Patent Publication Number: US-10786354-B2

Title: Transcatheter valve implantation access sheaths

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a divisional of U.S. patent application Ser. No. 14/496,041, filed Sep. 25, 2014, which claims the benefit of the filing date of U.S. Provisional Patent Application No. 61/893,473 filed Oct. 21, 2013, the disclosures of which are both hereby incorporated herein by reference. 
    
    
     BACKGROUND 
     The present disclosure relates to prosthetic heart valve replacement and, in particular, delivery systems and introducers for use with prosthetic heart valves. 
     Prosthetic heart valves that are collapsible to a relatively small circumferential size can be delivered into a patient less invasively than valves that are not collapsible. For example, a collapsible valve may be delivered into a patient via a tube-like delivery apparatus such as a catheter, a trocar, a laparoscopic instrument, or the like. This collapsibility can avoid the need for a more invasive procedure such as full open-chest, open-heart surgery. 
     Collapsible prosthetic heart valves typically take the form of a valve structure mounted on a stent. There are two types of stents on which the valve structures are ordinarily mounted: a self-expanding stent and a balloon-expandable stent. To place such valves into a delivery apparatus and ultimately into a patient, the valve must first be collapsed or crimped to reduce its circumferential size. 
     Generally, when implanting a prosthetic heart valve into a patient, an introducer sheath is first introduced into the desired blood vessel or other anatomy. This may occur after a guidewire and one or more dilators are introduced into the patient. The introducer sheath is advanced to the site of valve implantation, for example through the apex of the left ventricle to the desired heart valve annulus (transapical) or through the femoral artery to the desired heart valve annulus (transfemoral). As described in greater detail below, other delivery routes for heart valve replacement are possible. Once the introducer sheath is in place, it is used as a conduit to pass other devices, as necessary, from outside the patient to the site of implantation. For example, a delivery device containing the prosthetic heart valve in a collapsed condition may be passed through the introducer sheath so that the prosthetic heart valve may be deployed and implanted at the desired native heart valve annulus. 
     When the collapsed prosthetic valve has reached the desired implant site in the patient (e.g., at or near the annulus of the heart valve that is to be replaced by the prosthetic valve), the prosthetic valve can be deployed or released from the delivery apparatus and re-expanded to full operating size. For balloon-expandable valves, this generally involves releasing the entire valve, assuring its proper location, and then expanding a balloon positioned within the valve stent. For self-expanding valves, on the other hand, the stent automatically expands as the sheath covering the valve is withdrawn. 
     Generally, introducer sheaths have elongated portions with a hollow core to allow passage of devices through the introducer sheath. Often, the hollow core of the introducer sheath has a diameter that is larger than the largest device that would be passed through the introducer sheath. However, it is generally desired to have the smallest possible diameter for an introducer sheath to accommodate the small and often tortuous anatomy of the vasculature or other delivery route through the body. Additionally, despite different possible routes of delivery, introducer sheaths often have little or no route-dependent variation. It would thus further be desirable to have a single introducer sheath design that could better facilitate delivery of a prosthetic heart valve via different delivery routes. 
     BRIEF SUMMARY 
     According to one embodiment of the disclosure, an introducer provides access to a surgical site in a patient. The introducer may include a proximal housing configured to be positioned outside the patient. A sheath has a first portion coupled to the proximal housing and a second portion extending distally of the proximal housing. The second portion has a first edge, a second edge, and a middle section extending from the first edge to the second edge. The second portion has a rolled configuration in which the middle section at least partially overlies the first edge, and the second edge at least partially overlies the middle section. 
     According to another embodiment of the disclosure, an introducer for providing access to a surgical site in a patient and includes a proximal housing configured to be positioned outside the patient. A sheath extends from the proximal housing to a distal end of the introducer. A first handle is housed at least partially within the proximal housing and is configured to translate axially in a proximal direction and a distal direction with respect to the proximal housing. 
     According to a further embodiment of the disclosure, an introducer provides access to a surgical site in a patient. The introducer includes a proximal housing configured to be positioned outside the patient and a sheath extending from the proximal housing to a distal end of the introducer. A securing element is slideably coupled to the sheath and has a flange extending radially outwardly from the sheath. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view of a delivery device for a prosthetic heart valve assembled to an introducer. 
