Patent Publication Number: US-2016220241-A1

Title: Suture collar for use with an introducer during direct aortic procedures

Description:
FIELD OF THE INVENTION 
     The invention relates to introducer assemblies for use during direct aortic procedures, and more particularly, relates to suture collars for use with an introducer during direct aortic procedures. 
     BACKGROUND OF THE INVENTION 
     Currently, the replacement of a deficient cardiac valve is often performed by opening the thorax, placing the patient under extracorporeal circulation, temporarily stopping the heart, surgically opening the heart, excising the deficient valve, and then implanting a prosthetic valve in its place. This procedure generally requires prolonged patient hospitalization, as well as extensive and often painful recovery. 
     Recently, minimally invasive approaches have been developed to facilitate catheter-based implantation of valve prostheses in the beating heart, intending to obviate the need for the use of classical sternotomy and cardiopulmonary bypass. For example, U.S. Pat. No. 8,016,877 to Seguin et al. illustrates a technique and a device for replacing a deficient heart valve by percutaneous route. An expandable prosthetic valve is compressed about a catheter, inserted inside a lumen within the body, such as the femoral artery, and delivered to a desired location in the heart. Additionally, U.S. Pat. No. 7,914,569 to Nguyen et al. discloses advancing the catheter containing the prosthesis in a retrograde manner through the femoral artery and into the descending aorta, over the aortic arch, through the ascending aorta and inside the defective aortic valve. This procedure can be assisted by fluoroscopic guidance. Once the position of the catheter containing the prosthesis is confirmed, a sheath containing the prosthesis can be moved proximally, allowing the valve prosthesis to self-expand. Alternatively, a balloon catheter may be used to expand the valve prosthesis. 
     However, percutaneous delivery routes require peripheral arterial access and cannulation. In some patients, these routes are contraindicated or have an increased risk of vascular complications due to the presence of small vessel size, severe atherosclerosis, tortuosity and/or calcification. For patients with no suitable femoral or axillary access, a direct aortic approach may be utilized to deliver a transcatheter prosthetic heart valve. A direct aortic approach may be carried out via a mini-thoracotomy. An introducer is positioned directly onto the exterior surface of the aorta, and a prosthetic valve implantation is performed by advancing a standard delivery system through the introducer. Direct aortic valve implantation includes special advantages of high control of valve deployment with no adverse effect on the left ventricle structure or function. 
     Proper positioning and alignment of the delivery system is essential to a successful prosthetic valve deployment. Thus, when the standard delivery system is advanced through the introducer, it may be necessary to selectively steer or angle the delivery system toward the target implantation site, thereby resulting in pulling or stretching the aorta which may cause damage thereto. Embodiments hereof relate to a component that permits selective tilting of the introducer and delivery system during a direct aortic procedure. 
     BRIEF SUMMARY OF THE INVENTION 
     Embodiments hereof relate to a suture collar configured for use with an introducer sheath. The suture collar includes an outer ring component defining an opening there-though and an inner ring component concentrically disposed within the opening of the outer ring component. The outer ring component is configured to be sutured to a target surface of a patient. The inner ring component defines an opening there-through that is configured to receive the introducer sheath. In a first configuration of the suture collar, a longitudinal axis of the inner ring component is aligned with a longitudinal axis of the outer ring component. The inner ring component is configured to move relative to the outer ring component such that in a second configuration of the suture collar the longitudinal axis of the inner ring component is angularly offset with the longitudinal axis of the outer ring component. 
     Embodiments hereof also relate to an introducer assembly including an introducer sheath and a suture collar configured to be positioned over the introducer sheath. The suture collar includes an outer ring component defining an opening there-though and an inner ring component concentrically disposed within the opening of the outer ring component. The outer ring component is configured to be sutured to a target surface of a patient and an inner surface of the outer ring component is concave. The inner ring component defines an opening there-through that is configured to receive the introducer sheath. In a first configuration of the suture collar, a longitudinal axis of the inner ring component is aligned with a longitudinal axis of the outer ring component. An outer surface of the inner ring component is convex and is configured to slidingly mate with the concave inner surface of the outer ring component to permit the inner ring component and the introducer sheath received therein to move relative to the outer ring component such that in a second configuration of the suture collar the longitudinal axes of the inner ring component and the introducer sheath received therein are angularly offset with the longitudinal axis of the outer ring component. 
