EXPANDABLE BRAIDED INTRODUCER SHEATH

In some examples, an introducer sheath extends from a proximal end to a distal end, and includes a hub disposed at the proximal end, and a body coupled to the hub and extending between the proximal end and the distal end, the body defining a lumen and having a collapsed condition and an expanded condition, the body having a braided material and an elastomeric material covering the braided material, the body having a flared distal end.

BACKGROUND OF THE DISCLOSURE

The present disclosure is related to percutaneous medical procedures, and more particularly to devices providing access into the body for performing percutaneous medical procedures. Still more particularly, the present disclosure is related to prosthetic heart valve replacement, including devices, systems, and methods for transcatheter delivery of collapsible prosthetic heart valves into a patient.

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 or braided structure. 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.

When a collapsed prosthetic valve has reached the desired implant site in the patient (e.g., at or near the annulus of the patient's 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 deploying the 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 For self-expanding valves, on the other hand, the stent automatically expands as the sheath covering the valve is withdrawn.

Despite the various improvements that have been made to the collapsible prosthetic heart valve delivery process, conventional delivery devices, systems, and methods suffer from some shortcomings. For example, in conventional delivery devices for heart valves, large introducers risk traumatizing the iliac or femoral arteries, and the risk of trauma increases with introducers having larger diameters. Additionally, the large diameters of these devices continue to be a challenge due to the size of the collapsed valve. As an example, the outer diameter of a transcatheter mitral valve replacement device can be in the range of 36 F and the corresponding introducer sheath may be 40 F, requiring a surgical cut down for most cases. The ideal procedure for the interventional cardiologist is a minimal profile access with no vascular complications.

There therefore is a need for further improvements to the devices, systems, and methods for transcatheter delivery of collapsible prosthetic heart valves, and in particular, the introduction of such prosthetic heart valves into the heart. Among other advantages, the present disclosure may address one or more of these needs.

BRIEF SUMMARY OF THE DISCLOSURE

In some examples, an introducer sheath extends from a proximal end to a distal end, and includes a hub disposed at the proximal end, and a body coupled to the hub and extending between the proximal end and the distal end, the body defining a lumen and having a collapsed condition and an expanded condition, the body having a braided material and an elastomeric material covering the braided material, the body having a flared distal end.

In some examples, an introducer sheath extends from a proximal end to a distal end and includes a hub disposed at the proximal end, and a body having a lumen and extending between the proximal end and the distal end, the body having a collapsed condition and an expanded condition, the body having a double layer of a braided material and an elastomeric material covering the braided material.

DETAILED DESCRIPTION

As used herein, the terms “proximal,” “distal,” “leading” and “trailing” are to be taken as relative to a user using the disclosed delivery devices. “Proximal” or “trailing end” are to be understood as relatively close to the user, and “distal” or “leading end” are to be understood as relatively farther away from the user. Also, as used herein, the words “substantially,” “approximately,” “generally” and “about” are intended to mean that slight variations from absolute are included within the scope of the structure or process recited.

In the description which follows, the structure and function of a transaortic or transfemoral delivery device will be described. It will be understood, however, that the devices and methods disclosed herein also may be used with a transapical or transseptal delivery device. Indeed, the devices and methods described herein may be used in connection with any minimally invasive procedure to provide a passageway for any type of small profile medical device or instrument into a patient's body. An exemplary transaortic delivery device10for delivering a prosthetic heart valve into a patient is shown inFIGS.1A and1B. Transaortic delivery device10has a catheter assembly16for delivering the heart valve to and deploying the heart valve at a target location, and an operating handle20for controlling deployment of the valve from the catheter assembly. Delivery device10extends from a proximal end12to an atraumatic tip14at the distal end of catheter assembly16. Catheter assembly16is adapted to receive a collapsible prosthetic heart valve (not shown) in a compartment23defined around an inner shaft26and covered by a distal sheath24.

Inner shaft26may extend from operating handle20to atraumatic tip14of the delivery device, and may include a retainer25affixed thereto at a spaced distance from tip14and adapted to hold a collapsible prosthetic valve in compartment23. Retainer25may have recesses80therein that are adapted to hold corresponding retention members of the valve. Inner shaft26may be made of a flexible material such as braided polyimide or polyetheretherketone (PEEK), for example. Using a material such as PEEK may improve the resistance of inner shaft26to kinking while catheter assembly16is tracking through the vasculature of a patient.