         FIG. 2A  is a top plan view of a portion of an operating handle for the delivery device of  FIG. 1 , shown with a partial longitudinal cross-section of the distal portion of a transfemoral catheter assembly. 
         FIG. 2B  is a side view of the handle of  FIG. 2A . 
         FIG. 3A  is a perspective view of the introducer of  FIG. 1 . 
         FIG. 3B  is a transverse cross-sectional view of the introducer taken along line  3 B- 3 B of  FIG. 3A . 
         FIG. 4  is a transverse cross-sectional view of the delivery device and introducer assembly taken along line  4 - 4  of  FIG. 1 . 
         FIG. 5A  is a schematic side view of an introducer according to an embodiment of the disclosure. 
         FIG. 5B  is a schematic side view of a prior art introducer during use within the vasculature. 
         FIG. 5C  is a schematic side view of the introducer of  FIG. 5A  during use within the vasculature. 
         FIG. 5D  is a schematic side view of the introducer of  FIG. 5A  with a deflected tip. 
         FIG. 5E  is a schematic side view of the introducer of  FIG. 5A  with handle portions in an extended configuration. 
         FIG. 5F  is a diagram of the introducer of  FIG. 5A  delivered through the aortic artery and the subclavian artery with handle portions in the extended configuration. 
         FIGS. 5G and 5H  are schematic side and perspective views, respectively, of the introducer of  FIG. 5A  with a securing element coupled thereto. 
         FIG. 5I  is a cutaway view of the introducer of  FIG. 5A  inserted into the aorta with the securing element coupled to the aorta. 
     
    
    
     DETAILED DESCRIPTION 
     As used herein, the term “proximal,” when used in connection with an introducer and/or delivery device, refers to an end of the device closer to the user of the device when the device is being used as intended. On the other hand, the term “distal,” when used in connection with an introducer and/or delivery device, refers to an end of the device farther away from the user. In the figures, like numbers refer to like or identical parts. As used herein, the terms “substantially,” “generally,” “approximately,” and “about” are intended to mean that slight deviations from absolute are included within the scope of the term so modified. When ranges of values are described herein, those ranges are intended to include sub-ranges. For example, a recited range of 1 to 10 includes 2, 5, 7, and other single values, as well as all sub ranges within the range, such as 2 to 6, 3 to 9, 4 to 5, and others. 
       FIG. 1  shows a prosthetic heart valve delivery device  10  assembled to an introducer  100 . Generally, delivery device  10  includes an operating handle  20  coupled to an outer catheter shaft  22  extending through introducer  100 . The delivery device  10  may also include a distal sheath  24  for holding a prosthetic heart valve therein. Introducer  100  may generally include a hollow distal sheath  110  connected to a proximal sheath  120 , which in turn is connected to a housing  130 . 
     Referring now to  FIGS. 2A-2B , delivery device  10  includes catheter assembly  16  for delivering the heart valve to, and deploying the heart valve at, a target location, and operating handle  20  for controlling deployment of the valve from the catheter assembly. Delivery device  10  extends from proximal end  12  ( FIG. 2B ) to atraumatic tip  14  at the distal end of catheter assembly  16 . Catheter assembly  16  is adapted to receive a collapsible prosthetic heart valve (not shown) in compartment  23  defined around inner shaft  26  and covered by distal sheath  24 . 
     Inner shaft  26  may extend through operating handle  20  to atraumatic tip  14  of delivery device  10 , and may include retainer  25  affixed thereto at a spaced distance from tip  14  and adapted to hold a collapsible prosthetic valve in compartment  23 . Retainer  25  may have recesses  80  therein that are adapted to hold corresponding retention members of the valve. 
     Distal sheath  24  surrounds inner shaft  26  and is slidable relative to inner shaft  26  such that it can selectively cover or uncover compartment  23 . Distal sheath  24  is affixed at its proximal end to outer shaft  22 , the proximal end of which is connected to operating handle  20 . The distal end  27  of distal sheath  24  abuts atraumatic tip  14  when the distal sheath is fully covering the compartment  23 , and is spaced apart from the atraumatic tip when compartment  23  is at least partially uncovered. 
