Abstract:
A delivery device ( 10 ) for an implantable medical device includes an inner shaft ( 26 ) extending in a longitudinal direction and defining a compartment ( 23 ) adapted to receive the medical device in an assembled condition, an outer shaft ( 22 ) surrounding a longitudinal portion of the inner shaft, and a distal sheath ( 24 ) operatively attached to the outer shaft ( 22 ). The distal sheath ( 24 ) is slidable between a first position enclosing the compartment ( 23 ) and a second position exposing the compartment ( 23 ) for deployment of the medical device. A sleeve  30  surrounds at least a longitudinal portion of the outer shaft ( 22 ) and provides a substantially blood tight bearing surface that facilitates sliding movement of the delivery device ( 10 ) in an introducer ( 2 ).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of the filing date of U.S. Provisional Patent Application No. 61/374,409 filed Aug. 17, 2010, the disclosure of which is hereby incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention is related to prosthetic heart valve replacement, and more particularly to devices, systems, and methods for reducing friction when using catheters and similar devices for transfemoral delivery of collapsible prosthetic heart valves. 
         [0003]    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. 
         [0004]    Collapsible prosthetic heart valves typically take the form of a valve structure mounted on a stent. To place such a valve into a delivery apparatus and ultimately into a patient, the valve must first be collapsed or crimped to reduce its circumferential size. For example, a conventional stent is typically collapsed and inserted into a distal sheath for delivery into a patient, for example, through a femoral artery. 
         [0005]    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 released from the delivery apparatus and re-expanded to full operating size by unsheathing the stent containing the valve. 
         [0006]    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. 
         [0007]    In conventional transfemoral valve delivery devices, the distal sheath of the delivery device must have an inner diameter sufficiently large (e.g., a size of about 16 French) to cover a collapsed prosthetic heart valve, while the outer shaft of the delivery device that extends between the distal sheath and the handle must have a diameter sufficiently small (e.g., a size of about 12 French) to allow the outer shaft enough flexibility to bend around the aortic arch. When such a device is inserted into the femoral artery through an introducer, a hemostasis valve (e.g., a flat sheet of silicone rubber having a vertical slit and a horizontal slit) admits the distal sheath of the delivery device and seals around the outer shaft of the delivery device to prevent excessive bleeding. 
         [0008]    A design tradeoff may exist because the hemostasis valve must be flexible enough to admit the larger distal sheath yet stiff enough to create a seal against the smaller outer shaft. If the hemostasis valve is too flexible, the seal against the outer shaft may be too weak, potentially resulting in excess bleeding. If the hemostasis valve is too stiff, the seal against the outer shaft may be too strong, potentially resulting in high operating friction when a user (e.g., a surgeon or an intervention cardiologist) needs to slide the outer shaft proximally within the hemostasis valve to deploy the heart valve. 
         [0009]    If the force required to overcome a high amount of friction between the hemostasis valve and the outer shaft exceeds the force required to deploy the heart valve (i.e., the force required to overcome the friction between the stent portion of the valve and the distal sheath), the user may be forced to deploy the valve by pushing it out of the distal sheath towards the aortic annulus, rather than the preferred method of withdrawing the distal sheath from the heart valve while maintaining the position of the valve at the aortic annulus. 
         [0010]    One potential solution to this design tradeoff could be to increase the diameter of the introducer and the hemostasis valve, but too large of an introducer (e.g., a size greater than about 20 French) may make it necessary to perform an additional surgical procedure to seal the entry point into the femoral artery. 
         [0011]    Another potential solution to this design tradeoff could be to decrease the outer diameter of the distal sheath (e.g., to a size less than about 18 French), thereby allowing the use of an introducer and hemostasis valve having a smaller diameter. However, the distal sheath must accommodate a collapsible valve that is large enough to properly fit in the aortic annulus. Even in a collapsed state, a typical valve has a size of about 16 French, so a typical distal sheath must have an outer diameter size of at least about 18 French to accept a 16 French collapsed state implant, and a typical introducer must have an inner diameter sufficient to accept an 18 French outer diameter device. 
         [0012]    There therefore is a need for further improvements to the devices, systems, and methods for transcatheter delivery of collapsible prosthetic heart valves. Among other advantages, the present invention may address one or more of these shortcomings. 
       BRIEF SUMMARY OF THE INVENTION 
       [0013]    A delivery device for an implantable medical device, a system for implantable medical device delivery, and a method of delivering an implantable medical device are disclosed. 