     Embodiments hereof also relate to an introducer assembly including an introducer sheath and a suture collar configured to be positioned over the introducer sheath. The suture collar includes an outer ring component defining an opening there-though and an inner ring component concentrically disposed within the opening of the outer ring component. The outer ring component is configured to be sutured to a target surface of a patient. The inner ring component defines an opening there-through that is configured to receive the introducer sheath. In a first configuration of the suture collar, a longitudinal axis of the inner ring component is aligned with a longitudinal axis of the outer ring component. A membrane radially extends between the outer and inner ring components, wherein the membrane is formed from an elastic material to permit the inner ring component and the introducer sheath received therein to move relative to the outer ring component such that in a second configuration of the suture collar the longitudinal axes of the inner ring component and the introducer sheath received therein are angularly offset with the longitudinal axis of the outer ring component. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The foregoing and other features and advantages of the invention will be apparent from the following description of embodiments hereof as illustrated in the accompanying drawings. The accompanying drawings, which are incorporated herein and form a part of the specification, further serve to explain the principles of the invention and to enable a person skilled in the pertinent art to make and use the invention. The drawings are not to scale. 
         FIG. 1  is a perspective view of a suture collar according to an embodiment hereof, wherein the suture collar includes an inner ring component that is configured to tilt or pivot relative to an outer ring component. 
         FIG. 2  is a top end view of the suture collar of  FIG. 1 . 
         FIG. 2A  is a cross-sectional view taken along line A-A of  FIG. 2 . 
         FIG. 3  is a bottom end view of a suture collar according to another embodiment hereof, wherein the suture collar includes a plurality of suture holes for receiving one or more purse string sutures to attach the suture collar to an outer surface of a body vessel such as an aorta. 
         FIG. 4  is a side view of the suture collar of  FIG. 1  disposed over an introducer sheath of an introducer. 
         FIG. 5  is a cross-sectional view of the suture collar of  FIG. 1  with the introducer sheath of the introducer of  FIG. 4  shown in phantom, wherein the suture collar is in a first configuration in which a longitudinal axis of the inner ring component, as well as a longitudinal axis of the introducer sheath of the introducer, is aligned with a longitudinal axis of the outer ring component. 
         FIG. 6  is a cross-sectional view of the suture collar of  FIG. 1  with the introducer sheath of the introducer of  FIG. 4  shown in phantom, wherein the suture collar is in a second configuration in which the longitudinal axis of the inner ring component, as well as the longitudinal axis of the introducer sheath of the introducer is angularly offset with the longitudinal axis of the outer ring component. 
         FIG. 7  is an illustration of the suture collar of  FIG. 1  and the introducer of  FIG. 4  being utilized for a direct aortic procedure within the aortic arch. 
         FIG. 8  is a top view of a suture collar according to another embodiment hereof, wherein the suture collar includes an inner ring component that is configured to tilt or pivot relative to an outer ring component via a flexible membrane extending between the inner and outer ring components. 
         FIG. 8A  is a cross-sectional view taken along line A-A of  FIG. 8 . 
         FIG. 9  is a side view of an adjustable suture collar according to another embodiment hereof disposed over an introducer sheath of an introducer, wherein the adjustable suture collar is shown in a first longitudinal position along the introducer sheath. 
         FIG. 10  is a side view of the adjustable suture collar of  FIG. 9  disposed over the introducer sheath of the introducer, wherein the adjustable suture collar is shown in a second longitudinal position along the introducer sheath. 
         FIG. 11  is a sectional perspective exploded view of the adjustable suture collar of  FIG. 9 . 
         FIG. 12  is a sectional perspective exploded view of an adjustable suture collar according to another embodiment hereof. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Specific embodiments of the present invention are now described with reference to the figures, wherein like reference numbers indicate identical or functionally similar elements. The terms “distal” and “proximal” are used in the following description with respect to a position or direction relative to the treating clinician. “Distal” or “distally” are a position distant from or in a direction away from the clinician. “Proximal” and “proximally” are a position near or in a direction toward the clinician. 
     The following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Although the description of the invention is in the context of treatment of blood vessels such as the aorta, the invention may also be used in any other body passageways where it is deemed useful. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary or the following detailed description. 