     Operating handle  20  is adapted to control deployment of a prosthetic valve located in compartment  23  by permitting a user to selectively slide outer shaft  22  proximally or distally relative to inner shaft  26 , thereby respectively uncovering or covering compartment  23  with distal sheath  24 . The proximal end of inner shaft  26  may be connected in a substantially fixed relationship to outer housing  30  of operating handle  20 , and the proximal end of outer shaft  22  is affixed to carriage assembly  40  that is slidable along a longitudinal axis of the handle housing, such that a user can selectively slide outer shaft  22  relative to inner shaft  26  by sliding carriage assembly  40  relative to the handle housing. For example, a user may rotate deployment actuator  21  to move carriage assembly  40  proximally, thus moving outer shaft  22  and distal sheath  24  proximally to uncover a prosthetic heart valve positioned within compartment  23  in the collapsed condition. As distal sheath  24  begins to clear the prosthetic heart valve, the prosthetic heart valve begins to expand to an expanded condition so that it may be fixed within the native heart valve annulus of interest. 
     In one embodiment, distal sheath  24  of delivery device  10  may have an outer diameter of between about 18 French and about 19 French. Outer shaft  22  may have an outer diameter of between about 12 French and about 13 French. 
     The distal end of handle  20  may include a latching element configured to latch or otherwise lock onto a complementary latching element of introducer  100 . Although shown in  FIGS. 2A-B  as a pair of hooks  28 , any other suitable latching mechanism, including snaps, knobs, or similar mechanisms may be used, as described in greater detail below. One handle that may be suitable for use is described in greater detail in U.S. Patent Publication No. 2013/0297011, the disclosure of which is hereby incorporated by reference herein. 
     Now referring to  FIG. 3A , introducer  100  generally includes a hollow distal sheath  110  connected to a hollow proximal sheath  120 . Housing  130  may be connected to proximal sheath  120 , and may include additional components including, for example, flush port  140  and one or more seals or hemostasis valves (not illustrated) to prevent blood from flowing proximally out of introducer  100 . Housing  130  may also include a latching element  132  complementary to latching element  28  of handle  20 . For example, latching element  132  may be a groove, snap, aperture, or other locking mechanism configured to lockingly couple with latching element  28 . In one embodiment, proximal sheath  120  may have an outer diameter of approximately 19 French and include a tapered portion at its distal end  125 . The distal end  115  of distal sheath  110  may also taper to a reduced diameter. 
       FIG. 3B  illustrates a transverse cross-section of distal sheath  110  of introducer  100  taken along line  3 B- 3 B in  FIG. 3A . Distal sheath  110  may be in a rolled configuration. In other words, distal sheath  110  may include a first edge  112  that is not connected to second edge  114 , and a middle section  116  connecting the first edge  112  to the second edge  114 . Distal sheath  110  may be rolled so that at least a portion of middle section  116  overlies first edge  112 , and second edge  114  overlies at least a portion of middle section  116 . Distal sheath  110  may be formed from materials including, but not limited to, polymers, braided materials, coiled materials, Nitinol, silicone, or combinations thereof. Preferably, distal sheath  110  should be formed of a material so that, in the absence of applied force, distal sheath  110  tends to take a configuration similar to the rolled configuration illustrated in  FIG. 3B . This may be achieved, for example, by forming distal sheath  110  from Nitinol and heat-setting distal sheath  110  to the rolled configuration. Other materials and processes may also be suitable. For example, extruded polyethylene tubing may be heat-set on a mandrel in the rolled configuration. In one embodiment, in the absence of applied force, distal sheath  110  may have a relaxed inner diameter IDR of less than or equal to about 12 French. With the rolled configuration, distal sheath  110  may radially expand so that the inner diameter of distal sheath  110  increases from the relaxed inner diameter IDR to an expanded inner diameter IDE when an object having a diameter greater than the relaxed inner diameter IDR passes through distal sheath  110 . 
