Patent Publication Number: US-2016235530-A1

Title: Introducer sheath for transcatheter heart valve delivery

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims the benefit of the filing date of U.S. Provisional Patent Application No. 62/117,630 filed Feb. 18, 2015, the disclosure of which is hereby incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention is related to prosthetic heart valve replacement, and more particularly to devices, systems, and methods for transcatheter delivery of collapsible prosthetic heart valves. 
     Prosthetic heart valves that are collapsible to a relatively small circumferential size can be delivered into a patient less invasively than valves that are not collapsible. For example, a collapsible valve may be delivered into a patient via a tube-like delivery apparatus such as a catheter, a trocar, a laparoscopic instrument, or the like. This collapsibility can avoid the need for a more invasive procedure such as full open-chest, open-heart surgery. 
     Collapsible prosthetic heart valves typically take the form of a valve structure mounted on a stent. There are two types of stents on which the valve structures are ordinarily mounted: a self-expanding stent and a balloon-expandable stent. To place such valves into a delivery apparatus and ultimately into a patient, the valve must first be collapsed or crimped to reduce its circumferential size. 
     When a collapsed prosthetic valve has reached the desired implant site in the patient (e.g., at or near the annulus of the patient&#39;s heart valve that is to be replaced by the prosthetic valve), the prosthetic valve can be deployed or released from the delivery apparatus and re-expanded to full operating size. For balloon-expandable valves, this generally involves releasing the entire valve, assuring its proper location, and then expanding a balloon positioned within the valve stent. For self-expanding valves, on the other hand, the stent automatically expands as the sheath covering the valve is withdrawn. 
     Despite the various improvements that have been made to the collapsible prosthetic heart valve delivery process, conventional delivery devices, systems, and methods suffer from some shortcomings. For example, in conventional delivery devices for self-expanding valves, it may be difficult to introduce the delivery device into the body. Specifically, it may be difficult to simultaneously manipulate a delivery device and an introducer sheath while keeping the introducer sheath in the correct position. 
     There therefore is a need for further improvements to the devices, systems, and methods for transcatheter delivery of collapsible prosthetic heart valves, and in particular, the introduction of such prosthetic heart valves into the heart. Among other advantages, the present invention may address one or more of these needs. 
     BRIEF SUMMARY OF THE INVENTION 
     In some embodiments, an introducer sheath includes a tubular cannula extending between a leading end and trailing end, the cannula defining a lumen therethrough, a first balloon disposed adjacent the leading end of the cannula, the first balloon being configured and arranged to dilate from a collapsed condition to an expanded condition, and an inflation port configured to receive an inflation medium to dilate the first balloon. 
     In some embodiments, a method of delivering a collapsible prosthetic heart valve includes piercing an insertion location of a patient&#39;s body, partially inserting an introducer sheath into the patient&#39;s body, the insertion sheath having (i) a tubular cannula extending between a leading end and trailing end, the cannula defining a lumen therethrough, (ii) a first balloon disposed adjacent the leading end of the cannula, the first balloon being configured and arranged to dilate from a collapsed condition to an expanded condition, and (iii) an inflation port configured to receive an inflation medium to dilate the first balloon, and dilating the first balloon inside the patient&#39;s body to prevent movement of the introducer sheath in at least one direction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various embodiments of the present invention will now be described with reference to the appended drawings. It is to be appreciated that these drawings depict only some embodiments of the invention and are therefore not to be considered limiting of its scope. 
         FIG. 1A  is a top plan view of a portion of an operating handle of a delivery device for a collapsible prosthetic heart valve, shown with a partial longitudinal cross-section of the distal portion of a catheter assembly; 
         FIG. 1B  is a side view of the handle of  FIG. 1A ; 
         FIG. 2  is a side elevational view of a conventional prosthetic heart valve; 
         FIG. 3A  is a side view of an introducer for a delivery device having a balloon; 
         FIG. 3B  is a side view of the introducer of  FIG. 3A  after the balloon has been inflated; 
         FIG. 4  is a highly schematic illustration showing the use of an introducer sheath for transcatheter valve replacement using a transaortic approach; 
         FIG. 5  is a highly schematic illustration showing the use of an introducer sheath for transcatheter valve replacement using a transapical approach; and 
         FIG. 6  is a side view of a second example of an introducer for a delivery device having two balloons. 