     Embodiments hereof relate to suture collars configured for use with an introducer during a direct aortic procedure. Suture collars according to embodiments hereof are configured to be positioned over an introducer sheath and are configured to abut against, and optionally be sutured to, an outer surface of the aorta during a direct aortic procedure. An inner ring component of the suture collar, as well as the introducer sheath received there-through, is configured to tilt or pivot relative to a stationary outer ring component of the suture collar so that the introducer sheath may be selectively steered or angled toward a target implantation site. Further, a delivery system positioned through the introducer sheath may be selectively steered or angled toward a target implantation site without pulling or stretching the aorta to which the suture collar is attached as will be explained in more detail herein. 
     With reference to  FIGS. 1-2A , suture collar  100  includes an outer ring component  102  defining an opening  104  there-though and an inner ring component  112  concentrically disposed within opening  104  of the outer ring component.  FIG. 1  is a perspective view of suture collar  100 ,  FIG. 2  is a top view of suture collar  100 , and  FIG. 2A  is a cross-sectional view of suture collar  100  taken along line A-A of  FIG. 2 . Outer ring component  102  is configured to be sutured to a target surface of a patient as will be explained in more detail herein. Inner ring component  112  defines an opening  114  there-through that is configured to receive an introducer sheath (not shown in  FIGS. 1-2A ). In a first configuration of suture collar  100 , as shown and described below with respect to  FIG. 5 , a longitudinal axis of inner ring component  112  is aligned with a longitudinal axis of outer ring component  102 . Inner ring component  112  is configured to move relative to outer ring component  10  such that in a second configuration of suture collar  100 , as shown and described below with respect to  FIG. 6 , the longitudinal axis of inner ring component  112  is angularly offset with the longitudinal axis of outer ring component  102 . 
     More particularly, outer ring component  102  is an annular or ring element having opening  104  there-though. An inner surface  106  of outer ring component  102  is concave or curved in a first direction, and is sized to house a spherical or ball-shaped element. An outer surface  107  of outer ring component  102  includes a first annular ridge or flange  108  at a first end or edge thereof and a second annular ridge or flange  110  at a second or opposing end or edge thereof. An intermediate portion  109  is formed between first and second flanges  108 ,  110  and may be considered a groove or channel between first and second flanges  108 ,  110 . Each flange  108 ,  110  extends radially outward relative to intermediate portion  109  of outer ring component  102  such that the outer diameter of the outer ring component at each flange is greater than the outer diameter of the outer ring component at intermediate portion  109 . Each flange  108 ,  110  also extends around the full circumference of outer ring component  102 . In an embodiment, one or more purse string sutures (not shown) wrap or circle around intermediate portion  109  to attach or sew suture collar  100  to an outer surface of a body vessel such as an aorta. Flanges  108 ,  110  thus define a region, i.e., intermediate portion  109 , that receives one or more purse string sutures for attachment to the outer surface of a body vessel and prevents the sutures from slipping off suture collar  100 . Although separately described, it will be understood by one of ordinary skill in the art that first and second flanges  108 ,  110  are integrally formed on outer ring component  102 . 
     In another embodiment, rather than tying one or more sutures around intermediate portion  109  of suture collar  100 , the suture collar may additionally and/or alternatively include suture holes for receiving one or more purse string sutures for attachment to the outer surface of a body vessel. More particularly, as shown in the embodiment of  FIG. 3 , which is a bottom view of a suture collar  300 , a second annular ridge or flange  310  includes a plurality of suture holes  332  there-through for receiving one or more purse string sutures (not shown) to attach or sew suture collar  300  to an outer surface of a body vessel such as an aorta. Suture collar  300  includes an outer ring component  302  and an inner ring component  312  which defines an opening  314 . Suture collar  300  is similar in structure to suture collar  100  except that second annular flange  310  may optionally extend further radially outward than flange  110  and a first or top flange such as flange  108  may optionally be omitted. When second annular ridge or flange  310  is placed in contact with the outside of the aorta, purse string sutures can be positioned through suture holes  332  to secure outer ring component  302  to the aorta. Although shown with eight suture holes  332  equally spaced around flange  310 , it will be understood by one of ordinary skill in the art that the number of suture holes  332  may vary according to application. 
