Abstract:
Apparatus for sealing a vascular wall penetration disposed at the end of the tissue tract comprises a shaft, an occlusion element, a hemostatic implant, and a protective sleeve. The apparatus is deployed through the tissue tract with the occlusion element temporarily occluding the vascular wall penetration and inhibiting backbleeding therethrough. The hemostatic implant, which will typically be a biodegradable polymer such as collagen carrying an anti-proliferative agent or coagulation promoter, will then be deployed from the sealing apparatus and left in place to enhance closure of the vascular wall penetration with minimum scarring. The implant may be radiopaque to allow observation before release.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of provisional Application No. 61/077,104 (Attorney Docket No. 021872-002600US), filed on Jun. 30, 2008, the full disclosure of which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates generally to medical devices and methods. More particularly, the present invention relates to apparatus and protocols for closing arteriotomies and other vascular wall penetrations. 
         [0004]    Angiography, angioplasty, atherectomy, and a number of other vascular and cardiovascular procedures are performed intravascularly and require percutaneous access into the patient&#39;s vasculature, most often into the arterial vasculature. The most common technique for achieving percutaneous access is called the Seldinger technique, where access to an artery, typically the femoral artery in the groin, is first established using a needle to form a “tract,” i.e., a passage through the tissue overlying the blood vessel. The needle tract is then dilated, and an access sheath is placed into the dilated tract and through a penetration in the vascular wall, such as an arteriotomy to allow the introduction of guidewires, interventional catheters, catheter exchange, and the like to perform the desired procedure. 
         [0005]    Once the desired procedure is completed, the access sheath must be removed and the arteriotomy or other vascular wall penetration closed. For many years, such closure was achieved by applying manual pressure onto the patient&#39;s skin over the site of the vascular wall penetration. Patients, however, have often been heparinized to limit the risk of thrombosis during the procedure, and clotting of the vascular wall penetration can often take an extended period, particularly when the penetration is relatively large for performing procedures needing larger diameter catheters. For these reasons, improved methods for closing and sealing vascular wall penetrations have been sought. 
         [0006]    In the last decade, a variety of new procedures and devices have been introduced to more effectively seal the arteriotomies and other vascular wall penetrations associated with percutaneous intravascular access. Some of the new protocols rely on suturing, others rely on clipping, plug placement, energy-based closure, and the like. One problem with many of the new procedures, however, is that they leave material behind, and/or induce scar formation at the access site. Both the leaving of materials and the formation of scar tissue can be problematic, particularly if the patient requires subsequent access to the same vascular site for performance of another vascular or cardiovascular procedure. 
         [0007]    For these reasons, it would be advantageous to provide protocols and apparatus which would leave no material behind and which would further limit the likelihood of forming scar tissue after the procedure is complete. One device that can meet these objectives in many instances is the Boomerang Catalyst™ system available from Cardiva Medical, Inc., assignee of the present application. The Boomerang system includes an expansible element at its tip for providing temporary hemostasis when placed in the blood vessel adjacent to the vascular wall penetration. The catheter further includes a catalytic material on its shaft which helps induce hemostasis and clotting within the tissue tract immediately above the vessel wall penetration. The construction and use of this system is described in copending application Ser. No. 11/302,951 (Attorney Docket No. 021872-002200US); Ser. No. 11/772,718 (Attorney Docket No. 021872-002210US); and Ser. No. 11/614,276 (Attorney Docket No. 021872-002400US), the full disclosures of which are incorporated herein by reference. 
         [0008]    Despite the success of the Boomerang systems, there may still be some instances where hemostasis is not achieved as rapidly. For this reason, it would be desirable to provide further improved systems and protocols for closing and sealing arteriotomies and other vascular wall penetrations, where the closure may be achieved with rapid hemostasis, with a minimum risk of scar formation, and without leaving any materials or implants permanently behind in the vessel or the tissue tract. At least some of these objectives will be met by the inventions described below. 
