Stepwise expansion of the sheath

Abstract

The sheath assembly includes a first sheath, a second sheath, and an attachment mechanism. The first sheath includes an inner surface defining a first sheath lumen extending along a central longitudinal axis of the first sheath between a first end portion of the first sheath and a second end portion of the first sheath. The second sheath includes an inner surface defining a second sheath lumen extending along a central longitudinal axis of the second sheath between a first end portion of the second sheath and a second end portion of the second sheath. The attachment mechanism couples the second sheath to the first sheath. The attachment mechanism includes a step-up extension of the attachment mechanism. At least a portion of the attachment mechanism is asymmetric about the central longitudinal axis of the first sheath at the step-up extension of the attachment mechanism.

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS) This application claims priority to U.S. Provisional Patent Application No. 63 / 113,921, filed November 15, 2020.

[0002] FIELD OF THE INVENTION The present disclosure relates generally to sheaths, sheath assemblies, and related systems and methods, and certain such embodiments are described herein in the context of medical percutaneous interventional and diagnostic procedures as an exemplary type of application in which the sheaths, sheath assemblies, and related systems and methods may be used to facilitate the introduction of catheters or other devices, for example, through blood vessels, to a region of interest. [Background technology]

[0003] Medical diagnostic and interventional procedures are performed to evaluate one or more conditions at various anatomical locations and, if necessary, take steps to address them. In many such procedures, an intravascular device, such as a catheter sheath, is inserted into a patient's blood vessel (e.g., an artery) at an access site and traversed through the vessel to a particular area of ​​interest.

[0004] In one such example, where the cardiac region is the region of interest, medical diagnostic and interventional procedures typically require two separate access sites on the patient. Typically, such procedures use one access site in the femoral artery and another separate access site in the radial artery, contralateral femoral artery, or other similarly sized vessel (e.g., the subclavian artery). These separate access sites are then used to insert the necessary diagnostic and interventional instruments into the patient and separately guide these instruments to the cardiac region of interest. Because such procedures typically utilize multiple instruments in the cardiac region of interest, the separate access sites on the patient can allow the necessary capacity to traverse the instrument payload to the cardiac region of interest (e.g., via both the femoral and radial arteries).

[0005] Furthermore, regardless of which particular access site on a patient is utilized to gain arterial, or in some cases venous, access, vascularization can be difficult, adding additional complications to an already challenging percutaneous procedure. Factors contributing to the difficulty of access include atrophy of the vessel's muscle layer as a result of puncturing the vessel, the thickness of the vessel wall and its tendency to roll inward toward the vessel lumen when placed under pressure, possible interference with the fascia lata layer before reaching the vessel itself, and the slipperiness of the vessel, which makes the vessel an unstable and unsecured target. For many years, percutaneous interventionalists have used the Seldinger technique to insert catheters into vasculature. This method works well when the device is perfectly axially symmetric and includes a smooth, gradual, axisymmetric transition surface that does not involve any sudden increases in diameter as the device enters the vasculature. As a result, most intravascular devices have been designed to be axisymmetric, with a smooth, gradual, axisymmetric transition surface. However, when a non-axisymmetric (eg, asymmetric) device is inserted into the vasculature, the factors that contribute to the difficulty of access described above may hinder the access of the non-axisymmetric device to the neovascularization. Summary of the Invention

[0006] While prior art techniques have enabled the introduction of axisymmetric devices into the vasculature, a need exists for features that can facilitate efficient access of non-axisymmetric devices to arterial, or in some cases venous, angiogenesis. For example, certain procedures may require additional device capacity and thus the ability to deliver multiple devices, which can benefit from using multiple catheters or multi-lumen asymmetric catheters at a single access site to increase the delivery volume or payload possible through a single access site. The present disclosure describes various features for facilitating efficient access of non-axisymmetric (e.g., asymmetric) devices to angioplasty in a patient through a single access site. Examples include a sheath assembly with at least two sheaths spaced apart from one another (e.g., radially spaced apart in a generally "stacked" configuration) and a series of two or more step-up extensions spaced longitudinally along the length of the sheath assembly such that the cross-sectional diameter of the sheath assembly increases from distal to proximal.

[0007] Generally, various embodiments are disclosed herein relating to sheaths, sheath assemblies, add-on sheath kits, and related systems and methods. Specifically, the embodiments disclosed herein can facilitate medical diagnostic and interventional procedures through a single patient access site using a non-axisymmetric (e.g., asymmetric) sheath or sheath assembly. Accordingly, the embodiments disclosed herein can facilitate percutaneous medical interventional procedures using a single patient access site (e.g., the femoral artery), thereby eliminating the need for a second access site (e.g., eliminating the need for a radial artery access site) and reducing the number of access sites required for such procedures, thereby eliminating the risks associated with second access sites and shortening overall procedure time. Consequently, the embodiments disclosed herein can enable less invasive procedures and preserve the second access site for any future procedures. At the same time, the embodiments disclosed herein can provide such benefits while facilitating efficient access of non-axisymmetric (e.g., asymmetric) sheaths, thus facilitating the ability to deliver additional payload capacity, the ability to vascularize the patient through a single access site, and even preserving functionality typically provided through a second access site.

[0008] One embodiment includes a sheath assembly. This sheath assembly embodiment includes a first sheath, a second sheath, and an attachment mechanism. The first sheath includes a first end portion, a second end portion opposite the first end portion, an inner surface, and an outer surface opposite the inner surface of the first sheath. The inner surface of the first sheath defines a first sheath lumen extending along a central longitudinal axis of the first sheath between the first end portion and the second end portion of the first sheath. The second sheath includes a first end portion, a second end portion opposite the first end portion of the second sheath, an inner surface, and an outer surface opposite the inner surface of the second sheath. The inner surface of the second sheath defines a second sheath lumen extending along a longitudinal axis of the second sheath between a first end portion of the second sheath and a second end portion of the second sheath. An attachment mechanism couples the second sheath to the first sheath. The attachment mechanism includes a step-up extension of the attachment mechanism. At least a portion of the attachment mechanism is asymmetric about the central longitudinal axis of the first sheath at the step-up extension of the attachment mechanism.

[0009] In a further embodiment of the sheath assembly, the step-up extension of the attachment mechanism is positioned between the second end portion of the first sheath and the second end portion of the second sheath.

[0010] In a further embodiment of the sheath assembly, the attachment mechanism step-up extension includes a first attachment mechanism step-up extension at the first attachment mechanism portion and a second attachment mechanism step-up extension at the second attachment mechanism portion, the second attachment mechanism step-up extension being different from the first attachment mechanism step-up extension. The attachment mechanism includes a first longitudinal cross-sectional profile at the first attachment mechanism portion that is asymmetric about the central longitudinal axis of the first sheath, and the attachment mechanism includes a second longitudinal cross-sectional profile at the second attachment mechanism portion that is symmetric about the central longitudinal axis of the first sheath. In one such example, the first attachment mechanism portion and the second attachment mechanism portion can be included at a common longitudinal position on the attachment mechanism. The first attachment mechanism portion can interface with the outer surface of the second sheath, and the second attachment mechanism portion can face the second sheath. The step-up extension of the first attachment feature can have a first slope defined by the longitudinal length of the step-up extension of the first attachment feature and the radial height of the step-up extension of the first attachment feature, and the step-up extension of the second attachment feature can have a second slope defined by the longitudinal length of the step-up extension of the second attachment feature and the radial height of the step-up extension of the second attachment feature, the second slope being different from the first slope. For example, the radial height of the step-up extension of the first attachment feature can be on a side of the attachment feature facing the second sheath, and the radial height of the step-up extension of the second attachment feature can be on another side of the attachment feature facing the second sheath, with the radial height of the step-up extension of the first attachment feature being higher than the radial height of the step-up extension of the second attachment feature. The first slope of the step-up extension of the first attachment mechanism may be greatest proximal to the distal-most junction between the attachment mechanism and the first sheath, and the first slope of the step-up extension of the first attachment mechanism may decrease in a direction proceeding proximally toward the second sheath.For example, the first slope of the step-up extension of the first attachment mechanism can include a first slope region and a second slope region, the first slope region having a greater slope magnitude than the second slope region, the first slope region being distal to the second slope region, and the first slope region extending a portion of the longitudinal length of the step-up extension of the first attachment mechanism from the distal-most junction between the attachment mechanism and the first sheath to the second slope region. The radial height of the step-up extension of the first attachment mechanism can be greater than the longitudinal length of the step-up extension of the first attachment mechanism. In some embodiments, the radial height of the step-up extension of the first attachment mechanism is between 0.254 and 1.27 cm, and the longitudinal length of the step-up extension of the first attachment mechanism is between 0.254 and 0.635 cm.

[0011] In a further embodiment of the sheath assembly, the attachment mechanism includes a non-expanding region defining a portion of the attachment mechanism along which the cross-sectional diameter of the attachment mechanism is constant, the non-expanding region of the attachment mechanism being positioned longitudinally between the step-up extension of the first attachment mechanism and the distal-most end of the second sheath. The non-expanding region can extend along its longitudinal length from the proximal end of the step-up extension of the first attachment mechanism to the distal-most end of the second sheath, and the longitudinal length of the non-expanding region can be at least 5 cm. The second sheath can include a second sheath step-up extension, and the second sheath step-up extension can be included at the distal-most end of the second sheath that joins the non-expanding region of the attachment mechanism. For example, the second sheath can include a first distal wall portion forming a first portion of the opening of the second sheath lumen adjacent to the attachment mechanism, and the second sheath can include a second distal wall portion forming a second portion of the opening of the second sheath lumen opposite the attachment mechanism, the first distal wall portion being positioned distally on the sheath assembly relative to the second distal wall portion. An angle defined relative to the central longitudinal axis of the first sheath can define a slope extending between the first and second distal wall portions over the longitudinal length of the step-up extension of the second sheath, and the angle can be between 15 and 75 degrees.

[0012] In a further embodiment of the sheath assembly, the second sheath can be configured to transition between a deployed state and a contracted state. The second sheath can be biased to the deployed state, and the second sheath can be configured to overcome the bias to the deployed state when an outer surface of the second sheath contacts a blood vessel wall defining the blood vessel lumen, thereby transitioning the second sheath to the contracted state.