     Inner ring component  112  is housed within outer ring component  102 . Inner ring component  112  is an annular or ring element having opening  114  there-through that is configured to receive an introducer sheath (not shown in  FIGS. 1-2A ). Opening  114  of inner ring component  112  is sized to snugly receive the introducer sheath. Stated another way, the introducer sheath is disposed within inner ring component  112  such that there is sufficient space or room there-between for the introducer sheath to be moved or slidable in a longitudinal direction relative to inner ring component  112 . In other words, there is not a tight interference or friction fit between the introducer sheath and inner ring component  112 . However, the introducer sheath is disposed within inner ring component  112  such that inner ring component  112  tilts or pivots with tilting or pivoting of the introducer sheath. In other words, when the introducer sheath (or a catheter or delivery system disposed within the introducer sheath) is tilted or pivoted by a clinician, the introducer sheath contacts an inner surface of inner ring component  112  and thereby tilts or pivots inner ring component  112 . The two components may move simultaneously as an ensemble structure, or there may be a slight delay in the rotation of inner ring component  112  by the introducer sheath. 
     An outer surface  116  of inner ring component  112  is convex or curved in a second direction that opposes the first direction of concave outer surface  106 . As such, convex outer surface  116  of inner ring component  112  is configured to slidingly mate or correspond to concave inner surface  106  of outer ring component  102 . Stated another way, inner ring component  112  may be considered a spherical or ball-shaped element having a first truncated end  118  and a second or opposing truncated end  120 . Similar to a sphere or ball, inner ring component  112  rolls, revolves, spins, swivels, or otherwise moves within outer ring component  102  due to the mating convex and concave surfaces. 
     As shown in  FIG. 4 , opening  114  of inner ring component  112  is configured to receive an introducer sheath  422  of an introducer  430  as described above such that suture collar  100  is configured to be positioned over the introducer sheath. Suture collar  100  is typically formed as a separate component that is placed or positioned over introducer sheath  422  prior to a procedure. Stated another way, suture collar  100  is removable from introducer sheath  422 . For example, suture collar  100  and introducer  430  are manufactured as separate or distinct components that are shipped and/or stored together and then assembled into an introducer assembly prior to the procedure. As will be understood by those of ordinary skill in the art, introducer  430  is merely exemplary and suture collar  100  may be utilized with other introducers known in the art. In this embodiment, introducer  430  includes introducer sheath  422  which is a tubular component sized to slidingly receive a delivery system such as a prosthetic valve delivery system. Introducer sheath  422  also includes a depth gauge  426 , which as the name implies, measures the depth that the introducer sheath extends beyond a fixed reference point, such as the exterior surface of the aorta, into a patient&#39;s body. A hub  428  is attached to a proximal end of introducer sheath  422 . A hemostatic valve (not shown) is positioned within hub  428  and is configured to permit passage of a delivery system or catheter into introducer sheath  422  while preventing blood leakage as will be understood by one of ordinary skill in the art. 
     As shown in  FIG. 4 , a removable dilator  424  extends through introducer sheath  422 . Dilator  424  is a separate or independent component from introducer  430 , and is removable from introducer  430 . Dilator  424  is shown in  FIG. 4  as extending from a distal end of introducer  430 . Dilator  424  is configured to expand or enlarge an incision that is made on a body vessel such as an aorta when introducer  430  is being positioned in the body vessel. The length of dilator  424  varies according to application, and a relatively short dilator is utilized when suture collar  100  and introducer  430  are used on the aorta. Dilator  424  extends the entire length of introducer sheath  422 , and is proximally retracted or removed once introducer  430  is positioned in the body vessel. 
     Referring now to  FIG. 5 , which is a cross-sectional view of suture collar  100  with introducer sheath  422  shown in phantom, suture collar  100  is shown in its first configuration, i.e., when in a nominal or normal configuration in which no force is applied thereto. In the first or nominal configuration of suture collar  100 , a longitudinal axis L A2  of inner ring component  112  is aligned with or overlaps a longitudinal axis L A1  of outer ring component  102 . Since introducer sheath  422  is disposed or positioned through opening  114  of inner ring component  112 , the longitudinal axis of the introducer sheath corresponds to longitudinal axis L A2  of inner ring component  112 . Stated another way, when assembled together, introducer sheath  422  and inner ring component  112  have the same longitudinal axis, i.e., longitudinal axis L A2 . 