     
    
    
     DETAILED DESCRIPTION 
     As used herein, the terms “proximal,” “distal,” “leading” and “trailing” are to be taken as relative to a user using the disclosed delivery devices. “Proximal” or “trailing end” are to be understood as relatively close to the user and “distal” or “leading end” are to be understood as relatively farther away from the clinician. Also, as used herein, the words “substantially,” “approximately,” “generally” and “about” are intended to mean that slight variations from absolute are included within the scope of the structure or process recited. 
     Referring now to  FIGS. 1A and 1B , the structure and function of a transaortic or transfemoral delivery device will be described. It will be understood, however, that the devices and methods disclosed herein also may be used with a transapical or transseptal delivery device. An exemplary transaortic delivery device  10  is shown for delivering a prosthetic heart valve, which will be described in greater detail below with reference to  FIG. 2 . Transaortic delivery device  10  has a catheter assembly  16  for delivering the heart valve to and deploying the heart valve at a target location, and an operating handle  20  for controlling deployment of the valve from the catheter assembly. Delivery device  10  extends from a proximal end  12  to an atraumatic tip  14  at the distal end of catheter assembly  16 . Catheter assembly  16  is adapted to receive a collapsible prosthetic heart valve (not shown) in a compartment  23  defined around an inner shaft  26  and covered by a distal sheath  24 . 
     Inner shaft  26  may extend from operating handle  20  to atraumatic tip  14  of the delivery device, and may include a retainer  25  affixed thereto at a spaced distance from tip  14  and adapted to hold a collapsible prosthetic valve in compartment  23 . Retainer  25  may have recesses  80  therein that are adapted to hold corresponding retention members of the valve. Inner shaft  26  may be made of a flexible material such as braided polyimide or polyetheretherketone (PEEK), for example. Using a material such as PEEK may improve the resistance of inner shaft  26  to kinking while catheter assembly  16  is tracking through the vasculature of a patient. 
     Distal sheath  24  surrounds inner shaft  26  and is slidable relative to the inner shaft such that it can selectively cover or uncover compartment  23 . Distal sheath  24  is affixed at its proximal end to an outer shaft  22 , the proximal end of which is connected to operating handle  20  in a manner to be described. Distal end  27  of distal sheath  24  abuts atraumatic tip  14  when the distal sheath is fully covering compartment  23 , and is spaced apart from the atraumatic tip when compartment  23  is at least partially uncovered. 
     Operating handle  20  is adapted to control deployment of a prosthetic valve located in compartment  23  by permitting a user to selectively slide outer shaft  22  proximally or distally relative to inner shaft  26 , thereby respectively uncovering or covering the compartment with distal sheath  24 . Outer shaft  22  may be made of a flexible material such as nylon 11 or nylon 12, and it may have a round braid construction (i.e., round cross-section fibers braided together) or flat braid construction (i.e., rectangular cross-section fibers braided together), for example. 
     The proximal end of inner shaft  26  may be connected in a substantially fixed relationship to an outer housing  30  of operating handle  20 , and the proximal end of the outer shaft  22  may be affixed to a carriage assembly  40  that is slidable along a longitudinal axis of the handle housing, such that a user can selectively slide the outer shaft relative to the inner shaft by sliding the carriage assembly relative to the housing. Operating handle  20  may further include a hemostasis valve  28  having an internal gasket adapted to create a seal between inner shaft  26  and the proximal end of outer shaft  22 . 
