Abstract:
The present invention is directed to an improved delivery system to deliver and deploy a prosthesis in a body lumen, and methods of use thereof. The improved delivery system allows for operation of the delivery system with one hand while maintaining accuracy in delivery and deployment of the prosthesis. An exemplary embodiment of the delivery system includes a first sheath control on a housing so as to be accessible from the exterior of the housing, wherein the first sheath control is operatively engaged with the sheath and controls movement of the sheath axially proximally with respect to the housing, thereby releasing at least a portion of the prosthesis.

Description:
RELATED APPLICATION DATA 
     This application claims priority to U.S. Provisional Patent Application No. 61/379,146, filed Sep. 1, 2010. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Exemplary embodiments of the present invention relate to systems and methods for delivering a prosthesis to a desired location in the body. More particularly, the present invention relates to a delivery system for deploying a prosthesis within a body lumen and to methods of delivering a prosthesis to a desired location in a body. The delivery system can be operated with one hand while maintaining accuracy and providing mechanical advantage in deployment of a prosthesis in a body lumen. 
     2. Background 
     Vascular aneurysms are the result of abnormal dilation of a blood vessel, usually resulting from disease and/or genetic predisposition that weakened the arterial wall and allowed it to expand. While aneurysms could occur in any blood vessel, most occur in the aorta and peripheral arteries, with the majority of aortic aneurysms occurring in the abdominal aorta, usually beginning below the renal arteries and often extending into one or both of the iliac arteries. 
     Aortic aneurysms were commonly treated in open surgical procedures where the diseased vessel segment was bypassed and repaired with an artificial vascular graft. While considered to be an effective surgical technique, particularly considering the alternative of a fatal ruptured abdominal aortic aneurysm, conventional vascular graft surgery suffered from a number of disadvantages. The surgical procedure was complex and required experienced surgeons and well-equipped surgical facilities. Even with the best surgeons and equipment, however, patients frequently were elderly and weakened from cardiovascular and other diseases, reducing the number of eligible patients. 
     Even for eligible patients prior to rupture, conventional aneurysm repair had a relatively high mortality rate, usually from 2% to 10%. Morbidity related to the conventional surgery included myocardial infarction, renal failure, impotence, paralysis, and other conditions. Additionally, even with successful surgery, recovery took several weeks, and often required a lengthy hospital stay. 
     In order to overcome some or all of these drawbacks, endovascular prosthesis placement for the treatment of aneurysms has been used. Although promising, many of the proposed methods and apparatuses suffered from undesirable limitations. In particular, accurate delivery and placement of the endovascular prosthesis within the vasculature was problematic. 
     Stent-grafts (endovascular prostheses) are resilient structures, usually biased to expand against a surrounding luminal wall. Such resiliently-expanding stent-grafts may be tightly compressed within a catheter for delivery, imposing significant radial expansion forces against the surrounding catheter sheath. This may lead to high levels of friction between the stent-graft and the sheath, particularly if the resiliently-expanding structure becomes partially embedded in the sheath material. Thus, a delivery system must be capable of imparting a significant, yet controlled, force to retract the sheath and deploy the stent-grafts. 
     U.S. Pat. No. 7,419,501 to Chiu et al., which is incorporated herein by reference in its entirety, discloses a delivery system that attempts to address these issues by providing a delivery system having a handle that allows for accurate placement of a stent-graft in a body lumen. The delivery system includes a sheath and a handle. The handle includes: a slide shaft having a threaded outer surface; and a hub assembly coupled to the sheath. The hub assembly includes: an inner slider having a thread tooth pivot support; a thread tooth pivotably mounted to the thread tooth pivot support; and a sleeve having a thread tooth press member pressing on the thread tooth, where motion of the sleeve relative to the inner slider pivots the thread tooth on the thread tooth pivot support to engage and disengage the hub assembly with the threaded outer surface. 
