Patent Publication Number: US-6712791-B2

Title: Splittable medical valve

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority of provisional application Ser. No. 60/173,758, filed Dec. 30, 1999 and Ser. No. 60/232,519, filed Sep. 14, 2000. 
    
    
     TECHNICAL FIELD 
     This invention relates to medical devices, in particular to hemostatic valves for intravascular devices. 
     BACKGROUND OF THE INVENTION 
     Percutaneous placement of intravascular catheters, pacemaker leads, etc. involves blood loss, that while easily controllable, especially during venous access, can become significant during long procedures. For example, procedures such as placement of leads in the coronary sinus for biventricular pacing, can last 4 hours, during which time the blood loss of up to 500-600 cc can represent a risk to the patient. Additionally, the open conduit into the body can become a source of infection to the patient. To help reduce these potential risks, self-sealing hemostatic valves have been developed for use with introducer sheaths. These valves provide a seal against flashback of blood from the proximal end of the sheath, including when a second device is being manipulated within the introducer. 
     Medical devices with large proximal fittings, such as pacemaker leads and PICC lines, cannot be readily used through standard hemostasis valves and introducers because of the need to remove the introducer while leaving the other device in place. To address this need, splittable sheaths and hemostasis valves were developed so that the introducer and valve can be removed while the inner device remains in the patient. Combinational devices exist, such as the SAFE-SHEATH™ Splittable Valved Sheath System (Pressure Products, Inc., Rancho Palos Verdes, Calif.), which is comprised of a splittable valve attached to the end of a scored introducer sheath. The valve housing containing the valve membrane is split along scores lines which are aligned with score lines that continue down the length of the integral introducer. Thus, the valve and introducer are split together. One disadvantage of this combinational system is the lack of flexibility in how the device is used. For example, to place a coronary sinus pacemaker lead, a physician will often wish to advance the long introducer sheath into the coronary vessel, then partially withdraw the sheath, perhaps 10 cm, prior to introducing the pacing lead. The large integral valve at the proximal end of the sheath cannot enter the patient; therefore, the physician must have an undesirably long section of introducer exiting the patient, where ideally, he or she would like to peel the introducer back closer to the entry site. In addition, the scored introducer portion of the SAFE-SHEATH™ lacks the structural integrity to negotiate tortuous bends of the coronary vessels. Because the valve and introducer are designed only to be used together, the system cannot be adapted to work with different sheaths and other intravascular devices that may offer important clinical advantages in certain procedures. 
     What is needed is a simple system that offers greater flexibility to fully manipulate and adjust the splittable sheath prior to splitting away the valve. It would also be desirable to have a splittable valve that can be used with different splittable sheaths that did not require integral attachment or alignment of split lines. Further considerations include having a splittable hemostatic valve of simple construction that is easy to use, inexpensive to manufacture, and can provide superior sealing characteristics, even in the presence of high backflow pressures such as are seen in arterial applications. 
     SUMMARY OF THE INVENTION 
     The foregoing problems are solved and a technical advance is achieved in a splittable hemostatic valve that includes an interfacing region sized and configured to permit the valve to be coupled to a separate splittable introducer sheath or other tubular medical device to permit passage of a catheter or device therethrough with minimal blood flashback. In a first embodiment, the hemostatic valve can be placed over a splittable introducer sheath, such as a PEEL-AWAY® Introducer Sheath (COOK Incorporated, Bloomington, Ind.) while typically, a dilator is initially co-introduced, followed by the device being placed, such as a pacemaker lead or intravenous catheter having a large proximal hub or fitting. The hemostatic valve can then be split and removed from the introducer, which is also split apart, leaving the indwelling device undisturbed. Advantageously, the replaceable aspect of the valve allows the physician the ability to partially withdraw the introducer and peel it back down, as is often done when placing certain intravascular devices, and then place the hemostatic valve back over the new proximal end that is formed. This provides a significant clinical benefit over existing splittable introducers that include an integral valve at the proximal end that is split along with introducer, thereby not allowing for replacement at a more distal location. In another embodiment, the interfacing region can be configured to be placed at least partially within the passageway of the introducer sheath, instead of over the sheath&#39;s outer surface. 
     The hemostatic valve comprises a valve body which is typically made of silicone or another elastic material that allows the valve to be fitted over or into the introducer sheath while offering some sealing characteristics. The hemostatic valve includes one or more sealing elements located within the valve passageway. In some embodiments of the invention, one or more of the sealing elements are formed to be integral with the valve body. They can be positioned at the proximal end or within the body of the valve and may include slits or apertures to allow passage of a medical device. Other embodiments include a valve insert disk made of silicone foam that is separately formed and affixed within the hemostatic valve passageway. 
     In various other aspects of the present invention, the proximal end of the hemostatic valve may be configured to receive and lock a dilator hub such that the dilator and introducer can be maintained in the proper longitudinal alignment with each other during the procedure. In addition, the distal end of the valve can be configured to accept a series of specific-sized introducers by including a multiple steps of different diameters (e.g., 3.5 to 6.0 Fr). In another aspect, the valve can include a side port to allow access to the passageway for procedures such as an I.V. drip, system flushing, air evacuation, or the infusing of medicaments or contrast media. 
     The hemostatic valve includes at least one line of fissure through which the valve is opened to allow external access to the passageway. In one embodiment, the silicone valve body is formed with opposing scores or grooves formed nearly all the way through the inside or outside of the valve wall such that the two valve halves can be readily pulled apart when the two integral tabs are pulled outward to initiate the split. Typically, the sealing elements are correspondingly scored or split to facilitate a complete separation of the valve assembly. 
     In another aspect of the invention, the valve is constrained by a splittable outer sheath, such as one made of molecularly oriented, anisotropic PTFE used to make the PEEL-AWAY® Introducer Sheath. The embodiment also includes a means to grasp and tear the sheath away to open the valve, which may be restrained as two separated halves that fall apart, or scored or so affixed as to be torn apart by the separating action of the sheath. 