     As shown, handle housing  30  includes a top portion  30   a  and a bottom portion  30   b . Top and bottom portions  30   a  and  30   b  may be individual pieces joined to one another as shown in  FIG. 1B . Collectively, top and bottom portions  30   a  and  30   b  define an elongated space  34  in housing  30  in which carriage assembly  40  may travel. Optionally, top and bottom portions  30   a  and  30   b  may further form a substantially cylindrical boss  31  for accepting a clip, as will be described below. Elongated space  34  preferably permits carriage assembly  40  to travel a distance that is at least as long as the anticipated length of the prosthetic valve to be delivered (e.g., at least about 50 mm), such that distal sheath  24  can be fully retracted from around the prosthetic valve. Carriage assembly  40  includes a pair of carriage grips  42 , each attached to a body portion  41 . Although the carriage assembly  40  is shown in  FIGS. 1A and 1B  as having two carriage grips  42 , that need not be the case. 
     Handle housing  30  further defines a pocket  37  that extends through top portion  30   a  and bottom portion  30   b  for receiving a deployment actuator  21 . Pocket  37  is sized and shaped to receive deployment actuator  21  with minimal clearance, such that the location of deployment actuator remains substantially fixed relative to housing  30  as it is rotated. Deployment actuator  21  may be internally coupled to body portion  41  via a threaded shaft or other suitable connection such that rotation of the deployment actuator in one direction (either clockwise or counterclockwise) pulls the body portion  41  of carriage assembly  40  proximally through elongated space  34 . 
     To use operating handle  20  to deploy a prosthetic valve that has been loaded into compartment  23  and covered by distal sheath  24 , the user may rotate deployment actuator  21 , causing carriage assembly  40  to slide proximally within elongated space  34  in housing  30 . Because distal sheath  24  is affixed to outer shaft  22 , which in turn is affixed to carriage assembly  40 , and because inner shaft  26  is fixed to housing  30 , sliding the carriage assembly proximally relative to the housing will retract the distal sheath proximally from compartment  23 , thereby exposing and initiating deployment of the valve located therein. 
     Delivery device  10  may be used to implant a medical device such as a collapsible stent-supported prosthetic heart valve  100  having a stent  102  and a valve assembly  104  ( FIG. 2 ). The prosthetic heart valve  100  is designed to replace a native tricuspid valve of a patient, such as a native aortic valve. It should be noted that while the devices disclosed herein are described predominantly in connection with their use with a prosthetic aortic valve and a stent having a shape as illustrated in  FIG. 2 , the valve could be a bicuspid or other valve, such as the mitral valve, and the stent could have different shapes, such as a flared or conical annulus section, a less-bulbous aortic section, and the like, and a differently shaped transition section. 
     The expandable stent  102  of prosthetic heart valve  100  may be formed from biocompatible materials that are capable of self-expansion, such as, for example, shape memory alloys, such as the nickel-titanium alloy known as “nitinol,” or other suitable metals or polymers. Stent  102  extends in a length direction L 1  from proximal or annulus end  110  to distal or aortic end  112 , and includes annulus section  120  adjacent proximal end  110 , transition section  121 , and aortic section  122  adjacent distal end  112 . Annulus section  120  has a relatively small cross-section in the expanded condition, while aortic section  122  has a relatively large cross-section in the expanded condition. Preferably, annulus section  120  is in the form of a cylinder having a substantially constant diameter along its length. Transition section  121  may taper outwardly from annulus section  120  to aortic section  122 . Each of the sections of stent  102  includes a plurality of struts  130  forming cells  132  connected to one another in one or more annular rows around the stent. For example, as shown in  FIG. 2 , annulus section  120  may have two annular rows of complete cells  132  and aortic section  122  and transition section  121  may each have one or more annular rows of partial cells  132 . Cells  132  in aortic section  122  may be larger than cells  132  in annulus section  120 . The larger cells in aortic section  122  better enable prosthetic valve  100  to be positioned in the native valve annulus without the stent structure interfering with blood flow to the coronary arteries. Each of cells  132  has a length in length direction L 1  of the stent and a width W 1  in a perpendicular direction. 