     U.S. application Ser. No. 13/106,110, filed May 12, 2011, which is incorporated herein by reference in its entirety, discloses a delivery system having an improved handle that allows for operation of the delivery system with one hand while maintaining accuracy in delivery and deployment of a prosthesis in a body lumen. The delivery system includes a sheath and a handle. The handle includes: a slide shaft having a threaded outer surface; and a hub assembly coupled to the sheath. The hub assembly includes: an inner slider having a thread tooth pivot support; a thread tooth pivotably mounted to the thread tooth pivot support; a distal sleeve having a thread tooth press member pressing on the thread tooth; and a proximal sleeve. Motion of the distal sleeve relative to the inner slider pivots the thread tooth on the thread tooth pivot support to engage and disengage the hub assembly with the threaded outer surface. The distal sleeve is rotatably coupled to the proximal sleeve, and the proximal sleeve is prevented from rotating in order to provide a stable grip to allow operation of the catheter with one hand. 
     BRIEF SUMMARY OF THE INVENTION 
     Some embodiments of the present invention provide improved delivery systems that allow for operation of the delivery system with one hand while maintaining accuracy in delivery and deployment of a prosthesis in a body lumen. 
     Some embodiments of the present invention also provide methods of using an improved delivery system that allows for operation of the delivery system with one hand while maintaining accuracy in delivery and deployment of a prosthesis in a body lumen. 
     Additional features of the invention will be set forth in the description that follows, and in part will be apparent from the description, or may be learned by practice of the invention 
     Some embodiments of the present invention provide a delivery system for delivering a prosthesis to a location in a body, the delivery system including a housing having a longitudinal axis and a distal end hole, a sheath extending from within the housing through and outwardly beyond the distal end hole, wherein the sheath contains the prosthesis at a distal end thereof, a first sheath control disposed on the housing so as to be accessible from the exterior of the housing, wherein the first sheath control is operatively engaged with the sheath, a stop disposed within the housing, the stop being engagable and disengagable with respect to the sheath and configured to, when engaged, confine axial motion of the sheath with respect to the housing within set parameters, and a stop control accessible from the exterior of the housing and operatively connected to the stop, wherein actuation of the stop control causes the stop to disengage or engage with respect to the sheath, wherein a first actuation of the first sheath control causes the sheath to move axially proximally with respect to the housing, thereby releasing at least a portion of the prosthesis. 
     Some embodiments of the present invention also provide a method of delivering a prosthesis to a desired location in a body, the method including introducing a sheath of a delivery system into a patient&#39;s vasculature, wherein a distal tip of the sheath contains the prosthesis, advancing the distal tip of the sheath to the desired location in the body, actuating, in a first direction, a sheath control of the delivery system to cause the sheath to move axially proximally with respect to the housing until further motion of the sheath is prevented by a stop, thereby releasing at least a portion of the prosthesis, actuating a stop control to disengage the stop, and continuing to actuate the sheath control in the first direction until the prosthesis is fully released, wherein the sheath control is disposed on a housing of the delivery system so as to be accessible from the exterior of the housing, and wherein the sheath control is operatively engaged with the sheath, and wherein the stop control is disposed on the housing of the delivery system so as to be accessible from the exterior of the housing, and wherein actuation of the stop control causes the stop to disengage or engage with respect to the sheath. 
     Both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The accompanying figures, which are incorporated herein, form part of the specification and illustrate embodiments of prosthetic delivery systems and methods of delivering a prosthesis to a desired location in a body. Together with the description, the figures further serve to explain the principles of and to enable a person skilled in the relevant art(s) to make and use the delivery systems and methods described herein. In the drawings like reference characters indicate identical or functionally similar elements. 
         FIG. 1  is a perspective view of a delivery system according to an exemplary embodiment of the present invention. 
         FIG. 2  is a top view of a delivery system according to an exemplary embodiment of the present invention. 
         FIG. 3  is a side view of a delivery system according to an exemplary embodiment of the present invention. 
         FIG. 4  is a perspective view of a delivery system according to an exemplary embodiment of the present invention. 
         FIG. 5  is a perspective view of a delivery system according to an exemplary embodiment of the present invention. 
         FIG. 6  is a perspective view of a delivery system according to an exemplary embodiment of the present invention. 