       FIG. 6  is a cross-sectional view of suture collar  100  with introducer sheath  422  shown in phantom, with suture collar  100  shown in a second or tilted configuration in which the longitudinal axis L A2  of inner ring component  112  (and introducer sheath  422 ) is angularly offset with longitudinal axis L A1  of outer ring component  102 . As described above, inner ring component  112  rolls, revolves, spins, swivels, or otherwise moves in any direction within outer ring component  102  due to the mating convex and concave surfaces  116 ,  106 , respectively. Inner ring component  112  and introducer sheath  422  received therein tilt or pivot relative to outer ring component  102 , which is fixed or stationary since it is sutured or secured to the exterior surface of the aorta. In  FIG. 6 , the longitudinal axis L A2  of inner ring component  112  (and introducer sheath  422 ) is shown to be angularly offset with longitudinal axis L A1  of outer ring component  102  by a tilting angle θ. Tilting angle θ as shown is only exemplary because tilting angle θ is a user-controlled variable. Stated another way, a user controls the amount or degree that inner ring component  112  (and introducer sheath  422 ) is titled relative to outer ring component  102 . In an embodiment, tilting angle θ is limited due to the contact between introducer sheath  422  and outer ring component  102  and may range between 0 and 45 degrees. In addition, although  FIG. 6  illustrates inner ring component  112  (and introducer sheath  422 ) being tilted in a first tilting direction indicated by directional arrow  634 , such a tilting direction is exemplary because the tilting direction is also a user-controlled variable. Stated another way, a user controls which direction inner ring component  112  (and introducer sheath  422 ) is tilted relative to outer ring component  102 . With respect to the tilting direction, inner ring component  112  (and introducer sheath  422 ) is configured to be tilted in any direction relative to outer ring component  102 . 
     During use, inner ring component  112  (and introducer sheath  422 ) is configured to be selectively steered or angled toward a target implantation site. For example,  FIG. 7  illustrates suture collar  100  attached to an exterior surface of an aorta A near the aortic arch. Introducer sheath  422  is shown positioned through suture collar  100 . Further, a prosthetic valve delivery system  736  is shown positioned through introducer sheath  422 . Introducer sheath  422  and prosthetic valve delivery system  736  may be selectively steered or angled toward a target implantation site, such as a native aortic valve AV, without pulling or stretching the aorta A to which suture collar  100  is attached. 
     More particularly, as previously described, suture collar  100  and introducer  430  are manufactured as separate or distinct components that are shipped and/or stored together and then assembled prior to the procedure. Prior to use, suture collar  100  is positioned over introducer sheath  422 . Generally, a mini-thoracotomy is made, the pericardium is opened to expose the aorta, and an incision is made on the aorta A. The aorta, as defined herein, can include the exterior surface and lumen of the descending aorta, aortic arch, ascending aorta and aortic sinus. A purse string suture procedure may be performed prior to making an incision. After an incision is made on the aorta A, introducer  430  is passed through the incision using dilator  424  to dilate the incision, with suture collar  100  positioned over or assembled onto the introducer sheath  422 . As introducer  430  is positioned through the incision, the surgeon can use the purse string sutures to minimize bleeding and then the purse string sutures are tied to suture collar  100  to hold it in place via intermediate portion  109  of suture collar  100  as described above, and/or alternatively via a plurality of suture holes  332  as described above. Thus, outer ring component  102  of suture collar  100  is secured to the exterior surface of the aorta A via one or more purse string sutures. Tying the purse string suture(s) from the aorta around suture collar  100 , or through suture holes of the suture collar, maintains a haemostatic seal as well as controls the position of introducer sheath  422  while the physician is performing the direct aortic procedure. Stated another way, suture collar  100  is coupled to and sealed against the aorta A via the purse string sutures and thus suture collar  100  prevents blood from exiting the body. In addition, the hemostatic valve of hub  428  (not shown in  FIG. 7 ) of introducer  430  also prevents blood from exiting the body. 