         [0009]    2. Description of the Background Art 
         [0010]    U.S. Pat. No. 7,335,219 describes a device for delivering a plug of hemostatic material to a location just above a blood vessel wall penetration. The hemostatic material is encapsulated in a dissolvable structure and a non-expandable control tip assembly helps advance the device through the tissue tract and may also provide hemostasis and bleedback. US2007/0123817 describes an apparatus for sealing a vascular wall penetration which releases a porous lyophilized hydrogel into the tissue tract above the puncture. Other apparatus for closing blood vessel wall punctures are described in U.S. Pat. Nos. 4,744,364; 5,061,271; 5,728,133; and 7,361,183 and U.S. Published Patent Application Nos. 2003/0125766; 2004/0267308; 2006/0088570; 2007/0196421; and 2007/0299043. The incorporation of anti-proliferative materials in hemostatic materials for blood vessel closure and other purposes is described in U.S. Pat. Nos. 7,025,776 and 7,232,454; 6,554,851; and U.S. Published Patent Application Nos. 2005/0004158; 2005/0038472; 2007/0060895/ 2007/0032804; and 2008/0039362. 
       BRIEF SUMMARY OF THE INVENTION 
       [0011]    The present invention provides apparatus and methods for sealing a blood vessel wall penetration with little or no material being permanently left behind and with a reduced likelihood of scar tissue formation. The invention relies on placing a hemostatic implant in the tissue tract at a location over the vascular wall penetration while the penetration is temporarily closed with an expansible occlusion element present in the blood vessel lumen. The hemostatic implant is preferably biodegradable, typically over a period of less than one year, preferably over a period of less than six months, more preferably less than three months, and may carry an anti-proliferative agent to reduce scar formation. Additionally or alternatively, the implant may carry a coagulation promoter to accelerate hemostasis and/or radiopaque material to enhance visualization. The use of the hemostatic implant together with the temporary hemostasis provided by the occlusion element increases the likelihood that even relatively large vascular penetrations can be successfully closed and usually reduces the time needed to achieve such closure. 
         [0012]    Apparatus according to the present invention for sealing a blood vessel wall penetration disposed at an end of a tissue tract comprise a shaft, an occlusion element, a hemostatic implant, and a protective sleeve. The shaft has a proximal and distal end and is adapted to be introduced through the tissue tract so that the shaft distal end can be positioned within the blood vessel lumen. Usually, the shaft will be adapted so that it can be introduced through the vascular access sheath which is in place after performance of the interventional procedure. 
         [0013]    The occlusion element is disposed near the distal end of the shaft and is configured so that it may be shifted between a radially contracted configuration which facilitates introduction through the tissue tract and a radially expanded configuration for deployment within the blood vessel to occlude the penetration and provide temporary hemostasis. The hemostatic element could be a balloon or other inflatable structure, but will more usually be an expansible braid, coil, or other element which may be radially expanded by axial foreshortening. Typically, the shaft comprises an outer tube and an inner rod where a distal end of the occlusion element is attached to a distal end of the rod and a proximal end of the occlusion element is attached to a distal end of the outer tube. Thus, the occlusion element can be expanded and contracted by retracting and advancing the rod relative to the tube, respectively. The preferred occlusion element comprises a braided mesh covered with an elastic membrane. As described thus far, the shaft and occlusion element may be similar or identical to those described in the earlier referenced commonly owned patent applications. 
         [0014]    The hemostatic implant of the present invention is disposed over an exterior surface of the shaft proximal to the occlusion element. The protective sleeve is retractably disposed over the hemostatic implant to protect it while the shaft is being introduced to the tissue tract. The hemostatic implant will typically comprise a body or wrapped sheet which partially or fully circumscribes the shaft, but other configurations could also be utilized. In a first embodiment, the hemostatic implant comprises a cylindrical body which is coaxially mounted about the shaft of the delivery device. Such fully circumscribing implants, however, can have difficulty being released from the shaft after they are exposed and hydrated. Thus, it will often be preferable to provide hemostatic implant configurations where the body partially circumscribes the shaft or is disposed in parallel to the shaft. When the implant is not disposed about the shaft, release upon rehydration will be greatly simplified as the rehydrated implant will lie adjacent to the shaft, allowing the shaft and the collapsed occlusion element to be drawn proximally past the rehydrated hemostatic implant with minimum interference. The hemostatic implant typically comprises a swellable, biodegradable polymer which swells upon hydration. Hydration is prevented when the polymer is introduced by the protective sleeve. The polymer hydrates and swells when the sleeve is retracted within the tissue tract, exposing the polymer to the body fluids. Suitable polymers include biodegradable hydrogels such as polyethylene glycols, collagens, gelatins, and the like. 