     For example,  FIG. 4  is a transverse cross-section taken along line  4 - 4  of  FIG. 1 , and showing a portion of delivery device  10  inserted in introducer  100 . When delivery device  10  is inserted into introducer  100 , distal sheath  110  of introducer  100  may cover a portion of outer shaft  22  (as well as inner shaft  26 ) of delivery device  10 . If the outer diameter of outer shaft  22  is greater than the relaxed inner diameter IDR of distal sheath  110 , distal sheath  110  radially expands by unrolling or unraveling to the expanded inner diameter IDE, which would be substantially equal to the outer diameter of outer shaft  22 . In some embodiments, the distal sheath  24  of delivery device  10  has the largest outer diameter of all the portions of catheter assembly  16  intended for insertion into a patient. For example, in the embodiment in which outer shaft  22  has an outer diameter of between about 12 French and about 13 French, the outer diameter of distal sheath  24  may be between about 18 French and about 19 French. In this case, it is preferable that the distal sheath  110  of introducer  100  be capable of expanding from a relaxed inner diameter IDR of about 12 French to an expanded inner diameter IDE of between about 18 French and about 19 French, as is described in greater detail below. However, it should be understood that these are just illustrative values. For example, the distal sheath  110  of introducer  100  may be capable of radially expanding to an expanded inner diameter IDE of up to about 21 French or more. 
     According to an aspect of the disclosure, introducer  100  may be assembled to delivery device  10  prior to insertion of the assembly into a patient. For example, the tip  14  of delivery device  10  may be inserted through housing  130 , proximal sheath  120 , and distal sheath  110  of introducer  100 , until housing  130  is adjacent a distal end of operating handle  20 . As delivery device  10  passes through introducer  100 , distal sheath  110  radially expands from its relaxed inner diameter IDR to a first expanded inner diameter IDE substantially equal to the outer diameter of the distal sheath  24  of delivery device  10 . After the distal sheath  24  of the delivery device  10  clears introducer  100 , the distal sheath  110  of introducer  100  radially contracts or relaxes to a second expanded inner diameter IDE substantially equal to the outer diameter of the outer shaft  22  of delivery device  10 . This expansion and contraction is possible at least in part due to the rolled configuration and material properties of distal sheath  110 , as described above. In the assembled configuration, the tapered portion at the distal end  115  of distal sheath  110  may help provide a fluid-tight seal between introducer  100  and the outer shaft  22  of delivery device  10 . Similarly, the tapered portion at distal end  125  of proximal sheath  120  may help provide a fluid-tight seal between proximal sheath  120  and distal sheath  110 . Proximal sheath  120  may be coupled to distal sheath  110  in any suitable manner. For example, proximal sheath  120  and distal sheath  110  may be created from a single tube of material, with a slit made along the longitudinal length of the distal sheath  110 . Distal sheath  110  may be placed around a mandrel or similar device and heat set such that, in the absence of applied forces, it is in a rolled configuration. In this case, proximal sheath  120  may be coupled to housing  130  and biocompatible elastomer or other suitable covering may be fit over at least the transition from the cylindrical proximal sheath  120  to the rolled distal sheath  110 . Alternatively, a sheath may be formed as described immediately above, with a separate proximal sheath  120  placed over the transition from a straight distal tube portion to rolled distal sheath  110 . In this case, some portion of rolled distal sheath  110  may reside inside proximal sheath  120 . Taper  125  may be covered with a biocompatible elastomer or other suitable material to provide a smooth transition and to help keep the transition fluid tight. In addition, an expandable outer layer of material may surround part or all of distal sheath  110 , for example to help provide a fluid seal around distal sheath  110  and prevent fluid leakage between the layers of the sheath. The expandable outer layer may provide a smooth outer surface, and may also help prevent devices from protruding through distal sheath  110  between first and second edges  112  and  114  as distal sheath  110  expands. The expandable outer layer may be formed from a biocompatible elastomer such as Chronarene provided by AdvanSource Biomaterials, although other expandable materials may be suitable. 