     In another aspect of the invention, the distal portion of the hemostatic valve assembly includes a splittable distal extension of the valve body that is adapted to fit over or couple with a particular medical device. Many intravascular introducers and other devices, unlike the Cook PEEL-AWAY® Introducer, have a large proximal fitting. In one embodiment, a distal portion is adapted to accept and seal about the proximal fitting of a standard introducer sheath. The distal portion could include a series of seals that are designed to fit over a multiplicity of fittings, making it a ‘universal’ splittable hemostatic valve. 
     In yet another aspect of the invention, a sealant filler material is provided within the passageway of the hemostatic valve, preferably within one or more cavities formed between the self-sealing membranes. While the self-sealing membranes provide an adequate barrier against fluid backflow when used in the venous system where pressures typically average around 0.2 psi, arterial pressures represent over a ten fold increase over that of the venous side, making sealing much more difficult. This sealant filler material, which provides an additional blood barrier, can comprise virtually any biocompatible material that can provide a seal around a device being passed through the valve. Possible materials include a viscous liquid such as glycerine; a gel; a foam or sponge; densely-packed solid particles such as minute beads or fibrous material; and strips of material such as collagen. These materials can be affixed to or incorporated into the valve body or introduced into the existing cavity, such as via a side port or injected through the valve body wall. Membranes can be used to longitudinally divide the cavity into two halves that are filled with a substance that allows the subcavities to be resiliently depressed. The resulting counter force against the residing device provides a seal with the membranes allowing the contents of the subcavities to remain contained when the valve is separated. 
     In still yet another aspect of the invention, a biasing means is included to provide additional force against the leaflets of the distal seal, such as a duck-bill valve, to provide improved sealing properties. In one embodiment, the biasing means comprising two biasing elements of a material such as silicone which are added to the valve after fabrication. The biasing elements are added by applying force to the valve on opposite sides such that the force is in line with a valve slit, thereby causing it to open slightly. The silicone or other material is then added adjacent to the valve leaflets at points perpendicular to the valve slit and allowed to cure. The force is released, returning the valve to its original shape with the cured biasing elements now functioning to continuously urge the leaflets closed. In other embodiments, the biasing means comprises an O-ring or sleeve that is included within the valve after the valve with slit is formed to provide a biasing force to urge the leaflets into the closed position. 
     In still yet another aspect of the invention, the valve assembly can include a plurality of valves whose passageways are joined distally into a common passageway. In an embodiment having two proximal seals with two passageways each representing bifurcations of the single common passageway, there are two oppositely placed lines of fissure that allow the valve assembly to be separated into two halves. In an embodiment having three proximal seals and three passageways that feed into a single common passageway, there are three lines of fissure that allow the valve assembly to be separated into three pieces to allow introduced devices to remain in place. Additional valves and entry passageways are also contemplated. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 depicts a partially-sectioned pictorial view of an embodiment of the splittable hemostatic valve assembly having a outer sheath; 
     FIG. 2 depicts a pictorial view of an alternative embodiment of the present invention having an outer sheath; 
     FIG. 3 depicts a cross-sectional side view of an embodiment of the present invention having a plurality of sealing elements; 
     FIG. 4 depicts a cross-sectional side view of the hemostatic valve assembly of FIG. 2; 
     FIG. 5 depicts a top view of the embodiment of FIG. 1; 
     FIGS. 6-8 depicts cross-sectional views of various sealing element embodiments of the present invention; 
     FIG. 9 depicts a pictorial view of an embodiment of the present invention having a side port; 
     FIG. 10 depicts a top view of an embodiment of a valve body of the present invention having a external score line; 
     FIG. 11 depicts a bottom view of an alternative embodiment of a valve body of the present invention having an internal score line; 
     FIG. 12 depicts a side view of the embodiment of FIG. 1 being used with a splittable introducer sheath; 
     FIG. 13 depicts a cross-sectional view of an embodiment of the present invention adapted for placement over a proximal fitting; 
     FIG. 14 depicts a partially-sectioned side view of an embodiment of the present invention adapted to be placed within an introducer sheath; 
     FIG. 15 depicts a pictorial views of a second embodiment that is adapted for placement within a introducer sheath; 
     FIG. 16 depicts a partially-sectioned pictorial view of an embodiment of the present invention adapted to be partially placed within an introducer sheath; 
     FIG. 17 depicts a partially-sectioned side view of a second embodiment that is adapted to be partially placed within an introducer sheath; 
     FIG. 18 depicts a pictorial view of an embodiment of the present invention used with a helical splitting introducer sheath; 
     FIGS. 19-20 depict a pictorial views of embodiments of the present invention having a grasping member or members located at the distal end of the valve body; 
     FIGS. 21-22 depict cross-sectional views of a hemostatic valve having a sealant filler material therein; 
     FIG. 23 depicts a cross-sectional view of a hemostatic valve having a biasing means; 
     FIG. 24 depicts a cross-sectional view taken along line  24 — 24  of the embodiment in FIG. 23; 
     FIG. 25 depicts the embodiment of FIG. 24 during the manufacturing process; 
     FIG. 26 depicts a cross-sectional view of a hemostatic valve having a second embodiment of a biasing means; 
     FIG. 27 depicts a top view of the biasing means of FIG. 26; 
     FIG. 28 depicts a pictorial view of a third embodiment of a biasing means; 
     FIG. 29 depicts a pictorial view of an embodiment of a splittable valve assembly having two proximal valves with a common central passageway; 
     FIG. 29A depicts a cross-sectional view taken along line  29 A— 29 A of the embodiment of FIG. 29; 
     FIG. 30 depicts a pictorial view of an embodiments of a splittable valve assembly having three proximal valves with a common central passageway; 
     FIG. 31 depicts a sectioned view of the embodiment of FIG. 9; 
     FIG. 32 depicts an exploded pictorial view of the embodiment of FIG. 9; 
     FIG. 33 depicts a partially sectioned view of an embodiment similar to that of FIG. 9 being used with a dilator and introducer sheath; and 
     FIG. 34 depicts an embodiment of the present invention adapted to be placed within the passageway of an introducer sheath. 
    
    
     DETAILED DESCRIPTION 
     A better understanding of the present invention will now be had upon reference to the following detailed description, when read in conjunction with the accompanying drawing, wherein like reference characters refer to like parts throughout the several views and different embodiments of the present invention. 