Distal sheath24surrounds inner shaft26and is slidable relative to the inner shaft such that it can selectively cover or uncover compartment23. Distal sheath24is affixed at its proximal end to an outer shaft22, the proximal end of which is connected to operating handle20in a manner to be described. Distal end27of distal sheath24abuts atraumatic tip14when the distal sheath is fully covering compartment23, and is spaced apart from the atraumatic tip when compartment23is at least partially uncovered.

Operating handle20is adapted to control deployment of a prosthetic valve located in compartment23by permitting a user to selectively slide outer shaft22proximally or distally relative to inner shaft26, thereby respectively uncovering or covering the compartment with distal sheath24. Outer shaft22may be made of a flexible material such as nylon 11 or nylon 12, and it may have a round braid construction (i.e., round cross-section fibers braided together) or flat braid construction (i.e., rectangular cross-section fibers braided together), for example.

The proximal end of inner shaft26may be connected in a substantially fixed relationship to an outer housing30of operating handle20, and the proximal end of the outer shaft22may be affixed to a carriage assembly40that is slidable along a longitudinal axis of the handle housing, such that a user can selectively slide the outer shaft relative to the inner shaft by sliding the carriage assembly relative to the housing. Operating handle20may further include a hemostasis valve28having an internal gasket adapted to create a seal between inner shaft26and the proximal end of outer shaft22.

As shown, handle housing30includes a top portion30aand a bottom portion30b. Top and bottom portions30aand30bmay be individual components joined to one another as shown inFIG.1B. Collectively, top and bottom portions30aand30bdefine an elongated space34in housing30in which carriage assembly40may travel. Optionally, top and bottom portions30aand30bmay further form a substantially cylindrical boss31for accepting a clip, as will be described below. Elongated space34preferably permits carriage assembly40to travel a distance that is at least as long as the anticipated length of the prosthetic valve to be delivered (e.g., at least about 50 mm), such that distal sheath24can be fully retracted from around the prosthetic valve. Carriage assembly40includes a pair of carriage grips42, each attached to a body portion41. Although the carriage assembly40is shown inFIGS.1A and1Bas having two carriage grips42, that need not be the case.

Handle housing30further defines a pocket37that extends through top portion30aand bottom portion30bfor receiving a deployment actuator21. Pocket37is sized and shaped to receive deployment actuator21with minimal clearance, such that the location of deployment actuator remains substantially fixed relative to housing30as it is rotated. Deployment actuator21may be internally coupled to body portion41via a threaded shaft or other suitable connection such that rotation of the deployment actuator in one direction (either clockwise or counterclockwise) pulls the body portion41of carriage assembly40proximally through elongated space34.

To use operating handle20to deploy a prosthetic valve that has been loaded into compartment23and covered by distal sheath24, the user may rotate deployment actuator21, causing carriage assembly40to slide proximally within elongated space34in housing30. Because distal sheath24is affixed to outer shaft22, which in turn is affixed to carriage assembly40, and because inner shaft26is fixed to housing30, sliding the carriage assembly proximally relative to the housing will retract the distal sheath proximally from compartment23, thereby exposing and initiating deployment of the valve located therein.

Delivery device10may be used to implant a medical device such as a collapsible stent-supported prosthetic heart valve100having a stent102and a valve assembly104(FIG.2). Prosthetic heart valve100is designed to replace a native tricuspid valve of a patient, such as a native aortic valve. It should be noted that while the devices disclosed herein are described predominantly in connection with their use to implant a prosthetic aortic valve and a stent having a shape as illustrated inFIG.2, the valve could be a bicuspid or other valve, such as the mitral valve.

The expandable stent102of prosthetic heart valve100may be formed from biocompatible materials that are capable of self-expansion, such as, for example, shape memory alloys, such as the nickel-titanium alloy known as “nitinol,” or other suitable metals or polymers. Stent102extends in a length direction L1from proximal or annulus end110to distal or aortic end112, and includes annulus section120adjacent proximal end110, transition section121, and aortic section122adjacent distal end112. Annulus section120has a relatively small cross-section in the expanded condition, while aortic section122has a relatively large cross-section in the expanded condition. Preferably, annulus section120is in the form of a cylinder having a substantially constant diameter along its length. Transition section121may taper outwardly from annulus section120to aortic section122. Stent102may also have different shapes, such as a flared or conical annulus section, a less-bulbous aortic section, and the like, and a differently shaped transition section121. Each of the sections of stent102includes a plurality of struts130forming cells132connected to one another in one or more annular rows around the stent. For example, as shown inFIG.2, annulus section120may have two annular rows of complete cells132and aortic section122and transition section121may each have one or more annular rows of partial cells132. Cells132in aortic section122may be larger than cells132in annulus section120to better enable prosthetic valve100to be positioned in the native valve annulus without the stent structure interfering with blood flow to the coronary arteries. Each of cells132has a length in length direction L1of the stent and a width in a perpendicular direction W1.