[0013] Various embodiments described herein, including the sheath assembly embodiments described above, can provide a sheath configured to transition between an deployed state and a retracted state. Such a sheath can enable a low profile in the retracted state, for example, while the sheath is traversing a vessel, while also providing the ability to accommodate one or more instruments when in the deployed state, for example, once the sheath reaches the region of interest. This sheath can be configured to be added to another sheath by securing the two sheaths together via one or more attachment mechanisms. In this manner, an add-on sheath configured to transition between an deployed state and a retracted state can be used with another sheath already intended for use at an access site where available space is limited.

[0014] An additional embodiment includes a method of using a sheath assembly. This method embodiment includes securing a second sheath to a first sheath via an attachment mechanism such that a first portion of an outer surface of the second sheath interfaces with an outer surface of the first sheath. The first sheath defines a central longitudinal axis of the first sheath, and the attachment mechanism includes a step-up extension of the attachment mechanism, and at least a portion of the attachment mechanism is asymmetric about the central longitudinal axis of the first sheath at the step-up extension of the attachment mechanism. This method embodiment also includes inserting a guidewire into a region of interest in a patient, positioning the first sheath over the guidewire, and inserting the first and second sheaths into the patient through a single access site in the patient. The method further includes contacting the single access site with a step-up extension of the attachment mechanism and then with a second sheath, and transitioning the second sheath from the deployed state to the contracted state while retracting the second sheath toward the first sheath to the contracted state upon insertion of the second sheath into the patient. This method embodiment also includes inserting an instrument through the second sheath to transition the second sheath from the contracted state to the deployed state.

[0015] In a further embodiment of the method, the method may additionally include contacting the single access site with a non-expanded region of the attachment mechanism after contacting the single access site with the step-up extension of the attachment mechanism and before contacting the single access site with the second sheath. The non-expanded region of the attachment mechanism may define a portion of the attachment mechanism along which the cross-sectional diameter of the attachment mechanism is constant.

[0016] The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will become apparent from the description and drawings. [Brief explanation of the drawings]

[0017] The following drawings are illustrative of certain embodiments of the invention and therefore do not limit the scope of the invention. The drawings are intended to be used in conjunction with the description that follows. Embodiments of the invention are hereinafter described in conjunction with the accompanying drawings, in which like numerals represent like elements. The drawings are not necessarily to scale, although certain embodiments may include one or more components at the scale shown. [Figure 1] FIG. 1 is a side elevational view of one embodiment of a sheath assembly. [Figure 2] 2 is a side elevational view of a portion of the embodiment of the sheath assembly of FIG. 1 being inserted into a blood vessel lumen. [Figure 3] 2 is a side elevational view of a portion of the sheath assembly embodiment of FIG. 1 in a region of interest in a blood vessel lumen. [Figure 4] 2 is an enlarged side elevational view of a portion of the sheath assembly of FIG. 1 illustrating an exemplary stepwise expansion feature. [Figure 5] 5 is a cross-sectional view of the sheath assembly of FIG. 1 taken along line AA of FIG. 4, with the second sheath of the sheath assembly in a deployed state. [Figure 6] 2 is an exploded perspective view of a second sheath and attachment mechanism of the sheath assembly embodiment of FIG. 1. FIG. [Figure 7]FIG. 10 is a flow diagram of an embodiment of a method of using a sheath assembly. DETAILED DESCRIPTION OF THE INVENTION

[0018] The following detailed description is exemplary in nature and is not intended to limit the scope, applicability, or configuration of the present invention in any way. Rather, the following description provides some practical specific examples for implementing embodiments of the present invention. Examples of construction, materials, and / or dimensions are provided for selected elements. Those skilled in the art will recognize that many of the described examples have a variety of suitable alternatives.

[0019] FIG. 1 shows a side elevation view of an exemplary embodiment of a sheath assembly 100. The sheath assembly 100 includes a first sheath 105 and a second sheath 110. As shown in this illustrated embodiment, the first sheath 105 and the second sheath 110 are secured together in a stacked arrangement by an attachment mechanism 115 such that the first sheath 105 and the second sheath 110 are positioned side-by-side with their respective outer surfaces abutting one another. Also shown in the illustrated embodiment, the attachment mechanism 115 extends over at least a portion of the outer surface of the first sheath 105. In this stacked arrangement, a first sheath central longitudinal axis 106 of the first sheath 105 is offset from and generally parallel to a second sheath central longitudinal axis 111 of the second sheath 110.

[0020] In sheath assembly 100, first sheath 105 includes first sheath first end portion 120, first sheath second end portion 121, first sheath inner surface 122, and first sheath outer surface 123. First sheath second end portion 121 faces first sheath first end portion 120. First sheath outer surface 123 faces first sheath inner surface 122. First sheath inner surface 122 defines first sheath lumen 124 extending along first sheath longitudinal axis 106 between first sheath first end portion 120 and first sheath second end portion 121. The second end portion 121 of the first sheath may include a first sheath opening 129, for example, to allow instruments and / or guidewires inserted within the first sheath lumen 124 to extend out of the first sheath 105 at the first sheath opening 129.

[0021] In the first sheath, the first end portion 120 is a proximal hub 125. The proximal hub 125 can open to and communicate with the first sheath lumen 124. As such, the proximal hub 125 can be configured to facilitate access to the first sheath lumen 124. For example, the proximal hub 125 can be configured to receive one or more diagnostic or interventional instruments (e.g., catheters) used for a procedure and delivered through the first sheath lumen 124. As shown here, the proximal hub 125 includes a flush port 126 and a clip attachment joint 127. The flush port 126 is configured to facilitate fluid communication with the first sheath lumen 124 and / or the diagnostic and / or interventional instruments within the first sheath lumen 124. The clip attachment joint 127 is configured to receive a clip 130 for securing the proximal end portion of the sheath 105, 110.

[0022] Also in sheath assembly 100, second sheath 110 includes second sheath first end portion 135, second sheath second end portion 136, second sheath inner surface 137, and second sheath outer surface 138. Second sheath second end portion 136 faces second sheath first end portion 135. Second sheath outer surface 138 faces second sheath inner surface 137. Second sheath inner surface 137 defines second sheath lumen 139 extending along second sheath central longitudinal axis 111 between second sheath first end portion 135 and second sheath second end portion 136. Second sheath second end portion 136 may include second sheath opening 149, for example, to allow instruments and / or guidewires inserted within second sheath lumen 139 to extend out of second sheath 110 at second sheath opening 149. As shown in FIG. 1 , first sheath 105 and second sheath 110 may be of substantially similar lengths between their respective end portions 120, 135 and end portions 121, 136. Specifically, the first sheath first end portion 120 and the second sheath first end portion 135 may terminate at a similar proximal location, and the first sheath second end portion 121 and the second sheath second end portion 136 may terminate at a similar distal location (e.g., in FIG. 1, the second sheath second end portion 136 is slightly shorter than or terminates slightly proximal to the first sheath second end portion 121 (e.g., 1 to 10 cm shorter, such as 3 to 6 cm, than the first sheath second end portion 121)).

[0023] In the second sheath, the first end portion 135 is a proximal hub 140. The proximal hub 140 can open to and communicate with a second sheath lumen 139. In this manner, the proximal hub 140 can be configured to facilitate access to the second sheath lumen 139. For example, the proximal hub 140 can be configured to receive one or more diagnostic or interventional instruments (e.g., catheters) used for a procedure and delivered through the second sheath lumen 139. As shown here, the proximal hub 140 includes a flush port 141, a clip attachment joint 142, and an instrument insertion port 143. The flush port 141 is spaced from the instrument insertion port 143 and communicates with the second sheath lumen 139. In this manner, the flush port 141 is configured to facilitate fluid communication with the second sheath lumen 139 and / or the diagnostic and / or interventional instruments within the second sheath lumen 139. Clip attachment joint 142 is configured to receive clip 130 for securing the proximal end portions of sheaths 105, 110. As shown in the illustrated embodiment, clip attachment joint 142 includes a recessed slot formed in proximal hub 140 and configured to create an interference fit with clip 130, although in other embodiments, clip attachment joint 142 can include other types of structure configured to receive clip 130. Instrument insertion port 143 communicates with second sheath lumen 139 and is configured to receive diagnostic and / or interventional instruments (e.g., guidewires and catheters) therein and pass the instruments through second sheath lumen 139.

[0024] Clip 130 is configured to secure second sheath 110 to first sheath 105. Specifically, clip 130 is configured to secure hub 125 to hub 140. Clip 130 may include a first clip securing portion 131 configured to receive second sheath 110 and a second clip securing portion 132 spaced from first clip securing portion 131 and configured to receive first sheath 105. Clip attachment joint 142 is configured to receive first clip securing portion 131, and clip attachment joint 127 is configured to receive second clip securing portion 132 to secure proximal hub 140 to proximal hub 125. In the illustrated embodiment, the first clip fastening portion 131 is non-parallel to the second clip fastening portion 132, and the first clip fastening portion 131 extends at an angle of 15 to 85 degrees (e.g., 25 to 75 degrees, 40 to 60 degrees) from the plane in which the second clip fastening portion 132 lies. Each clip fastening portion 131, 132 can include a fastening aperture around at least a portion (e.g., all) of the respective clip attachment joint 142, 127.

[0025] 2 and 3 illustrate a portion of sheath assembly 100 deployed within a blood vessel 150, such as a patient's blood vessel (e.g., an artery). As shown here, sheath assembly 100, along with both first sheath 105 and second sheath 110, are inserted into blood vessel 150 via a single access site 155. In one exemplary application, blood vessel 150 may be a femoral artery, and sheath assembly 100 may be inserted into the femoral artery via the single access site 155. In this manner, first sheath 105 and second sheath 110 may facilitate a percutaneous diagnostic and / or interventional procedure using the single access site 155, thereby eliminating the risks and complications associated with a second access site for deploying one of the sheaths.

[0026] To facilitate deployment of the sheath assembly 100 through the single access site 155, the second sheath 110 can be configured to transition between an expanded state and a contracted state. In this manner, the second sheath 110 can enable the sheath assembly 100 to have a low profile when the second sheath 110 is in the contracted state, for example, while the sheath assembly 100 is inserted into and traversed through the blood vessel 150. In this manner, the second sheath 110 can also provide the ability to house one or more diagnostic and / or interventional devices (e.g., diagnostic catheters or auxiliary catheters) within the second sheath 110 when the second sheath 110 is in the expanded state, for example, once the sheath reaches the region of interest 152. FIG. 2 illustrates a side elevation view of a portion of the sheath assembly 100 inserted into the vascular lumen 151 of the blood vessel 150, with the second sheath 110 in a substantially contracted state. FIG. 3 illustrates a side elevation view of a portion of the sheath assembly 100 having reached the region of interest 152 of the vessel lumen 151, with the secondary sheath 110 now in a generally deployed state.