         FIG. 7  is a perspective view of a delivery system according to an exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following detailed description of prosthetic delivery systems and methods of delivering a prosthesis to a desired location in a body refers to the accompanying figures that illustrate exemplary embodiments. Other embodiments are possible and may fall within the scope of the present invention. Modifications can be made to the exemplary embodiments described herein without departing from the spirit and scope of the present invention. Therefore, the following detailed description is not meant to be limiting. Further, it would be apparent to one of skill in the art that the systems and methods described below can be implemented in many different embodiments of hardware. Any actual hardware described is not meant to be limiting. The operation and behavior of the systems and methods presented are described with the understanding that various modifications and variations of the exemplary embodiments may be within the scope of the present invention. 
       FIG. 1  is a perspective view of a delivery system  100  according to an exemplary embodiment of the present invention.  FIG. 2  is a top view of an exemplary embodiment of delivery system  100 .  FIG. 3  is a side view of an exemplary embodiment of delivery system  100 . Delivery system  100  includes a housing  120 , a first sheath control  150 , a stop control  152 , and a sheath  170 . Housing  120  can include proximal portion  110  (sometimes referred to as a “handle” or “grip”) and distal portion  130 . Distal portion  130  can include a distal end hole  138 . 
     A distal tip of sheath  170  can releasably contain a prosthesis (not shown). A user can operate delivery system  100  by inserting sheath  170  containing the prosthesis in its distal tip into a body lumen of a patient. The user can then position the distal tip of sheath  170  within the patient&#39;s body lumen in a desired location. The user can then operate delivery system  100  to withdraw sheath  170 , thereby releasing the prosthesis at the desired location in the patient&#39;s body lumen. 
     Sheath  170  extends from within housing  120  through and outwardly beyond distal end hole  138 . Sheath  170  can removably contain a prosthesis (not shown) within its distal end. The prosthesis can be held in position by a prosthesis retainer (not shown) mounted to a delivery shaft (not shown) connected to housing  120 . 
     U.S. application Ser. No. 13/106,110, filed May 12, 2011, which is hereby incorporated by reference in its entirety, discloses systems and methods of controlling motion of a sheath with respect to a housing. As one skilled in the art would appreciate, similar systems and methods can be used in conjunction with the present invention. The present invention, however, is not limited to such use. 
     First sheath control  150  is mounted to housing  120  so as to be accessible and operable from the exterior of housing  120 . First sheath control  150  can be selectively engaged and disengaged with sheath  170 . When engaged, first sheath control  150  can be operated to move sheath  170  axially with respect to housing  120 . When first sheath control  150  is operated to move sheath  170  proximally with respect to housing  120 , sheath  170  can gradually release the prosthesis from its distal end, because the prosthesis will be held axially stationary with respect to housing  120  by the prosthesis retainer and/or delivery shaft. If the prosthesis is only partially released, first sheath control  150  can be operated to move sheath  170  distally with respect to housing  120 , thereby recapturing the prosthesis within the distal end of sheath  170 . 
     First sheath control  150  can operatively engage with sheath  170  in a variety of ways that would be apparent to one of skill in the art. For example, first sheath control  150  can include interior threads or other engagement members that align with exterior threads or other engagement members on sheath  170  such that rotation of first sheath control  150  causes axial translation of sheath  170  with respect to housing  120 , or sheath  170  can be fixed to a slide shaft that engages first sheath control  150  to cause axial translation of sheath  170  in response to operation of first sheath control  150 . Preferably first sheath control  150  can engage with sheath  170  so as to provide mechanical advantage and precise control to a user of sheath control  150  in order to facilitate release or recapture of the prosthesis. 