Stent102may include one or more retaining elements134at distal end112thereof, retaining elements134being sized and shaped to cooperate with recesses80in retainer25of delivery device10. The engagement of retaining elements134with portions of delivery device10helps maintain prosthetic heart valve100in assembled relationship with the delivery device, minimizes longitudinal movement of the prosthetic heart valve relative to the delivery device during unsheathing or resheathing procedures, and helps prevent rotation of the prosthetic heart valve relative to the delivery device as the delivery device is advanced to the target location and the heart valve deployed.

Valve assembly104of prosthetic heart valve100preferably is positioned in annulus section120of stent102and secured to the stent. Valve assembly104includes cuff136and a plurality of leaflets138which collectively function as a one-way valve by coapting with one another. As a prosthetic aortic valve, valve100has three leaflets138.

Although cuff136is shown inFIG.2as being disposed on the luminal or inner surface of annulus section120, it is contemplated that cuff136may be disposed on the abluminal or outer surface of annulus section120or may cover all or part of either or both of the luminal and abluminal surfaces. Both cuff136and leaflets138may be wholly or partly formed of any suitable biological material or polymer such as, for example, polytetrafluoroethylene (PTFE).

Leaflets138may be attached along their belly portions to cuff136or to stent102, with the commissure between adjacent leaflets138being attached to a commissure feature140. As can be seen inFIG.2, each commissure feature140may lie at the intersection of four cells132, two of the cells being adjacent one another in the same annular row, and the other two cells being in different annular rows and lying in end-to-end relationship. Preferably, commissure features140are positioned entirely within annulus section120or at the juncture of annulus section120and transition section121. Commissure features140may include one or more eyelets which facilitate the suturing of the leaflet commissure to stent102.

Prosthetic heart valve100may be used to replace a native aortic valve, a surgical heart valve or a heart valve that has undergone a surgical procedure. Prosthetic heart valve100may be delivered to the desired site (e.g., near the native aortic annulus) using any suitable delivery device, including delivery device10described above. During delivery, prosthetic heart valve100is disposed inside compartment23of delivery device10in the collapsed condition. The delivery device may be introduced into a patient using a transfemoral, transapical, transseptal or any other percutaneous approach. Once the delivery device has reached the target site, the user may deploy prosthetic heart valve100in the manner described above. Upon deployment, prosthetic heart valve100expands so that annulus section120is in secure engagement within the native aortic annulus. When prosthetic heart valve100is properly positioned inside the heart, it works as a one-way valve, allowing blood to flow from the left ventricle of the heart to the aorta, and preventing blood from flowing in the opposite direction.

FIG.3illustrates conventional polymer-based introducers300that utilize a folding technique to insert the sheath at a smaller diameter. Specifically, a portion of the introducer is folded upon itself in a first condition300A for insertion and then unfurls to define a larger diameter of a second condition300B. One disadvantage of a folded sheath is that blood may exit or leak through the folds when the sheath is expanded post insertion. Furthermore, it may be challenging to subsequently reduce the diameter of a folded sheath to a smaller diameter when the sheath is withdrawn after use. Thus, it would be desirable to provide a sheath that radially expands and collapses, which will minimize the friction against the vessel wall. Additionally, conventional sheaths may not have the ability to expand enough to enable large bore catheter to pass through. Regular expandable sheath might be capable of expansion by a maximum rate, whereas higher expansion rates might be desirable. Conventional sheath may also not be large enough to accommodate larger transcatheter mitral valve replacement and transcatheter tricuspid valve replacement devices without defeating the purpose of having a small introducer sheath to minimize vessel trauma.

An introducer sheath may be useful to provide access into a vessel to allow for advancing a delivery device to a target location in patients whose native anatomy has calcified legions or may be compromised due to degeneration of the vessel. Generally, the target is just beyond the femoral bifurcation point as to reduce the risk of tearing or lacerating the vessel during insertion of the larger delivery system profile. Specifically, an incision may be formed in the patient's body and the introducer sheath may be placed through the incision to provide a passageway for advancing a medical device into the patient's body. It has been found that larger introducers risk traumatizing body tissue and that the risk of trauma increases with time. Thus, it is desirable to have a small introducer sheath that locally expands as necessary. Although introducer sheaths are described below in connection with the delivery of a prosthetic heart valve into a patient, it will be understood that the concepts described may be useful for any interventional procedure in which an apparatus, such as a medical device or instrument, is passed through an introducer sheath for delivery, implantation or surgical procedures, such as other cardiac repair procedures, balloon angioplasty, laparoscopic surgical procedures, peripheral interventional procedures, and the like. In some examples, an introducer sheath that can be inserted at a small diameter (<18 F) and expand to the required diameter of a therapeutic or diagnostic device may reduce trauma to the vessel and the connecting tissue. It will be understood that arterial and venous access requirements for the devices may differ with respect to the desired diameter and expansion.