[0027] As shown, the sheath assembly 100 can be inserted into a blood vessel lumen 151 and traversed through the blood vessel 150 to a region of interest 152 using a guidewire 160. The first sheath 105 can be positioned over the guidewire 160 such that the guidewire 160 is received within the first sheath lumen 124. The sheath assembly 100 can then be advanced over the guidewire 160 of the first sheath 105 and through a single access site 155 into the blood vessel lumen 151. In some embodiments, the first sheath 105 can include an introducer 161 at the first sheath second end portion 121 to assist in deploying and passing the sheath assembly 100 within the blood vessel lumen 151.

[0028] As noted, the second sheath 110 can be configured to transition between a deployed state and a contracted state. In the illustrated embodiment, the second sheath 110 can be biased to the deployed state, and the second sheath 110 can be configured to transition from the deployed state to the contracted state when the outer surface 138 of the second sheath contacts the vessel wall 153, e.g., defining the single access site 155 and the vessel lumen 151. In this manner, the second sheath 110 can be configured to overcome the bias to the deployed state when the outer surface 138 of the second sheath contacts the vessel wall 153. Thus, in such an embodiment, when the sheath assembly 100 is inserted into and traversed within the vessel lumen 151, as shown in FIG. 2 , the second sheath 110 generally contacts the vessel wall 153 and can therefore be in the contracted state. Also, in such embodiments, the sheath assembly 100 can be configured such that the second sheath 110 is configured to transition from the deployed state to a contracted state and be maintained in the contracted state while the first sheath 105 is maintained in the first sheath's deployed state. This can maintain the first sheath lumen 124 at its design volume, as may be useful, for example, when the first sheath 105 receives a guidewire 160 for advancing the sheath assembly 110 to the region of interest 152. In some cases, the first sheath 105 may not be contractible, although certain embodiments may include a first sheath configured to transition between a contracted state and a deployed state.

[0029] The second sheath 110 can include one or more features to facilitate the transition between the deployed state and the contracted state. For example, the first sheath 105 can have a first hardness X, and the second sheath 110 can have a second hardness Y, where the first hardness X of the first sheath 105 is greater than the second hardness Y of the second sheath 110. By way of example, the first sheath 105 can have a Rockwell hardness of 70 A to 100 A, such as 80 A to 90 A, and the second sheath 110 can have a Rockwell hardness of 30 A to 70 A, such as 40 A to 60 A. In this manner, the second sheath 110 can be configured to contract upon the application of a force to the second sheath 110 by the stiffer first sheath 105 and the vessel wall 153, respectively. More specifically, when the second sheath 110 contacts the vessel wall 153, the vessel wall 153 can apply a force 156 in a first direction to the second sheath outer surface 138, while the stiffer first sheath 105 can apply a force 157 in a second, opposing direction to the second sheath outer surface 138, causing the second sheath to contract between the first force 156 and the second force 157. In this case, the second sheath 110 contracts in a direction toward the first sheath 105. Thus, the second sheath 110 transitions from an expanded state to a contracted state, thereby allowing the sheath assembly 100 to become more compact within the vessel lumen 151.

[0030] As mentioned, the second sheath 110 can have one or more dimensions and / or can include one or more materials that enable it to contract (e.g., contribute to the hardness or rigidity of the second sheath 110) when inserted into and traversed through the blood vessel lumen 151. For example, the second sheath 110 can include a wall thickness defined between the second sheath outer surface 138 and the second sheath inner surface 137 that is thinner than the wall thickness of the first sheath 105 defined between the first sheath outer surface 123 and the first sheath inner surface 122. As one example, the wall thickness of the second sheath can be between 0.1 mm and 1.5 mm, such as between 0.15 mm and 0.75 mm (e.g., between 0.15 mm and 0.5 mm) or between 0.25 mm and 0.5 mm. As another example, the second sheath 110 can be made of a shrinkable polymer or mesh material configured to shrink under a force exerted by the vessel wall 153 (e.g., the vessel wall of the femoral artery). For example, the second sheath 110 can include a biocompatible polyurethane (e.g., Pellethane™). Depending on the particular application, the combination of materials including the biocompatible polyurethane, along with the hardness and / or wall thickness of the second sheath 110 relative to the first sheath 105, can enable the second sheath 110 to transition from a deployed state to a shrinked state when inserted into and traversed through the vessel lumen 151 as a result of contact with the vessel wall 153.

[0031] To allow the second sheath 110 to retract to its maximum extent, no hardware (e.g., instruments, guidewires, etc.) can be present within the second sheath lumen 139 when the sheath assembly 100 is inserted into and traversed through the blood vessel lumen 151, as in Figure 2. Then, as in Figure 3, once the sheath assembly 100 reaches the region of interest 152, one or more hardware components (e.g., guidewires and / or diagnostic and / or interventional instruments such as diagnostic or auxiliary catheters) can be inserted into the second sheath lumen 139.

[0032] The second sheath 110 can be configured to transition from a contracted state, as in FIG. 2 , toward a deployed state, as in FIG. 3 , in response to the insertion of a hardware component (e.g., a rigid hardware component) within the second sheath lumen 139 when the second sheath 110 contacts a blood vessel wall 153. FIG. 3 shows a catheter 165 (e.g., a pigtail catheter) inserted within the second sheath lumen 139 and extending out of the second sheath opening 149 at the region of interest 152. The insertion of a hardware component, such as the catheter 165, within the second sheath lumen 139 can impart a force 158 in a second direction to the second sheath 110, causing the second sheath 110 to deploy from the contracted state. This second direction force 158 applied by the catheter 165 to the second sheath 110 can therefore counter some or all of the force 156 applied by the vessel wall 153 and allow the second sheath 110 to transition from a contracted state such as that of FIG. 2 towards or to an expanded state such as that of FIG. 3 when the second sheath 110 contacts the vessel wall 153.

[0033] Depending on the particular application, such as inserting hardware into the second sheath lumen 139, the second sheath 110 may only partially transition from a contracted state to a deployed state, such as that of FIG. 3, when a hardware component is present within the second sheath lumen 139 (e.g., the second sheath 110 extends less out of the first sheath 105 than when the sheath assembly 100 is not present within the blood vessel 150). The second sheath 110 may be configured to contract upon contact with the blood vessel wall 153, such that when a hardware component, such as a catheter 165, is present within the second sheath lumen 139, force 156 applied by the blood vessel wall 153 can oppose force 158, thereby continuing to restrain the deployment of the second sheath 110. Thus, the second sheath 110 can be configured to transition from the contracted state toward the deployed state only to the extent necessary to accommodate hardware components within the second sheath lumen 139, thereby maintaining a minimal required profile of the sheath assembly 100 even when the second sheath 110 is actively being used during a procedure. In this manner, the second sheath 110 configured to transition between the deployed and contracted states can facilitate a low profile of the sheath assembly 100 both during insertion and placement, and during use of the second sheath 110 during a procedure. As a result, the sheath assembly 100 may be usable through the access site 155.

[0034] Additional details regarding the second sheath 110 configured to transition between a contracted state and an deployed state can be found in U.S. patent application Ser. No. 16 / 871,299, the entire contents of which are incorporated herein by reference.

[0035] Additionally, to facilitate deployment of the sheath assembly 100 through the single access site 155, the sheath assembly 100 may include one or more features, some or all of which may be referred to as graduated expansion features, to facilitate efficient insertion of the sheath assembly 100 into the blood vessel 150 through the single access site 155. FIGS. 4 and 5 show a portion of the sheath assembly 100 equipped with exemplary features that may be useful for facilitating efficient insertion of the sheath assembly 100 into the blood vessel 150 through the single access site 155. Specifically, FIG. 4 is an enlarged side elevation view of a portion of the sheath assembly 100 illustrating such exemplary features, and FIG. 5 is a cross-sectional view of the sheath assembly 100, taken along line AA in FIG. 4, equipped with such exemplary features and with the second sheath 110 in a deployed state.

[0036] 4 and 5, the sheath assembly 100 can be a non-axisymmetric (e.g., asymmetric) device. For example, as best seen in FIG. 5, the sheath assembly 100 is configured to be asymmetric about a central longitudinal axis of the sheath assembly 100. More specifically, in the illustrated embodiment, the sheath assembly 100 is configured to be asymmetric about the guidewire 160 received in the first sheath lumen 124, and thus asymmetric about the first sheath longitudinal axis 106.

[0037] As shown in the illustrated embodiment, sheath assembly 100 can include one or more profile step-up extensions on introducer 161, first sheath 105, second sheath 110, attachment mechanism 115 (as mentioned and illustrated, attachment mechanism 115 can be positioned on and around at least a portion of first sheath 105), and / or second sheath 110. Specifically, in some embodiments, sheath assembly 100 can include two or more stepped extensions that sequentially increase in longitudinal cross-sectional diameter progressing from the distal end toward the proximal end of sheath assembly 100. Thus, the one or more profile step-up extensions can act to increase the profile (e.g., longitudinal cross-sectional diameter) of sheath assembly 100 progressing from the distal to the proximal direction along sheath assembly 100.

[0038] In the illustrated embodiment, a portion of the sheath assembly 100 may be symmetric about the longitudinal axis 106 of the first sheath, and another portion of the sheath assembly 100 may be asymmetric about the longitudinal axis 106 of the first sheath. Specifically, in the illustrated embodiment, the sheath assembly 100 is symmetric about the longitudinal axis 106 of the first sheath, proceeding proximally from the distal end of the sheath assembly 100 (e.g., the distal end of the introducer 161) to a distal-most position where the attachment mechanism 115 is present (e.g., where the attachment mechanism 115 joins with the first sheath 105). In the illustrated embodiment, at the distal-most position where the attachment mechanism 115 is present (e.g., where the attachment mechanism 115 joins with the first sheath 105), the sheath assembly 100 becomes asymmetric about the longitudinal axis 106 of the first sheath. More specifically, in the illustrated embodiment, the sheath assembly 100 can have a first asymmetric configuration 230 centered about the longitudinal axis 106 of the first sheath, across a longitudinal length 240 along the sheath assembly 100 from a distal-most position where the attachment mechanism 115 is present (e.g., where the attachment mechanism 115 joins with the first sheath 105) to a distal-most position where the second sheath 110 is present (e.g., where the second sheath 110 joins with the attachment mechanism 115). The sheath assembly 100 may also have a second asymmetric configuration 232 that is different from the first asymmetric configuration 230 and centered on the longitudinal axis 106 of the first sheath, over a longitudinal length 242 along the sheath assembly 100 from the distal-most position where the second sheath 110 is present (e.g., where the second sheath 110 joins with the attachment mechanism 115) to the position where the second sheath 110 terminates (e.g., the second sheath first end portion 135).