         [0015]    An anti-proliferative agent will usually be distributed within or otherwise carried by the material of the hemostatic implant. As most anti-proliferative agents, such as sirolimus, paclitaxel, and the like, are hydrophobic, it will usually be desirable to incorporate the anti-proliferative agents in a carrier, such as a biodegradable polymer, such a polylactic acid (PLA), poly(lactide-co-glycolide), and the like. The anti-proliferative agents may be incorporated into pores of polymeric beads or other structures which are dispersed or distributed within the biodegradable hydrogel or other swellable polymer. In certain embodiments, the anti-proliferative agents may be incorporated into nanoparticles, typically having dimensions in the range from 10 nm to 100 μm. 
         [0016]    Agents useful as coagulation promoters, such as thrombin, tissue factors, components of the clotting cascade, and the like may also be incorporated into the body of the hemostatic implant. In some instances, it may be desirable to incorporate such coagulation promoters into particulate or other carriers as described above with regard to the anti-proliferative agents. 
         [0017]    In addition to the anti-proliferative agents and the coagulation promoters, the hemostatic implants of the present invention may further incorporate radiopaque materials in or on at least a portion of the implant body. For example, a radiopaque material, such as barium, may be incorporated into the polymer, either by dispersion or chemical bonding. Alternatively, radiopaque rings, markers, and other elements, may be attached on or to the hemostatic implant, for example at each end of the implant to facilitate visualization of the implant as it is being implanted. Additionally or alternatively, radiopaque markers may be provided on the tube or shaft which carries the hemostatic implant so that the marker(s) align with a portion of the implant, typically either or both ends of the implant, prior to deployment. 
         [0018]    In a preferred aspect of the present invention, the protective sleeve is held in place by a latch mechanism while it is being introduced. A separate key element is provided to release the latch mechanism and permit retraction of the sleeve after the device has been properly placed through the tissue tract and into the target blood vessel. The latch will be disposed on the shaft and will engage the protective sleeve to immobilize the sleeve during introduction. The key, which is usually slidably disposed on the shaft proximal of the latch, is able to shift the latch between a locking configuration where the sleeve is immobilized and an open configuration which allows the sleeve to be proximally retracted. Usually, the latch is spring-loaded to deflect radially outwardly from the shaft in a manner which engages the sleeve. The key is then adapted to radially depress the latch to release the sleeve. In a preferred embodiment, the latch and key mechanism will extend over a distal portion of the shaft having a length sufficient to allow manual access to the key latch even when the shaft is placed in the tissue tract. 
         [0019]    In a further preferred aspect of the present invention, a backstop structure is provided on the shaft to engage the hemostatic implant to immobilize the implant while the sleeve is being proximally refracted. The backstop usually comprises a tube disposed on or coaxially over the shaft and having a distal end which engages a proximal end of the hemostatic implant. The backstop engages the hemostatic implant to prevent accidental dislodgement while the occlusion element is being proximally retracted through the implant. The backstop may include a space or receptacle for receiving the retracted occlusion element, allowing the backstop to be held in place until the occlusion element has been fully retracted through the hemostatic implant. 
         [0020]    The protective sleeve of the present invention may comprise an outer sleeve and a separately retractable inner release sheath. The outer sleeve and inner release sheath are usually mounted coaxially so that the outer sleeve may be retracted over the inner release sheath while the inner release sheath remains stationary over the implant and acts as a friction barrier between the outer sleeve and implant. Without the inner release sheath, the protective sleeve, which applies the compressive and constrictive forces to the hemostatic implant, could stick to the hemostatic implant and make refraction of the protective sleeve and deployment of the implant difficult. The inner release sheath is preferably axially split so that, once the outer sleeve is retracted, the inner release sheath opens to release the implant and facilitate retraction of the release sheath. In preferred embodiments, the outer sleeve can engage the inner release sheath after the outer sleeve has been partly retracted. During the remainder of the outer sleeve retraction, the outer sleeve will then couple to and retract the inner release sheath to fully release the hemostatic implant. In addition to the use of the inner release sheath, the distal end of the protective sleeve may be sealed with a biodegradable substance, such as a glycerin gel, which can inhibit premature hydration of the hemostatic implant prior to release. 
         [0021]    In a further preferred aspect of the present invention, the key of the latch mechanism can include a coupling element which attaches to the protective sleeve as the key is advanced and the latch is released. After the key couples to the protective sleeve, the key can be used to retract the protective sleeve. That is, rather than having to separately retract both the key and the protective sleeve, only the key needs to be retracted. 