Moreover, the principles described herein may be applicable to other applications such as percutaneous ventricular assist devices (pVAD), leadless pacemakers, or any other large bore catheter inserted into a vessel of a patient where vascular access is deemed an operative risk (e.g., difficult to navigate iliac, jugular vein, small vessels, etc.). The present disclosure describes a sheath that may be introduced at a small outer diameter and can expand to accept larger devices, the sheath interaction against the native anatomy limiting circumferential fluid leak, and minimizing trauma of the vessel and connecting tissue. In some examples, a sheath according to the present disclosure is capable of accessing the vasculature approximately at an angle of 20-45 degrees (e.g., 30 degrees) with respect to the patient's back. In some examples, a sheath utilizes an access point that is just distal to the profunda and superficial artery bifurcation point. The sheath may navigate through the vasculature to beyond the main arterial bifurcation. The sheath may also be used for venous applications as well. Additionally, other access points (e.g., radial access, jugular access, etc.) may be possible. The sheath may be able to navigate tortuous patient anatomy, including potentially calcified vasculature. In some examples, a sheath may have appropriate bending stiffness to be trackable and insertable, while conforming to how the artery may naturally curve throughout the body.

FIG.4A-Billustrates one example of an introducer sheath400that generally extends between a proximal end402and a distal end404. Introducer sheath400may be introduced at a small outer diameter and expand to accept larger devices. Due to the introducer sheath construction, the risk of leakage is reduced compared to conventional devices. Introducer sheath400may include a hub405disposed adjacent the proximal end, and a body410that extends from the hub adjacent proximal end402to the distal end404. InFIG.4A, a dilator “D” is shown disposed within body410of the introducer. As shown in the schematic ofFIG.4C, body410may comprise an inner braided material412(e.g., NiTi or “nitinol” braid) and an outer elastomeric material414at least partially covering the braided material412, the body defining a central lumen420for receiving instruments, devices, dilators, prosthetic implants and the like. Additional support structures (not shown) may be added to the body410. While conventional sheaths include an inner polymeric liner, body410may include a braided material412having an inner surface capable of receiving instruments, devices and prosthetic implants therethrough. In some examples, the braided material412includes NiTi with a high surface finish that is not prone to catching on material passing along its surface. In some examples, braided material412may include NiTi braid having round or flat wire. Optionally, additional polymeric layer(s)416may be added over outer elastomeric material414and/or within braided material412. This may yield additional benefits such, as for example, increased column strength. In some examples, the additional polymeric layer(s)416may comprise Pebax. The additional polymeric layer416may be the outermost layer, the innermost layer, or may sandwich elastomeric material414and braided material412. The additional polymeric layer(s)416may also include a double layer disposed on the outside the elastomeric material414, or within braided material412. In some examples, elastomeric material414and/or additional polymeric layer(s)416may be integrated (e.g., dipped, sprayed, extruded, etc.) over braided material412to cover the entire braided material412or into a pattern (e.g., candy-cane striped extrusions of different durometers). In some examples, a Heparinized saline may be utilized during a procedure to ensure no thrombus are created within braided material412.

Turning toFIGS.4D-E, certain details of the introducer sheath400will be described. As shown inFIG.4D, body410may be coupled to the hub405adjacent the proximal end. In some examples, body410is flared at the proximal end and couples to the outer diameter of hub405to create a smooth transition. In some examples, body410may be between 160 and 900 mm in length, or between 300 and 400 mm in length (e.g., between 350 mm and 400 mm in length, or approximately 360 mm in length). Elastomeric material414may be bonded, heat-bonded, or flowed onto braided material412along the length of the body410. In some examples, the internal diameter d1of the braided material is between 2 mm and 8 mm (e.g., 4 mm), and in some examples, the outer diameter d2is between 2 mm and 8 (e.g., 4.97 mm).