         [0014]    A delivery device for an implantable medical device includes an inner shaft extending in a longitudinal direction, the inner shaft defining a compartment adapted to receive the medical device in an assembled condition, an outer shaft surrounding at least a longitudinal portion of the inner shaft, the outer shaft being slidable relative to the inner shaft in the longitudinal direction, a distal sheath operatively attached to the outer shaft and surrounding a longitudinal portion of the inner shaft, the distal sheath having an outer diameter and being slidable in the longitudinal direction between a first position enclosing the compartment and a second position exposing the compartment for deployment of the medical device, and a sleeve surrounding at least a longitudinal portion of the outer shaft, the sleeve having an inner diameter less than the outer diameter of the distal sheath. 
         [0015]    The sleeve and the outer shaft may define an average clearance therebetween of between about 0.001 inches and about 0.002 inches. The delivery device may further include a handle coupled to the inner and outer shafts and adapted to slide the outer shaft in the longitudinal direction relative to the inner shaft. The sleeve may be configured to be non-removable from the outer shaft. The sleeve may be splittable in the longitudinal direction for removal from the outer shaft. The sleeve may have an outer surface that tapers in the longitudinal direction from a relatively large proximal diameter to a relatively small distal diameter. The sleeve may include a distal steerable portion and a proximal portion, the steerable portion being more flexible than the proximal portion. The delivery device may further include a steering actuator coupled to the sleeve, wherein operation of the steering actuator bends the steerable portion of the sleeve. The delivery device may further include a pull-wire extending in the longitudinal direction from the steering actuator to a distal end of the steerable portion, whereby operation of the steering actuator causes the pull-wire to pull on the distal end of the steerable portion. 
         [0016]    A system for implantable medical device delivery includes an introducer having an interior lumen and an introducer valve located in the interior lumen, and a delivery device including an inner shaft extending in a longitudinal direction, the inner shaft defining a compartment adapted to receive the medical device in an assembled condition, an outer shaft surrounding at least a longitudinal portion of the inner shaft, the outer shaft being slidable relative to the inner shaft in the longitudinal direction, a distal sheath operatively attached to the outer shaft and surrounding a longitudinal portion of the inner shaft, the distal sheath being slidable in the longitudinal direction between a first position enclosing the compartment and a second position exposing the compartment for deployment of the medical device, and a sleeve surrounding at least a longitudinal portion of the outer shaft, the delivery device being assembled in the introducer so that the sleeve is positioned in the interior lumen of the introducer and extends through the introducer valve. 
         [0017]    The sleeve and the outer shaft may define an average clearance therebetween of between about 0.001 inches and about 0.002 inches. The delivery device may further include a handle coupled to the inner and outer shafts and adapted to slide the outer shaft in the longitudinal direction relative to the inner shaft. The sleeve may be configured to be non-removable from the outer shaft. The sleeve may be splittable in the longitudinal direction for removal from the outer shaft. The sleeve may have an outer surface that tapers in the longitudinal direction from a relatively large proximal diameter to a relatively small distal diameter. The sleeve may include a distal steerable portion and a proximal portion, the steerable portion being more flexible than the proximal portion. The delivery device may further include a steering actuator coupled to the sleeve, wherein operation of the steering actuator bends the steerable portion of the sleeve. The delivery device may further include a pull-wire extending in the longitudinal direction from the steering actuator to a distal end of the steerable portion, whereby operation of the steering actuator causes the pull-wire to pull on the distal end of the steerable portion. 
         [0018]    A method of delivering an implantable medical device includes providing a delivery device including an inner shaft extending in a longitudinal direction, the inner shaft defining a compartment adapted to receive the medical device in an assembled condition, an outer shaft surrounding at least a longitudinal portion of the inner shaft, the outer shaft being slidable relative to the inner shaft in the longitudinal direction, a distal sheath operatively attached to the outer shaft and surrounding a longitudinal portion of the inner shaft, the distal sheath being slidable in the longitudinal direction between a first position enclosing the compartment and a second position exposing the compartment for deployment of the medical device, and a sleeve surrounding at least a longitudinal portion of the outer shaft, mounting the medical device in the compartment with the distal sheath in the first position, providing an introducer in a tract extending from an opening in a blood vessel of a patient and through tissue overlying the opening, the introducer having an interior lumen and an introducer valve located in the interior lumen, inserting the distal sheath of the delivery device into the patient through the introducer to position the medical device at a target location, positioning the sleeve in the introducer, the introducer valve creating a substantially leak-proof seal against an outer surface of the sleeve, advancing the distal sheath of the delivery device into the aortic arch of the patient, and deploying the medical device by withdrawing a proximal portion of the outer shaft out of the introducer, thereby sliding the distal sheath into the second position. 