     Once the housing  130  of introducer  100  is substantially adjacent to the distal end of operating handle  20 , introducer  100  and delivery device  10  are in a fully assembled condition, as shown in  FIG. 1 . If desired, the latching mechanism  28  of operating handle  20  may be connected to the complementary latching mechanism  132  of introducer  100  so that delivery device  10  and introducer  100  are in locked configuration with respect to one another. If the surgeon desires introducer  100  to be freely moveable with respect to delivery device  10 , he may leave the complementary latching mechanisms  28  and  132  unconnected. In the assembled condition, a prosthetic heart valve may be inserted into the compartment  23  of delivery device  10  in a collapsed condition. It should be noted that the prosthetic heart valve may be positioned within compartment  23  prior to inserting delivery device  10  into introducer  100 . With delivery device  10  assembled to introducer  100 , and with the prosthetic heart valve loaded in compartment  23  in the collapsed condition and covered by distal sheath  24 , a surgeon may introduce delivery device  10  into the patient, for example via the femoral artery. Once the prosthetic heart valve is positioned at the site of implantation, it may be released from delivery device  10  as described above. Delivery device  10  and introducer  100  may then be removed from the patient while still in the assembled condition. 
     The use of introducer  100  with the procedure described above may have a number of benefits. For example, if the surgeon wants or needs to insert another device to the site of implantation, such as another delivery device or an interventional device such as an expandable balloon, he can remove delivery device  10  while leaving introducer  100  in place. As delivery device  10  is removed from the body, the distal sheath  110  of introducer  100  radially expands as necessary to permit the withdrawal of delivery device  10 . Once delivery device  10  has been removed, the surgeon may introduce another device to the site of implantation by advancing that device through introducer  100 , which provides a path to the site of implantation. Further, use of an expandable distal sheath  110  allows introducer  100  to have a relatively small outer diameter, which may reduce vascular complications. Generally, smaller diameters are more preferred for devices being passed through the vasculature. If it became necessary to withdraw delivery device  10  from the patient so that another device could be inserted through the non-expandable introducer, the introducer would only permit such withdrawal if the inner diameter of the introducer was greater than the largest diameter of the catheter assembly  16  of delivery device  10 . If a non-expandable introducer were used with delivery device  10 , it would need to have an inner diameter greater than the outer diameter of distal sheath  24 . Even further, assembling introducer  100  to delivery device  10  prior to inserting the assembly into the patient may allow for a reduced diameter of the assembly as the assembly is advanced to the site of implantation. For example, if the procedure is completed without removing the delivery device  10  from the introducer  100 , the greatest outer diameter experienced by the assembled device is the outer diameter of distal sheath  24  (assuming the largest outer diameter of introducer  100  is less than the outer diameter of distal sheath  24 ). On the other hand, if introducer  100  were first advanced to the site of implantation with delivery device  10  later advanced through introducer  100 , the greatest outer diameter experienced within the vasculature would be the outer diameter of distal sheath  24  plus the thickness of additional material of distal sheath  110  surrounding distal sheath  24  as delivery device  10  passes through the introducer  100 . The provision of the complementary locking mechanisms  28  and  132  may also simplify advancement of the delivery device  10  and deployment of the prosthetic heart valve, as the surgeon may not need to manage each device separately once they are locked together. 
     Although a heart valve replacement procedure is described above with reference to advancement of delivery device  10  and introducer  100  through the femoral artery to the site of implantation, other deliver routes may be desirable. For example, a collapsible prosthetic heart valve may be delivered with a similar or identical delivery device as described above with delivery directly through the apex of the left ventricle (transapical), directly through the aortic artery (transaortic), through the subclavian artery, or through the axillary artery. Previously, whether delivering a collapsible prosthetic heart valve via the transfemoral approach or an alternative approach (including transapical, transaortic, subclavian, and axillary), an introducer sheath designed for the transfemoral approach, with possible minor variations, was used. While this strategy reduced complexity, the use of an introducer sheath created for transfemoral delivery may not be optimal for alternative delivery routes. For example, the tortuosity of the subclavian and axillary arteries may make introducer sheaths more prone to kinking compared to transfemoral delivery. Similarly, an introducer with a completely straight distal sheath may not be ideal for all delivery routes. For example, while transaortic delivery may occur along a relatively straight path through the body to the site of implantation, an introducer with an angle may be preferable for other routes to center the delivery device within the native heart valve. This might be the case for transfemoral delivery, which generally requires the introducer to bend around the aortic arch, or transapical delivery, in which the center of the native valve annulus does not align with the apex of the heart. 