Turning toFIG.4E, in some embodiments, a single length of braided material is used, which is double the final catheter length. For example, a braided material of approximately 726 mm in length may be used to create a body length of 363 mm. Thus, the braided material412may comprises two or more layers including an inner braided layer412aand an outer braided layer412b, the two layers being at least partially covered by elastomeric material414. A flared distal end422may also be formed, and the flare may have an angle α1of between 1 and 45 degrees (e.g., 5 degrees, 7 degrees, 10 degrees or 15 degrees) defined with respect to the longitudinal axis of the body410to facilitate instrument withdrawal. The braided material may transition between a collapsed condition and an expanded condition. In some examples, the PIC count (i.e., the per inches wire crosses, or wire cross density), density and lead may be high enough not to interfere with the devices passing through the inner diameter of the sheath. The braided material may be heat-set in the collapsed condition (i.e., at the unexpanded diameter) with an appropriate tip shape applied to not interfere with any of the passed through devices in case device withdrawal is desired. In some examples, a “roll” may be applied to the distal tip, as seen inFIG.4F, so that the tip does not break under an acute bend. This tip configuration may be advantageous because the NiTi freetails of the braid are not exposed, which may otherwise limit the expansion due to the need to manage the freetails.

After the doubling over and the heat-setting process, the braided material is reduced to about half its original single-layer length. In some examples, the thickness of the wire strands of the braided material may be between 0.001″ to 0.008″ depending on the stiffness required of the sheath. This results in a relatively thin wall thickness of between 0.002″ and 0.016″ (e.g., 0.015″) and a thickness of between 0.007″ and 0.030″ with a polymeric coating.

In some examples, a tubular braided material412may be configured and arranged to avoid “finger trapping” when a tool or instrument is pushed through its lumen. Without being bound by any particular theory, it is believed that one or more of a combination of the PIC count, the angle of the braid, the materials of the braid and/or the specific process of heat setting may contribute to a reduction in finger-trapping. For example, starting with a larger diameter and a high PIC count may yield a relatively high resulting lead angle of braid after heat setting. As shown inFIG.4G, when collapsed the wires of the braided material overlap and display a relatively high density within a certain region, and the angle between wires is relatively acute (e.g., less than 20 degrees, less than 15 degrees, or less than 10 degrees). Conversely, as shown inFIG.4H, the expanded PIC angle is larger (e.g., between 30 and 60 degrees, or approximately 45 degrees as shown), and the density of wires is relatively lower in the same region. As shown in certain models, the angle between wires of a 144 braided material increased from between 20-40 degrees, between 25-30 degrees or 27 degrees (as shown inFIG.4I) in the collapsed condition when the braided material forms a tube with a 6 mm outer diameter, to between 80 and 90 degrees, or 84 degrees (FIG.4J) in the expanded condition when the braided material forms a tube with 25 mm outer diameter.

As shown inFIG.4C, elastomeric material414may be arranged as a single layer or double layer. In some examples, the elastomeric material414includes a single layer at least partially covering the outer diameter on the braided material412. In some examples, elastomeric material414comprises a double layer, which includes a first layer on the outer diameter of the braided material and a second elastomeric material disposed in between braid layers. Embodiments that include multiple elastomeric materials may allow the melting of the two materials for superior adhesion to the braided material. In some examples, wall thicknesses of the elastomer may be as thin as 0.001″ and as thick as 0.015″, depending on the desired force required to open the elastomer. In some examples, the elastomeric material414comprises chronoprene, Pebax (e.g., 25D Pebax), silicone, Tecothane, Hydrothane, Chronoflex, ePTFE, bicarbonate and other similar materials or combinations thereof. These elastomers can also be strategically striped, hydrophilic coated, and controlled via material design parameters. In some embodiments, the term “elastomeric” is used to describe any polymer capable of forming a tube that is expandable to at least twice its diameter with acceptable forces and returning to its initial state absent external forces.

FIGS.5A-Dillustrate several examples of attaching the elastomeric material to the braided material. In some examples, the elastomeric material may be coupled, or attached, to the braided material in a way to allow appropriate expansion and/or reduction in diameter as the introducer sheath transitions from the collapsed condition to the expanded condition and vice versa. In the example shown inFIG.5A, an introducer sheath500amay include an elastomeric material414coupled to the braided material412at segmented reflow attachment regions or bands501athat are axially-spaced apart from one another. The bands501amay be disposed adjacent only the distal end, only the proximal end or throughout the body. In some examples, the bands501aare axially-spaced apart from one another by 1-5 centimeters. In another example shown inFIG.5B, an introducer sheath500bmay include an elastomeric material414coupled to the braided material412with a complete reflow of the elastomeric material along the entire length of the body. InFIG.5C, introducer sheath500cincludes a spine reflow attachment501calong the length of the body. In some examples, a spine reflow includes a thin axial attachment approximately 1 mm wide. Sheath500cmay include a single spine reflow attachment501cor multiple spine reflow attachments (e.g., two, three, four or more), circumferentially disposed along the body and spaced from one another (e.g., separated by a constant radial distance from one another). Finally, inFIG.5D, dimplings or spot welds501dare used to couple the elastomeric material to the braided material. In this examples, five welds501dare shown, axially spaced from one another adjacent the distal end. It will be understood that any number of welds may be disposed adjacent the proximal and/or distal ends, and that the welds may be disposed along a single side of the sheath500d, or radially disposed about the body (e.g., two or more welds circumferentially spaced from on another at each axial extent). Any of these configurations may be used to couple the elastomeric material to the braided material and to reduce or eliminate bunching of the elastomeric material during insertion. Optionally, an outer hydrophilic coating may be applied to the elastomeric material to reduce the friction between the elastomer and the native tissue. Hydrophilic elastomers may also be used as the elastomeric material.