     Once suture collar  100  and introducer  430  are positioned as desired, a prosthetic valve delivery system  736  is advanced through introducer  430 . Delivery system  736  may be any delivery system known in the art for percutaneously delivering a prosthesis, such as but not limited to a heart valve prosthesis. Delivery system  736  includes a radially collapsed heart valve prosthesis (not shown in  FIG. 7 ) that is loaded into a capsule  738  at a distal end of the delivery system. If necessary, in order to direct delivery system  736  to the target implantation site of the native aortic valve AV, introducer sheath  422  and prosthetic valve delivery system  736  may be selectively steered or angled toward the native aortic valve AV. More particularly, as described above, the inner ring component of suture collar  100  and introducer sheath  422  (having longitudinal axis L A2  shown in  FIG. 7 ) are configured to be tilted or moved relative to the outer ring component of suture collar  100  (having longitudinal axis L A1  shown in  FIG. 7 ). Since the outer ring component of suture collar  100  remains stationary and sutured to the aorta A, the inner ring component of suture collar  100  and introducer sheath  422  are configured to be moved relative to the outer ring component of suture collar  100  without pulling or stretching the aorta A. Thus, advantageously, prosthetic valve delivery system  736  that is advanced through introducer  430  may be selectively steered or angled toward the native aortic valve AV without pulling or stretching the aorta A. Proper positioning and alignment of prosthetic valve delivery system  726  is essential to a successful prosthetic valve deployment. 
     After the inner ring component of suture collar  100  and introducer sheath  422  are tilted relative to the outer ring component of suture collar  100  as desired in order to direct prosthetic valve delivery system  736  toward the native aortic valve AV, the delivery system is advanced in a retrograde manner within the aorta A until distal capsule  738  reaches the desired implantation location within the native aortic valve AV. The location of distal capsule  738  can be checked by medical imaging. Once in the proper position, distal capsule  738  is refracted in the proximal direction, thereby uncovering the heart valve prosthesis contained in distal capsule  738 . The prosthesis can be self-expanding or can be mechanically expanded, such as by balloon inflation. After the prosthesis is fully deployed, prosthetic valve delivery system  736  can be removed from the aorta A. Suture collar  100  can be detached from the aorta A, and the incision can be closed by sutures. 
     In another embodiment hereof, rather than mating convex and concave surfaces, the suture collar includes a flexible membrane that is configured to permit an inner ring component to tilt or pivot relative to an outer ring component. More particularly,  FIGS. 8-8A  illustrate a suture collar  800  according to another embodiment hereof.  FIG. 8  is a top view of suture collar  800 , while  FIG. 8A  is a cross-sectional view taken along line A-A of  FIG. 8 . Outer ring component  802  is similar to outer ring component  102 . More particularly, outer ring component  802  is an annular or ring element having opening  804  there-though. Further, outer ring component  802  includes a first annular ridge or flange  808  at a first end or edge thereof and a second annular ridge or flange  810  at a second or opposing end or edge thereof. Each flange  808 ,  810  extends radially outward from outer surface  807  of outer ring component  802  such that the outer diameter of the outer ring component at each flange is greater than the outer diameter of the outer ring component at intermediate portion  809 . Each flange  808 ,  810  also extends around the full circumference of outer ring component  102 . 
     Further, inner ring component  812  is similar to inner ring component  112 . More particularly, inner ring component  812  is an annular or ring element having opening  814  there-through that is configured to receive an introducer sheath (not shown in  FIGS. 8-8A ). In this embodiment, however, a flexible membrane  840  radially extends between outer and inner ring components  802 ,  812 . Flexible membrane  840  is a planar component that extends approximately through a center or mid-line plane of outer and inner ring components  802 ,  812 . Flexible membrane  840  is biased to position suture collar  800  in its first configuration, i.e., a nominal or normal configuration in which a longitudinal axis of inner ring component  812  is aligned with or overlaps a longitudinal axis of outer ring component  802 . Flexible membrane  840  is formed from an elastic material to permit inner ring component  812  to tilt or pivot relative to outer ring component  802 . Stated another way, the elastic material of membrane  840  allows suture collar  800  to assume its second or tilted configuration in which the longitudinal axis of inner ring component  812  (and introducer sheath received therein) is angularly offset with the longitudinal axis of outer ring component  802 . Inner ring component  812  and the introducer sheath received therein tilt or pivot relative to outer ring component  802 , which is fixed or stationary since it is sutured or secured to the exterior surface of the aorta. When no force is applied thereto, i.e., when a user does not apply any force to the inner ring component and/or introducer sheath received there-through, the elastic material of flexible membrane  840  causes suture collar  800  to resume its first configuration in which inner ring component  812  is longitudinally aligned within outer ring component  802 . As such, flexible membrane  840  is configured to be self-centering due to the elastic material thereof. Suitable materials for flexible membrane  840  include but are not limited to silicone rubber, a low-grade PEBAX, a low grade polyurethane, and other polymeric materials having elastic characteristics. Flexible membrane  840  may be molded or over-molded into position between outer and inner ring components  802 ,  812 . 