         [0019]    The medical device may be a prosthetic heart valve, and the target location may be the descending aorta. The method may further include removing the sleeve from the introducer by splitting it along a pre-determined longitudinal score and peeling the sleeve away from the outer shaft. The sleeve may include a distal steerable portion and a proximal portion, the steerable portion being more flexible than the proximal portion, and the delivery device may include a steering actuator coupled to the sleeve. The method may further include operating the steering actuator to bend the steerable portion of the sleeve. The delivery device may include a pull-wire extending in the longitudinal direction from the steering actuator to a distal end of the steerable portion. The method may further include operating the steering actuator to cause the pull-wire to pull on the distal end of the steerable portion, thereby bending the deflectable portion. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    Various embodiments of the present invention will now be discussed with reference to the appended drawings. It is appreciated that these drawings depict only some embodiments of the invention and are therefore not to be considered limiting of its scope. 
           [0021]      FIG. 1A  is a diagrammatic side view of a transfemoral delivery device having a short sleeve; 
           [0022]      FIG. 1B  is an enlarged side view of a proximal portion of the delivery device depicted in  FIG. 1A ; 
           [0023]      FIG. 1C  is a diagrammatic side view of the delivery device depicted in  FIG. 1A , shown inserted in an introducer; 
           [0024]      FIG. 1D  is a graph of the catheter tracking force acting on the sleeve of the delivery device depicted in  FIG. 1A  compared to the catheter tracking force acting on a conventional delivery device; 
           [0025]      FIG. 1E  is a perspective view of a short sleeve with a tapered outer diameter suitable for use in the device of  FIG. 1A ; 
           [0026]      FIG. 2A  is a diagrammatic side view of a transfemoral delivery device having a long sleeve; 
           [0027]      FIG. 2B  is a diagrammatic side view of the delivery device depicted in  FIG. 2A , shown inserted in an introducer; 
           [0028]      FIG. 3A  is a diagrammatic side view of a transfemoral delivery device having a long and actively deflectable sleeve; 
           [0029]      FIG. 3B  is a diagrammatic side view of the delivery device depicted in  FIG. 3A , shown inserted in a femoral artery and through an aortic arch; 
           [0030]      FIG. 4A  is a side view of a distal portion of a transfemoral delivery device having a long and actively deflectable sleeve; and 
           [0031]      FIG. 4B  is a side view of a proximal portion of the delivery device depicted in  FIG. 4A . 
       
    
    
     DETAILED DESCRIPTION 
       [0032]    Referring now to  FIGS. 1A and 1B  to illustrate the structure and function of the present invention, one embodiment of a delivery device  10  has a proximal end  12 , a distal end  14 , and a catheter assembly  16  extending from the proximal end  12  to the distal end  14 . The delivery device  10  is an exemplary transfemoral delivery device for a collapsible prosthetic heart valve. 
         [0033]    The catheter assembly  16  includes an inner shaft  26  extending from a hub  20  to the distal end  14 , and an outer shaft  22  assembled over the inner shaft and slidable relative thereto. At the distal end of the outer shaft  22 , the catheter assembly  16  includes a valve compartment  23  for securely holding a prosthetic heart valve in a collapsed condition around the inner shaft  26  for delivery into a patient. A distal sheath  24  encloses the valve compartment  23  and is connected to the distal end of the outer shaft  22  so that proximal movement of the outer shaft  22  relative to the compartment  23  moves the distal sheath  24  proximally to deploy the heart valve. At its proximal end, the outer shaft  22  includes a hemostasis valve  28 . The hemostasis valve  28  preferably is a conventional hemostasis valve having an adjustable sealing member and a side port for flushing the space between the outer shaft  22  and the inner shaft  26 , although in other example embodiments, any conventional hemostasis valve may be used. A sleeve  30  is slidably assembled over the outer shaft  22  distally of the hemostasis valve  28 . 
         [0034]    A handle (not shown) for controlling deployment of a collapsible heart valve located in the compartment  23  may be optionally coupled to the hemostasis valve  28  and the hub  20 , such that the handle can provide a user more controlled maneuverability of the outer shaft  22  relative to the inner shaft  26 . Such a handle may be included in any of the delivery device embodiments described herein. In embodiments not including a handle, a user (e.g., a surgeon or an intervention cardiologist) may slide the outer shaft  22  relative to the inner shaft  26  by gripping the hemostasis valve  28  and the hub  20  and sliding the hemostasis valve relative to the hub. 
         [0035]    To load the delivery device  10  with a collapsible prosthetic valve, a user places the valve around the inner shaft  26  and compresses or crimps the valve until it fits inside the distal sheath  24 , which holds the valve in a compressed state. When the valve is later unsheathed, the stent portion of the valve self-expands and disengages from the catheter assembly  16 . The valve can also be resheathed before full deployment by sliding the distal sheath  24  back over the portion of the stent that has expanded, thereby recollapsing the expanded portion of the stent. 