         [0022]    Methods according to the present invention for sealing a blood vessel penetration disposed at the end of a tissue tract comprise providing an apparatus including a shaft, an occlusion element, and a hemostatic implant disposed on an exterior surface of the shaft. The shaft is introduced through the tissue tract to position the occlusion element in the lumen of the blood vessel and the hemostatic implant within the tissue tract. The hemostatic implant is covered by a protective sleeve while the shaft is being introduced through the tissue tract, and the occlusion element is deployed to temporarily inhibit blood flow from the blood vessel into the tissue tract. The protective sleeve is then retracted to expose the hemostatic implant, where the implant typically absorbs fluid and expands to provide the desired seal within the tissue tract. After the hemostatic implant has expanded sufficiently, the occlusion element will be collapsed, and the shaft and collapsed occlusion element withdrawn leaving the hemostatic implant in the tissue tract. As described above, it will usually be preferred to position the hemostatic implant laterally or to the side of the shaft which carries the occlusion element. By thus positioning the occlusion element to bypass the hydrated hemostatic implant, withdrawal of the collapsed occlusion element past the hydrated hemostatic implant can be greatly facilitated. Preferably, the material of the hemostatic implant will degrade over time, preferably over a period of less than one year, more preferably over a period of less than six months, usually less than three months, leaving no material behind at the vascular access point. 
         [0023]    In a preferred aspect of the methods of the present invention, the protective sleeve is latched to the shaft while the shaft is introduced. By “latched” is meant that the sleeve will be fixed or immobilized to the shaft by some mechanical link, where the link may be selectively disconnected or “unlatched” when it is desired to retract the sleeve and expose the hemostatic implant. Thus, the methods of the present invention will preferably further comprise unlatching the sleeve before retracting the sleeve. In a specific embodiment, the unlatching comprises distally advancing a key over the latch to effect the desired unlatching. As described above in connection with the apparatus of the present invention, an exemplary latch and key comprises a spring-like element which is secured over an exterior portion of the shaft. The spring-like element typically projects radially outward from the shaft when unconstrained. In this way, the spring-like latch element can engage the protective sleeve to prevent proximal refraction of the sleeve. The latch can be released by advancing a cylindrical or other key element distally over the shaft to depress the spring-like lock element. 
         [0024]    In a further preferred aspect of the method of the present invention, a proximal portion of the sleeve will be configured to lie proximal to, i.e., outside of, the tissue tract when the occlusion element is deployed in the blood vessel lumen. Usually, the key element will lie further proximal of the sleeve, permitting the user to manually deploy the key to unlock the latch and to further manually retract the protective sleeve by manually clasping an exposed portion of the sleeve and pulling it proximally from the tissue tract. Typically, the sleeve will have a length in the range from 2 cm to 30 cm, more typically from 5 cm to 15 cm. 
         [0025]    In a still further preferred aspect of the method, the hemostatic implant will be constrained to prevent it from being displaced proximally while the shaft is being introduced through the tissue tract. In particular, the backstop or other element may be fixed to the shaft in a location selected to engage the hemostatic implant or an extension thereof to prevent the implant from being displaced proximally, either as the shaft is being introduced or more likely as the protective sleeve is being proximally retracted over the implant. Usually, the backstop or other element will be slidably mounted over the shaft so that it may be held in place as the occlusion element is retracted past the hemostatic implant. 
         [0026]    In a specific aspect of the method of the present invention, radiopaque markers on or within the shaft or hemostatic implant are used to verify the location of implant prior to release. Inclusion of radiopaque markers on the delivery shaft is particularly useful when no radiopaque material is incorporated within the hemostatic implant. Preferably, there will be at least two distinct radiopaque bands, with one at each end of the implant. By observing the orientation of the two markers, the physician can determine whether the implant is properly aligned adjacent to the vascular penetration or has inadvertently advanced into a lumen of the blood vessel prior to deployment. In particular, by measuring or visually assessing the apparent distance between the bands when the device is being fluoroscopically imaged from an anterior aspect, the apparent distance between the bands will be longer if the hemostatic implant is within the blood vessel lumen than if it is within the tissue tract immediately above the blood vessel wall penetration. Such apparent differences in the positions of the two radiopaque marker bands results from the foreshortening of the vertical angle at the entry through the wall penetration into the blood vessel lumen. For example, if the tissue tract is disposed at a 45° angle with respect to the horizontal orientation of the blood vessel lumen, in an anterior view, the marker bands will appear to be approximately 30% closer to each other than they would in the horizontal view when they are present in the blood vessel lumen. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]      FIG. 1  illustrates an exemplary sealing apparatus constructed in accordance with the principles of the present invention, shown in section. 