     The splittable valve assembly  10  of the present invention, as embodied in FIGS. 1-34, comprises a hemostatic valve  11  that includes a valve body  50  with a passageway  14 , at least one line of fissure  15  to permit the valve to split and allow external access along the length of the passageway, and at least one sealing element  13  configured to traverse the passageway  14 , while permit the passage of an first medical device  57 , such as a catheter, dilator, pacemaker lead, etc., while substantially preventing or eliminating the leakage or ‘flashback’ of blood or other bodily fluids. The splittable valve assembly  10  is designed for use with a second medical device, typically a tubular medical conduit  23  such as a splittable introducer sheath  24 . The hemostatic valve  11  of the present invention comprises an interfacing region  120 , typically located at the distal end  49  of the valve assembly. The interfacing region  120  is configured to permit the valve to be coupled or attached to the tubular medical conduit  23  at some point prior to or during the procedure involving the tubular medical conduit and in some instances, reattached, particularly when the valve is removed intact and the splittable introducer sheath is partially peeled down to form a new proximal end. In the illustrative embodiments such as FIGS. 1,  2 , and  9 , as well as others discussed later, the interfacing region  120  permits the splittable valve assembly  10  to be placed over the proximal end  52  of a splittable introducer sheath  24 , as depicted in FIGS. 12,  19  and  33 . If during the course of the procedure, the physician decides to partially withdraw and peel back down the sheath  24 , the valve can be advantageously removed, rather than being split with the sheath  24 , thereby allowing it to be placed intact back over the new proximal end of the splittable introducer sheath  24  and resume its function as a hemostatic valve  11  until such time as the first medical device  57  is introduced to its target location and the splittable introducer sheath  23  and hemostatic valve  11  are split apart and discarded. It should be noted that while valve portion  11  is referred to herein as a ‘hemostatic valve,’ it has possible applications in other types of non-vascular procedures where there is a desire to prevent leakage of fluids and/or reduce exposure to air-borne pathogenic organisms. For example, the splittable valve assembly  10  of the present invention can be used in minimally invasive neurological procedures to limit contact of the cerebral spinal fluid with ambient air. Another possible application would be urological procedures where the valve could help prevent the introduction of pathogenic organisms into the urinary tract. 
     A basic embodiment of the present splittable valve assembly  10  is depicted in FIGS.  9  and  31 - 33 . In this embodiment, the valve body  50  is insert molded into a single piece or unit from medical grade silicone, although other elastomeric polymers can be used, including combinations of different compounds for different portions of the valve. To facilitate splitting of the valve body  50  into separate first and second halves  20 , 21  to expose the passageway  13  of the hemostatic valve  11 , opposing lines of fissure  15 , located about 180° with respect to each other, are formed in the wall  47  of the valve body. The lines of fissure  15  of the illustrative embodiment each comprise a score line  22  or groove formed partially through the wall  47 , leaving a small amount of material  83  (e.g., 0.01″) as a bridge to join the adjacent halves  20 , 21 . The hemostatic valve  11  can be molded as a single unit and scored to create a line of fissure  15  to facilitate rupture of the valve body  50  when the respective halves  20 , 21  are pulled outward in opposite directions. In the embodiments of FIGS. 9-10, the score line  22  is formed into the outside surface  35  of the valve wall  47 . To facilitate separation of the valve body  50  along the score line  22 , a starter split  56  or notch can be made at the distal end of the hemostatic valve  11  at the line of fissure  15 . The valve body  50  is separated by using the integral tabs  40 , thus permitting the initial separation force to be concentrated at the distal end  49  where the starter split  56  is located. FIG. 11 depicts yet another embodiment in which the score line  22  in formed into the inside surface  71  of the wall. If the hemostatic valve  11  is insert molded into the outer sheath  12 , scoring could occur by either running the scoring tool along the passageway  14  of the hemostatic valve  11 , or configuring the die to create a score line  22  in the valve body  50  during the molding process such that the two valve halves  20 , 21  were bridged by a thin membrane  83  of material. A line of fissure  15  can be formed using a number of well-known techniques and assume a variety of configurations to achieve the goal of providing a relatively predictable path through which the split in the valve body progresses, such that the hemostatic valve can be removed from around the first medical device  57 . 
     Returning to the embodiment of FIGS.  9  and  31 - 33 , at the proximal end  48  of the hemostatic valve  11  are located two grasping elements  40  which in this embodiment, comprise integral tabs  46  that integrally extend from valve body  50  of the hemostatic valve  11 . These grasping elements  40 , which facilitate splitting the valve, can assume a wide variety of configurations, both integral, and separate from the valve body  50  with selected examples being depicted in various other figures. When the operator pulls the integral tabs  46  in opposite directions away from the valve body  50 , the lines of fissure  15  split from the proximal end  48  progressing to the distal end  49 , causing the valve body  50  to separate into halves  20 , 21 . To initiate the split along the lines of fissure  15 , an optional starter split  56  is included at the proximal end  48  whereby the lines of fissure  15  completely traverse the wall  47  for a relatively short distance (e.g., 2-7 mm) relative to the length of the hemostatic valve, which in the illustrative embodiment used with 3-12 Fr intravascular introducer sheaths, measures about 30-50 mm, depending on the size of the companion sheath. 
     FIGS. 19-20 depict embodiments in which the hemostatic valve  11  is split starting from the distal end  49 , proceeding to the proximal end  48 . To better accomplish this, the grasping members  40  are located at the distal end  49  of the hemostatic valve assembly  10  for opening the line of fissure  15  toward the proximal direction, resulting in separation of the valve halves  20 , 21 . FIG. 19 depicts an embodiment that is similar to that of FIG. 9 with the exception of the reversal of the grasping member  40  and starter split  56  orientation. As shown, the grasping members  40  are advantageously located in proximity to the splittable introducer sheath handles  32 . If each pair of grasping members/handles are pinched together and pulled outward from the hemostatic valve assembly  10  and splittable introducer sheath  24 , both devices can be split together. In doing so, the hemostatic valve  11  split initially continues upward from the starter split  56 , while the splittable introducer sheath split initially progresses upward to the proximal end  52 , then continues downward along a distal path. The line of fissure  15  may not extend the entire length of the valve body  50  if the starter split  56  or starter split plus a partial score line are sufficient, given the wall thickness and material, to force a split that continues all the way to the opposite end  48 . FIG. 20 depicts a related embodiment that includes a single grasping member  40  and integral tab  46  that is located at the distal end  49  of the valve body  50  on only one half  20  of the valve. If the device over which the hemostatic valve  11  is placed extends a sufficient distance into the passageway  14  to provide adequate counter force against the opposite half  21 , a single grasping element  40  located on the first half  20  can be used to cause a split that allows full separation of the valve body  50 . 