[0039] These one or more profile step-up extensions can be sequenced and configured to reduce challenges associated with inserting a non-axisymmetric device into the vasculature through a single access site. For example, these one or more profile step-up extensions can help reduce the directness of the transition from the relatively small cross-sectional diameter of guidewire 160 (e.g., 0.0762 cm to 0.1016 cm) to the relatively larger cross-sectional diameter of sheath assembly 100 in which secondary sheath 110 is positioned (e.g., 0.508 cm to 0.889 cm when secondary sheath 110 is in a retracted state, or larger, such as when secondary sheath is in a deployed state).

[0040] As shown, an introducer 161 (also referred to as a "dilator") may be present at the distal end of the sheath assembly 100. Once the guidewire 160 is positioned in the vasculature of interest, the sheath assembly 100 may be delivered over the guidewire 160. The introducer 161 may be configured such that the first component of the sheath assembly 100 abuts a single access site 155. As shown in the illustrated embodiment, the introducer 161 may have an introducer distal end portion 162 and an introducer proximal end portion 163. The introducer 161 may have a smallest cross-sectional diameter (e.g., longitudinal cross-sectional diameter 164) at the introducer distal end portion 162 and a largest cross-sectional diameter (e.g., longitudinal cross-sectional diameter 164) at the introducer proximal end portion 163. The sheath assembly 100 may be axisymmetric about a central longitudinal axis of the introducer 161. In some embodiments as shown herein, introducer 161 may have a cross-sectional diameter that increases at a constant rate from introducer distal end portion 162 to introducer proximal end portion 163. In such embodiments, introducer 161 may be generally conical, for example, with a conical tip at introducer distal end portion 162 and a conical base at introducer proximal end portion 163. This increase in cross-sectional diameter of introducer 161 in the distal-to-proximal direction may be configured to gradually widen the vessel from the profile of guidewire 160 to the profile of first sheath 105 at a single access site 155 as introducer 161 is introduced into the vessel.

[0041] Advancing proximally from the introducer 161, the first sheath 105 may increase the profile of the sheath assembly 100 from the profile of the introducer 161. The first sheath 105 may be configured to be the next component of the sheath assembly 100 after the introducer 161 that abuts the single access site 155 as the sheath assembly 100 continues to be introduced into the vessel. As shown in the illustrated embodiment, the first sheath second end portion 121 may define the first sheath distal end portion. The first sheath 105 may include a first sheath step-up extension 250 at the first sheath second end portion 121, which may be configured to increase in cross-sectional diameter (e.g., longitudinal cross-sectional diameter 246) along a longitudinal length 248 of the first sheath step-up extension as it advances proximally. Specifically, the first sheath 105 may have a minimum cross-sectional diameter (e.g., longitudinal cross-sectional diameter 246) at the distal-most end of the first sheath 105 where the first sheath 105 joins with the introducer 161, and the step-up extension 250 of the first sheath may extend along the longitudinal length 248 of the step-up extension of the first sheath from this minimum cross-sectional diameter (e.g., longitudinal cross-sectional diameter 246) at the distal-most end of the first sheath 105 where the first sheath 105 joins with the introducer 161 in a proximal direction toward the attachment mechanism 115.

[0042] Where the first sheath step-up extension 250 terminates, and thus where the longitudinal length 248 of the first sheath step-up extension terminates, the first sheath 105 can extend a longitudinal length 244 from the end of the first sheath step-up extension 250 to the juncture with the attachment mechanism 115. This longitudinal length 244 can be long enough to allow the vessel sufficient time during introduction of the sheath assembly 100 at the single access site 155 to relax, stabilize, and straighten any folds that may have formed in the vessel wall during introduction of the first sheath step-up extension 250 at the single access site 155 and return to the initial shape it had at the start of introduction of the sheath assembly 100. In various embodiments, the longitudinal length 244 can be at least 5 cm, at least 8 cm, at least 10 cm, at least 12 cm, at least 15 cm, at least 20 cm, at least 25 cm, or at least 30 cm.

[0043] The first sheath step-up extension 250 can be configured to transition the first sheath 105 from its smallest cross-sectional diameter (e.g., longitudinal cross-sectional diameter 246) at the distal-most end of the first sheath 105 to its largest cross-sectional diameter (longitudinal cross-sectional diameter 246) at a more proximal location along the first sheath 105. Thus, the first sheath step-up extension 250 can begin at the distal-most junction of the first sheath 105 and the introducer 161. In the illustrated embodiment, the first sheath step-up extension 250 can be axisymmetric about the first sheath longitudinal axis 106, and the first sheath 105 itself can be axisymmetric about the first sheath longitudinal axis 106.

[0044] Proceeding proximally from the first sheath 105, the attachment mechanism 115 can further increase the profile of the sheath assembly 100 from the profile of the first sheath 105. The attachment mechanism 115 can be configured to be the next component of the sheath assembly 100 after the first sheath 105 that contacts a single access site 155 as the sheath assembly 100 continues to be introduced into the blood vessel. The attachment mechanism 115 can include an attachment mechanism step-up extension 252 that begins at a distal-most longitudinal position where the attachment mechanism 115 interfaces with the first sheath 105. The attachment mechanism step-up extension 252 can be configured to increase in cross-sectional diameter (e.g., longitudinal cross-sectional diameter 246) along a longitudinal length 249 of the attachment mechanism step-up extension, progressing proximally from the distal-most longitudinal position where the attachment mechanism 115 interfaces with the first sheath 105. Specifically, the attachment mechanism 115 can have a smallest cross-sectional diameter (e.g., longitudinal cross-sectional diameter 246) at the distal-most end of the attachment mechanism 115 where the attachment mechanism 115 joins with the first sheath 105, and the step-up extension 252 of the attachment mechanism can extend along the longitudinal length 249 of the step-up extension of the attachment mechanism from this smallest cross-sectional diameter (e.g., longitudinal cross-sectional diameter 246) at the distal-most end of the attachment mechanism 115 where the attachment mechanism 115 joins with the first sheath 105 along the longitudinal length 249 of the step-up extension of the attachment mechanism in a proximal direction toward the second sheath 110.

[0045] As mentioned and shown in the illustrated embodiment, at the attachment mechanism 115, the sheath assembly 100 can transition from an axisymmetric configuration distal to the attachment mechanism 115 to a first asymmetric configuration 230 present at the attachment mechanism 115 (e.g., about the central longitudinal axis 106 of the first sheath). Specifically, the step-up extension 252 of the attachment mechanism can be configured to transition the sheath assembly 100 from an axisymmetric configuration distal to the attachment mechanism 115 to the first asymmetric configuration 230 present at the attachment mechanism 115 (e.g., about the central longitudinal axis 106 of the first sheath).

[0046] To do so, the attachment mechanism step-up extensions 252 may be asymmetric about the first sheath longitudinal axis 106. For example, the attachment mechanism step-up extensions 252 may include a first attachment mechanism step-up extension 252a and a second attachment mechanism step-up extension 252b that is different from the first attachment mechanism step-up extension 252a. Thus, for example, as seen in FIG. 5, the step-up extension 252a of the first attachment mechanism can define a longitudinal cross-sectional profile of the attachment mechanism 115 that includes a first attachment mechanism portion 114a that is asymmetric about the first sheath 105 (e.g., asymmetric about the central longitudinal axis 106 of the first sheath), and the step-up extension 252b of the second attachment mechanism can define a longitudinal cross-sectional profile of the attachment mechanism 115 that includes a second attachment mechanism portion 114b that is symmetric about the first sheath 105 (e.g., symmetric about the central longitudinal axis 106 of the first sheath). The step-up extension 252a of the first attachment mechanism and the first attachment mechanism portion 114a may be present on the side 257 facing the second sheath, and the step-up extension 252b of the second attachment mechanism and the second attachment mechanism portion 114b may be present on one or more sides of the attachment mechanism 115 that do not face the second sheath 110.

[0047] In the illustrated embodiment, the first attachment feature step-up extension 252 a can have a different slope than the second attachment feature step-up extension 252 b. For example, the first attachment feature step-up extension 252 a can have a longitudinal length 255 of the first attachment feature step-up extension (e.g., beginning at the distal-most joint of the attachment feature 115 in the first sheath 105) and a radial height 258 of the first attachment feature step-up extension (e.g., extending outward from the outer surface of the first sheath 105) that defines a first slope of the first attachment feature step-up extension 252 a. Additionally, second attachment feature step-up extension 252b can have a second attachment feature step-up extension longitudinal length 256 (e.g., beginning at the distal-most joint of attachment feature 115 in first sheath 105) and a second attachment feature step-up extension radial height 259 (e.g., extending outward from the outer surface of first sheath 105) that defines a second slope of second attachment feature step-up extension 252b. To create different slopes in first attachment feature step-up extension 252a and second attachment feature step-up extension 252b, first attachment feature step-up extension longitudinal length 255 can be different from second attachment feature step-up extension longitudinal length 256 and / or first attachment feature step-up extension radial height 258 can be different from second attachment feature step-up extension radial height 259. In the embodiment shown, the longitudinal length 255 of the step-up extension of the first attachment mechanism is different (e.g., larger) than the longitudinal length 256 of the step-up extension of the second attachment mechanism, and the radial height 258 of the step-up extension of the first attachment mechanism is different (e.g., larger) than the radial height 259 of the step-up extension of the second attachment mechanism.

[0048] With respect to the first attachment mechanism step-up extension 252a, for example, the first slope of the first attachment mechanism step-up extension 252a can be greatest near the distal-most junction with the first sheath 105 and can decrease proximally toward the second sheath 110. For example, the first slope of the first attachment mechanism step-up extension 252a can include a first sloped region 260a and a second sloped region 260b that is different from the first sloped region. The first sloped region 260a can be distal to the second sloped region 260b and can extend the longitudinal length 255 of the first attachment mechanism step-up extension from the distal-most junction of the attachment mechanism 115 with the first sheath 105 to the second sloped region 260b. The first sloped region 260a can have a greater slope than the second sloped region 260b. In one particular such embodiment, the first and second sloped regions 260a, 260b forming the first attachment feature step-up extension 252a may together resemble a “bull nose” geometry from a side view, with the first sloped region 260a forming the larger sloped portion of the “bull nose” and the second sloped region 260b forming the smaller sloped portion of the “bull nose.” For example, the first attachment feature step-up extension 252a may be defined (e.g., by the combination of the first sloped region 260a and the second sloped region 260b) such that the radial height 258 of the first attachment feature step-up extension is greater than the longitudinal length 255 of the first attachment feature step-up extension. That is, in various embodiments, the radial height 258 of the step-up extension of the first attachment feature can be 0.254 to 1.27 cm, 0.508 to 1.016 cm, or 0.635 to 0.889 cm (e.g., 0.635 cm), and the longitudinal length 255 of the step-up extension of the first attachment feature can be 0.254 to 0.635 cm, 0.3175 to 0.5715 cm, or 0.381 to 0.508 cm (e.g., 0.4445 cm).