     Stent  102  may include one or more retaining elements  134  at distal end  112  thereof, retaining elements  134  being sized and shaped to cooperate with female retaining structures (not shown) provided on a deployment device. The engagement of retaining elements  134  with the female retaining structures on the deployment device helps maintain prosthetic heart valve  100  in assembled relationship with the deployment device, minimizes longitudinal movement of the prosthetic heart valve relative to the deployment device during unsheathing or resheathing procedures, and helps prevent rotation of the prosthetic heart valve relative to the deployment device as the deployment device is advanced to the target location and the heart valve deployed. 
     Valve assembly  104  of prosthetic heart valve  100  preferably is positioned in annulus section  120  of stent  102  and secured to the stent. Valve assembly  104  includes cuff  136  and a plurality of leaflets  138  which collectively function as a one-way valve by coapting with one another. As a prosthetic aortic valve, valve  100  has three leaflets  138 . 
     Although cuff  136  is shown in  FIG. 2  as being disposed on the luminal or inner surface of annulus section  120 , it is contemplated that cuff  136  may be disposed on the abluminal or outer surface of annulus section  120  or may cover all or part of either or both of the luminal and abluminal surfaces. Both cuff  136  and leaflets  138  may be wholly or partly formed of any suitable biological material or polymer such as, for example, polytetrafluoroethylene (PTFE). 
     Leaflets  138  may be attached along their belly portions to cells  132  of stent  102 , with the commissure between adjacent leaflets  138  attached to a commissure feature  140 . As can be seen in  FIG. 2 , each commissure feature  140  may lie at the intersection of four cells  132 , two of the cells being adjacent one another in the same annular row, and the other two cells being in different annular rows and lying in end-to-end relationship. Preferably, commissure features  140  are positioned entirely within annulus section  120  or at the juncture of annulus section  120  and transition section  121 . Commissure features  140  may include one or more eyelets which facilitate the suturing of the leaflet commissure to stent  102 . 
     Prosthetic heart valve  100  may be used to replace a native aortic valve, a surgical heart valve or a heart valve that has undergone a surgical procedure. Prosthetic heart valve  100  may be delivered to the desired site (e.g., near the native aortic annulus) using any suitable delivery device. During delivery, prosthetic heart valve  100  is disposed inside the delivery device in the collapsed condition. The delivery device may be introduced into a patient using a transfemoral, transapical, transseptal or any other percutaneous approach. Once the delivery device has reached the target site, the user may deploy prosthetic heart valve  100 . Upon deployment, prosthetic heart valve  100  expands so that annulus section  120  is in secure engagement within the native aortic annulus. When prosthetic heart valve  100  is properly positioned inside the heart, it works as a one-way valve, allowing blood to flow from the left ventricle of the heart to the aorta, and preventing blood from flowing in the opposite direction. 
     As briefly discussed, several approaches are possible to introduce the delivery device into the patient. With a transfemoral approach, the delivery device is introduced into the transfemoral artery of the patient. With transaortic and transapical approaches, shorter paths are taken to the aortic valve through the patient&#39;s chest. In such cases, an introducer sheath may be useful to advance the delivery device to the target location. 
       FIG. 3A  illustrates introducer sheath  300 , which extends between trailing end  302  and leading end  304 . Introducer sheath  300  includes hub  305  disposed adjacent trailing end  302  and cannula  310  extending from hub  305  to leading end  304 . Hub  305  and cannula  310  may be hollow to define lumen  312  between trailing end  302  and leading end  304 . In at least some examples, cannula  310  may include lumen  312  having an inner diameter of approximately 16 French. In at least some examples, the inner diameter of lumen  312  may be between about 17 French and about 20 French and able to accommodate delivery systems of varying diameters. Cannula  310  includes a plurality of markings  314  on its abluminal surface, markings  314  indicating certain distances along the length of cannula  310 . In at least some examples, markings  314  are spaced between approximately 0.25 and approximately 0.5 inches apart to indicate the depth of cannula  310  during use. Hemostasis seal  320  may also be disposed on the interior of hub  305  and configured to prevent backflow of liquid through lumen  312 . In some examples, hemostasis seal  320  is configured to prevent blood loss through introducer sheath  300  during the operation of the device. 