     In another embodiment hereof shown in  FIGS. 9-11 , rather than being configured to permit selectively tilting of an introducer sheath received there-through, an adjustable suture collar  900  is configured to be slidingly disposed over an introducer sheath  922  of an introducer  930  and is configured to be selectively tightened or locked into place. Introducer  930  is similar to introducer  130  and, in addition to introducer sheath  922 , a depth gauge  926 , and a hemostatic valve  928 . A dilator  924  is shown extending through introducer  930 . Suture collar  900  includes a base ring component  950  and a removable ring component  962 . In a first configuration, in which removable ring component  962  is removed or loosely disposed over base ring component  950 , suture collar  900  is configured to slide or move freely over the outer surface of introducer sheath  922  such that suture collar  900  is configured to be selectively positioned at a desired longitudinal position along depth gauge  926 . In a second configuration, in which removable ring component  962  is tightly disposed over or locked onto base ring component  950 , suture collar  900  is tightened or locked onto the outer surface of introducer sheath  922  at the desired longitudinal position along depth gauge  926  and is not able to slide or move freely over the outer surface of introducer sheath  922 .  FIG. 9  is a side view of suture collar  900  in its second configuration, locked on the outer surface of introducer sheath  922  at a first longitudinal position along introducer sheath  922 , and  FIG. 10  is a side view of suture collar  900  in its second configuration, locked on the outer surface of introducer sheath  922  at a second longitudinal position along introducer sheath  922 . When transitioning between the longitudinal positions of  FIG. 9  and  FIG. 10 , suture collar  900  is in its first configuration. 
     More particularly,  FIG. 11  is a sectional perspective exploded view of adjustable suture collar  900 . Base ring component  950  of suture collar  900  defines an opening  952  there-through that is configured to receive an introducer sheath (not shown in  FIG. 11 ). Base ring component  950  has a first longitudinal portion  954  having an outer surface  956  with a plurality of threads  958  formed thereon and a second longitudinal portion  960 . Second longitudinal portion  960  includes a first annular ridge or flange  908  at a first end or edge thereof and a second annular ridge or flange  910  at a second or opposing end or edge thereof. Each flange  908 ,  910  extends radially outward such that the outer diameter of the outer ring component at each flange is greater than the outer diameter of the outer ring component at an intermediate portion  909 . Each flange  908 ,  910  also extends around the full circumference of outer ring component  902 . 
     Removable ring component  962  of suture collar  900  defines an opening  963  there-through and has an inner surface  964  with a plurality of grooves  966  that are configured to mate with the plurality of threads  958  on first longitudinal portion  954  of base ring component  950 . A diameter or size of inner surface  964  tapers or decreases from a first end  967  to a second end  968 , and is sized such that at least a portion of inner surface  964 , i.e., second end  968 , has a smaller diameter than an outer diameter of first longitudinal portion  954  of base ring component  950 . First longitudinal portion  954  of base ring component  950  is formed from a flexible, compressible material, while second longitudinal portion  960  of base ring component  950  and removable ring component  962  are both formed from a relatively rigid, non-compressible material. The flexible material of first longitudinal portion  954  is an elastomeric material that is molded or over-molded onto second longitudinal portion  960  of base ring component  950 . 
     In order to be tightened or locked onto the outer surface of the introducer sheath, i.e., in order to change or transform suture collar  900  from its first configuration into its second configuration, removable ring component  962  is screwed onto base ring component  950  via mating grooves  966  and threads  958  of removable ring component  962  and base ring component  950 , respectively. When removable ring component  962  is screwed onto base ring component  950  and removable ring component  962  is concentrically disposed over first longitudinal portion  954  of base ring component  950 , first longitudinal portion  954  of base ring component  950  radially compresses onto the introducer sheath. Stated another way, due to the internal taper of removable ring component  962 , the flexible material of first longitudinal portion  954  is tightened or clasped onto the introducer sheath as first longitudinal portion  954  passes up through or is threaded into opening  930  of removable ring component  962  to releasably secure or lock suture collar  900  to the introducer sheath. Removable ring component  962  is thus tightly disposed over or locked onto base ring component  950 , which is tightened or locked onto the outer surface of the introducer sheath at a desired longitudinal position, and suture collar  900  is not able to slide or move freely over the outer surface of the introducer sheath. 