Instead of, or in addition to, reflowing materials, suture attachment of the elastomeric material to the braided material may also be possible (FIG.5E). In some examples, sutures501emay be disposed at the distal end of an introducer sheath500eto couple the layers together. In some examples, sutures501emay also be disposed at the proximal end, or at any point between the proximal end and the distal end. Sutures501emay be circumferentially disposed about the body with two, three, four or more stitches being radially spaced apart from one another. Sutures510emay also include between one and ten stitches disposed around the diameter at various axial positions.

Variations of the foregoing embodiments are possible. For example, an introducer sheath may be formed using a combination of elements described above. Additionally, in some examples, one or more elements of the introducer sheath may be capable of changing stiffness upon the application of heat, cooling, electricity or other external stimuli, such as pneumatics (i.e., pressure). For example, an introducer sheath may be relatively flexible and stiffen up once the external stimuli is applied. This may allow the introducer sheath to be trackable and insertable, but not too stiff where it cannot conform to how the artery may naturally curve throughout the body. The application of stimuli at certain points in the procedure may allow the clinician to alternate between a relatively stiff configuration and a relatively flexible configuration at different steps in the procedure. The introducer sheath may also include one or more radiopaque elements disposed on the circumference along one or more axial positions to allow the physician to take an image to see if a consistent tubular shape is defined within the vasculature by the introducer sheath. This may, for example, be useful for locating calcium deposits or to visualize post-dilator deployment to ensure that the introducer sheath is not buckled or deformed prior to insertion of a tool or implant.

As previously noted, an introducer sheath400may include a flared distal end422defining an angle of between 5 and 45 degrees (e.g., 7 degrees, 10 degrees or 15 degrees) to facilitate instrument withdrawal through the distal end of the sheath. In some examples, a flared distal end may reduce the potential for device prolapse (FIG.6A). Without being bound by any particular theory, it is believed that the distal flare inflects the tip of the sheath away from the center of the lumen. This tipping may allow an interrupted profile device (being passed through the introducer sheath) that may contain fabric, tissue, metal, or polymer features to be withdrawn without “catching” at the tip. The flare may provide a “ramp” for the introducer sheath to accommodate nonconformities in the shaft or delivery system being withdrawn. In some examples, during insertion of the expandable introducer sheath, the distal end of the introducer sheath may include a smooth transition from the sheath to the dilator to avoid damaging the vessel. In some examples, it may be desirable to design a dilator which will allow a smooth transition and/or to retain the flared distal end. Thus, in addition to the flared distal end, certain complementary features may be included on the dilator. Once inside the vessel the flared distal end is not expected to negatively interact with the anatomy. In some embodiments, features on the dilator may shield or retain the flared distal end of the sheath from the access tissue.

Several possible dilator features are shown inFIGS.6B-9Cto complement, retain or shield the flared distal end622of an introducer sheath600. InFIG.6B, dilator650bincludes an angled butt652disposed opposite flared distal end622, the angled butt652having a maximum outer diameter closer to the flared distal end622, and a linearly (or non-linearly) decreasing outer diameter distally thereof. InFIG.6C, dilator650cincludes an encapsulating segment654configured to slide and receive flared distal end622therein, encapsulating segment654being substantially domed to house the flared distal end622. InFIG.6D, dilator650dincludes a receiving segment656including a channel657for accepting the flared distal end622therein, the channel657being substantially equal in length to the flared distal end622. InFIG.6E, dilator650eincludes a radially undercut slot658for accepting the flared distal end622therein, the radially undercut slot658being defined radially inward of the outer diameter of dilator650d.