     Introducer sheath  300  further includes balloon  330  disposed adjacent leading end  304  and fixed at a predetermined distance x 1  from leading end  304  along cannula  310 . In at least some examples distance x 1  is between approximately 1.0 mm and approximately 30.0 mm. Introducer sheath  300  further includes inflation port  332  disposed on hub  305  and inflation tube  334  extending between inflation port  332  and balloon  330 . Inflation tube  334  may be in communication with the interior of balloon  330  and configured to deliver an inflation media to the interior of balloon  330  to expand the balloon from a collapsed condition to an expanded condition. In at least some examples, the inflation media includes a liquid, such as a saline solution, contrast media, or a bioabsorbable gas such as nitrogen. As shown in  FIGS. 3A and 3B , hub  305  may further include flush port  342  for flushing the interior of cannula  310  (i.e. lumen  312 ). Saline may also be used to flush lumen  312  to remove air and lubricate the interior of cannula  310  for smooth delivery. Moreover, to aid in placement, one or more radiopaque markers  350  may be disposed on the leading end  304  of introducer sheath  300 . In at least some examples, radiopaque marker  350  is disposed adjacent balloon  330 . 
       FIG. 3B  illustrates introducer sheath  300  after inflation of the balloon at the leading end  304  of the device. As shown in  FIG. 3B , inflation media is introduced inflation port  332  and travels through inflation tube  334  in the direction indicated by arrow “al.” As media fills balloon  330 , the balloon circumferentially swells to its expanded condition as shown in  FIG. 3B . While certain dimensions are provided herein, it will be understood that such dimensions are merely exemplary and not limiting. In at least some examples, balloon  330  has a first diameter d 1  of approximately 6.9 mm (0.273 inches) to 7.1 mm (0.28 inches) in the collapsed condition and a second diameter d 2  of approximately 7.1 mm (0.28 inches) to 30 mm (1.18 inches) in the fully expanded condition. In at least some examples, diameter d 1  is not much larger than the diameter of the cannula itself so that the balloon can easily pass through the insertion point in the collapsed condition. In such examples, diameter d 1  of balloon  330  in the collapsed condition is approximately less than 0.5 mm (0.020 inches) inches greater than the diameter of cannula  310 . After expansion, however, diameter d 2  may be approximately 1.0 mm (0.039 inches) to 23 mm (0.90 inches) greater than the diameter of cannula  310 . 
       FIG. 4  illustrates a transaortic approach using introducer sheath  300  to aid in advancing a delivery device to a native heart annulus  400 . A transaortic approach may be preferable to a transfemoral approach under certain conditions and clinical settings. For example, patients with severe pulmonary disease as well as patients with narrowed arteries may be better suitable for a transaortic approach. 
     As seen in  FIG. 4 , an incision is made in ascending aorta  410  at puncture location P 1 . A dilator (not shown) having an increasing diameter may be used to widen the incision at puncture location P 1 . Guidewire  450  may be advanced in retrograde fashion from puncture location P 1 , down ascending aorta  410  through native valve annulus  400 . Introducer sheath  300  may then be advanced over guidewire  450  from puncture location P 1  toward native valve annulus  400 . Markings  314  may aid the clinician in determining the depth of cannula  310  with respect to ascending aorta  410 . For example, cannula  310  may be advanced through puncture location P 1  until a specific marking (e.g., the second marking) or a specific depth (e.g., 3 cm) is reached. Additionally, radiopaque marker  350  and/or other echogenic materials may be used to guide introducer sheath  300  to the appropriate position using the assistance of three-dimensional echocardiography to visualize the therapeutic device within the patient. Alternative visualization techniques known in the art are also contemplated herein. 