[0049] With respect to second attachment mechanism step-up extension 252b, for example, the second slope of second attachment mechanism step-up extension 252b may be greatest near the distal-most junction with first sheath 105 and may decrease proximally toward second sheath 110. For example, the second slope of second attachment mechanism step-up extension 252b may be defined by second attachment mechanism step-up extension longitudinal length 256, which may be less than first attachment mechanism step-up extension longitudinal length 255, and second attachment mechanism step-up extension radial height 259, which may be less than first attachment mechanism step-up extension radial height 258. In certain embodiments, where first attachment mechanism step-up extension 252a is configured similar to a "bull nose," second attachment mechanism step-up extension 252b may have a different configuration, such as a parabolic, linear, or chamfered edge configuration. In some embodiments, the step-up extension 252b of the second attachment mechanism can form a portion of the step-up extension 252 of the attachment mechanism that is symmetrical about the first sheath 105, while the step-up extension 252a of the first attachment mechanism can form a remaining portion of the step-up extension 252 of the attachment mechanism that is asymmetrical about the first sheath 105.

[0050] The attachment mechanism step-up extensions 252, including the first attachment mechanism step-up extension 252a and / or the second attachment mechanism step-up extension 252b, can form a generally rigid outer surface at the attachment mechanism 115 (e.g., at the distal-most portion of the attachment mechanism 115). For example, the attachment mechanism step-up extensions 252, including the first attachment mechanism step-up extension 252a and / or the second attachment mechanism step-up extension 252b, can form an outer surface at the attachment mechanism 115 having a Shore A hardness of 30-100, 40-95, 40-90, 50-95, 50-90, or 80-85. The outer surface of the attachment mechanism 115, including the attachment mechanism step-up extensions 252, can be made of one or more of a variety of materials having the stated Shore A hardness ranges. As one example, the outer surface of the attachment mechanism 115, including the attachment mechanism step-up extensions 252, can comprise polyurethane having a Shore A hardness of 30-100, 40-95, 40-90, 50-95, 50-90, or 80-85. Configuring the attachment mechanism step-up extensions 252 to provide a generally rigid outer surface for the attachment mechanism 115 can help reduce instances of "fishmouthing" or stretching of material at the outer surface of the attachment mechanism 115. This, in turn, can help reduce instances of gaps forming between components of the sheath assembly 100 (e.g., forming a gap between the first sheath 105 and the attachment mechanism 115), which can catch or interfere with the vessel wall at the single access site 155 when the sheath assembly 100 is introduced into the vessel.

[0051] The attachment mechanism step-up extension 252 may terminate at a proximal end of the first attachment mechanism step-up extension longitudinal length 255, and proximal to the termination of the proximal end of the first attachment mechanism step-up extension longitudinal length 255 may be an attachment mechanism non-expansion region 261 of the attachment mechanism 115. The attachment mechanism non-expansion region 261 may define a region of the attachment mechanism 115 along which the cross-sectional diameter (e.g., longitudinal cross-sectional diameter 246) of the attachment mechanism 115 is substantially constant. The attachment mechanism non-expansion region 261 may have an attachment mechanism non-expansion region longitudinal length 262 extending from the proximal end of the first attachment mechanism step-up extension longitudinal length 255 where the first attachment mechanism step-up extension 252a terminates, toward the second sheath 110. The cross-sectional diameter (e.g., longitudinal cross-sectional diameter 246) of the attachment mechanism 115 can be substantially constant along the longitudinal length 262 of the non-expandable region of the attachment mechanism. In some such examples, the longitudinal length 262 of the non-expandable region of the attachment mechanism 261 can extend from the proximal end of the longitudinal length 255 of the first attachment mechanism step-up extension, where the first attachment mechanism step-up extension 252a terminates, to the distal-most end of the second sheath 110. In various embodiments, the longitudinal length 262 of the non-expandable region of the attachment mechanism can be, for example, at least 5 cm, at least 8 cm, at least 10 cm, at least 12 cm, at least 15 cm, at least 20 cm, at least 25 cm, or at least 30 cm. The presence of the non-expanding region 261 of the attachment mechanism, and therefore the longitudinal length 262 of the non-expanding region of the attachment mechanism as described, can be long enough to allow the blood vessel to relax, stabilize, and straighten any folds that may form in the vessel wall during introduction of the sheath assembly 100 at the single access site 155 during sufficient time to restore the vessel to the initial shape it had at the beginning of introduction of the sheath assembly 100 before facing the second sheath 110 at the single access site 155.

[0052] As noted, the attachment mechanism non-expanding region 261 of the attachment mechanism 115 can lead to the distal-most end of the second sheath 110. As shown in the illustrated embodiment, the second sheath 110 can include a second sheath step-up extension 265. The second sheath step-up extension 265 can be included at the distal-most end of the second sheath 110, for example, such that the second sheath step-up extension 265 begins where the attachment mechanism non-expanding region 261 terminates. Proceeding proximally from the attachment mechanism non-expanding region 261, the second sheath step-up extension 265 can be configured to further increase the profile of the sheath assembly 100 from the profile of the attachment mechanism 115. The second sheath step-up extension 265 can be configured to be the next component of the sheath assembly 100 after the non-expanded region 261 of the attachment mechanism that abuts the single access site 155 as the sheath assembly 100 continues to be introduced into the blood vessel. The second sheath 110 can include a second sheath step-up extension 265 that begins at the distal-most end of the second sheath 110 where the second sheath interfaces with the attachment mechanism 115. The second sheath step-up extension 265 can be configured to increase in cross-sectional diameter (e.g., longitudinal cross-sectional diameter 246) along the longitudinal length 266 of the second sheath step-up extension, progressing proximally from the distal-most longitudinal position where the second sheath 110 interfaces with the attachment mechanism 115. Specifically, the second sheath 110 can have a minimum cross-sectional diameter (e.g., longitudinal cross-sectional diameter 246) at the distal-most end of the second sheath 110 where the second sheath 110 joins with the attachment mechanism 115, and the step-up extension 265 of the second sheath can extend along the longitudinal length 266 of the step-up extension of the second sheath from this minimum cross-sectional diameter (e.g., longitudinal cross-sectional diameter 246) at the distal-most end of the second sheath 110 where the second sheath 110 joins with the attachment mechanism 115 in a proximal direction toward the proximal hub 125.

[0053] The second sheath step-up extension 265 can be configured to have an increasing cross-sectional diameter (e.g., longitudinal cross-sectional diameter 246) along a longitudinal length 266 of the second sheath step-up extension via an offset wall arrangement of the second sheath opening 149. For example, as shown in the illustrated embodiment, the second sheath 110 can have a first distal wall portion 267 that forms a first portion of the second sheath opening 149 adjacent to the attachment mechanism 115 and a second distal wall portion 268 that forms a second portion of the second sheath opening 149 opposite the attachment mechanism 115. The first distal wall portion 267 can be positioned in the sheath assembly 100 distally of the second distal wall portion 268, such that the first distal wall portion 267 can be closer to the introducer 161 than the second distal wall portion 268, for example. The second sheath step-up extension 265 can be configured to have an increasing cross-sectional diameter along the longitudinal length 266 of the second step-up extension between the first distal wall portion 267 and the second distal wall portion 268. The longitudinally offset wall arrangement of the first and second distal wall portions 267, 268 can facilitate the increase in cross-sectional diameter between the first and second distal wall portions 267, 268 created by the second sheath step-up extension 265 in a relatively gradual manner. For example, an angle θ can be defined with respect to the first sheath central longitudinal axis 106, and the angle θ can define a slope or rate or increase in cross-sectional diameter between the first and second distal wall portions 267, 268 over the longitudinal length 266 of the second sheath step-up extension. In various embodiments, the angle θ can be between 10 and 80 degrees, between 15 and 70 degrees, between 20 and 60 degrees, or between 25 and 50 degrees.

[0054] A radial height 269 of the second sheath step-up extension 265 of the second sheath 110 (e.g., extending outward from the outer surface of the attachment mechanism 115) can be formed between the first distal wall portion 267 and the second distal wall portion 268. As mentioned, the longitudinally offset wall arrangement of the first distal wall portion 267 and the second distal wall portion 268 can facilitate a relatively gradual increase in the cross-sectional diameter created by the second sheath step-up extension 265 to the second sheath step-up extension radial height 269. The radial height 269 of the second sheath step-up extension can vary depending on whether the second sheath 110 is in a deployed state or a retracted state. 4 and 5, when the second sheath 110 is in the deployed state, the radial height 269 of the second sheath step-up extension 265 can be between 1 mm and 5 mm, e.g., between 1.5 mm and 4.5 mm, between 2 mm and 4.5 mm, or between 2.5 mm and 4.0 mm. When the second sheath 110 is in the retracted state, the radial height 269 of the second sheath step-up extension 265 can be less than 1 mm, such as less than 0.75 mm, less than 0.67 mm, less than 0.5 mm, or less than 0.3 mm. The longitudinally offset wall arrangement of the first distal wall portion 267 and the second distal wall portion 268 can facilitate a relatively gradual increase in cross-sectional diameter created by the second sheath step-up extension 265 that can be present both when the second sheath 110 is in the expanded configuration and when the second sheath 110 is in the retracted configuration. To facilitate the ability of the second sheath 110 to transition between the deployed and retracted configurations, the second sheath 110 can have a second hardness, and the attachment mechanism 115 and / or the first sheath 105 can have a first hardness that is greater than the second hardness, for example, as described herein above. The second sheath 110 can be configured to be biased to the deployed state and can be configured to transition from the deployed state to the retracted state when the second sheath contacts a vessel wall.This configuration of the second sheath 110 to transition from a larger second sheath step-up extension radial height 269 in the deployed state to a smaller second sheath step-up extension radial height 269 in the contracted state can help reduce the area at the distal-most end of the second sheath that may be prone to catching or snagging on the vessel wall when the sheath assembly is inserted into the single access site 155, thereby helping to facilitate a more efficient sheath assembly introduction process, while also helping to provide the ability to deliver additional device payloads through the second sheath 110 when transitioned to the deployed state after insertion at the single access site 155.

