Abstract:
An introducer assembly includes a sheath and a dilator. A biodegradable shroud covers the distal portion of the introducer assembly on the surface of both the sheath and the dilator. The biodegradable shroud dissolves in blood after being exposed for a predetermined time. Afterwards, the dilator can be separated from the sheath without breaking the sheath. The shroud improves movement of the introducer assembly through a venous system by preventing body tissue from getting caught in the space between the dilator and the shroud, for example should a “fish mouth” separation occur between them.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority from U.S. Provisional Application Ser. No. 61/022,651, filed Jan. 22, 2008. 
    
    
     TECHNICAL FIELD 
     The present invention relates to introducers and introducer assemblies, and more specifically to an introducer assembly including a dilator received in the lumen of an introducer sheath. A biodegradable shroud is provided on the distal portion of the introducer assembly where the dilator extends beyond and out from the sheath. 
     BACKGROUND OF THE INVENTION 
     Introducer devices provide for access to the vascular system. They are employed for inserting medical devices such as catheters, guidewires, leads, infusion ports, dialysis ports, dialysis catheters, and other such devices into the vascular system. A typical procedure for gaining access to the central venous system or the arterial system with an introducer is the Seldinger Introduction Method. The Seldinger Method provides for insertion of a hollow needle into the vasculature of a patient. A guidewire is inserted through the needle, and the needle is removed over the guidewire, leaving the guidewire in the vessel. The introducer assembly including the dilator and the introducer sheath is inserted over the guidewire into the vessel. The introducer assembly is advanced into a suitable position within the vessel, i.e. so that the introducer&#39;s distal end is well within the vessel but the proximal end of the introducer assembly is outside the patient. With the introducer assembly in the vessel, the guidewire and dilator are removed sequentially, leaving only the introducer sheath in the vessel. The introducer sheath is left in position and therefore offers direct access from outside the patient into the blood vessel lumen. The desired medical device is inserted through the lumen of the sheath into the appropriate vessel, and is implanted at the desired location within the body. To minimize any disturbance to the medical device, the sheath is removed from the medical device by cracking apart the handle, and peeling apart the sheath. Such removal techniques are well known by those skilled in the art. 
     During insertion of the introducer assembly including the dilator/introducer sheath into the body along the guidewire, the distal end of the introducer has to pass through various types of body tissue and anatomy. Sometimes the body tissues are rigid. This can cause significant resistance to movement of the introducer assembly through the vasculature. If resistance is great enough, the distal portion of the introducer sheath can be damaged, resulting in an introducer that may not be able to be inserted to its desired location in the body, or that could become damaged to a point that it is non-functional. The larger the diameter of the introducer sheath the greater the opportunity for the introducer to encounter resistance as it passes through body tissue. 
     To reduce the chance of such damage being caused by different anatomical tissues during insertion of an introducer assembly, the distal ends of the introduce sheath and the dilator received therein are designed with tapers that provide a transition from the larger diameter portion of the introducer sheath to a more distal portion of the dilator having a reduced diameter with the tapered profile. While the tapers generally allow the introducer to enter the body with reduced resistance, the tapered transition between the introducer sheath and the dilator in an introducer assembly is still a primary source of resistance. When the cross sectional area of the transition between the dilator and introducer sheath increases, for example, when only the tip of the dilator bends in a curved blood vessel during insertion while the introducer sheath maintains a relatively straight shape, the resistance from this transitional area can increase significantly. 
     What would be desirable is an introducer assembly comprising a dilator/introducer sheath designed to have minimum resistance at its tapered distal end during insertion into the body. What would also be desirable is easy removal of the dilator from the sheath after insertion of the introducer assembly into the body. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a perspective view of a conventional introducer assembly  10  comprising a dilator  12  and an introducer sheath  30 . 
         FIG. 2  illustrates a partial sectional view of the introducer assembly  10  shown in  FIG. 1  being placed inside a blood vessel  46  along a guidewire  44 . 
         FIG. 2A  illustrates an expanded partial sectional view of the indicated area in  FIG. 2 . 
         FIG. 3  illustrates a top view of the distal end of the introducer assembly  10  shown in  FIG. 1  including a shroud  52  constructed in accordance with one embodiment of the current invention. 
         FIG. 4  is a partial cross-sectional view taken along line  4 - 4  of  FIG. 3 . 
         FIG. 5  is a partial cross-sectional view of the introducer assembly  10  shown in  FIG. 1  provided with another embodiment of a shroud  54  constructed in accordance with the present invention. 