     With introducer sheath  300  at the desired depth and position, inflation media may be introduced through the inflation port (not shown) through inflation tube  334  to dilate balloon  330 . After balloon  330  expands, upper surface s 1  of balloon  330  contacts a portion of the patient&#39;s heart tissue t 1  adjacent puncture location P 1  so that cannula  310  can no longer freely travel through puncture location P 1  due to the increased diameter of balloon  330 . Thus, though cannula  310  is pulled back toward the clinician, it does not travel any further once balloon  330  abuts puncture location P 1 , preventing the accidental removal of introducer sheath  300  during the procedure. Delivery device (not shown) may then be advanced through lumen  312  of introducer sheath  300  and the procedure may continue with introducer sheath  300  safely secured at the proper position. Upon completion of the procedure, balloon  330  may be deflated by removing the inflation medium (e.g., nitrogen), thereby reducing the diameter of the balloon  330  such that the balloon is capable of fitting through puncture location P 1 . Introducer sheath  300  may then be withdrawn. 
       FIG. 5  illustrates a second approach, this time a transapical approach, using introducer sheath  500  to aid in advancing a delivery device to a native heart annulus  400 . Introducer sheath  500  generally incorporates similar components to introducer sheath  300 , which extends between trailing end  502  and leading end  504  and includes a hub (not shown) disposed adjacent trailing end  502  and cannula  510  extending from the hub to leading end  504 . Hub  505  and cannula  510  define lumen  512  between trailing end  502  and leading end  504 . Cannula  510  includes a plurality of markings  514  on its abluminal surface to indicate depth and balloon  530  disposed adjacent leading end  504  and fixed at a predetermined location along cannula  510 . As seen in  FIG. 5 , in an introducer sheath for transapical applications, balloon  530  is fixed at a predetermined distance x 2  from leading end  504  that is different than predetermined distance x 1  of introducer sheath  300 . Specifically, distance x 2  is larger than distance x 1  such that balloon  530  is disposed further away from leading end  504  in introducer sheath  500  for transapical applications. Introducer sheath  500  may further include markers  550 , an inflation port (not shown), an inflation tube (not shown) and a flush port (also not shown) as described above. 
     In transapical applications, an incision is made in the heart at puncture location P 2  adjacent left ventricle  590  to create an opening across heart wall  592 . A dilator (not shown) having an increasing diameter may be used to widen the incision at puncture location P 2 . Guidewire  450  may be advanced from puncture location P 2  toward native valve annulus  400 . Introducer sheath  500  may then be advanced over guidewire  450  from puncture location P 1  toward native valve annulus  400 . Markings  514  may aid the clinician in determining the depth of cannula  510  with respect to native valve annulus  400 . 
     With introducer sheath  500  at the desired depth and position, inflation media may be introduced through the inflation port (not shown) through the inflation tube (also not shown) to dilate balloon  530 . After balloon  530  expands, cannula  510  can no longer freely travel through puncture location P 2  due to the increased diameter of balloon  530 . Thus, though cannula  510  is pulled back toward the clinician, it does not travel any further once balloon  530  abuts puncture location P 2 , preventing the accidental removal of introducer sheath  500  during the procedure. The procedure may then continue as desired. Upon completion of the procedure, balloon  530  may be deflated by removing the inflation medium (e.g., nitrogen), thereby reducing the diameter of the balloon  530  such that the balloon is capable of fitting through puncture location P 2 . Introducer sheath  500  may then be withdrawn. 
     In another example, shown in  FIG. 6 , introducer sheath  600  generally includes all the elements of introducer sheath  300  (e.g., hub  305 , cannula  310 , markings  314 , hemostasis seal  320 , balloon  330 , inflation port  332 , flush port  342 , and radiopaque marker  350 ). As shown, introducer sheath  600  further includes second balloon  630 , spaced from balloon  330 . Balloons  330  and  630  may be inflated by a single inflation medium through a single inflation port  332  via inflation tube  634 . Inflation tube  634  may be configured to be in communication with the interiors of both balloons  330 , 630  such that the inflation medium delivered through inflation tube  634  in direction of arrow al dilates both balloons. Alternatively, two independent inflation ports may be disposed on hub  305 , each port being in communication with a respective inflation tube to dilate a single balloon. In this example, balloons  330 , 630  may be independently dilated or deflated, sequentially or in concert, as desired. As shown, balloon  630  may be capable of dilating to a predetermined diameter d 3 , which is equal to or different than the dilated diameter d 2  of balloon  330 . In some examples, balloons  330 , 630  are spaced apart by a predetermined distance b 1 . Distance b 1  may be approximately equal to the thickness of the wall of the aorta or the wall the left ventricle. Thus, inflating balloons  330 , 630  serves to anchor introducer sheath  600  at a predetermined position with respect to the native valve annulus. 