[0055] 5 , the illustrated embodiment shows a portion of sheath assembly 100 that may be symmetric about first sheath longitudinal axis 106, while another portion of sheath assembly 100 may be asymmetric about first sheath longitudinal axis 106. For example, introducer 161 and first sheath 105 may be symmetric about first sheath longitudinal axis 106, while attachment mechanism 115 and at least a portion of second sheath 110 may be asymmetric about first sheath longitudinal axis 106. More specifically, second attachment mechanism step-up extension 252b of attachment mechanism step-up extension 252 of attachment mechanism 115 may be symmetric about first sheath longitudinal axis 106, while first attachment mechanism step-up extension 252a of attachment mechanism step-up extension 252 of attachment mechanism 115 may be asymmetric about first sheath longitudinal axis 106. This allows the first attachment mechanism step-up extension 252a to be configured to be "out of round" relative to the rest of the attachment mechanism 115, including the second attachment mechanism step-up extension 252b. In addition to the first attachment mechanism step-up extension 252a, the second sheath 110 may be asymmetric about the first sheath longitudinal axis 106. More specifically, the second sheath step-up extension 265 may extend away from the first sheath longitudinal axis 106 on the same side of the sheath assembly 100 on which the first attachment mechanism step-up extension 252a is located. Thus, as seen in the example of FIG. 5, the first attachment mechanism step-up extension 252a and the second sheath step-up extension 265, which are asymmetric relative to the first sheath longitudinal axis 106, may be on the same side of the sheath assembly 100. Additionally, other portions of the sheath assembly 100, including the step-up extension 252 of the attachment mechanism and one or more sides of the sheath assembly offset from the side of the sheath assembly 100 having the step-up extension 265 of the second sheath, may be symmetrical about the longitudinal axis 106 of the first sheath.

[0056] 5 also illustrates a connection joint 270 between the attachment mechanism 115 and the second sheath 110. The sheath assembly 100 may include a connection joint 270 between the attachment mechanism 115 and the second sheath 110 such that no gaps exist between the attachment mechanism 115 and the second sheath 110. More specifically, the attachment mechanism 115 may include an outer attachment mechanism surface 271, and the second sheath 110 may include an outer surface 272. The outer surfaces 271, 272 may be joined together in a manner that eliminates any gaps between the attachment mechanism 115 and the second sheath 110 at the connection joint 270. This can be particularly useful if the gap between the attachment mechanism 115 and the second sheath 110 at the connection joint between the first distal wall portion 267 of the second sheath 10 and the outer attachment mechanism surface 271 is eliminated, as this can reduce instances where the vessel wall may get caught during insertion of the sheath assembly at the single access site 155.

[0057] Further, to help prevent such vessel wall snagging on the second sheath 110, at least a portion 272a of the second sheath outer surface 272, such as the portion 272a extending away from the first sheath longitudinal axis 106, can abut the outer attachment mechanism surface 271. For example, the attachment mechanism 115 can include an upper half portion 115a defined on a plane 275 extending perpendicular to the first sheath longitudinal axis 106. The portion 272a of the second sheath outer surface 272 extending away from the first sheath longitudinal axis 106 can abut a point 271a located on both the outer attachment mechanism surface 271 and the upper half portion 115a. In some such embodiments, a portion 272a of the second sheath's outer surface 272 extending away from the first sheath's longitudinal axis 106 can have a radius of curvature equal to the radius of curvature of a point 271a located on both the outer attachment mechanism surface 271 and the top half portion 115a. In this manner, the portion 272a can extend away from the outer attachment mechanism surface 271 in a configuration that maintains a gap-free joint at the connection joint 270 between the outer attachment mechanism surface 271 and the second sheath's outer surface 272. In further such embodiments, the portion 272a can continue to extend away from the outer attachment mechanism surface 271 in the described configuration to a point 273 located on the top half portion of the second sheath 110, which can be defined as the top half of the radial height 269 of the second sheath's step-up extension in a deployed state farthest from the attachment mechanism 115.

[0058] Also, to help facilitate delivery of the sheath assembly 100 through the single access site 155, the second sheath 110 can be smaller than the first sheath 105, the attachment mechanism 115, and / or the combination of the first sheath 105 and the attachment mechanism 115. For example, the second sheath 110, when in the deployed state, can define a cross-sectional area that is less than half the cross-sectional area defined by the first sheath 105, the attachment mechanism 115, and / or the combination of the first sheath 105 and the attachment mechanism 115. In further certain such cases, the second sheath 110, when in the deployed state, can define a cross-sectional area that is less than one-third the cross-sectional area defined by the first sheath 105, the attachment mechanism 115, and / or the combination of the first sheath 105 and the attachment mechanism 115.

[0059] 6 illustrates an isolated perspective view of the second sheath 110 and attachment mechanism 115 of the sheath assembly 100. The second sheath 110 can be coupled to the attachment mechanism 115, which can secure the second sheath 110 to the first sheath such that a first portion of the outer surface of the second sheath 110 interfaces with a portion of the outer surface of the first sheath. In the illustrated embodiment, the attachment mechanism 115 can be said to be configured to secure the second sheath 110 to the first sheath in a stacked arrangement. In this illustrated embodiment, the attachment mechanism 115 does not pass over the second sheath 110; rather, the attachment mechanism 115 generally contacts the second sheath 110 only at the first portion of the outer surface of the second sheath that interfaces with the outer surface of the first sheath. This placement of the attachment mechanism 115 can be useful in securing the second sheath 110 to the first sheath while not inhibiting the ability of the second sheath 110 to transition between the deployed and contracted states.

[0060] In the illustrated embodiment, the attachment mechanism 115 is in the form of an elastic band. As shown, a second portion of the outer surface of the second sheath may be free of the elastic band, which, as noted, may facilitate the transition of the second sheath 110 between the deployed and contracted states. In the illustrated embodiment, the elastic band is configured to extend completely around the outer surface of the first sheath for a particular longitudinal length along the longitudinal axis 106 of the first sheath. The elastic band may be configured to stretch to increase the area defined within the elastic band (e.g., the internal lumen defined by the inner surface 206 of the attachment mechanism 115). This may be useful in securing the second sheath 110 to the first sheath 105, as the outer surface of the first sheath may have one or more geometric irregularities that may require the elastic band to be deployed to pass over such irregularities. In this manner, the deployable nature of the elastic band can be useful to allow the second sheath 110 to be added to a variety of first sheaths, while also providing sufficient securing force to keep the second sheath 110 in place relative to the first sheath 105.

[0061] As mentioned, the attachment mechanism 115 includes an attachment member inner surface 206. The attachment member inner surface 206 can define a lumen that receives the first sheath. The attachment member inner surface 206 can be configured to apply a frictional force to the outer surface of the first sheath sufficient to prevent relative movement between the first sheath and the second sheath 110. For example, the attachment mechanism inner surface 206 can be configured to apply a frictional force to the outer surface of the first sheath sufficient to prevent relative movement between the first sheath and the second sheath 110 when an insertion force of up to 15 lbf (pound-force), up to 12 lbf, up to 10 lbf, up to 8 lbf, up to 5 lbf, or up to 3 lbf is applied to the sheath assembly 100. The insertion force applied to the sheath assembly 100 can vary depending on the application (e.g., the size of the first sheath 105 and / or second sheath 110, the anatomical location of the access site 155, the blood vessel 150 through which the sheath assembly is advanced), and the attachment mechanism inner surface 206 can be configured to apply a frictional force at the outer surface of the first sheath sufficient to prevent relative movement between the first sheath and the second sheath 110 when a particular insertion force is expected to be applied to the sheath assembly 100 in a particular application.

[0062] The attachment mechanism 115 also includes an attachment mechanism outer surface 205. The attachment mechanism outer surface 205 may be coupled to the mating outer surface 138 of the second sheath 110. As one example, the attachment mechanism outer surface 205 may be coupled to the mating outer surface 138 of the second sheath 110 via a welded connection where the attachment mechanism outer surface 205 joins the outer surface 138 of the second sheath 110. As best seen in the embodiment of FIG. 5 , the welded connection between the attachment mechanism outer surface 205 and the outer surface 138 of the second sheath 110 may extend over less than about 50%, 40%, 35%, 30%, or 25% of the circumference of the outer surface 138 of the second sheath 110 at a given cross-sectional location where the second sheath 110 is coupled to the attachment mechanism 115.

[0063] In some embodiments, a welded bond of the second sheath 110 to the attachment feature 115 can help facilitate an asymmetric cross-sectional profile of the attachment feature 115 relative to the central longitudinal axis 106 of the first sheath. For example, melting the second sheath 110 into the outer surface 205 of the attachment feature 115 can increase surface tension at the outer surface 205 of the attachment feature 115. The increase in surface tension at the outer surface 205 of the attachment feature 115 can be of sufficient magnitude to pull the portion of the attachment feature 115 that connects with the second sheath 110 away from the central longitudinal axis 106 of the first sheath. This increase in surface tension can therefore pull the portion of the attachment feature 115 that connects with the second sheath 110 “out of round” relative to the central longitudinal axis 106 of the first sheath, thereby achieving an asymmetric cross-sectional profile of the attachment feature 115, as shown in FIGS. 4 and 5 . This bonding of the mating portions of the outer surface 205 of the attachment mechanism 115 may sometimes be referred to as a reflow manufacturing process.

[0064] In the illustrated embodiment, the attachment mechanism 115 may include perforations 222. The attachment mechanism 115 may be configured to break along the perforations 222, such as when the first sheath is deployed. The perforations 222 may be included along the outer surface 205 of the attachment mechanism 115, for example, at a location on the outer surface 205 opposite a portion of the outer surface 205 that interfaces with the second sheath 110; often, the perforations 222 may also face an asymmetric portion of the attachment mechanism 115. The perforations 222 may also extend along the outer surface 206 in a direction parallel to the central longitudinal axis 111 of the second sheath. When the perforations 222 are broken, the attachment mechanism 115 may change from a continuous loop shape to a generally “C”-shaped band, allowing the attachment mechanism 115 to accommodate an increase in the size of the first sheath while still maintaining the second sheath 110 secured to the first sheath.