         [0036]    Referring now to  FIG. 1C , the delivery device  10  is inserted through the skin  1  of a patient and into the patient&#39;s femoral artery through an introducer  2  located in a tract extending from an opening in the femoral artery and through tissue overlying the opening, the introducer having an interior lumen and an introducer valve  3  located in the interior lumen. The introducer valve  3  preferably is a hemostasis valve (e.g., a flat sheet of silicone rubber having a vertical slit and a horizontal slit). Alternatively, the introducer valve  3  may be a conventional sealing member suitable for use with an introducer, such as a rubber gasket having an o-ring or washer shape including a central aperture, or any other mechanism capable of providing a blood-tight seal between the introducer  2  and the sleeve  30  while allowing relative movement therebetween. Rather than having the introducer valve  3  directly contact the outer shaft  22  as in a conventional delivery device, the introducer valve contacts the outer surface of the sleeve  30 , while the outer surface of the outer shaft  22  contacts the inner surface of the sleeve  30 . The sleeve  30  includes a hub  32  having an outer diameter that is greater than the inner diameter of the introducer  2 , so that the hub  32  can prevent the sleeve  30  from fully passing into the introducer  2  and getting past the introducer valve  3 . 
         [0037]    The sleeve  30  preferably is designed to minimize bleeding and to minimize the friction force that must be overcome to deploy the valve into a patient (i.e., to withdraw the distal sheath  24  from over the valve). Sleeve  30  may have any length, including lengths from about 1″ to about 6″, and preferably from about 1″ to about 3″. In the embodiment shown in  FIG. 1B , the sleeve  30  has a length L 1  that is about 6″. 
         [0038]    To minimize bleeding between the introducer  2  and the sleeve  30 , the sleeve may be formed with an outer diameter that is slightly smaller than the inner diameter of the introducer  2 , and the introducer valve  3  may close the gap therebetween. For example, a sleeve  30  (or any of the other sleeve embodiments disclosed herein) having an outer size of 18 French (0.236″) may create a substantially leak-proof seal when used with an introducer  2  having an inner diameter (i.e., interior lumen) of 0.245″ and an introducer valve  3  that closes the 0.009″ gap therebetween. This may also be accomplished by making the outer diameter of the sleeve  30  greater than the diameter of the opening in the introducer valve  3 , producing an interference fit between the sleeve  30  and the introducer valve  3 . 
         [0039]    To minimize bleeding between the outer shaft  22  and the sleeve  30 , the sleeve may be formed with an inner diameter that is closely matched with the outer diameter of the outer shaft  22 , such that the gap therebetween is sufficiently small to prevent significant flow of blood into the gap (e.g., the surface tension of the blood may prevent the blood from flowing into a very small gap). For example, a sleeve  30  (or any of the other sleeve embodiments disclosed herein) with an inner diameter of about 0.160″ (equivalent to slightly larger than 12 French) and an outer shaft  22  with an outer diameter of about 0.158″ (equivalent to 12 French) together will produce an average clearance of about 0.001″ between the sleeve  30  and the outer shaft  22 . It is believed that an average clearance between the sleeve  30  and the outer shaft  22  of up to about 0.002″ will be sufficiently small to prevent significant blood flow therebetween. Accordingly, average clearances of between about 0.001″ and about 0.002″ are preferred. An average clearance between the sleeve  30  and the outer shaft  22  of greater than about 0.002″ may also be sufficiently small to prevent significant blood flow therebetween, but the required clearance may depend on the length of the sleeve (i.e., a longer sleeve may  30  permit a greater clearance between the sleeve and the outer shaft  22  while still preventing significant blood flow therebetween). 
         [0040]    It will be appreciated from the foregoing that the inner diameter of the sleeve  30  will be much less than the diameter of the distal sheath  24 . Accordingly, the distal sheath  24  cannot be passed through sleeve  30  during insertion of the delivery device  10  in a patient. Rather, the sleeve  30  must be pre-assembled to the delivery device  10 , either when the delivery device is manufactured or at any other time prior to insertion of the delivery device into a patient. 
         [0041]    To minimize the friction force acting on the outer shaft  22  during deployment of the valve, there preferably is a relatively low amount of friction between the outer shaft  22  and the sleeve  30 . This may be accomplished by making the sleeve  30  from a different material than the outer shaft  22 , and in particular, by using a material for the sleeve  30  that produces low friction when it is slid against a conventional outer shaft  22 . For example, the sleeve  30  preferably is made of a polymer material such as PTFE, PEEK, braided polyether block amide (Pebax®), or any other biocompatible material that produces relatively low friction when slid against a conventional outer shaft  22  made, for example, from nylon. 
         [0042]    Rather than making the entirety of the sleeve  30  from a different material than the outer shaft  22 , only the portion of the sleeve  30  that contacts the outer shaft need be made from a different material. In embodiments where the sleeve  30  and the outer shaft  22  are both made substantially of the same material, such as nylon or polyether block amide) (Pebax®, the sleeve may include a thin liner (e.g., about 0.001″ thick) made, for example, from PTFE, and attached to the interior surface of the sleeve. In such embodiments, the outer shaft  22  can slide without binding against the PTFE liner during use. 