           [0028]      FIG. 1A  is a detailed view of a distal portion of the sealing apparatus of  FIG. 1 , shown in partial section. 
           [0029]      FIG. 2  is a cross-sectional view of the sealing apparatus of  FIG. 1 , shown with an expanded occlusion element. 
           [0030]      FIGS. 3-7  illustrate the further steps of deployment of the hemostatic implant from the apparatus of  FIGS. 1 and 2 . 
           [0031]      FIGS. 8A-8I  illustrate placement and deployment of the hemostatic implant using the apparatus of  FIGS. 1 and 2  through a vascular sheath placed in a blood vessel. 
           [0032]      FIGS. 9A-9C  illustrate a sealing apparatus in accordance with the present invention having a protective sleeve including an outer sleeve and an inner release sheath. 
           [0033]      FIGS. 10A-10C  illustrate a sealing apparatus in accordance with the present invention having a key latch mechanism which engages the protective sleeve and may be used to proximally withdraw the sleeve to deploy the hemostatic implant. 
           [0034]      FIGS. 11A and 11B  illustrate a hemostatic implant which is coaxially disposed about the shaft of the deployment apparatus of the present invention. 
           [0035]      FIGS. 12A and 12B  illustrate the hemostatic implant which is laterally disposed relative to the shaft of the deployment mechanism. 
           [0036]      FIGS. 13A and 13B  illustrate how aligned radiopaque markers may be utilized to determine that the hemostatic implant is properly located prior to deployment. 
           [0037]      FIGS. 14A and 14B  illustrate how such radiopaque markers would appear when the hemostatic implant is improperly positioned prior to deployment. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0038]    Referring to  FIGS. 1 and 1A , an exemplary sealing apparatus  10  constructed in accordance with the principles of the present invention comprises a shaft assembly  70  including an outer tube  71  and an inner rod  76 . An expansible occlusion element  90  is mounted at a distal end (to the right in  FIGS. 1 and 1A ) of the shaft assembly  70  and includes a radially expansible mesh  74  covered by an elastomeric membrane  96 . A handle assembly  78  is attached to a proximal end of the shaft assembly  70  and is operatively attached to both the outer tube  71  and inner rod  76  so that the inner rod can be axially advanced and retracted relative to the outer tube. The inner rod  76  and outer tube  71  are coupled together at the distal tip of the sealing apparatus  10  by a plug  77  and a proximal anchor  75 , respectively. The occlusion element  90  is held between the plug  77  and the proximal anchor  75  so that axial retraction of the rod in the proximal direction (to the left as shown in  FIGS. 1 and 1A ) foreshortens the occlusion element  90 , causing the occlusion element to expand radially, as shown for example in  FIG. 2 . 
         [0039]    Axial advancement and retraction of the rod  76  relative to the outer tube  71  is effected using the handle assembly  78 . The handle assembly  78  includes a cylindrical body  103  attached to the proximal end of the outer tube  71  by a bushing  104  so that the body  103  will remain fixed relative to the outer tube as the inner rod  76  is retracted and advanced. The inner rod is retracted and advanced by a slide assembly  101  which includes a short tube  110  fixedly attached to an endcap  111  and a slide cylinder  109 . The inner rod  76  is secured by tube element  107  which carries locking element  106  and bearing elements  108  and  109 . Bearing element  109  is attached to proximal grip  101  and the assembly of the grip  101  and tube element  107  can slide freely within the interior of the cylindrical body  103  so that the rod  76  may be proximally retracted relative to the body  103  and outer tube  71 , as shown in  FIG. 2 . Once the expansible occlusion element  90  has been radially expanded, the rod  76  will remain retracted and is held in place by locking element  106  which is pulled over a detent  105 , again as shown in  FIG. 2 . An alignment bushing  108  is provided in the interior of the cylindrical body  103  to maintain alignment of the slide assembly  101  relative to the cylindrical body. 