     The number and configuration of sealing element  13  of the present invention represents a design choice influenced by the type of procedure involved and the instrumentation to be used with the valve. In the embodiments of FIGS. 31-33, the illustrative hemostatic valve  11  includes two sealing elements  13  which comprise a proximal seal  27  and a distal seal  28 . The distal seal  28  comprises a thin, 0.010″ membrane that is integrally formed with the valve  50 . A slit  29  is formed through the membrane to permit through passage of the first medical device  57 , such as a dilator shaft  119 , being introduced through the tubular medical conduit  23  for placement at the target site. In the illustrative embodiment, the proximal seal  27  comprises disk-shaped seal insert  112  made of silicone foam that is separately formed from the valve body  50 , inserted into the passageway  14  and affixed with silicone adhesive or otherwise secured in placed. The seal insert  112  includes a small aperture  113  that facilitates smooth passage of a relatively large-diameter medical device therethrough. A transverse fissure  126  is made partially through the seal insert  112  in line with the lines of fissure  15  in the valve body to allow the seal to split in half along with the remainder of the hemostatic valve  11 . 
     FIGS.  9  and  31 - 33  depict two related embodiments in which the proximal seal  27  is situated within the passageway  14  such that sufficient space exists between the proximal seal  27  and the proximal end  48  of the valve to form a proximal receiving chamber  110  that is configured to accept a dilator hub  117 . A locking lip  111  that is located at the proximal end of the proximal receiving chamber  110  helps hold the dilator hub  117  therein. This permits the dilator  58  and introducer sheath  24  to advantageously remain in a constant positional relationship in which the distal tapers of the two devices  58 , 24  match while being manipulated within the patient. Because the valve body  50  is typically made of a flexible silastic material the dilator hub  117  can easily be pulled back out of the proximal receiving chamber  110  once the dilator  58  is ready to be removed from the introducer sheath  24 . In the embodiments of FIGS. 31 and 33, the configuration of the proximal receiving chamber  110  varies depending on the size of the dilator and the design of its hub. The valve embodiment of FIG. 31 is designed for a smaller dilator hub (e.g., 4.5-7 Fr), while the embodiment of FIG. 33, accepts a larger, longer hub used with a larger dilator, such as that intended for use with a 10-12 Fr introducer sheath  24 . 
     In valve embodiments that do not include a proximal receiving chamber  110 , the proximal seal  27  is typically located at the proximal end  48  of the valve assembly  10  as depicted in a number of embodiments, including those in FIGS. 1-8. In one embodiment depicted in FIG. 5, the proximal seal  27  functions a self-sealing membrane  42  by virtue of one or more slits  29 . In the embodiment, of FIG. 5 there is a first slit  29  comprising a portion of the line of fissure  15  that extends across the self-sealing membrane. Also included are two diagonal slits  69  that along with the first slit  27 , define a series of opposing valve leaflets  62  that seal around a medical device placed through the passageway  14  of the hemostatic valve  11 . To ease passage of a device through the self-sealing membrane  42 , especially a small-diameter device such as a biventricular pacing lead, the valve leaflets  62  can be coated with a lubricious material such as SLIP-COAT™ or GRAFT-COAT™ (Sterilization Technical Services, Rush, N.Y.). With regard to the illustrative embodiment, the valve body  50  is contiguous with the sealing element  13 , as both are formed of the same elastomeric material. 
     FIGS.  3  and  6 - 8  depict additional sealing element  13  embodiments. In each of the illustrative examples, there is a proximal seal  27  comprising a self-sealing membrane  42  with at least one slit  29 , and at least one distal seal  28  to provide an additional barrier against flashback of blood or other bodily fluid. In the embodiment of FIG. 3, the distal seal  28  comprises an integral ring or constriction that provides an second sealing element  13  in addition to the self-sealing membrane  42  that comprises the proximal seal  27 . In the embodiment of FIG. 6, there are a pair of distal seals  28 , each comprising a disk-shaped self-sealing membrane  42  across the passageway  14  of the hemostatic valve  11 . In the embodiment depicted in FIG. 7, the distal seal  28  comprises a duck-bill valve  70  with a central slit  29  wherein fluid flowing back toward the proximal end  48  of the valve helps force two halve of the valve  70  together and thus, assists with sealing about an device positioned in the passageway  14 . It the embodiment of FIG. 8, the hemostatic valve  11  and proximal seal  27  are attachable to a series of additional seal components  43 , 44 , 45  that interlock into a single unit. Each component comprises a distal seal  28  and seal supporting structure  51  which collectively, form the valve body  50  of the expanded splittable valve assembly  10 . It is anticipated that number of components can be varied to achieve the desired amount of protection against flashback of blood or bodily fluid within the passageway  14  of the hemostatic valve  11 . 
     FIGS. 31-34 are exemplary of two basic types of interfacing regions  120  for coupling or attaching the hemostatic valve  11  to a tubular medical conduit  23 . In the type depicted in FIGS. 31-33, which also the type found the embodiments depicted in FIGS. 1-13 and  19 - 30 , the interfacing region  120  is sized and configured such that its contact surface  124  with the tubular medical conduit  23  is located within the passageway  14  of the hemostatic valve  11 . Coupling occurs with the hemostatic valve  11  being placed over the proximal end  52  of the tubular medical conduit  23 , as depicted in FIGS. 33, with other embodiments shown in FIGS. 12 and 19. Ideally, the passageway  14  at the distal end  49  of the hemostatic valve  11  is sized such that the proximal end  52  seals against the contact surface  124  to greatly reduce the possibility of leakage. Although it is within the scope of the invention for the valve body  50  to comprise a rigid or semi-rigid plastic or another non-elastic material, silicone or similar type materials provide superior sealing characteristics, as well as making it easier to split the valve body  50  along the lines of fissure  15 . 