         [0043]    To minimize the need to surgically seal the femoral artery after the introducer  2  has been removed, the outer diameter of the sleeve  30  (or any of the other sleeve embodiments disclosed herein) preferably is as small as possible, and more preferably is equal to or less than the outer diameter of the distal sheath  24 . Because both the distal sheath  24  and the sleeve  30  must be inserted into the introducer  2 , keeping the diameter of the sleeve  30  no greater than the diameter of the distal sheath  24  will help to minimize the diameter of the introducer  2 . 
         [0044]    Referring now to  FIG. 1D , graph  50  is a comparison of catheter tracking force acting on the delivery device  10  having a sleeve  30 , as depicted in  FIG. 1A , with the catheter tracking force acting on a conventional delivery device that has no sleeve. As used herein, the tracking force acting on a delivery device is the amount of force required to advance the delivery device through the patient&#39;s vasculature, as recorded by a force gauge coupled to the proximal end of the device. Catheter tracking force is measured with the inner and outer shafts of the delivery device locked together such that relative movement therebetween is prevented. Because there is no relative movement of the inner and outer shafts during measurement of the tracking force (and thus, no deployment of a valve), the force measured is almost entirely due to the friction between the introducer valve and either the sleeve or the outer shaft. During the trials depicted in graph  50 , a straight plastic shaft containing saline was used to simulate a vasculature containing blood, so a small amount of resistance may also have been generated between the saline and the catheter assembly. 
         [0045]    Lines  51 ,  52 , and  53  represent the catheter tracking force measured at the proximal end of a conventional delivery device (with no sleeve) as the outer shaft is advanced through the introducer valve and the simulated vasculature, over approximately a 24 cm travel distance. Lines  54 ,  55 , and  56  represent the catheter tracking force measured at the proximal end of the delivery device  10  as the outer shaft  22  is advanced through the sleeve  30  and the simulated vasculature (with the sleeve  30  positioned inside of the introducer valve), over approximately a 24 cm travel distance. 
         [0046]    As can be seen in  FIG. 1D , the tracking force measured for the delivery device  10  (using the sleeve  30 ) is between 50 and 100 grams throughout the travel distance. In contrast, the tracking force measured for the conventional delivery device (without using a sleeve) is generally between 300 and 450 grams throughout the travel distance. Hence, the delivery device  10  employing the sleeve  30  experiences approximately 80% less tracking force than the conventional delivery device without a sleeve. In an example wherein the force required to unsheathe a 2″ long self-expanding heart valve is approximately 1000 grams, the delivery device  10  may experience a total heart valve deployment force of 1050-1100 grams (tracking force plus unsheathing force), whereas a conventional delivery device may experience a total heart valve deployment force of 1300-1450 grams. Therefore, the delivery device  10  may require approximately 22% less heart valve deployment force than the conventional delivery device. 
         [0047]    Referring now to  FIG. 1E , a sleeve  30 ′ suitable for use in the device of  FIG. 1A  has a hub  32 ′ and a tapered outer surface, such that the diameter D 1  at the distal end of the sleeve is less than the diameter D 2  at the proximal end of the sleeve. Such a tapered outer surface may allow the sleeve  30 ′ to produce an increasingly tighter fit against the introducer valve  3  as the sleeve is inserted into the introducer  2 , thereby ensuring achievement of a sufficiently snug fit between the sleeve and the introducer valve to minimize bleeding. 
         [0048]    The sleeve  30 ′ has an inner diameter D 3  that remains substantially constant along the longitudinal length L 2  of the sleeve, so that the preferred average clearance between the inner surface of the sleeve and the outer surface of the outer shaft  22  (e.g., about 0.001″ to about 0.002″) is substantially maintained along the length L 2  of the sleeve. 
         [0049]    Referring now to  FIG. 2A , another embodiment of a delivery device  10   a  is shown. The delivery device  10   a  is substantially the same as the delivery device  10  shown in  FIGS. 1A-1C , except it has a sleeve  30   a  that is longer than sleeves  30  or  30 ′. The delivery device  10   a  has a proximal end  12 , a distal end  14 , and a catheter assembly  16   a  extending from the proximal end  12  to the distal end  14 . 