[0065] The embodiment of the sheath assembly 100 is illustrated as including one second sheath 110. In other additional embodiments, the sheath assembly 100 can include two or more second sheaths 110. For example, in one such additional embodiment, the sheath assembly 100 can include two second sheaths 110, e.g., spaced apart around the circumference of the attachment mechanism 115 (e.g., opposite each other around the circumference of the attachment mechanism 115). As another example, in another such additional embodiment, the sheath assembly 100 can include multiple second sheaths 110 distributed around the circumference of the attachment mechanism 115.

[0066] In these additional embodiments including two or more second sheaths 110, one or more of the various features (e.g., each of the various features) disclosed herein with respect to the single second sheath 110 embodiment of the illustrated sheath assembly 100 may be included in the second sheath 110 and attachment mechanism 115. For example, in additional embodiments where the sheath assembly includes two or more second sheaths 110, the first sheath 105 may include a first sheath step-up extension 250, the attachment mechanism 115 may include an attachment mechanism step-up extension 252 and an attachment mechanism non-expanded region 261 aligned with the position of each second sheath 110, and each second sheath 110 may include a second sheath step-up extension 265. Specifically, as noted, in these additional embodiments, the attachment mechanism step-up extension 252 and the attachment mechanism non-expanding region 261 may be included in the attachment mechanism 115 at positions circumferentially around the outer surface of the attachment mechanism 115 that are aligned with the circumferential positions of each of the second sheaths 110. For example, in one embodiment in which the sheath assembly includes two second sheaths 110 at opposing positions around the outer circumference of the attachment mechanism 115, the attachment mechanism step-up extension 252 and the attachment mechanism non-expanding region 261 may be included at opposing circumferential positions on the outer surface of the attachment mechanism 115. Similarly, in one embodiment in which the sheath assembly includes two second sheaths 110 positioned adjacent to each other around the outer periphery of the attachment mechanism 115, the attachment mechanism step-up extensions 252 and the attachment mechanism non-expansion regions 261 may be included at these adjacent circumferential positions on the outer surface of the attachment mechanism 115 (e.g., such that the attachment mechanism step-up extensions 252 and the attachment mechanism non-expansion regions 261 are continuous around these adjacent positions along the outer periphery of the attachment mechanism 115).

[0067] 7 is a flow diagram of one embodiment of a method 700 of using a sheath assembly. For example, the sheath assembly referenced in method 900 may be similar to or identical to sheath assembly 100 disclosed elsewhere herein.

[0068] In step 710, method 700 includes securing a second sheath to the first sheath to form a sheath assembly. The second sheath of method 700 can be similar to or identical to second sheath 110 disclosed herein. The first sheath of method 700 can be similar to or identical to first sheath 105 disclosed herein. Step 710 can include removing the second sheath from the packaging container and securing the second sheath to the first sheath via one or more attachment members, such as attachment mechanism 115. This can include securing the attachment members around the outer surface of the first sheath while leaving a majority of the outer surface of the second sheath free of the attachment members. Step 710 can also include securing the second sheath to the first sheath using attachment members, the attachment members including a symmetrical cross-sectional portion (e.g., symmetrical about the central longitudinal axis of the first sheath) and an asymmetrical cross-sectional portion (e.g., asymmetrical about the central longitudinal axis of the first sheath). The second sheath can be secured to the first sheath such that the symmetrical cross-sectional portion of the attachment mechanism is spaced apart from (e.g., located opposite) the second sheath, and the asymmetrical cross-sectional portion of the attachment mechanism is positioned at the junction with the second sheath.

[0069] At step 720, method 700 includes inserting a guidewire into the patient. The guidewire may be inserted into a vascular lumen and advanced to the region of interest through a single access site in the patient. The guidewire may be inserted into the vascular lumen at step 720 after an interventional technique is performed to puncture the target vessel and create an opening at the single access site for insertion of the guidewire.

[0070] At step 730, method 700 includes inserting a sheath assembly—e.g., first and second sheaths coupled together via the described attachment mechanism—into the patient through a single access site. For example, the first sheath can be placed over a guidewire, and the first and second sheaths together, along with the attachment mechanism, can be inserted into the vessel lumen through the single access site and advanced through the vessel lumen to the region of interest.

[0071] In some embodiments, inserting the sheath assembly in step 730 may involve contacting the vessel wall and inserting the sheath assembly into the single access site first by a step-up extension of the first sheath (e.g., step-up extension 250 of the first sheath), followed by a step-up extension of the first attachment mechanism (e.g., step-up extension 252 of the first attachment mechanism), followed by a step-up extension of the second attachment mechanism (e.g., step-up extension 252 of the attachment mechanism), followed by a non-expanded region of the attachment mechanism (e.g., non-expanded region 261 of the attachment mechanism), followed by a step-up extension of the second sheath (e.g., step-up extension 252 of the second attachment mechanism), etc. and defining a vessel lumen by a step-up extension 265 of the second sheath. As described elsewhere herein, this insertion sequence at a single access site, facilitated by the configuration of the sheath assembly, can help enable a more efficient sheath assembly insertion process at a single access site (e.g., by allowing sufficient time during introduction of the sheath assembly to relax and stabilize the vessel and straighten any folds that may have formed in the vessel wall during introduction of one portion of the sheath assembly, and return to the initial shape it had at the beginning of introduction of the sheath assembly, prior to the introduction of another larger cross-sectional diameter portion).

[0072] At step 740, method 700 includes transitioning the second sheath from the deployed state to the contracted state. For example, the second sheath may be transitioned from the deployed state to the contracted state when the second sheath contacts a vessel wall to define a vessel lumen through which the first and second sheaths are inserted and advanced. The second sheath may be transitioned to the contracted state as a result of a force imparted in a first direction by the vessel wall on the outer surface of the second sheath and a force imparted in a second, opposite direction by the outer surface of the first sheath. Transitioning the second sheath to the contracted state may result in a reduced profile of the sheath assembly within the vessel lumen (and moving at least a portion of the second sheath closer to the attachment mechanism, e.g., closer to an asymmetric portion of the attachment mechanism). This may be useful in enabling the sheath assembly to be used through a single access site on a patient.

[0073] At step 750, method 700 includes inserting an instrument through the second sheath. The instrument can be inserted through the second sheath lumen. The instrument can be, for example, a diagnostic and / or interventional instrument, such as a diagnostic and / or interventional catheter (e.g., a pigtail catheter and associated guidewire within the second sheath). Inserting the instrument through the second sheath can transition the second sheath from a contracted state toward a deployed state. That is, inserting the instrument into the second sheath lumen can impart a force to the inner surface of the second sheath, which counteracts the force imparted by the vessel wall to the outer surface of the second sheath, deploying the second sheath outward, away from the first sheath and toward the vessel wall. In particular, in this manner, the secondary sheath can transition from a contracted state toward an expanded state only to the extent necessary to accommodate an instrument within the secondary sheath lumen, thereby maintaining a minimal required profile for the sheath assembly even when an instrument is actively being used within the secondary sheath lumen during a procedure. Thus, allowing the secondary sheath to transition between the expanded and contracted states can facilitate a low profile for the sheath assembly both during insertion and placement, and during use of the secondary sheath during a procedure, thereby enabling the sheath assembly to be used through a single access site.

[0074] In some cases, method 700 may further include, after step 750, removing the instrument from the second sheath lumen and then removing the sheath assembly from the patient. For example, removing the instrument from the second sheath lumen may transition the second sheath from the deployed state to the contracted state. That is, as described above, without an instrument in the lumen of the second sheath, the second sheath may be configured to contract upon contact with the vessel wall as a result of forces applied to the outer surface of the second sheath by the vessel wall and the first sheath, respectively. The sheath assembly may then be removed from the blood vessel with the second sheath in the contracted state. Removing the sheath assembly from the blood vessel may include removing both the first and second sheaths and the attachment mechanism together over the guidewire. With the second sheath in the contracted state, the sheath assembly may be removed from the blood vessel while in a reduced, compact profile relative to when the sheath assembly is in the region of interest and when the instrument is in the lumen of the second sheath.