         FIG. 6  illustrates a partial sectional view of the introducer assembly  10  provided with the shroud  52  shown in  FIG. 3  after having been inserted into a blood vessel  46 . 
         FIG. 7  illustrates a partial sectional view of the introducer assembly  10  provided with the shroud  52  shown in  FIG. 6  as the shroud is being degraded inside the blood vessel  46 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the following detailed description, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that structural changes may be made without departing from the scope of the present invention. Therefore, the following detailed description is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims and their equivalents. 
     Turning now to the drawings,  FIG. 1  illustrates an introducer assembly  10  comprising a dilator  12  disposed inside an introducer  14 . The dilator  12  has a dilator handle  16  supported at the proximal end of a dilator tube  18  ( FIGS. 4 to 7 ). The dilator tube  18  comprises a dilator sidewall  20  surrounding a lumen extending along the entire length thereof including the handle  16  to a distal portion  22  having an open end  24 . The dilator tube  18  has a uniform circular cross-section normal to the longitudinal axis of the sidewall  20  extending along the majority of its length from the handle  16  to the distal portion  22 . There, the dilator sidewall  20  has a taper  26  that progressively narrows to the distal open end  24  of a reduced diameter. However, the lumen through the dilator  12  including the handle  16  and the tube  18  is of a uniform diameter. This means that the thickness of the sidewall  20  becomes thinner at the distal portion  22  to provide the taper  26  to the distal open end  24 . The dilator  12  is formed of, in an example, high density polyethylene, polypropylene, polyurethane, or fluorinated polymers such as, but not limited to, PTFE (polytetrafluoroethylene), FEP (fluorinated ethylene-propylene). 
     The introducer  14  comprises an introducer sheath  30  that is coupled with a handle  32 . The introducer sheath  30  is comprised of a tubular sidewall  34  surrounding an open passage extending from a sheath proximal portion  36  supported by the handle  32  to a sheath distal portion  38 . The sheath distal portion  38  has a taper  40  that progressively narrows from a larger outer diameter extending along a majority of the length of the sheath tubular sidewall  34  to an open sheath end  42  of the distal portion  38 . As with the distal portion  22  of the dilator  12 , the diameter of the sheath lumen does not reduce in diameter along its entire length. This means that the taper  40  is formed by a reduction in the thickness of the tubular sidewall  34  from one thickness along the majority of the length thereof to a reduced thickness at the open sheath end  42 . 
     In that respect, the taper  40  ( FIGS. 3 to 5 ) provides a slender profile from the introducer sheath  30  to the dilator  12  disposed through the sheath lumen. Similarly, the dilator taper  26  facilitates insertion of the introducer assembly  10  into a patient, for example, over a guidewire  44 . The dilator handle  16  optionally includes features, such as a luer hub or threads  16 A, that allows for other devices to be coupled thereto. 
     The introducer sheath  30  is formed of, in an example, fluorinated polymers such as, but not limited to, PTFE (polytetrafluoroethylene) and FEP (fluorinated ethylene-propylene), and non-fluorinated polymers, such as, but not limited to, polyethylene, polypropylene, nylon or polyimide. The sheath material, such as PTFE, can be molecularly oriented for optionally splitting the introducer sheath  30 . Molecularly oriented sheaths do not necessarily require an additional mechanical scoring operation to produce split lines, as in the case of a polyethylene sheath. Instead, the oriented molecules allow the introducer sheath  30  to naturally peel like a banana. The introducer handle  32  is typically provided with diametrically opposed score lines or some similar form of linear weakening to facilitate its removal along with the introducer sheath  30 . 
       FIGS. 2 and 2A  depict the introducer assembly  10  shown in  FIG. 1  including the dilator  12  received inside the lumen of the introducer sheath  14  being inserted into a body over a guidewire  44  according to the prior art. In this exemplary illustration, the body is part of the venous system  46 . According to the previously described Seldinger Introduction Method, a hollow needle (not shown) is first inserted into the venous system  46  crossing the skin  48  and other tissue until its distal end is in a desired location. The guidewire  44  is next inserted into the venous system  46  through the needle, and the needle is removed over the guidewire, leaving the guidewire in the vessel. The introducer assembly  10  including the dilator  12  partially housed inside the introducer  14  is inserted over the guidewire  44  into the venous system  46  and advanced to a suitable position so that the distal portion  38  of the introducer sheath  30  is well within the vessel but both the dilator handle  16  and the introducer handle  32  are outside the patient. With the introducer assembly  10  in the vessel, the guidewire  44  and dilator  12  are removed sequentially, leaving only the introducer sheath  30  therein. 