         [0050]    The catheter assembly  16   a  includes an inner shaft  26  extending from a hub  20  to the distal end  14 , and an outer shaft  22  assembled over the inner shaft so as to be slidable relative to same. At the distal end of the outer shaft  22 , the catheter assembly  16   a  includes a valve compartment  23  for holding a prosthetic heart valve in a compressed condition around the inner shaft  26  for delivery into a patient. A distal sheath  24  enclosing the valve compartment  23  is connected to the distal end of the outer shaft  22  so as to be movable therewith. Hence, proximal movement of the outer shaft  22  moves the distal sheath  24  proximally relative to the compartment  23  so as to deploy the heart valve. At its proximal end, the outer shaft  22  includes a hemostasis valve  28 . A sleeve  30   a  having a length L 3  and a hub  32  at its proximal end is assembled slidably over the outer shaft  22  distally of the hemostasis valve  28 . The sleeve  30   a  may have any length, but it preferably has a length L 3  that is slightly shorter (e.g., about 2″ shorter) than the length of the outer shaft  22 . For example, the sleeve  30   a  preferably extends from a location close to the hemostasis valve  28  to a location close to the distal sheath  24 , but sufficiently spaced from the distal sheath that the distal sheath  24  may be fully retracted off of the compartment  23  without contacting the sleeve  30   a . For example, where a heart valve having a length of about 2″ is positioned inside of the compartment  23 , the sleeve  30   a  preferably has a length L 3  that is about 2″ shorter than the distance between the hemostasis valve  28  and the proximal end of the distal sheath  24 , thereby allowing full deployment of the heart valve. In example embodiments, the sleeve  30   a  may have a length L 3  between about 24″ and about 42″. 
         [0051]    Referring now to  FIG. 2B , the delivery device  10   a  is inserted through the skin  1  of a patient and into the patient&#39;s femoral artery through an introducer  2  having an introducer valve  3 . Similar to the delivery device  10  shown in  FIGS. 1A-1C , the introducer valve  3  contacts the outer surface of the sleeve  30   a , while the outer surface of the outer shaft  22  contacts the inner surface of the sleeve, preferably in such manner as to minimize bleeding and the friction force that must be overcome to deploy the heart valve. 
         [0052]    Similar to the short sleeve  30 , the long sleeve  30   a  (and all of the other sleeves disclosed herein) may include a thin liner (e.g., about 0.001″ thick) made, for example, from PTFE, and attached to the interior surface of the sleeve. In such embodiments, the outer shaft  22  can slide without binding against the PTFE liner during use. 
         [0053]    The long sleeve  30   a  (and any of the other long sleeve embodiments disclosed herein) may permit a greater clearance and/or variation in clearance between the sleeve and the outer shaft  22  than with the short sleeves  30  and  30 ′, while still preventing significant blood flow therebetween. For example, although the clearance between the sleeve  30   a  and the outer shaft  22  may be greater than 0.002″ along some or all of the length L 3  of the sleeve, the greater distance the blood has to travel lessens the likelihood of excess bleeding than would be the case for the short sleeves  30  or  30 ′ providing a similar clearance. 
         [0054]    Both the short sleeve  30  and the long sleeve  30   a  (or any of the other sleeve embodiments disclosed herein) may be configured to be non-removable from their respective delivery devices  10  and  10   a . In some embodiments (not shown), the short sleeve  30  or the long sleeve  30   a  may be configured to be split along a pre-determined score line and peeled away from the outer shaft  22  by a user after acceptable placement of the heart valve in the proper location in the patient. 
         [0055]    In embodiments having a long sleeve, it is highly desirable for the delivery device to include a mechanism that enables the sleeve to steer the distal sheath through the aortic arch. In that regard, it is preferred that such delivery devices include a sheath that is steerable through operation by a user. One embodiment of such a delivery device including a steerable sheath is shown in  FIG. 3A . 
         [0056]    Referring now to  FIG. 3A , another embodiment of a delivery device  10   b  having a long and steerable sleeve  30   b  is shown. The delivery device  10   b  is substantially the same as the delivery device  10   a  shown in  FIGS. 2A and 2B , except that a distal portion of the sleeve  30   b  is steerable. 
         [0057]    The delivery device  10   b  has a proximal end  12 , a distal end  14 , and a catheter assembly  16   b  extending from the proximal end  12  to the distal end  14 . The catheter assembly  16   b  includes an inner shaft  26  extending from a hub  20  to the distal end  14 , and an outer shaft  22  assembled over the inner shaft for sliding movement therebetween. At the distal end of the outer shaft  22 , the catheter assembly  16   b  includes a valve compartment  23  for holding a prosthetic heart valve in a collapsed condition around the inner shaft  26  for delivery into a patient. A distal sheath  24  encloses the compartment  23  and is connected to the distal end of the outer shaft  22  so that sliding movement of the outer shaft  22  along the inner shaft  26  results in a corresponding movement of the distal sheath  24  relative to the compartment  23  for deployment of the heart valve. At its proximal end, the outer shaft  22  includes a hemostasis valve  28 . A long and steerable sleeve  30   b  having a hub  32   b  at its proximal end is assembled slidably over the outer shaft  22  distally of the hemostasis valve  28 . Similar to the sleeve  30   a  shown in  FIGS. 2A and 2B , the sleeve  30   b  preferably has a length L 4  that is about 2″ shorter than the distance between the hemostasis valve  28  and the proximal end of the distal sheath  24 , thereby allowing full deployment of a heart valve that is about 2″ long. In example embodiments, the sleeve  30   b  may have a length L 4  between about 24″ and about 42″. 