     In an exemplary embodiment, first sheath control  150  includes a wheel-shaped control member aligned coaxially with housing  120  and rotatable thereabout. First sheath control  150  can be positioned between proximal portion  110  and distal portion  130  so as to be easily accessible to a user of delivery system  100 . First sheath control  150  can cover a portion of housing  120  where proximal portion  110  and distal portion  130  meet, or first sheath control  150  can itself form a part of housing  120  by itself joining proximal portion  110  and distal portion  130 . A user will typically grasp proximal portion  110  in one hand such that the forefinger and thumb of the user are positioned proximate to first sheath control  150 . Because of the location of first sheath control  150  relative to proximal portion  110  (i.e., grip), as well as the mechanical advantage and precision control provided by first sheath control  150 , the user can operate first sheath control  150  to release or recapture the prosthesis with the forefinger and thumb of the user&#39;s hand while grasping proximal portion  110  with the remaining fingers and the palm, without the need to employ the user&#39;s other hand. First sheath control  150  can be configured such that it does not travel in an axial direction with respect to housing  120 . 
     Delivery system  100  can also include a sheath stop that, when engaged, limits the axial motion of sheath  170  with respect to housing  120 . The sheath stop can be configured to allow axial motion of sheath  170  to release only a portion of the prosthesis. Such a feature can provide an indication of how much of the prosthesis has been released, or indicate the point after which recapture of the prosthesis cannot effectively take place. Stop control  152  (sometimes referred to as “stop release” or “⅔ stop release”) can be actuated to disengage the sheath stop, thereby allowing axial motion of sheath  170  beyond the limits imposed when the sheath stop is engaged (e.g., allowing axial motion of sheath  170  to its full proximal position). Typically a user would operate stop control  152  to release the sheath stop once the user is certain of proper placement of the prosthesis. Thereafter, the user can operate first sheath control  150  to further and fully release the prosthesis. As shown in  FIG. 1 , in an exemplary embodiment stop control  152  is a ring located at the distal end of first sheath control  150 . To actuate stop control  152  and thereby disengage the sheath stop, a user applies pressure to stop control  152  in a distal direction. 
     First sheath control  150  can include gripping enhancements  154  on its surface to assist a user in turning first sheath control  150 .  FIGS. 1-3  depicts ridges extending longitudinally and disposed around the exterior of the wheel of first sheath control  150 . Other gripping enhancements can also be used. For example, raised bumps, circular ridges, surface texture, or indents can be disposed on a surface of first sheath control  150 . Such gripping enhancements decrease the likelihood that a user&#39;s fingers will slip while operating first sheath control  150 , and increase the ease with which the user can operate first sheath control  150 . 
     Additionally, first sheath control  150  can include a control indicator  156 . Control indicator  156  also can enhance a user&#39;s grip on first sheath control  150 , however it is shaped differently from gripping enhancements  154 . The different shape of control indicator  156  provides tactile feedback to a user operating first sheath control  150 , and can thereby indicate to the user the degree to which the first sheath control  150  has rotated. 
     In some situations, it may be desirable to have more direct control over the movement of sheath  170  than may be provided by first sheath control  150 . In an exemplary embodiment, housing  120  includes a second sheath control  112  (also referred to as a “proximal indicator”) accessible through a proximal slot  114  extending longitudinally along and through a portion of proximal portion  110 . Second sheath control  112  can be fixed to sheath  170  and axially slidable with respect to housing  120 . Second sheath control  112  moves within slot  114  during operation of first sheath control  150  as a consequence of first sheath control  150  moving sheath  170 . Because second sheath control  112  is accessible through slot  114 , it can be viewed by a user, thereby providing to the user an indication of the extent of movement of sheath  170 . As an alternative to moving sheath  170  using first sheath control  150 , a user can choose instead to move sheath  170  using second sheath control  112 . As the user grips proximal portion  110 , the user can position his or her thumb (or other portion of his or her hand) on second sheath control  112  and slide second sheath control  112  proximally or distally within proximal slot  114 , thereby causing a corresponding movement of sheath  170 . Such use of second sheath control  112  to control sheath  170  may be desirable to a user for a variety of reasons. For example, the user can withdraw sheath  170  more quickly with second sheath control  112  than operation of first sheath control  150  would allow. 