       FIG. 12  illustrates a sectional perspective exploded view of another embodiment of an adjustable suture collar  1200  that is configured to be slidingly disposed over an introducer sheath (not shown in  FIG. 12 ) and is configured to be selectively tightened or locked into place. Adjustable suture collar  1200  includes three main components including a base ring component  1250 , a removable ring component  1262 , and a gasket  1270 . Base ring component  1250  is similar to base ring component  950  and defines an opening  1252  there-through that is configured to receive an introducer sheath (not shown in  FIG. 12 ). Base ring component  1250  has a first longitudinal portion  1254  having an outer surface  1256  with a plurality of threads  1258  formed thereon and a second longitudinal portion  1260 . Second longitudinal portion  1260  includes a first annular ridge or flange  1208  at a first end or edge thereof and a second annular ridge or flange  1210  at a second or opposing end or edge thereof. Each flange  1208 ,  1210  extends radially outward such that the outer diameter of the outer ring component at each flange is greater than the outer diameter of the outer ring component at an intermediate portion  1209 . Each flange  1208 ,  1210  also extends around the full circumference of outer ring component  1202 . 
     Removable ring component  1262  is similar to removable ring component  962  and defines an opening  1263  there-through and having an inner surface  1264  with a plurality of grooves  1266  that are configured to mate with the plurality of threads  1258  on first longitudinal portion  1254  of base ring component  1250 . A diameter or size of inner surface  1264  tapers or decreases from a first end  1267  to a second end  1268 , and is sized such that at least a portion of inner surface  1264 , i.e. second end  1268 , has a smaller diameter than an outer diameter of first longitudinal portion  1254  of base ring component  1250 . First and second longitudinal portions  1254 ,  1260  of base ring component  1250  and removable ring component  1262  are formed from a relatively rigid, non-compressible material. 
     First longitudinal portion  1260  of base ring component  1250  includes an annular groove  1272  formed on an inner surface  1274  thereof. Annular groove  1272  is sized to receive gasket  1270  that is formed from a flexible, compressible material. Gasket  1270  may be a removable component that is positioned within annular groove  1272 , or may be molded into annular groove  1272  so as to not be removable therefrom. In order to be tightened or locked onto the outer surface of the introducer sheath, i.e., in order to change or transform suture collar  1200  from its first configuration into its second configuration, removable ring component  1262  is screwed onto base ring component  1250  via mating grooves  1266  and threads  1258  of removable ring component  1262  and base ring component  1250 , respectively. When removable ring component  1262  is screwed onto base ring component  1250  and removable ring component  1262  is concentrically disposed over first longitudinal portion  1254  of base ring component  1250 , gasket  1270  radially compresses onto the introducer sheath. Stated another way, due to the internal taper of removable ring component  1262 , the flexible material of gasket  1270  is tightened or clasped onto the introducer sheath as first longitudinal portion  1254  passes up through or is threaded into opening  1230  of removable ring component  1262  to releasably secure or lock suture collar  1200  to the introducer sheath. Removable ring component  1262  is thus tightly disposed over or locked onto base ring component  1250 , which is tightened or locked onto the outer surface of the introducer sheath at a desired longitudinal position via gasket  1270 , and suture collar  1200  is not able to slide or move freely over the outer surface of the introducer sheath. Removable ring component  1262  may be screwed or rotated in an opposite direction to loosen the removable ring component relative to the introducer sheath so that the longitudinal position of suture collar  1200  may be slidingly readjusted as desired. 
     While various embodiments according to the present invention have been described above, it should be understood that they have been presented by way of illustration and example only, and not limitation. It will be apparent to persons skilled in the relevant art that various changes in form and detail can be made therein without departing from the spirit and scope of the invention. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the appended claims and their equivalents. It will also be understood that each feature of each embodiment discussed herein, and of each reference cited herein, can be used in combination with the features of any other embodiment. All patents and publications discussed herein are incorporated by reference herein in their entirety.