Another embodiment is shown inFIGS.7A-C, which illustrate various stages of a two-part dilator. Specifically, introducer sheath600is shown with a flared distal end622, and a dilator670having a distal segment680and a proximal segment690, the distal segment and the proximal segment being coupleable with one another. Distal segment680may include a leading nosecone tip682and one or more recesses684, and proximal segment690may include a bulbous portion692and one or more locking pins694. In some examples, the number of recesses684and the number of locking pins694are equal, and the two elements are aligned or alignable with one another. As shown inFIG.7A, proximal segment690may be initially disposed within introducer sheath600. As distal segment680and proximal segment690are brought together for engagement, flared distal end622may be inwardly biased and sandwiched between the two elements (FIG.7B). The operator may continue to bring distal segment680and proximal segment690into engagement until the one or more recesses684receive the one or more locking pins694, and the locking pins694are secured within the recesses (FIG.7C). In some examples, the operator may “assemble” the dilator and the introducer sheath. Alternatively, the two components may be “preassembled” with the operator only having to insert the assembled sheath into the vessel. In this condition, the flared distal end622is secured between distal segment680and proximal segment690. Specifically, flared distal end622may overlie bulbous portion692and be secured within distal segment680. In use, dilator670may be engaged with introducer sheath600as shown inFIG.7C, and delivered to the target position. Distal segment680and proximal segment690may begin to be disengaged from one another (e.g., by pushing distal segment680forward and keeping proximal segment690stationary, or by pulling proximal segment690backward while keeping distal segment680stationary, or some combination thereof). Disengagement of distal segment680from proximal segment690, may release flared distal end622of introducer sheath600so that the flared distal end622returns to its resting, radially-opened condition.

An elastomer may also be used to provide a smooth transition between a dilator and an introducer sheath, and to at least partially retain the flared distal end of an introducer sheath closer to the dilator. InFIG.8, an elastomer675is bonded to the surface of the dilator670and extends proximally beyond the flare distal end622of the introducer sheath600. Just proximal to the flared tip end622of introducer sheath600, the elastomer675may include a horizontally scored or perforated line676to allow a controlled tearing of the elastomer so that it can be removed once the dilator670is extended a set distance distal to the tip of the introducer sheath600. In some examples, the elastomer675may be released by pushing the dilator distally, thereby deploying the flared distal end of the introducer sheath.

Because the outer diameter of a braided introducer sheath is relatively small, it may be possible to add a “cover” sheath on the outer diameter to restrict full expansion of the distal flared end and allow a seamless transition with the dilator. A split sheath900(or “peel-away sheath”) is shown inFIG.9A, which includes two pull tabs902and a cylindrical tube divided into two portions904a,904b. Split sheath900may include a longitudinal scoring906that allows the two portions904a,904bto separate from one another when the pull tabs902are pulled apart. As shown inFIG.9B, a split sheath900may cover an introducer sheath600having a flared distal end622, and retain the flared distal end622in a substantially axial configuration. When tabs902are pulled apart, the split sheath900may separate into two portions904a,904band be removed, thereby releasing the flared distal end622and allowing it to extend radially outward as shown inFIG.9C.

In some embodiments, a dilator and introducer sheath hub may lock together to give column strength to the braided material and the elastomer. In some examples, both the braid material and elastomeric material are not strong when compressed axially. Once the tip of the sheath is starting to enter the surrounding soft tissue towards the vascular access, the physician should be able to push on the hub without prolapse of the device. To reduce the risk of prolapse, the dilator may lock into, or with, the hub. In some examples, three positions are used, as ordered in the procedure flow chart ofFIG.10. In this example, the hub and dilator begin in the locked position in step1010, then the dilator is unlocked from the hub and pushed to release the tip mechanism in step1020, followed by dilator removal in step1030.

FIGS.11A-Fillustrate the use of an introducer sheath600that extends between a proximal end602adjacent a hub, and a distal end604. In the example shown inFIG.11A, the introducer sheath600includes a dual layer of braided material and a single elastomeric material. A 12 French (4 mm) dilator670is shown extending through introducer sheath600. The outer diameter of introducer sheath600is shown to be 4.86 mm or approximately 15 French with the dilator670being disposed therein. InFIG.11C, a collapsed prosthetic heart valve1100is being shown within a delivery catheter1150, and this assembly has an outer diameter of approximately 8.14 mm or approximately 24 French. This same assembly of a prosthetic heart valve1100housed within a delivery catheter1150is being introduced through hub605of introducer sheath600inFIG.11D, and is within the introducer sheath body610inFIG.11E. As shown inFIG.11F, the outer diameter of the introducer sheath600with prosthetic heart valve1100and delivery catheter1150being disposed therein is approximately 8.63 mm or approximately 26 French.