     Depending on the configuration of first sheath control  150 , a user&#39;s control of the movement of sheath  170  by way of second sheath control  112  may be inhibited by the engagement of first sheath control  150  with sheath  170 . To alleviate this difficulty, an exemplary embodiment of the present invention includes a sheath engagement control  118 , operable to disengage or engage first sheath control  150  with sheath  170 . As shown in  FIG. 1 , in an exemplary embodiment sheath engagement control  118  coexists with second sheath control  112 . This configuration allows a user to apply pressure to sheath engagement control  118  (e.g., by pressing down on sheath engagement control  118  with his or her thumb) to disengage first sheath control  150  from sheath  170 , at which point the user can slide second sheath control  112  so as to control movement of sheath  170 . The user can release the pressure applied to sheath engagement control  118  in order to re-engage first sheath control  150  with sheath  170 . In some exemplary embodiments, sheath engagement control  118  need not be held down to keep first sheath control  150  disengaged with sheath  170 , but need only be pressed once to disengage, and once again to re-engage. 
     Housing  120  can optionally include a proximal flush port  116  in proximal portion  110 , and/or a distal flush port  136  in distal portion  130 . Proximal flush port  116  and distal flush port  136  can be used to flush cavities within sheath  170  with fluid in order to prevent introducing air into a patient during delivery of the prosthesis. 
     Distal portion  130  can include a distal slot  134  extending longitudinally along and through distal portion  130 . A distal indicator  132  may be viewable to a user through distal slot  134 . Distal indicator  132  is connected to sheath  170  and slidable within distal portion  130  along with motion of sheath  170 . As such, distal indicator  132  can indicate to a user the extent to which sheath  170  has moved in response to the user&#39;s operation of either first sheath control  150  or second sheath control  112 . 
       FIG. 4  is a perspective view of a delivery system  400  according to an exemplary embodiment of the present invention. Description of elements of the exemplary embodiment depicted in  FIG. 4  that are the same or operate similarly as those described above with reference to  FIGS. 1-3  may be omitted or abbreviated. 
     In an exemplary embodiment of the present invention, a delivery system  400  includes a first sheath control  450  that includes a wheel-shaped control member rotatably mounted to a housing  420  (housing  420  including a proximal portion  410  and a distal portion  430 ). First sheath control  450  can be positioned on housing  420  so as to be easily accessible to a user of delivery system  400 . A user will typically grasp proximal portion  410  (i.e., grip) in one hand such that the forefinger and thumb of the user are positioned proximate to first sheath control  450 . Because of the location of first sheath control  450  relative to proximal portion  410 , as well as the mechanical advantage and precision control provided by first sheath control  450 , the user can operate first sheath control  450  to release or recapture the prosthesis with the forefinger and/or thumb of the user&#39;s hand that is grasping proximal portion  410 , without the need to employ the user&#39;s other hand. In order to facilitate such operation, first sheath control  450  can be provided with grip enhancers  454 , which, in the embodiment of  FIG. 4 , are grooves extending around the circumference of first sheath control  450  in an axial direction with respect to first sheath control  450 . 
     Delivery system  400  can also include a sheath stop that, when engaged, limits the axial motion of sheath  170  with respect to housing  420 . A stop control  452  can be actuated to disengage the sheath stop, thereby allowing axial motion of sheath  170  beyond the limits imposed when the sheath stop is engaged (e.g., allowing axial motion of sheath  170  to its full proximal position). Typically a user would operate stop control  452  to release the sheath stop once the user is certain of proper placement of the prosthesis. Thereafter, the user can operate first sheath control  450  to further and fully release the prosthesis. As shown in  FIG. 4 , in an exemplary embodiment stop control  452  is a button located in the center of first sheath control  450 . To actuate stop control  452  and thereby disengage the sheath stop, a user applies pressure to stop control  452 . 