     In the embodiments of FIGS. 31-33, the interfacing region  120  is configured to accept different-sized introducer sheaths  24  by including a series of steps  114 , 115 , 116 , each corresponding to a specific sized introducer. For example, in the embodiment of FIGS. 31-32, the first step  114 , located closest to the distal end  49 , a diameter to readily accommodate up to a 6.0 Fr introducer sheath  24  before the proximal end  52  of sheath abuts the proximal lip of the stop  114  and cannot be advanced further into the passageway  14 . The second step  115 , located proximal the first step  114 , can accept up to a 4.5-5.0 Fr introducer sheath, while a 3.5-4.0 Fr introducer sheath can pass through the first two steps  114 , 115  before abutting the third step  116 . Depending on the durometer of the valve body  50  material, it is possible for the valve body  50  to yield somewhat and accommodate a larger-size introducer sheath  24  that for which the particular stop is configured. The embodiment of FIG. 33 depicts an interfacing region  120  sized to accept either a 10, 11, or 12 Fr introducer sheath  24 , the proximal end  52  of the latter of the three being shown positioned at the first step  114 . The examples of FIGS. 31-33 are merely illustrative as to the number and range of steps. It is possible to configure the interfacing region  120  to accept multiple sizes of introducer sheaths  24  without having steps. One solution is to gradually taper the interfacing region  120  to accommodate a range of different-sized introducer sheaths  24 . Additionally both steps and tapers can be combined to accommodate a range of different introducer sheath diameters. 
     Other types of introducer sheaths  24  and tubular medical conduits  23  for whose functionality could be improved by the present invention often include large proximal hubs or fittings, such as luer fittings, that the splittable valve assembly  10  must fit over in order to provide a proper seal. FIG. 13 depicts an embodiment in which the distal portion  33  of the hemostatic valve  11  includes a coupling mechanism  60  such as threads that allow the hemostatic valve assembly  10  to be placed over an introducer sheath with a fitting such as a luer lock hub. A valve O-ring  61 , located within the passageway  14  toward the distal end  49 , provides a seal  13  that is located against or below the fitting when the tubular medical conduit  23  is coupled to the hemostatic valve  11 . It is also contemplated that the coupling mechanism  60  could be eliminated with the distal portion  33  being adapted to slide over and seal a standard proximal hub or fitting. This could occur by configuring the distal portion  33 , which would include a series of seals  13  or O-rings  61 , such that it can resiliently stretch over large fittings and provide a tight seal for a variety devices. Requirements include making the passageway of a sufficient diameter to accommodate the fitting, constructing the valve body  50  from a sufficiently elastic material to provide adequate contact with the fitting, and appropriately configuring the seal  13  or seals that would lie distal to the fitting to prevent flashback of blood after the hemostatic valve assembly  10  is in place. 
     FIG. 34 depicts an second main type of interfacing region  120  in which the contact surface  124  with the tubular medical conduit  23  occurs on the outside surface of the hemostatic valve  11  such that at that the distal end  49  is inserted into the passageway  121  of the tubular medical conduit  23 . In the illustrative embodiment, the passageway  121  represents a proximal receiving chamber that has been specially configured to mate with the distal portion  33  of an appropriately configured hemostatic valve  11 . An optional distal lip  122  is included at the distal end  49  of the hemostatic valve  11  to help couple the valve within the passageway  122 . Additionally or alternatively, the proximal end  52  of the tubular medical conduit  23  could be modified to include a locking lip similar in structure to element  111  of the hemostatic valve  11  depicted in FIGS. 31-33. The interfacing region  120  of the embodiment of FIG. 34 is configured such that only the distal portion of the valve body  50  is inserted into the proximal receiving chamber  122  of the introducer sheath  24 ; however it is also within the scope of the invention to have all or a substantial portion of the hemostatic valve be inserted into the passageway  121  of the introducer sheath  24  as depicted in FIGS. 14-18. 
     Included in the embodiments of FIGS.  9 , 13 , and  31 - 33  is a side port  54  that communicates with the central passageway  14 . The side port  54  can be used for a variety of purposes, for example, slow-drip intravenous administration (e.g., 1-10 cc/hr) to keep the vein open and prevent coagulation. A length of tubing  123 , as depicted in FIG. 33, is attached to the side port  54  which in turn, would include a luer lock port or similar-type fitting to connect with the I.V. line at the end distal to the patient. The side port  54  would be available to perform other functions such as infusion of medicaments, saline for flushing, or contrast media. It would also have utility for instances when air must be evacuated from the system. The side port  54  of FIG. 33 is depicted as a nipple over which the tubing  123  is attached; however, other embodiments are possible such as a luer or other fitting, or merely an aperture into which the tubing  123  is inserted. 
     In various embodiments depicted in FIGS. 1-2,  4 - 5 , and  12 - 13 , the hemostatic valve assembly  10  of the illustrative embodiment further comprises a section of outer sheath  12  material that surrounds the hemostatic valve  11  and offers structural reinforcement and an alternative means of splitting the hemostatic valve  11  open to expose the passageway  14 . In the illustrative embodiment of FIG. 1, the outer sheath  12  comprises a thin-walled tube of an molecularly-oriented, anisotropic material such as polytetrafluoroethylene (PTFE) whose molecular properties permit it to be torn longitudinally along a predetermined split line  16  whose path is determined by a cut point  55  formed in the material. The cut point  55  comprises a V-shaped notch in the illustrative embodiment, although a short linear cut could also work. The cut point  55  provides a starting point for the tear such that when the grasping members  40  are pulled apart, the tear continues from cut point  55  and maintains a straight path along the predetermined split line  16  that extends from cut point  55 , thereby separating the outer sheath  12  longitudinally into two pieces. Separation of the outer sheath  12  permits the hemostatic valve  11  to also separate, which allows the hemostatic valve assembly  10 , when no longer needed during the procedure, to be removed from an indwelling medical device without having to slide the valve over the proximal end of the indwelling device, which may be precluded if the device has a proximal fitting larger than the passageway  14  of the hemostatic valve  11 . In the embodiment of FIG. 5, the hemostatic valve  11  has been pre-split into two halves  20 , 21  and then glued together with a layer of adhesive  41  such as silicone adhesive. Because the outer sheath  12  constrains the hemostatic valve  11 , it should be noted that the hemostatic valve  11  can be split into two mated valve halves  20 , 21  that are not interconnected, but rather only held together by the inward radial force of the outer sheath  12 . For example, by taking a split 7.0 Fr O.D. hemostatic valve  11  and pressure fitting the two valve halves  20 , 21  together inside a 7.0 Fr I.D. outer sheath  12 , the resiliency and surface properties of the silicone material help provide a good seal along the lines of fissure  15 . When the sheath is removed, the first and second valve halves  20 , 21  fall away from each other. Although a material having preferred directional properties such as anisotropic PTFE is preferred, the present invention encompassed any known method of predisposing a sheath to separate along a predetermined split line. Other methods of making a sheath splittable include scoring or perforating the walls of the sheath. Also included are multi-layered sheaths where one or more split or scores sheath layers are bonded to regular sheath to guide the tear through the underlying solid sheath, or subjecting the outer sheath  12  material to chemical or energy treatment along a desired predetermined split line  16  to create a preweakened feature. 