         [0058]    Because the long sleeves  30   a  and  30   b  extend farther into the vasculature than the short sleeves  30  and  30 ′, and because the long sleeves  30   a  and  30   b  have a greater diameter than the outer shaft  22 , the long sleeves  30   a  and  30   b  may contract the vasculature over a higher surface area during advancement of the devices  10   a  and  10   b  than would the outer shaft  22  of the device  10  having a shorter sleeve. A higher contact surface area may produce a higher friction force during advancement of the devices  10   a  and  10   b . Furthermore, the assembly of the sleeves  30   a  and  30   b  over the outer shaft  22  for a longer distance may cause the catheter assemblies  16   a  and  16   b  to be stiffer than the catheter assembly  16 . Stiffer catheter assemblies may increase the risk of damaging the vasculature during advancement of the devices  10   a  and  10   b  due to a higher contact force between the distal tip  14  of the devices and the vasculature as the distal tip is advanced through the aortic arch. 
         [0059]    The sleeve  30   b  includes a steerable portion  40  located near the distal end of the sleeve and a proximal portion  41 , a steering actuator  42  located near the proximal end of the sleeve, a pull-ring (not shown) embedded in a distal end  44  of the steerable portion  40 , and one or more pull-wires (not shown) extending longitudinally along a side wall of the sleeve and coupled at one end to the pull-ring and at the other end to a pull mechanism of the steering actuator  42 . The steerable portion  40  may have any length, including for example, a length between about 1″ and about 3″. In preferred embodiments, however, the steerable portion  40  has a length of about 2″. The inclusion of a steerable portion  40  in the long sleeve  30   b  may help reduce friction acting on the catheter assembly  16   b  and the contact force between the distal tip  14  and the vasculature during advancement of the device  10   b  through the vasculature. 
         [0060]    The steerable portion  40  of the sleeve  30   b  that may bend around the aortic arch preferably is softer (and thus, more flexible) than the proximal portion  41  that may remain relatively straight during use of the delivery device  10   b . The inclusion of a relatively soft material in the long sleeves  30   a  and  30   b  may help to make the sleeves more flexible, thereby minimizing any increase in the stiffness of the catheter assemblies  16   a  and  16   b  (compared to the catheter assembly  16 ) and the potential for damage during advancement through the vasculature. The long sleeves  30   a  and  30   b  preferably are made of a soft plastic material such as nylon, polyether block amide (Pebax®), or polyurethane. The steerable portion  40  of the sleeve  30   b  may have a hardness of about 40D to about 45D, while the proximal portion  41  may have a hardness of about 72D. The steerable portion  40  and the proximal portion  41  may be made from the same or different materials. If the steerable portion  40  and the proximal portion  41  are made from the same material, the steerable portion may be made more flexible by using different compounding parameters than the proximal portion. 
         [0061]    As shown in  FIGS. 3A and 3B , the steerable portion  40  is actively steerable, whereby a user can use the steering actuator  42  to actively maneuver the steerable portion  40  through the vasculature (e.g., through the aortic arch). In some embodiments (not shown), the steerable portion  40  may be passively steerable because it is sufficiently more flexible than the proximal portion  41 , whereby the steering actuator  42 , the pull-ring, and the pull wires may be omitted from the delivery device  10   b . A steerable portion  40  that is either actively or passively steerable may be able to deflect or curve more easily than the proximal portion  41  as the sleeve  30   b  is advanced through the vasculature. 
         [0062]    Making the proximal portion  41  stiffer than the steerable portion  40  (rather than having the entire sleeve  30   b  be as flexible as the steerable portion  40 ) may help to maintain a sufficient axial strength in the sleeve  30   b  to avoid kinking of the sleeve as it is advanced through the vasculature. Also, to help avoid such potential kinking, either or both of the steerable portion  40  and the proximal portion  41  may be reinforced by braided metal wires. 
         [0063]    Referring now to  FIG. 3B , the presence of the steerable portion  40  in the sleeve  30   b  may allow the catheter assembly  16   b  to more easily conform to the shape of the aortic arch  5  while the distal sheath  24  containing the heart valve is being advanced towards the aortic annulus  6 . 
         [0064]    In use, a user may insert the distal end  14  of the delivery device  10   b  into the femoral artery  4  of a patient to deliver a collapsible prosthetic valve to the aortic annulus  6 . The user may advance the delivery device  10   b  over a guide wire  18  to guide the distal end  14  of the delivery device  10   b  through the femoral artery  4 , the aortic arch  5 , and the aortic annulus  6 , and into the left ventricle of the heart  7 . 