     Referring to  FIG. 5A , an introducer  200  includes a housing  230  and a distal sheath  210 . Introducer  200  may be the same as introducer  100  described in connection with  FIGS. 3A-B . Alternately, introducer  200  may include a generally tubular non-expandable distal sheath  210 . Although not illustrated in  FIG. 5A , introducer  200  may also include a separate proximal sheath, flush ports, hemostatic valves and/or seals, and the like. As noted above, distal sheath  210  may be prone to kinking as it advances through the vasculature, particularly vasculature with relatively high tortuosity. Kinks may become a larger problem as introducer sheaths become thinner Thinner introducer sheaths may be preferable to maximize the inner diameter of the introducer while minimizing the outer diameter of the introducer. As shown in  FIG. 5B , as an introducer passes through a blood vessel BV, it may develop one or more kinks K along the sheath. Kinks K may make it difficult for a delivery device to pass through the introducer sheath to the site of implantation. Although an introducer prone to kinking may not be problematic for the relatively straight path of a transaortic delivery route, for example, it may not be suitable for the more tortuous subclavian or axillary delivery routes. To increase kink resistance, distal sheath  210  may be formed from a polymer such as Pebax co-extruded or braided with stainless steel wire or coil. Similarly, a metal tube, such as a Nitinol tube, may be cut longitudinally along the length thereof and provided with a number of slots or cut-outs to provide flexibility. The metal tube may be impregnated with a polymer such as Pebax to form distal sheath  210 . In this case, a liner or other material may be provided on an inner and/or outer surface of the polymer and tube to provide a smooth surface. Further, the material forming distal sheath  210 , whether a polymer or other material, may be braided or coiled to increase kink resistance. In addition, with a braided and/or coiled distal sheath  210 , kink resistance increases as distal sheath  210  is more likely to conform to the turns and bends in the blood vessel BV, as shown in  FIG. 5C . 
     Introducer  200  may additionally or alternately include pull wires (not shown) extending from a distal end  215  of distal sheath  210  to a proximal end of introducer  200  that can be manipulated from outside the patient. For example, pull wires may pass through one or more channels formed longitudinally in the walls of distal sheath  210 . As shown in  FIG. 5D , the pull wires may be manipulated by the surgeon to deflect the distal end  215  of distal sheath  210  so that a longitudinal axis L 1  of a proximal portion of distal sheath  210  and a longitudinal axis L 2  of the distal end  215  of distal sheath  210  form an oblique angle with respect to one another. By using such pull wires to deflect the distal end  215  of distal sheath  210 , it may be easier to align the distal end  215  of distal sheath  210  with the center of the native valve annulus of the heart valve being replaced. 
     In addition or as an alternate to using a deflectable introducer  200 , it may be beneficial to use a deflectable dilator. When introducing devices to the site of implantation, a thin guidewire may be the first device advanced through the vasculature to the site of implantation. A dilator may then be assembled over the guidewire and advanced to the site of implantation. If desired, additional dilators of increasing size may be passed over dilators of smaller sizes or may be inserted over the guidewire following removal of the previously inserted dilator. Once a large enough dilator is in place, introducer  200  may be advanced over the dilator to the site of implantation. The dilator(s) may include pull wires to provide for deflection similar to the introducer  200  of  FIG. 5D . By deflecting the dilator, it may be easier for the introducer  200  to be initially placed at the site of implantation in alignment with the center of the native valve annulus of the heart valve being replaced. It should be clear that a non-deflectable introducer may be placed over a deflectable dilator, with deflection of the dilator being translated to the introducer overlying the dilator. 
     Referring now to  FIG. 5E , introducer  200  may alternately or additionally include an adjustable length handle. Housing  230 , in addition to including hemostatic valves, seals, and/or other similar components, may house one or more extendable handle portions at least partially therein, such as handle portions  230   a  and  230   b . The handle portions  230   a  and  230   b  may slide proximally out of housing  230  in a telescoping fashion, for example by manually pulling the handle portions  230   a  and  230   b  proximally. Each handle portion  230   a  and  230   b  may include a flange F at a distal end to act as a stop to limit the distance the handle portion may be pulled proximally with respect to other handle portions. However, other stop mechanisms may be suitable. In addition, each handle portion  230   a  and  230   b  may include a locking element. For example, flange F of handle portion  230   b  may include threads configured to mate with corresponding threads on the internal surface at the proximal end of handle portion  230   a . Once in the extended condition, shown in  FIG. 5E , a user may rotate handle portion  230   b  to lock handle portion  230   b  from sliding axially with respect to handle portion  230   a . Handle portion  230   a  may include a similar locking element configured to mate with a complementary locking element in housing  230 . If more than two extendable handle portions  230   a  and  230   b  are desired, those additional portions may also include locking elements. 