         [0040]    The sealing apparatus of the present invention may optionally include a tensioning mechanism  80  which includes a coil spring  86 , a gripping element  85 , and a coupling element  87 . The tensioning mechanism  80  may be selectively positioned along the length of shaft assembly  70 , and will provide a tension determined by the constant of coil spring  86  to hold the expanded occlusion element  74  against the vascular penetration, as described in more detail in copending, commonly-owned application Ser. No. 10/974,008, (Attorney Docket No. 021872-002010US), the full disclosure of which is incorporated herein by reference. As described thus far, the construction and use of the sealing apparatus including shaft assembly  70 , handle assembly  78 , tensioning mechanism  80 , and expansible occlusion element  90  are generally the same as illustrated in copending application Ser. No. 10/974,008. The present invention is directed at modifications and improvements to the earlier device for delivering a hemostatic implant into the tissue tract generally above the vascular wall penetration, as will be described in more detail below. 
         [0041]    As best seen in  FIG. 1A , hemostatic implant  121 , which will typically be a biodegradable polymer as described in more detail above, is carried coaxially or in parallel over the outer tube  71  near the distal end thereof proximal to the expansible occlusion element  90 . While the hemostatic implant  121  is shown to be positioned coaxially over outer tube  71  in  FIG. 1A , it will often be desirable to modify or reposition the implant in order to facilitate release from the sealing apparatus after the implant has been deployed. More simply, the hemostatic implant could be axially split to allow it to partially open after it is rehydrated and facilitate passage of the collapsed occlusion element  74  as the sealing apparatus is being withdrawn. Alternatively, the hemostatic implant may be reconfigured and carried laterally (i.e., to one side of) with respect to the shaft of the sealing apparatus, as described in more detail hereinafter with respect to  FIGS. 9A and 9C . The hemostatic implant  121  could alternatively be carried on the inner surface of a protective sleeve  123  which is slidably carried over the outer tube  71 . The protective sleeve  123  slides over a backstop  127  which is slidably mounted over the outer tube  71  and which is prevented from moving proximally by stop member  125  which is fixed to the outer surface of the outer tube. Backstop  127  has a distal end  128  which engages a proximal end of the hemostatic implant  121 . Thus, by proximally retracting the protective sleeve  123 , the hemostatic implant  121  can be exposed to the tissue tract and released from the sealing apparatus. 
         [0042]    Accidental axial retraction of the protective sleeve  123  is prevented by a latch mechanism including a latch element  120  and a key  126  ( FIGS. 1 and 2 ). The latch element  120  is typically a spring-loaded component, for example a conical spring having a narrow diameter end attached to the outer tube  71  and a flared or larger diameter end  129  which engages a stop ring  124  formed on the inner surface of the protective sleeve  123 . So long as the flared end  129  of the latch element  120  remains in its flared or open configuration, as illustrated in  FIG. 1A , accidental proximal retraction of the sleeve is prevented. It is further noted that the stop ring  124  engages stop member  125  of the backstop  127  preventing accidental distal movement of the protective sleeve  123 . Thus, when the sealing apparatus  10  is introduced to a tissue tract, as described in more detail below, movement of the protective sleeve  123  in either the distal or proximal direction is inhibited. 
         [0043]    To allow selective proximal refraction of the protective sleeve  123 , the key  126  ( FIGS. 1 and 2 ) may be axially advanced to engage the latching element  120 , as illustrated in  FIG. 3 . The key  126  fits inside of the protective sleeve  123  and depresses or radially contracts the latch element  120  so that it fits within the interior circumference of the stop ring  124 , thus allowing proximal retraction of the protective sleeve  123 , as shown in  FIG. 4 . 
         [0044]    Once the key  126  has engaged and constrained the latch element  120 , as shown in  FIG. 3 , the protective sleeve  123  may be proximally withdrawn past the hemostatic implant  121  and the backstop  127 , as shown in  FIG. 4 . Thus, the hemostatic implant  121  will be released from constraint and exposed to the environment in the tissue tract. The environment in the tissue tract will include blood and other body fluids which can hydrate the hemostatic implant  121 , causing swelling as shown in  FIG. 4 . The swelling will continue, as shown in  FIG. 5 , and the radially expanded occlusion element  90  can be collapsed using the handle assembly, as shown in  FIG. 5 . The collapsed occlusion element  90  can then be proximally withdrawn into and through the backstop assembly  127 , as shown in  FIG. 6  (where an annular space may be provided to accommodate the occlusion element). When the occlusion element has been fully withdrawn within the backstop  127 , the hemostatic implant is completely released, as shown in  FIG. 6 , and the remaining portions of the sealing apparatus can be pulled away from the hemostatic implant, as shown in  FIG. 7 . 