When introducer sheath is inserted into tissue, a column load will be applied to the sheath. While the tipping is designed to carry the brunt of the load, the braided material and elastomeric material may expect load when passing through tissue. If the load is too high, there is a risk of prolapsing the sheath with the braid expanding under compression, as seen inFIG.12which shows an introducer sheath600X at maximum expansion. To prevent or reduce the risk of prolapse, an introducer sheath1300may include a braided material1312and buttressing axial wires1315(e.g., NiTi wires). Axial wires1315may be interwoven into the braided material1312, or disposed between two layers of braided material1312and attached distally at the hub. Axial wires1315may be generally parallel with a longitudinal axis of the body, as shown inFIGS.13A-B. In some examples, axial wires1315are serpentine. The elastomeric material (not shown) may then be applied over the combination of the axial wires and the braided material. In this example, when force is applied to the braided material1312, it is limited in its expansion by the strength of the axial wires1315. Optionally, the axial wires1315may be co-braided and double backed in the same nature as the braid is described above.

In some embodiments, it may be useful to tension the introducer sheath (e.g., the braided material) against a dilator to prevent prolapse of the introducer sheath during insertion. This may be particularly advantageous for expected higher insertion forces due to calcification of the vessel restricting the percutaneous site. In some examples, an introducer sheath1400includes a braided material1412having a plurality of peripheral lumens1430as shown inFIG.14A. In this example, introducer sheath1400included a braided material1412with six peripheral lumens. It will be understood that one, two, three, four, five, six, seven or eight or more peripheral lumens are possible. Introducer sheath1400may also include a stabilizing wire1435corresponding to each peripheral lumen. The stabilizing wire(s)1435may put the braided material in tension and prevent pullback during insertion. In some examples, stabilizing wires(s)1435may be pulled from the proximal end to release the braided material and relieve the tension on the braided material.

In some embodiments, non-elastic elements (e.g., Polyethylene, PET, polyesters, Polyurethane, Pebax, nylon et.) may be used to create an expandable introducer sheath. Additionally, pleating and/or folding may be used to reduce the diameter of an introducer sheath. It will be understood that non-elastic elements and/or pleating and/or folding techniques may be used with any combination of the embodiments described herein.FIG.15illustrates on embodiment of an introducer sheath1500that utilizes such these techniques. As shown, introducer sheath1500may generally include three layers from the inside to the outside, as follows. First, introducer sheath1500may include a braided material1512or a lasercut tube (e.g., NiTi lasercut tube). If a lasercut tube is used, a folded inner liner1511may be disposed therein. In some examples, the folded inner liner1511is pleated and folded as shown. Suitable materials for the folded inner liner1511may include PTFE, Pebax, polyethylene, etc. A folded outer jacket1513may be disposed on the outside of the braided material1512or lasercut tube. In some examples, folded outer jacket1513is lubricious and safe enough to abut a vessel. The folded outer jacket1513may be pleated and folded, and may comprise PTFE, Pebax, polyethylene, etc. Finally, a dilator1550is shown being disposed inside the folded inner liner1511, and the dilator1550may comprise high-density polyethylene, low-density polyethylene, BaSO4or other similar materials.

In the example above, the braided material1512is expandable and is shown as being unfolded. In some, the pleating and/or folding may be applied to the braided material in addition to, or instead of, the inner liner and the outer jacket. This may be advantageous if the braided material itself creates too much force for a device to easily expand the sheath during use. As shown inFIGS.16A-B, the braided material1600may be formed into a tube, heat-set in its expanded form, then axially folded along pleat1605, once or multiple times depending on the application to form a tube with a smaller diameter. Without being bound by any particular theory, it is believed that the force to expand a pleated/folded braided material may be far less than the elastomeric concepts described above. With this embodiment, one or more clastic polymeric jackets may be used, or one or more pleated and folded non-elastic jackets, or combinations thereof.

It will be understood that various modifications may be made to the disclosed embodiments without departing from the spirit of the disclosure. For example, an introducer sheath may be used to introduce a delivery device into the heart for prosthetic heart valve replacement, or may be used to introduce devices for valve repair at any of the heart valves (e.g., aortic valve, mitral valve, pulmonary valve, tricuspid valve). Additionally, an introducer sheath may be used to deliver instruments to repair other structures in the heart, such as the chordae tendineae, papillary muscles and the like. Introducer sheaths may also be used to deliver embolism prevention devices and stents, grafts and other cardiovascular devices into a patient, to introduce devices and instruments for other cardiac repair, to introduce any other medical instruments or devices into a patient's body in applications other than cardiovascular applications, and to access any bodily location where temporarily affixing a sheath within body tissue is useful.