     Even though the introducer assembly  10  encounters a variety of different tissue layers providing varied levels of resistance, the taper  40  at the distal portion  38  of the introducer sheath  30  narrowing down to the taper  26  at the distal portion  22  of the dilator  12  normally facilitates relatively easy insertion of the introducer assembly  10  into the body. The distal portion  22  of the dilator  12  and the distal portion  38  of the introducer sheath  30  normally bend upon entering the blood vessel  46  and as they follow the path of the guidewire  44 . However, as shown in  FIG. 2A , in some cases this distal bending may create a zone of increased “fish mouth” separation  50  between the dilator&#39;s distal portion  22  and the introducer sheath&#39;s distal portion  38  as the introducer assembly  10  encounters different tissue layers. This separation  50  can occur if the bending force exerted by the tissue, or the blood vessel wall, on the distal open end  24  of the dilator  12  is higher than that on the distal open end  42  of the sheath  30 . Typically the mechanical strengths of the respective distal ends of the dilator  12  and the introducer sheath  30  are different. Different materials of construction for the dilator  12  and the introducer  14  can cause this, or there may be dimensional differences between their respective open ends. 
     As shown in  FIG. 2A , this separation  50  can cause the distal open end  42  of the introducer sheath  30  to cut into tissue during advancement of the introducer assembly  10  along the insertion path of the guidewire  44 , resulting in internal bleeding. Tissue can also get caught in the distal open end  42  of the introducer sheath  30  and impede advancement of the introducer assembly  10  along the guidewire  44 . If the impeding force is high enough, the distal portion  38  of the introducer sheath  30  can be deformed or even damaged. 
     Referring now to  FIGS. 3 to 7 , the introducer assembly  10  previously illustrated in  FIG. 1  is shown provided with a biodegradable shroud  52  according to the present invention. The shroud  52  continuously covers the distal portion  38  of the introducer sheath  30  and extends over at least some of the distal portion  22  of the dilator  12 . The shroud  52  is preferably of a biodegradable material that is conformably deposited on the introducer assembly  10  to continuously cover the distal portion  38  of the introducer sheath  30  to a position proximate the open end  24  of the distal dilator portion  22 . Preferably, the shroud  52  tapers from a shroud proximal end  52 A to a shroud distal end  52 B. This not only helps minimize resistance of the dilator  12  and introducer sheath  30  to movement through the vasculature  46 , but also resistance attendant to the shroud  52  itself is minimized. 
     Examples of degradable materials include, but are not limited to, mannitol (hexan-1,2,3,4,5,6-hexol (C 6 H 8 (OH) 6 ) is a sugar alcohol or a polyol), gelatin, starch, cellulose, alginate, hyaluronic acid, polylactides (PLA), polyglycolides (PGA), polycaprolactone (PCL) and copolymers, non-cross linked water soluble salts of chitosan, or inorganic salt, such as sodium chloride mixtures, and combinations thereof. As used herein, the term “degradable” refers to a partial or a complete degradation of the material integrity of the shroud  52 , which occurs through contact with blood or other body fluids. Such degradation can include dissolution, hydrolytic degradation, bioabsorption, and other degradation mechanisms well known to those skilled in the art. 
       FIG. 6  illustrates insertion of the introducer assembly  10  including the shroud  52  into a blood vessel  46  after crossing the skin  48  and other tissue layers. The thin shroud  52  covers the distal portion  38  of the introducer sheath  30  including the open sheath end  42  and extends along a majority of the length of the distal portion  22  of the dilator  12 . Underneath the shroud  52 , if there is any separation  50  created between the distal open sheath end  42  and the distal portion  22  of the dilator  12  during bending of the introducer assembly  10  in the blood vessel  46 , the shroud  52  prevents direct contact between the open sheath end  42  and the tissue. In that manner, the shroud  52  virtually eliminates any possibility that blood vessel tissue will be damages by the open sheath end  42  at the separation zone  50 . In a preferred embodiment, the shroud  52  is made of a material having a thickness of from about 0.01 mm to about 1 mm and that degrades after contact with blood within a pre-determined period of time. Use of the shroud  52  is in direct contrast to the potentially damaging situation illustrated in  FIGS. 2 and 2A . 
     The shroud  52  can be made by any one of a number of coating processes including, but are not limited to, dip coating, spray coating, and vapor deposition. The shroud  52  can also be attached to the distal portions  22  and  38  of the introducer assembly  10  as a prefabricated thin film. Attaching methods includes, but are not limited to, gluing, heat reflow and mechanical interference fitting. 