     The inclusion of extendable handle portions  230   a  and  230   b  in introducer  200  may provide the ability for a surgeon to avoid placing his hand in a radiation field during a heart valve replacement procedure. For example, during heart valve replacement, an x-ray field may be applied around the site of implantation to allow the surgeon to visualize the heart as well as surgical components in real time. With some delivery routes, such as a transfemoral delivery, the surgeon is relatively far away from the heart and thus from the radiation field. However, as shown in  FIG. 5F , if introducer  200  is inserted via a transaortic delivery route TA or via a subclavian delivery route SC, housing  230  may be in close proximity to the surgical site, and thus close to or within the radiation field. This may be problematic because during manipulation of introducer  200 , housing  230  is generally gripped or held by the user, for example when inserting another device through introducer  200 . If the particular delivery route used results in housing  230  being in or close to the radiation field, the surgeon may extend the housing  230  proximally by pulling handle portions  230   b  and  230   a  proximally in a telescoping fashion. Once the handle portions are extended, the surgeon may twist or rotate the handle portions  230   a  and/or  230   b  to lock them in place. In the locked condition, the surgeon can handle introducer  200  while, for example, inserting a delivery device through the introducer  200 , without the extendable handle portions  230   a  and  230   b  moving unintentionally. It should be noted that in  FIG. 5F , although introducer  200  is shown delivered through the aortic artery as well as the subclavian artery, generally only a single introducer  200  would be used via a single delivery route in any given heart valve replacement procedure. 
     Introducer  200  may also include a securing element  250 . As shown in  FIGS. 5G-H , securing element  250  may include a cylindrical handle  254  assembled over distal sheath  210  and a flange  252  extending radially outwardly from handle  254  and from distal sheath  210 . The fit between handle  254  and distal sheath  210  may be loose enough so that application of force slides securing element  250  axially along distal sheath  210  in the proximal or distal directions indicated by the arrows D, while being tight enough that securing element  250  is unlikely to slide unintentionally. Alternately or in addition, handle  254  may include a locking mechanism to lock securing member  250  from axial movement with respect to distal sheath  210 . For example, handle  254  may include a simple set screw arrangement or an internal split nut structure that may lockingly clamp over distal sheath  210  upon rotation of handle  254 . Other locking mechanisms may also be suitable. For example, a rotating collar that tightens down on handle  254  when rotated, for example via a threaded connection, may also be suitable for the locking mechanism. Flange  252  may include a plurality of apertures  256  therethrough to allow for securing flange  252  to native anatomy, for example by suturing flange  252  to the vasculature. Flange  252  may be formed of a flexible material so that it better conforms to the surface of the anatomy to which it is being secured. 
     Securing member  250  may be particularly useful when implanting a prosthetic heart valve via the transaortic delivery route. As shown in  FIG. 5I , during a transaortic prosthetic heart valve replacement procedure, introducer  200 , and specifically distal sheath  210 , may be passed a relatively short distance X into aorta A. During an aortic valve replacement procedure, there may be relatively little working space between the point of entry of distal sheath  210  in aorta A and the aortic valve AV. Thus, slight movement of introducer  200  proximally may result in introducer  200  exiting the aorta A, while slight movement of introducer  200  distally may reduce the amount of working space and cause difficulties in completing the procedure. Once introducer  200  is advanced the desired distance X into aorta A, the surgeon may slide securing member  250  distally until flange  252  abuts the external surface of aorta A. When in this position, the surgeon may lock securing member  250  from additional sliding motion relative to distal sheath  210 , for example by rotating handle  254 , and then pass sutures through apertures  256  and aorta A to secure flange  252  to aorta A. Once suturing is complete, distal sheath  210  is positioned the desired distance X into aorta A and cannot readily move proximally or distally with respect to aorta A until the sutures are removed and/or securing member  250  is unlocked with respect to distal sheath  210 . This may reduce the complexity of the surgery by allowing the surgeon to concentrate more fully on the valve implantation without worrying about introducer  200  being moved during the procedure. 