[0075] Various non-limiting, exemplary embodiments have been described. It will be recognized that suitable substitutions are possible without departing from the scope of the embodiments described herein. These and other embodiments are within the scope of the following claims. The present disclosure also includes the following aspects. [Aspect 1] 1. A sheath assembly comprising: a first sheath including a first sheath first end portion, a first sheath second end portion opposite the first sheath first end portion, a first sheath inner surface, and a first sheath outer surface opposite the first sheath inner surface, wherein the first sheath inner surface defines a first sheath lumen extending along a central longitudinal axis of the first sheath between the first sheath first end portion and the first sheath second end portion; a second sheath including a second sheath first end portion, a second sheath second end portion opposite the second sheath first end portion, an inner surface of the second sheath, and an outer surface of the second sheath opposite the inner surface of the second sheath, wherein the inner surface of the second sheath defines a second sheath lumen extending along a longitudinal axis of the second sheath between the second sheath first end portion and the second sheath second end portion; an attachment mechanism coupling the second sheath to the first sheath, the attachment mechanism including a step-up extension of the attachment mechanism, at least a portion of the attachment mechanism being asymmetric about a central longitudinal axis of the first sheath at the step-up extension of the attachment mechanism. [Aspect 2] 2. The sheath assembly of claim 1, wherein the step-up extension of the attachment mechanism is positioned between the second end portion of the first sheath and the second end portion of the second sheath. Aspect 3 2. The sheath assembly of claim 1, wherein the step-up extension of the attachment mechanism includes a first attachment mechanism step-up extension at a first attachment mechanism portion and a second attachment mechanism step-up extension at a second attachment mechanism portion, the second attachment mechanism step-up extension being different from the first attachment mechanism step-up extension. Aspect 4 A sheath assembly as described in aspect 3, wherein the attachment mechanism includes a first longitudinal cross-sectional profile at the first attachment mechanism portion that is asymmetric about the longitudinal central axis of the first sheath, and wherein the attachment mechanism includes a second longitudinal cross-sectional profile at the second attachment mechanism portion that is symmetric about the longitudinal central axis of the first sheath. Aspect 5 5. The sheath assembly of embodiment 4, wherein the first attachment mechanism portion and the second attachment mechanism portion are included at a common longitudinal position on the attachment mechanism. Aspect 6 A sheath assembly according to aspect 4, wherein the first attachment mechanism portion interfaces with an outer surface of the second sheath and the second attachment mechanism portion faces the second sheath. Aspect 7 4. The sheath assembly of aspect 3, wherein the step-up extension of the first attachment mechanism has a first slope defined by a longitudinal length of the step-up extension of the first attachment mechanism and a radial height of the step-up extension of the first attachment mechanism, and the step-up extension of the second attachment mechanism has a second slope defined by a longitudinal length of the step-up extension of the second attachment mechanism and a radial height of the step-up extension of the second attachment mechanism, the second slope being different from the first slope. Aspect 8 A sheath assembly as described in aspect 7, wherein a radial height of a step-up extension of the first attachment mechanism is on a side of the attachment mechanism facing the second sheath, a radial height of a step-up extension of the second attachment mechanism is on another side of the attachment mechanism facing the second sheath, and the radial height of the step-up extension of the first attachment mechanism is greater than the radial height of the step-up extension of the second attachment mechanism. Aspect 9 A sheath assembly as described in aspect 7, wherein the first slope of the step-up extension of the first attachment mechanism is greatest at a position proximal to the distal-most joint between the attachment mechanism and the first sheath, and the first slope of the step-up extension of the first attachment mechanism decreases in a direction progressing proximally toward the second sheath. Aspect 10 A sheath assembly as described in aspect 9, wherein the first slope of the step-up extension of the first attachment mechanism includes a first slope region and a second slope region, the first slope region having a greater slope magnitude than the second slope region, the first slope region being distal to the second slope region, and the first slope region extending from the distal-most joint between the attachment mechanism and the first sheath to the second slope region for only a portion of the longitudinal length of the step-up extension of the first attachment mechanism. Aspect 11 A sheath assembly according to aspect 10, wherein a radial height of the step-up extension of the first attachment mechanism is greater than a longitudinal length of the step-up extension of the first attachment mechanism. Aspect 12 11. The sheath assembly of claim 10, wherein the radial height of the step-up extension of the first attachment mechanism is 0.254 to 1.27 cm and the longitudinal length of the step-up extension of the first attachment mechanism is 0.254 to 0.635 cm. Aspect 13 A sheath assembly as described in aspect 3, wherein the attachment mechanism includes a non-expanding region defining a portion of the attachment mechanism along which a cross-sectional diameter of the attachment mechanism is constant, the non-expanding region of the attachment mechanism being positioned longitudinally between a step-up extension of the first attachment mechanism and a distal-most end of the second sheath. Aspect 14 A sheath assembly as described in aspect 13, wherein the non-expanding region extends along a longitudinal length of the non-expanding region from a proximal end of the step-up extension portion of the first attachment mechanism to the distal-most end of the second sheath, and the longitudinal length of the non-expanding region is at least 5 cm. Aspect 15 A sheath assembly as described in aspect 13, wherein the second sheath includes a second sheath step-up extension, the second sheath step-up extension being included at a distal-most end of the second sheath that joins with the non-expanded region of the attachment mechanism. Aspect 16 A sheath assembly according to aspect 15, wherein the second sheath includes a first distal wall portion forming a first portion of the opening of the second sheath lumen at a position adjacent to the attachment mechanism, and the second sheath includes a second distal wall portion forming a second portion of the opening of the second sheath lumen at a position opposite the attachment mechanism, and the first distal wall portion is positioned distally on the sheath assembly than the second distal wall portion. Aspect 17 17. The sheath assembly of claim 16, wherein an angle defined relative to a central longitudinal axis of the first sheath defines a slope extending between the first and second distal wall portions over the longitudinal length of the step-up extension of the second sheath, the angle being between 15 and 75 degrees. Aspect 18 2. The sheath assembly of claim 1, wherein the second sheath is configured to transition between an deployed state and a contracted state, the second sheath is biased to the deployed state, and the second sheath is configured to overcome the bias to the deployed state when an outer surface of the second sheath contacts a blood vessel wall defining a blood vessel lumen, thereby transitioning the second sheath to the contracted state. Aspect 19 1. A method of using a sheath assembly, comprising: securing the second sheath to the first sheath via an attachment mechanism such that a first portion of an outer surface of the second sheath interfaces with an outer surface of the first sheath, the first sheath defining a central longitudinal axis of the first sheath, the attachment mechanism including an attachment mechanism step-up extension, and at least a portion of the attachment mechanism being asymmetric about the central longitudinal axis of the first sheath at the attachment mechanism step-up extension; inserting a guidewire into a region of interest in a patient; placing the first sheath over the guidewire and inserting the first sheath and the second sheath into the patient through a single access site in the patient; contacting the single access site with a step-up extension of the attachment mechanism and then with the second sheath; transitioning the second sheath from an expanded state to a contracted state upon insertion of the second sheath into the patient, wherein the second sheath contracts to the contracted state in a direction toward the first sheath; and inserting an instrument through the second sheath to transition the second sheath from the contracted state to the deployed state. Aspect 20 The method of aspect 19, further comprising the step of contacting the single access site with a non-expanded region of the attachment mechanism after contacting the single access site with the step-up extension of the attachment mechanism and before contacting the single access site with the second sheath, wherein the non-expanded region of the attachment mechanism defines a portion of the attachment mechanism along which the cross-sectional diameter of the attachment mechanism is constant.

Claims

1. 1. A sheath assembly comprising: a first sheath including a first sheath first end portion, a first sheath second end portion opposite the first sheath first end portion, an inner surface of the first sheath, and an outer surface of the first sheath opposite the inner surface of the first sheath, the inner surface of the first sheath defining a first sheath lumen extending along a central longitudinal axis of the first sheath between the first sheath first end portion and the first sheath second end portion; a second sheath including a second sheath first end portion, a second sheath second end portion opposite the second sheath first end portion, an inner surface of the second sheath, and an outer surface of the second sheath opposite the inner surface of the second sheath, wherein the inner surface of the second sheath defines a second sheath lumen extending along a longitudinal axis of the second sheath between the second sheath first end portion and the second sheath second end portion; an attachment mechanism coupling the second sheath to the first sheath, the attachment mechanism including a step-up extension defining an increase in cross-sectional diameter at the attachment mechanism, at least a portion of the attachment mechanism being asymmetric about the central longitudinal axis of the first sheath at the step-up extension of the attachment mechanism; the attachment mechanism step-up extension includes a first attachment mechanism step-up extension at a first attachment mechanism portion and a second attachment mechanism step-up extension at a second attachment mechanism portion, the second attachment mechanism step-up extension being different from the first attachment mechanism step-up extension; the attachment mechanism includes a non-expanding region defining a portion of the attachment mechanism along which a cross-sectional diameter of the attachment mechanism is constant, the non-expanding region of the attachment mechanism being positioned longitudinally between a step-up extension of the first attachment mechanism and a distal-most end of the second sheath; a second sheath step-up extension defining an increase in cross-sectional diameter of the second sheath, the second sheath step-up extension being included at a distal-most end of the second sheath that interfaces with the non-expanded region of the attachment mechanism.

2. The sheath assembly of claim 1 , wherein the step-up extension of the attachment mechanism is positioned between the second end portion of the first sheath and the second end portion of the second sheath.

3. 2. The sheath assembly of claim 1, wherein the attachment mechanism includes a first longitudinal cross-sectional profile at the first attachment mechanism portion that is asymmetric about the central longitudinal axis of the first sheath, and wherein the attachment mechanism includes a second longitudinal cross-sectional profile at the second attachment mechanism portion that is symmetric about the central longitudinal axis of the first sheath.

4. The sheath assembly of claim 3 , wherein the first attachment mechanism portion and the second attachment mechanism portion are included at a common longitudinal location on the attachment mechanism.

5. The sheath assembly of claim 3 , wherein the first attachment mechanism portion interfaces with an outer surface of the second sheath and the second attachment mechanism portion faces the second sheath.

6. 2. The sheath assembly of claim 1, wherein the step-up extension of the first attachment mechanism has a first slope defined by a longitudinal length of the step-up extension of the first attachment mechanism and a radial height of the step-up extension of the first attachment mechanism, and the step-up extension of the second attachment mechanism has a second slope defined by a longitudinal length of the step-up extension of the second attachment mechanism and a radial height of the step-up extension of the second attachment mechanism, the second slope being different from the first slope.

7. 7. The sheath assembly of claim 6, wherein a radial height of a step-up extension of the first attachment mechanism is on a side of the attachment mechanism facing the second sheath and a radial height of a step-up extension of the second attachment mechanism is on another side of the attachment mechanism facing the second sheath, and wherein the radial height of the step-up extension of the first attachment mechanism is greater than the radial height of the step-up extension of the second attachment mechanism.

8. 7. The sheath assembly of claim 6, wherein the first slope of the step-up extension of the first attachment mechanism is greatest proximate a distal-most junction between the attachment mechanism and the first sheath, and the first slope of the step-up extension of the first attachment mechanism decreases in a direction proceeding proximally toward the second sheath.

9. 9. The sheath assembly of claim 8, wherein the first slope of the step-up extension of the first attachment mechanism includes a first slope region and a second slope region, the first slope region having a greater slope magnitude than the second slope region, the first slope region being distal to the second slope region, and the first slope region extending a portion of a longitudinal length of the step-up extension of the first attachment mechanism from the distal-most junction between the attachment mechanism and the first sheath to the second slope region.

10. The sheath assembly of claim 9 , wherein a radial height of the step-up extension of the first attachment feature is greater than a longitudinal length of the step-up extension of the first attachment feature.

11. 10. The sheath assembly of claim 9, wherein a radial height of the step-up extension of the first attachment mechanism is between 0.254 and 1.27 cm and a longitudinal length of the step-up extension of the first attachment mechanism is between 0.254 and 0.635 cm.

12. 2. The sheath assembly of claim 1, wherein the non-expanding region extends from a proximal end of a step-up extension of the first attachment mechanism to the distal-most end of the second sheath along a longitudinal length of the non-expanding region, the longitudinal length of the non-expanding region being at least 5 cm.

13. 2. The sheath assembly of claim 1, wherein the second sheath includes a first distal wall portion forming a first portion of an opening of the second sheath lumen adjacent to the attachment mechanism, and the second sheath includes a second distal wall portion forming a second portion of the opening of the second sheath lumen opposite the attachment mechanism, the first distal wall portion being positioned distally on the sheath assembly than the second distal wall portion.

14. 14. The sheath assembly of claim 13, wherein an angle defined relative to a central longitudinal axis of the first sheath defines a slope extending between the first and second distal wall portions across the longitudinal length of the step-up extension of the second sheath, the angle being between 15 and 75 degrees.

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