         [0065]    As the distal end  14  of the delivery device  10   b  advances into the aortic arch  5 , the user may operate the steering actuator  42  to maneuver the steerable portion  40  of the sleeve  30   b , for example, by rotating the steering actuator  42  about the rest of the sleeve. As the steering actuator  42  is rotated, a pull mechanism (not shown) of the steering actuator  42  may pull a pull-wire extending along one side of the sleeve  30   b  that pulls one side of the pull-ring and bends the steerable portion  40  of the sleeve  30   b  to more easily conform to the curved shape of the aortic arch  5 . Alternatively, as mentioned above, the steerable portion  40  may passively curve around the aortic arch  5  as the distal end  14  is advanced towards the annulus  6 . 
         [0066]    Preferably, the sleeve  30   b  is initially positioned with the steerable portion  40  contacting the proximal end of the distal sheath  24  (e.g., as shown in  FIG. 4A ), so that the steerable portion can more effectively steer the distal sheath  24  around the aortic arch  5  during advancement of the device  10   b  through the vasculature. After the distal sheath  24  has reached the annulus  6 , the sleeve  30   b  can be retracted proximally, preferably by about 2″ or the length of the distal sheath  24  (e.g., to the location shown in  FIG. 3B ), so that the distal sheath  24  will have sufficient room to retract and fully expose the compartment  23  to deploy a self-expandable heart valve contained therein. 
         [0067]    In some embodiments (not shown), the pull-ring and the steerable portion  40  may not be located at the distal end of the sleeve  30   b . In such embodiments, the steerable portion  40  and the pull-ring may be located in a middle portion of the sleeve  30   b , and there may be more rigid portions of the sleeve located on both ends of the steerable portion  40 . 
         [0068]    Additionally, the steering actuator may be operated by techniques other than rotation, including pulling on the steering actuator, pressing a button on the steering actuator, or any other conventional actuation technique. 
         [0069]    Referring now to  FIG. 4A , another embodiment of a delivery device  10   c  is shown. The delivery device  10   c  is substantially the same as the delivery device  10   b  shown in  FIGS. 3A and 3B , except that the steerable portion  40   c  of the sleeve  30   c  is located more distally along the outer shaft (not visible in  FIGS. 4A and 4B ), and the steering actuator  42   c  extends at an angle from the hub  32   c  of the sleeve  30   c . The delivery device  10   c  has a proximal end (not shown), a distal end  14 , and a catheter assembly  16   c  extending from the proximal end to the distal end  14 . 
         [0070]    The catheter assembly  16   c  includes an inner shaft (not shown, but located inside the sleeve) extending from a hub (not shown) to the distal end  14 , and an outer shaft (not shown, but located inside the sleeve) assembled over the inner shaft for sliding movement relative thereto. At the distal end of the outer shaft, the catheter assembly  16   c  includes a valve compartment  23  for holding a prosthetic heart valve in a collapsed condition around the inner shaft for delivery into a patient. A distal sheath  24  encloses the compartment  23  and is connected to the distal end of the outer shaft so that sliding movement of the outer shaft along the inner shaft results in a corresponding movement of the distal sheath  24  relative to the compartment  23  for deployment of the heart valve. At its proximal end, the outer shaft includes a hemostasis valve (not shown). A long and steerable sleeve  30   c  having a hub  32   c  at its proximal end is assembled over the outer shaft distally of the hemostasis valve. Similar to the sleeve  30   a  shown in  FIGS. 2A and 2B  and the sleeve  30   b  shown in  FIGS. 3A and 3B , the sleeve  30   c  preferably has a length that is about 2″ shorter than the distance between the hemostasis valve and the proximal end of the distal sheath  24 . In example embodiments, the sleeve  30   c  may have a length between about 24″ and about 42″. 
         [0071]    The sleeve  30   c  includes a steerable portion or distal section  40   c  located at the distal end of the sleeve and abutting the proximal end of the distal sheath  24 , a proximal portion  41   c , a steering actuator  42   c  extending from the catheter assembly  16   c  near the proximal portion of the sleeve, a pull-ring (not shown) embedded in a distal end  44   c  of the steerable portion  40   c , and one or more pull-wires (not shown) extending longitudinally along a side wall of the sleeve and coupled at one end to the pull-ring and at the other end to a pull mechanism of the steering actuator  42   c.    
         [0072]    As described above with reference to the steering actuator  42  shown in  FIGS. 3A and 3B , a user may actuate the steering actuator  42   c  to maneuver the steerable portion  40   c  of the sleeve  30   c  through the curved shape of the aortic arch, for example, by rotating the steering actuator  42   c  about its longitudinal axis. 
         [0073]    Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims. 
         [0074]    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.