     The maximum pre-determined time for a partial or a complete degradation of the shroud  52  should be less than 30 seconds. The preferred time is about 15 seconds with the actual degradation period being controlled by the selection of the degradable material and the thickness of the shroud material, especially at the dilator/sheath transition. To achieve degradation within 30 seconds, a shroud  52  comprising mannitol should have a thickness of from about 0.03 mm to about 0.1 mm. 
       FIG. 7  illustrates the biodegradable shroud  52  in a partially degraded condition after being placed inside the blood vessel  46 . In the case of partial degradation, the shroud  52  is weakened through contact with blood to enable relatively easy separation and removal of the dilator  12  from the introducer sheath  30  after introducer placement. This weakening is associated with one or more of a combination of the degradation mechanisms discussed above. 
       FIG. 5  illustrates a further embodiment of a shroud  54  according to the current invention. The shroud  54  is composed of an outer layer  56  and an inner layer  58 . Multi-layer structures can be used to fine tune the shroud&#39;s required mechanic strength during insertion, and the required speed of degradation after insertion. For an exemplary two layer structure, the distal portion  38  of the introducer sheath  30  housing the distal portion  22  of the dilator  12  is dip coated in a 15 wt % mannitol aqueous solution to form the inner layer  58  having a thickness of about 0.05 mm. This sub-assembly is then dip coated in a second mannitol aqueous solution containing 10 wt % of mannitol and 10 wt % of sodium chloride (NaCl). The second outer layer has a thickness of about 0.1 mm. 
     It should be understood that different degradable materials having different degradation periods and mechanical strengths can be selected to build the shroud  54  from the inner layer  58  to the outmost layer  56 . While  FIG. 5  illustrates a shroud  54  comprising two layers  56 ,  58 , that should not be viewed as limiting. Shrouds of three or more layers are contemplated by the scope of the present invention. However, in any such multi-layer construction, it&#39;s preferred that the outer layer  56  degrades faster than the inner layer  58 . Having a multi-layer shroud construction may be beneficial to tailor the slip resistance and structural integrity of the shroud. For example, it may be beneficial to provide the outer layer  56  with a high degree of lubricity, but that may detrimentally impact its structural integrity. A lack of structural integrity can be compensated for by having the inner layer  58  being somewhat more durable than the outer layer  56 . 
     After the introducer assembly  10  is inserted in the vasculature system  46  to its intended location and the shroud  52  has degraded to a significant extent, the dilator  12  is removable from the introducer sheath  30  to allow other instruments to enter the blood vessel through the sheath inner lumen. The medical procedure is then performed in its normal manner, for example, placement of a cardiac lead, and the like. 
     Once the lead is in place and the introducer is no longer needed, the physician removes the introducer  14  without disturbing the lead. This is done by holding the wings  60 ,  62  of the introducer  14  shown in  FIG. 1  between the thumb and fore finger and counter rotating them with respect to each other while slowly moving the wings further apart. The introducer valve housing  64  including a valve membrane (not shown) supported therein is readily separated. This occurs at a score line  66  running along the valve housing  64  and the valve membrane supported therein. 
     In a preferred embodiment of the introducer assembly  10 , the tubular sidewall  34  of the introducer sheath  30  does not require a score line. Instead, it is made of PTFE which has a unique molecular structure. Once a sufficient amount of force is exerted at opposed stress points (not shown) provided at the proximal end of the tubular sidewall  34  underneath the valve housing  64 , the PTFE molecules begin to sever. Further pulling force causes the resulting tear to propagate in a linear manner along the entire length of the sheath tubular sidewall  34  to its distal end  42 . The tear is extremely straight and parallel to the longitudinal axis of the sheath  14 . Importantly, the tear is smooth and provides the physician with an even tactile feel that gives the physician a high degree of confidence that the lead, and the like, was not disturbed during removal of the introducer  14  from the venous system.  46 . For a more detailed description of structures that are suitable for removing an introducer from a venous system, and the like, without disrupting a medical device inserted into the vasculature through the introducer, reference is made to U.S. Provisional Application Ser. No. 61/107,447, filed Oct. 22, 2008. This application is assigned to the assignee of the present invention and incorporated herein by reference. 
     Another technique for removing the introducer  14  is to pull it out of the venous system against the cutting edge of the slitter (not shown) as the lead or like medical device remains positioned in the body. This technique is well known by those skilled in the art. 
     It is to be understood that the above description is intended to be illustrative, and not restrictive. Many other embodiments will be apparent to those of skill in the art upon reading and understanding the above description. It should be noted that embodiments or portions thereof discussed in different portions of the description or referred to in different drawings can be combined to form additional embodiments of the present invention. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitle.