately 0.154 inch (˜3.91 mm), respectively. 
         [0022]    The shaft of inner member  220 , according to some preferred embodiments, has an outer diameter of approximately 0.112 inch (˜2.85 mm) and includes a pair of lumens; a first of the lumens has a diameter of approximately 0.015 inch (˜0.38 mm), and a second of the lumens has a diameter of approximately 0.077 inch (˜1.96 mm). The first lumen accommodates pull wire  225 , while the second lumen may accommodate a tether, which is initially attached to device  100  during the implant procedure. As system  200  is advanced and maneuvered into position in proximity to the target implant site, the tether may be means by which device  100  is retained within the distal-most portion of outer tube  230  with proximal end  121  abutting flared distal end  222  of inner member  220 ; alternately, flared distal end  222  may be configured to retain device  100  until outer tube  230  is retracted for the deployment of device  100 . (After device  100  is deployed, the tether is useful for pulling device  100  back into distal end  232  of outer tube  230 , if device  100  needs to be repositioned at an alternative site, otherwise the tether is detached from device  100  and pulled proximally within the second lumen of inner member  220 .) 
         [0023]    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.