     In reference to FIG. 1, the integral tabs  46  not only serve as grasping members  40  for the clinician to separate the hemostatic valve  11 , they also provide a means to secure the outer sheath  12  to the hemostatic valve  11  such that separation of the former results in the separation of the latter. Two longitudinally aligned apertures  38  are made through opposite sides of the outer sheath. A generally cylindrical die is used having recesses external to the apertures  38  such that when the silicone is injected into the die, it flows out the apertures  38  and cures to form a silicone bead  39  on the exterior surface  35  of the outer sheath  12 . In the illustrative embodiment, the respective silicone beads  39  are molded so that they extend upward to the proximal end  48  of the hemostatic valve were they are extended outward to conveniently form the grasping members  40 . In the embodiment of FIG. 2, the silicone bead  39  itself is not a grasping member  40 , this function being provided by the ears  37  or extensions of the splittable PTFE material, and the associated handles  32  attached to the terminal ends of the ears  37 . The embodiment of FIG. 2, shown also in cross-section in FIG. 4, basically represents a modified PEEL-AWAY® Introducer Sheath that has been truncated and coupled to an internal hemostatic valve  11 . The outer sheath  12  forms a double layer  36  of material with the cut line  55  made to tear upward to the proximal end  48  of the assembly  10 , then downward, continuing along the predetermined split line  16 . The method of attaching the outer sheath  12  to the hemostatic valve  11  is not considered critical and as previously noted, an attachment is may not be necessary. In addition to the attachment method shown in FIGS. 1-2, the valve halves  20 , 21  can be bonded to the sheath with adhesive or another well-known method. When using PTFE, etching of the inner surface  17  can improve adherence of the hemostatic valve  11  to the outer sheath  12 . 
     The hemostatic valve assembly  10  of the present invention, as shown in FIGS. 1-13 and  19 - 34 , is used as a device that is separate from the splittable introducer sheath  24 , or the hemostatic valve assembly  10  can be constructed such that the outer sheath  12  includes an introducer extension  18  as depicted in FIGS. 14-18, thereby obviating the need for a separate introducer. Essentially, the hemostatic valves  11  of these same embodiments, if not pre-coupled to the outer sheath  12  and distal extension  18 , can also be regarded as a separate components from the sheath, such as the FIGS. 1-13 and  19 - 34  embodiments which are adapted to be placed into a separate tubular medical conduit  23  or introducer sheath  24 . In either case, the interfacing region  120  extends a substantial portion (FIG. 16) or the entire length (FIGS.  15 , 17 - 18 ) of the external surface  35  of the valve. If the hemostatic valve  11  is not fixedly positioned within the introducer sheath  24 /introducer extension  18  prior to use, this would allow the physician to insert the hemostatic valve into the introducer sheath  24  at some point into the procedure, and in some instances, back into the introducer sheath  24  once it has been partially peeled back to form a new proximal end. In the embodiment of FIG. 14, the outer sheath  12  and introducer extension  18  comprise a single tear-apart PTFE sheath that resembles the COOK PEEL-AWAY® Introducer Sheath with a hemostatic valve insert molded thereinside. Optionally, the hemostatic valve  11  may be attached to the outer sheath  12  in a manner similar to the embodiment of FIG.  2 . The predetermined split line  16  extends the length of the outer sheath  12  and continues down the length of the contiguous introducer extension  18  as well. In another embodiment, the outer sheath configuration of FIG. 1, lacking the double layer  36  of material and ears  37  at the proximal end  48 , can be simply modified to include a introducer extension  18  as well. 
     The embodiment of FIG. 15 depicts a simplified hemostatic valve  11  in which the seal  13  and valve body  50 , are essentially united into a single cylindrical-shaped structure that is inserted into the outer sheath  12  and introducer extension  18  (or introducer sheath  24 ). In the illustrative embodiment, a single line of fissure  15  permits the intravascular medical device, such as a pacemaker lead, to be removed from the valve. Rather than being torn apart or falling apart from the splitting action of the outer sheath  12 , the hemostatic valve  11  is simply slid off the lead via the line of fissure  15  when the two pieces  25 , 26  of the outer sheath  12 /introducer extension  18  are torn away. More than one hemostatic valve  11  may be placed in the outer sheath  12  to be used in this manner. To prevent distal migration of the hemostatic valve  11  in embodiments where the hemostatic valve  11  and, the outer sheath  12  are not securely interconnected, the outer sheath  12  portion of the hemostatic valve assembly  10  can be made to have a slightly greater I.D. than that of the outer sheath/introducer extension  18  or introducer sheath  24 . 