         [0045]    Referring now to  FIGS. 8A-8I , deployment and use of the sealing apparatus  10  of the present invention through an introducer sheath  40  will be described in more detail. Introducer sheath  40  will typically be in place within a blood vessel lumen  41  passing from the skin surface  46  through tissue  45  in a tissue tract. A vascular wall penetration  42  will thus be present in the vascular wall  43 , all as shown in  FIG. 8A . The sealing apparatus  10  is then introduced through the access sheath  40  so that the expansible occlusion element  90  passes out through the distal end of the sheath, as shown in  FIG. 8B . Handle assembly  78  will remain outside of the sheath and accessible to the user so that the slide assembly  101  may be pulled relative to the cylindrical body  103  to radially expand the occlusion element  90 , as shown in  FIG. 8C . The vascular access sheath  40  may then be withdrawn over the exterior of the sealing apparatus  10  while the sealing apparatus is simultaneously withdrawn to seat the expanded occlusion element  90  against the vascular penetration  42 , as shown in  FIG. 8D . 
         [0046]    At that point, the protective sleeve  123  and key  126  become exposed and available to the user for manipulation. The key may then be distally advanced over the outer tube  71  so that the key engages and depresses the latch  120  ( FIG. 1A ) as illustrated in  FIG. 8E . The key  126  and protective sleeve  123  may then be manually pulled in a proximal direction over the outer tube  71  to release the hemostatic implant  121 , as shown in  FIG. 8F . The expandable element  90  may then be collapsed, as shown in  FIG. 8G , and the collapsed element withdrawn into the distal end of the sealing apparatus, as shown in  FIG. 8H . The entire sealing apparatus  10 , except for the hemostatic implant  121 , may then be withdrawn from the tissue tract, leaving the hemostatic implant  121  in place over the now closed vascular wall penetration, as shown in  FIG. 8I . The hemostatic implant, which may optionally carry the anti-proliferative, coagulation promoting, and/or radiopaque substances described above, will remain in place inhibiting bleeding through the upper portions of the tissue tract and allowing the vascular wall penetration to heal. Over time, the hemostatic implant  121  will preferably biodegrade, leaving a healed tissue tract and vascular wall penetration which are usually suitable for re-entry at a subsequent time. 
         [0047]    Referring now to  FIGS. 9A-9C , a protective sleeve  123 ′ comprises an outer sleeve  150  and an inner release sheath  152 . The outer sleeve  150  and inner release sheath  152  are separately retractable so that the outer sleeve may first be retracted relative to the hemostatic implant  121  ( FIG. 9C ) while the inner release sheath initially remains over the implant. The release sheath  152  will thus provide an anti-friction interface so that the outer sleeve  150  slides over the implant  121  with reduced sticking The inner release sheath  152  is preferably formed from a relatively lubricious or slippery material and will preferably include an axial opening or slit  158  which permits the distal portion thereof to partially open after the outer sleeve  150  has been retracted, as shown in  FIG. 9B . Once the outer sleeve  150  has been retracted to relieve constraint over the hemostatic implant, the inner sleeve may then be retracted to completely release the hemostatic implant, as shown in  FIG. 9C . Conveniently, the outer sleeve  150  may be coupled to the inner release sheath  152  so that proximal retraction of the outer sleeve will automatically retract the inner release sheath at the proper point in travel. For example, a cavity or channel  154  may be formed in an inner surface of the outer sleeve  150  and a ring or other engaging element  156  may be formed on the outer surface of the inner release sheath  152 . Initially, the ring  156  will be positioned at the distal end of the cavity or channel  154 , as shown in  FIG. 9A . After the outer sleeve  150  has been retracted so that it no longer lies over the implant  121 , the ring may then engage a distal end of the cavity or channel  154 , as shown in  FIG. 9B , and engage the ring  156 , allowing the outer sleeve to then pull the inner sleeve proximally, as shown in  FIG. 9C , to fully release the hemostatic implant  121 . 