     It will be understood that various modification may be made to the disclosed embodiments without departing from the spirit of the disclosure. For example, introducer sheath may be used to introduce a delivery device into the heart for prosthetic heart valve replacement, or may be used to introduce devices for valve repair at any of the heart valve (e.g., aortic valve, mitral valve, pulmonary valve, tricuspid valve). Additionally, introducer sheath may be used to deliver instruments to repair other structures in the heart, such as the chordae tendineae, papillary muscles and the like. Introducer sheath may also be used to deliver embolism prevention devices and stents, grafts and other cardiovascular devices. Introducer sheath may also be used to introduce any other medical instruments or device into a patient&#39;s body in applications other than cardiovascular applications and may be useful in any bodily location where temporarily affixing a sheath a certain distance from body tissue is useful. 
     In some embodiments, an introducer sheath includes a tubular cannula extending between a leading end and trailing end, the cannula defining a lumen therethrough, a first balloon disposed adjacent the leading end of the cannula, the first balloon being configured and arranged to dilate from a collapsed condition to an expanded condition, and an inflation port configured to receive an inflation medium to dilate the first balloon. 
     In some examples, the sheath may include a plurality of spaced markings disposed on the abluminal surface of the cannula; and/or the first balloon may be configured to circumferentially dilate from a first diameter in the collapsed condition to a second diameter in the expanded condition; and/or the first diameter may be less than 0.039 inches greater than a diameter of the cannula; and/or the second diameter may be between approximately 0.273 inches and approximately 0.280 inches; and/or the first balloon may be disposed a distance of between approximately 1 mm (0.039 inches) and approximately 30 mm (1.181 inches) from the leading end of the cannula; and/or the sheath may further include a hollow hub coupled to the cannula, and wherein the inflation port is defined in the hub; and/or the sheath may further include an inflation tube extending between the port and the first balloon, the inflation tube being in communication with the inflation port and an interior of the first balloon; and/or the sheath may further include a hemostasis seal disposed within the hub and configured to prevent fluid flow therethrough; and/or the inflation medium may be saline; and/or the inflation medium may be nitrogen; and/or the hub may further define a flush port for receiving a solution to remove air and lubricate the lumen; and/or the solution may include saline; and/or the sheath may further include a second balloon disposed on the cannula and spaced from the first balloon by a predetermined distance, the second balloon being configured and arranged to dilate from a collapsed condition to an expanded condition having a third diameter; and/or the third diameter of the second balloon may be substantially equal to the second diameter of the first balloon; and/or the predetermined distance between the first balloon and the second balloon may be substantially equal to at least one of a thickness of an ascending aorta and a thickness of a left ventricle. 
     In some embodiments, a method of delivering a collapsible prosthetic heart valve includes piercing an insertion location of a patient&#39;s body, partially inserting an introducer sheath into the patient&#39;s body, the insertion sheath having (i) a tubular cannula extending between a leading end and trailing end, the cannula defining a lumen therethrough, (ii) a first balloon disposed adjacent the leading end of the cannula, the first balloon being configured and arranged to dilate from a collapsed condition to an expanded condition, and (iii) an inflation port configured to receive an inflation medium to dilate the first balloon, and dilating the first balloon inside the patient&#39;s body to prevent movement of the introducer sheath in at least one direction. 
     In some examples, the insertion location may be the ascending aorta; and/or the insertion location may be the left ventricle; and/or the method may further include deflating the first balloon prior to removing the introducer sheath from the patient&#39;s body. 
     It will be appreciated that the various dependent claims and the features set forth therein can be combined in different ways than presented in the initial claims. It will also be appreciated that the features described in connection with individual embodiments may be shared with others of the described embodiments.