     FIGS. 16-17 depict alternative embodiments having a number of features, including alternative methods of providing an secure interface between the hemostatic valve  11  and outer sheath  12 . In the embodiment of FIG. 16, a band  63 , which can be made of metal or hard plastic, is inserted into an annular recess  64  in the outer surface  35  of the valve body  50 . The band  63  includes a series of teeth  65  that engage the inside surface  71  of the wall, preventing slippage of the hemostatic valve  11  toward the proximal end. Integral tabs  46  at the proximal end of the hemostatic valve  11  prevent its migration distally. Alternatively, the teeth  65  can be directed both proximally and distally to eliminate the need for making the proximal end of the hemostatic valve  11  larger than the outer sheath  12 /introducer sheath  24 . Having reverse-directed teeth  65  allows the physician to advance the hemostatic valve  11  into the sheath after it has been introduced into the patient, such as after a dilator has been removed. The band  63  can act as a means to hold the valve halves  20 , 21  together. In the illustrative embodiment the band  63  includes a break line  66  designed to fracture when the outer sheath  12  is separated. With the band  63  securing the two valve halves  20 , 21 , can remain as separate pieces and the line of fissure  15  need not be aligned with the break line  66  or the predetermined split line  16  of the outer sheath  12 . The teeth  65  embedded in the valve wall  47  provide a positive fixation that allows the band to separate along the break line  66 . Alternatively, the band  63  can be made on only partially circumscribe the valve body  50  with the closed end being attached to the valve wall  47  of one valve half and not the other. Therefore, the C-shaped band  63  is pulled off the valve with the attached valve half, making a break line  66  unnecessary. 
     The embodiment of FIG. 17 depicts a hemostatic valve  11  with a annular recess  64 , wherein the annular recess is used to receive projections  72 , such as annular ridges, that are molded into the inner surface  17  of the other sheath  12  or introducer sheath  24 . A second projection  73  distal to the position of the hemostatic valve  11  acts as a stop, while the proximal projection  74  prevents backward migration of the valve. The predetermined split line  16  of the outer sheath  12  or introducer sheath  24  in FIG. 17 comprises a preweakened feature  19  extending downward to the distal end of the sheath. The preweakened feature  19  can include a groove molded into the wall  47  of the outer sheath  12 /introducer extension  18 /introducer sheath  24  or the wall  47  can be scored after extrusion. In another aspect of the embodiment of FIG. 17, the hemostatic valve assembly  10  includes both integral tabs  46  on the hemostatic valve  11  and ears  37  extending laterally from the outer sheath  12 /introducer sheath  24 . The integral tabs  46  and ears  37  can be made to interlock as shown so that both form the grasping member  40 , thereby creating additional force to separate the hemostatic valve assembly  10 . In this particularly embodiment, the integral tabs  46  contain terminal knobs  67  that snap into receptacles  68  in the outer sheath ears  37 . 
     In another embodiment shown in FIG. 18, the predetermined split line  16  of the outer sheath  12  and introducer extension  18  or introducer sheath comprises a helical-shaped preweakened feature  19 , such as a groove, extending generally longitudinal along the length of the sheath. A single grasping member  40  is used to tear apart the outer sheath  12 /introducer extension  18 , resulting in a single piece of sheath material. The hemostatic valve  11  can be made to fall apart when the outer sheath  12  or introducer sheath is separated, or it may be attached to the outer sheath near a line of fissure such that when splitting of the sheath is initiated, the valve body  50  is at least partially slit along a line of fissure  15 . 
     To improve sealing performance, which is especially desirable for arterial applications, FIG. 21 depicts a hemostatic valve embodiment that provides an increase in protection against blood flashback. Lying between the proximal seal  27  and the distal seal  28  is a valvular cavity  76  in which a sealant filler material  77  is placed to provide an additional blood barrier. This sealant filler material  77  can comprises virtually any biocompatible material capable of filling the valvular cavity and allowing passage of an intravascular device therethrough. Possible materials include, but are not limited to, a viscous liquid, such as glycerine; a gel; a foam (such as silicone); a sponge material; densely-packed solid particles such as minute beads or fibrous material; and strips of material such as collagen. Collagen and other certain other materials are able to absorb and retain blood providing an additional mechanism of protection. A pathway may be preformed through the sponge or other solid material to ease the passage of a medical device. Materials can be used in combination, for example, a gel-impregnated foam or collagen sponge. Solid materials can be affixed to, or incorporated into the valve body  50  so that they are carried away with the respective valve halves  20 , 21  during separation. In embodiments such as FIG.  6  and FIG. 8 having more than one valvular cavity  76 , each can be filled with material and these materials can vary between the valvular cavities  76 . The sealant filler material  77  of the illustrative embodiment can be placed in the placed within the mold prior to fabrication, placed within the valvular cavity  76  after the valve has been presplit, or injected into the valve, including through a side port  54  as shown in FIG. 13 or  31 - 33  or through the valve wall  47  using a small or non-coring needle. If so desired, a fluidized sealant filler material  77  could be aspirated from the valvular cavity  76  via the side port  54  prior to splitting the hemostatic valve  11 , at which time any contents of the cavity would be exposed and be subject to leakage. 
     As shown in FIG. 22, a liquid, foam, gel, or other semi-solid or resilient solid material can be contained within the valvular cavity  76  by the inclusion of one or more longitudinal membranes  79  that divide the valvular cavity  76  into two subcavities  80 , 81 . In the illustrative embodiment, each subcavity is enclosed by a longitudinal membrane  79  and completely filled with a sealant filler material  77  such as gel or foam. When an intravascular device  57  such a dilator, pacemaker lead, etc., is introduced through the passageway  14  of the hemostatic valve  11 , the filled subcavities  80 , 81  which have been laterally compressed by the introduced device, each exert a counteracting force upon the device and thus, provide a seal to impede blood flashback passing through the distal seal  28  at the distal end of the valvular cavity  76 . During separation of the hemostatic valve  11 , the valve halves fall away and the contents of the subcavities  80 , 81  remain intact. 