         [0048]    Referring now to  FIGS. 10A-10C , it is also possible to selectively couple the key  126 ′ to a protective sleeve  123 ′. The key  126 ′ has a coupling element, such as plurality of proximally disposed barbs  160  at its distal end. The key  126 ′ may be advanced into the protective sleeve  123 ′ where a distal end  162  of the key  126 ′ engages latching element  120 ′ on the outer tube  71 ′. Latching mechanism  120 ′ may conveniently comprise a plurality of barbs so that advancement of the key  123 ′ radially closes the barbs along the protective sleeve  123 ′ to be proximally retracted relative to the tube  71 ′. Once the key  126 ′ is fully distally advanced, as shown in  FIG. 10B , the proximally disposed barbs  160  will engage an inner lip  164  at the proximal end of the protective sleeve  123 ′. Thus, as the key  126 ′ is proximally retracted, as shown in  FIG. 10C , the key will pull the protective sleeve  123 ′ in a proximal direction, thus exposing the implant  121 . 
         [0049]    A further aspect of the present invention is illustrated in  FIGS. 10A and 10B . Radiopaque marker bands  170  and  172  may be provided at the proximal and distal ends of the implant  121 , respectively. Usually, these bands will be disposed on the outer tube  71 ′, but they could also be disposed on or incorporated within the hemostatic implant  121 . In either case, they are useful to evaluate positioning of the hemostatic implant prior to deployment, as described in more detail below in  FIGS. 13A ,  13 B,  14 A, and  14 B. 
         [0050]    Referring now to  FIGS. 11A and 11B , the hemostatic implant  121  may be disposed coaxially over the outer tube  71  and in a rod  76 . By then proximally retracting the protective sleeve  123 , the implant  121  is released and can hydrate as shown in  FIG. 11B . As described previously, however, it will still be necessary to withdraw the outer tube  71  as well as the collapsed occlusion element  90  past the hemostatic implant  121 . When the hemostatic implant  121  fully circumscribes the outer tube  71 , however, both the tube  71  and the collapsed occlusion element  90  can tend to dislodge the implant within the tissue tract. 
         [0051]    Therefore, in some instances, it will be desirable to modify the geometry of the implant to facilitate withdrawal of the outer tube and the collapsed occlusion element. For example, as shown in  FIGS. 12A and 12B , hemostatic implant  121 ′ can be formed with a crescent-shaped cross-section so that it does not fully circumscribe the outer tube  71  which carries it. By laterally displacing the outer tube  71  an inner rod  76  within the protective sleeve  123 , as shown in  FIG. 12A , the volume of the hemostatic implant  121  will be generally the same as that shown in  FIG. 11A . When the protective sleeve  123  is withdrawn, however, as shown in  FIG. 12B , the hemostatic implant  121  will hydrate and expand laterally on one side of the outer tube  71 , as shown in  FIG. 12B . By disposing the outer tube  71  and collapsed occlusive element  90  to one side of the implant, it is much easier to withdraw the apparatus and collapsed occlusion member past the implant without dislodging the implant within the tissue track. 
         [0052]    Referring now to  FIGS. 13A and 13B , the radiopaque markers  170  and  172  can be used to determine whether the hemostatic implant  121  is oriented properly prior to deployment. For simplicity, the protective sleeve and other components of the deployment system are not shown in  FIGS. 13A and 13B  (or in  14 A and  14 B as described below). The radiopaque markers  170  and  172  may be formed as part of the deployment instrument, for example being placed on outer tube  71 , and/or may be formed as part of the hemostatic implant  121 . In either case, when the deployment apparatus is properly oriented as shown in  FIG. 13A , the radiopaque markers  170  and  172  will appear to be stacked generally vertically when viewed in an anterior view, as shown in  FIG. 13B . In contrast, if the apparatus has been improperly deployed so that the hemostatic implant has been advanced into the vessel lumen past the tissue tract TT as shown in  FIG. 14A , then the radiopaque markers  170  and  172  will be spaced apart in the anterior view as shown in  FIG. 14B . As these views will be readily distinguishable by the physician using conventional fluoroscopy, the radiopaque markers provide a convenient and reliable indicator of when it is acceptable to deploy the hemostatic implant. 
         [0053]    While the above is a complete description of the preferred embodiments of the invention, various alternatives, modifications, and equivalents may be used. Therefore, the above description should not be taken as limiting the scope of the invention which is defined by the appended claims.