     It should be noted that delivery devices other than delivery device  10  may be suitable for use with the introducers described above. For example, delivery device  10  may be suitable for a transfemoral aortic valve implantation, but may not be suitable for a transapical aortic valve implantation. A modified version of delivery device  10  for transapical aortic valve implantation may still, however, be used with the introducers described herein. Additionally, any of the components described above with respect to introducers  100  and  200  may include radiopaque markers, such as radiopaque rings, to better visualize the position of the component within the body during any given procedure, for example by using X-ray fluoroscopy. It should further be noted that introducers  100 ,  200  can be used for other laparoscopic or percutaneous medical procedures including angioplasty, stent implantation, laparoscopic surgery, etc. 
     According to one embodiment of the disclosure, an introducer for providing access to a surgical site in a patient comprises:
         a proximal housing configured to be positioned outside the patient; and   a sheath having a first portion coupled to the proximal housing and a second portion extending distally of the proximal housing, the second portion having a first edge, a second edge, and a middle section extending from the first edge to the second edge,   wherein the second portion has a rolled configuration in which the middle section at least partially overlies the first edge, and the second edge at least partially overlies the middle section; and/or   the second portion of the sheath is radially expandable from a relaxed inner diameter to an expanded inner diameter greater than the relaxed inner diameter; and/or   the relaxed diameter is less than or equal to about 12 French; and/or   the second portion of the sheath is radially expandable to an inner diameter of between about 18 French and about 19 French; and/or   the second portion of the sheath is radially expandable to an inner diameter of about 21 French; and/or   the second portion of the sheath is formed of a braided material; and/or   a system for delivering a collapsible prosthetic heart valve to the surgical site in the patient further comprises a delivery device assembled to the introducer and having a handle and a catheter assembly extending distally from the handle, wherein the introducer surrounds at least a portion of the catheter assembly; and/or       

     the catheter assembly includes a proximal catheter shaft having a first outer diameter and a distal catheter shaft having a second outer diameter larger than the first outer diameter, the distal catheter shaft being configured to house the collapsible prosthetic heart valve in a collapsed condition; and/or
         the second portion of the sheath has a relaxed inner diameter that is radially expandable to expanded inner diameter that is greater than the second outer diameter of the distal catheter shaft.       

     According to another embodiment of the disclosure, an introducer for providing access to a surgical site in a patient comprises:
         a proximal housing configured to be positioned outside the patient;   a sheath extending from the proximal housing to a distal end of the introducer; and   a first handle housed at least partially within the proximal housing and configured to translate axially in a proximal direction and a distal direction with respect to the proximal housing; and/or   a second handle housed at least partially within the proximal housing and at least partially within the first handle, the second handle being configured to translate axially in the proximal direction and the distal direction with respect to the proximal housing and the first handle; and/or   a first locking element on the first handle and a second locking element on the proximal housing, the first locking element configured to engage the second locking element to restrict axial translation of the first handle with respect to the proximal housing; and/or   the first locking element is a first thread and the second locking element is a second thread configured to mate with the first thread; and/or   a flange on a distal end of the first handle and configured to limit axial translation of the first handle in the proximal direction with respect to the proximal housing.       

     In a further embodiment of the disclosure, an introducer for providing access to a surgical site in a patient comprises:
         a proximal housing configured to be positioned outside the patient;   a sheath extending from the proximal housing to a distal end of the introducer; and   a securing element slideably coupled to the sheath, the securing element having a flange extending radially outwardly from the sheath; and/or   the flange includes a plurality of apertures extending therethrough; and/or   the flange is flexible; and/or   the securing element has a handle portion coupled to the flange and a locking element configured to restrict sliding motion of the sealing element with respect to the sheath.       

     Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. For example, features described in connection with one embodiment may be combined with features described in connection with another embodiment without varying from the scope of the invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.