     Referring now to FIGS. 23-28, the hemostatic valve assembly  10  of the present invention can also include a biasing means  84  that urges the valve leaflets together, thereby providing improved functionality to the sealing element  13 , which in the illustrative embodiments, include the distal seal  28  comprising a duck-bill valve  70 . In the embodiment depicted in FIGS. 23-25, the biasing means  84  comprises a first and a second biasing member  85 , 86  that are added to the valve assembly  10  after fabrication of the main hemostatic valve  11  body. In the illustrative example in which the body of the valve  11  is made of silicone, the first and second biasing members  85 , 86  comprise additional silicone material that is applied against each of the opposing valve leaflets  62  and allowed to cure. One example of manufacture is depicted in FIG. 25 wherein the steps include the application of external force  89  to the valve  11  using a fixture (not shown) capable of maintaining the valve in a given position. The force  89  is applied at opposite points along the circumference of the valve such that it is aligned with the main slit  29  that is to be urged closed. This causes the slit  29  to open slightly as the valve body  11  is deformed from its original circular cross-sectional shape. With the hemostatic valve  11  in a deformed condition, the material  92  that will form the second biasing member  86  (shown in FIG. 24) is applied, using an injection device  88  such as a syringe, within an intravalvular space  107  between the inner surface of the passageway  14  and a leaflet  62  of the distal valve  28 . In the illustrative embodiment, the biasing material  92  is injected through an aperture  87  in the valve wall and allowed to cure while the pressure is maintained on the valve. The procedure is repeated for the opposing leaflet on opposite side of the valve  11 . An alternative method of providing biasing material  92  that functions as a biasing means  84  is to inject the material  92  into the same intravalvular space  107  via the main passageway  14 , rather than through an aperture  87  in the valve wall. Once curing has taken place, the external force  89  that is compressing the valve is removed, allowing the valve to return to its previous shape. As it does, each biasing member  85 , 86  urges the respective opposing leaflets  62  together. This cantilever action provided by the biasing members  85 , 86  allows the valve to maintain the desired level of function under higher backflow pressures than might be otherwise possible. 
     Another embodiment that includes a biasing means  84  is depicted in FIG.  26 . The embodiment includes separate ring element  90  that is placed over the sealing element  13  (duckbill valve  70 ) to urge the leaflets  62  closed. The ring element  90 , a top view of which is shown in FIG. 27, can be comprise a rubber O-ring or some other material, such as metal, and is placed within the central passageway  14  into the valvular space  107  to hold the leaflets  62  of the valve  11  together. In the illustrative embodiment, the ring element  90  has an ovoid configuration with lines of fissure  94  that align with the those of the valve body, as well as aligning with the main slit  29 . The ring element  90 , being elastic, is compressed into a more rounded configuration to permit the duck-bill valve  70  to pass therethrough, whereby the ring element  90  is released to impinge on the leaflets  62  of the sealing element  13  to urge them closed. As noted, the lines of fissure  94  permit the ring element  90  to be separated when the two halves  20 , 21  of FIG. 26 are split apart during removal of the valve assembly  10 . 
     FIG. 28 depicts yet another embodiment of a biasing means  84  comprising a sleeve  91  that functions in a manner similar to that of the ring element  90  of FIGS. 26-27. The sleeve  91  of the illustrative embodiment features an optional thickened portion  95  that projects into the aperture space  93  of the sleeve  91  and acts to further urge the valve closed when the latter is situated therewithin. The embodiments of FIGS. 26-27 are merely exemplary constraining elements and certainly do not represent the full range of possibilities that exist. Those skilled in medical arts would recognize that a multitude of configurations and materials are possible for constructing a suitable biasing means  84  that yields the desired characteristics. Although the illustrative embodiments each include lines of fissure  15  for splitting the valve  11  to expose the central passageway  14 , conventional, non-splittable valves that include the disclosed biasing means  84  are to be considered to all within the scope of the invention. 
     Referring now to FIGS. 29-30, the valve assembly  10  of the present invention can include a plurality of valves  11  or proximal seals  28 , each with separate passageways that merge into a central common passageway  100  that communicates with a common introducer sheath or medical conduit, therein allowing multiple devices to be used together without the disadvantage of having to share a common sealing element  13 . For example, dual-chamber cardiac pacing requires introduction of separate leads for placement in both the atrium and the ventricle. The embodiment of FIGS. 29-29A, which includes a first proximal seal  27  and a second proximal seal  96 , allows each lead to enter the introducer sheath over which the valve assembly  10  is situated via a dedicated sealing element  13 , rather than requiring that a single sealing element  13  provide a tight seal for a pair of leads passing therethrough. Having dedicated proximal seals  27 , 96  for each device can also allow the clinician to better identify and track the individual leads or devices being placed during a procedure, especially if indicia  108  are used to distinguish the different proximal seals. These indicia  108  can include unique alphabetic or numeric identifiers, such as shown in the figure, or other standard means such as color coding, dots, different shapes, etc. The first and second proximal seals  27 , 96  communicate with a first and a second passageway  97 , 98 , respectively, which unite distal to the point of bifurcation  99  to form a central common passageway  100  as depicted in FIG.  29 A. In the illustrative embodiment, the main passageway  14  is designed to receive the proximal end of a standard or splittable introducer, however, the valve assembly  10  can include an integral introducer (introducer extension  18 ) such as in the embodiment of FIG.  14 . 
     In reference to FIG. 29, the lines of fissure  15  are locate such that each of the proximal seals  27 , 96  are split down the middle along a main slit  29  when the two halves  20 , 21  of the valve assembly  10  are separated from each other by pulling apart the integral tabs  46 . When the valve assembly includes a third proximal seal  104  such as in the embodiment depicted in FIG. 30, the valve assembly  10  is preferably configured to separate into three portions  101 , 102 , 103  with the lines of fissure  15  that divide the respective portions being configured to split two adjacent proximal seals  27 , 96 , 104  along the centrally located slit  29  of each. All three of the lines of fissure  15  converge at a central point  109  located between the three proximal seals  27 , 96 , 104 . As with the embodiment of FIGS. 29-29A, the three proximal seals  27 , 96 , 104  of FIG. 30 each communicate with dedicated passageways that join distally to form a central common passageway  100 . One can appreciate that embodiments having more that three sealing elements  13  and passageways are possible, each proximal seal added generally requiring an additional line of fissure and corresponding portion in order that the valve assembly  10  can be split and removed from around each of the multiple devices that remains in position. 
     It is thus seen that the present invention has utility in a variety of medical procedures, and that variations and modifications of the splittable valve assembly of the present invention additional to the embodiments described herein are within the spirit of the invention and the scope of the claims.