     Delivery system  400  can also include a sheath engagement control  418  that is separate from second sheath control  112  and is slidably disposed on the exterior surface of housing  420 . Sheath engagement control  418  is located proximate to first sheath control  450  so as to allow for single-handed access by a user. Sheath engagement control  418  is slidable in an axial direction with respect to housing  420  between a proximal position and a distal position. Sliding sheath engagement control  418  from one position to the other disengages or engages first sheath control  450  with sheath  170 . For example, sliding sheath engagement control from the proximal position to the distal position can cause sheath engagement control  418  to disengage first sheath control  450  with sheath  170 , at which point a user can slide second sheath control  112  so as to control movement of sheath  170 . The user can slide sheath engagement control  418  from the distal position to the proximal position in order to re-engage first sheath control  450  with sheath  170 . In some exemplary embodiments, sheath engagement control  418  is spring-loaded such that it resists sliding from the proximal position to the distal position. In such an exemplary embodiment, a user who has slid sheath engagement control  418  to a distal position in order to disengage first sheath control  450  with sheath  170  need only release sheath engagement control  418  in order to allow sheath engagement control  418  to return to the proximal position and re-engage first sheath control  450  with sheath  170 . 
       FIG. 5  is a perspective view of a delivery system  500  according to an exemplary embodiment of the present invention. Description of elements of the exemplary embodiment depicted in  FIG. 5  that are the same or operate similarly as those described above may be omitted or abbreviated. 
     In the embodiment shown in  FIG. 5 , a delivery system  500  includes a first sheath control  550  that includes a wheel-shaped control member rotatably mounted to a housing  520  (housing  520  including a proximal portion  510  and a distal portion  530 ) such that the axis of the wheel is offset from the longitudinal axis of housing  520 . First sheath control  550  can be partially recessed within housing  520  such that a portion of the exterior surface of first sheath control  550  extends through the surface of housing  520  so as to be accessible from the exterior of housing  520 . A user can operate first sheath control  520  by rotating the portion of first sheath control  520  that extends outside housing  520 . A user will typically grasp proximal portion  510  in one hand such that the thumb of the user is positioned proximate to first sheath control  550 . Because of the location of first sheath control  550  relative to proximal portion  510  (i.e., grip), as well as the mechanical advantage and precision control provided by first sheath control  550 , the user can operate first sheath control  550  to release or recapture the prosthesis with the thumb of the user&#39;s hand that is grasping proximal portion  510 , without the need to employ the user&#39;s other hand. In order to facilitate such operation, first sheath control  550  can be provided with grip enhancers  554 , which, in the exemplary embodiment of  FIG. 5 , are grooves extending around the circumference of first sheath control  550  in an axial direction with respect to first sheath control  550 . 
     Delivery system  500  can also include a combination stop control and sheath engagement control  556 . Combination stop control and sheath engagement control  556  can be a three-position switch, with a middle position, a left position, and a right position. Combination stop control and sheath engagement control  556  can be a cylindrical element extending through a portion of housing  520  so as to protrude from opposing sides of housing  520 , where a user can operate combination stop control and sheath engagement control  556  by pressing on either end. Combination stop control and sheath engagement control  556  is not limited to a cylindrical element. For example, combination stop control and sheath engagement control  556  can be rectangular, triangular, or hexagonal. 
     Combination stop control and sheath engagement control  556  is shown in  FIG. 5  in the middle position. When in the middle position, pressing on a right side of combination stop control and sheath engagement control  556  will cause combination stop control and sheath engagement control  556  to slide from the middle position to the left position, and pressing on the left side of combination stop control and sheath engagement control  556  will cause combination stop control and sheath engagement control  556  to slide from the middle position to the right position. When in the left position, pressing on a left side of combination stop control and sheath engagement control  556  will cause combination stop control and sheath engagement control  556  to slide from the left position to either the middle position or the right position, depending on how far combination stop control and sheath engagement control  556  is pressed. When in the right position, pressing on a right side of combination stop control and sheath engagement control  556  will cause combination stop control and sheath engagement control  556  to slide from the right position to either the middle position or the left position, depending on how far combination stop control and sheath engagement control  556  is pressed. 
     Of the three potential positions for combination stop control and sheath engagement control  556 , one will be a first position in which first sheath control  550  is engaged with sheath  170  and a sheath stop is engaged. Another will be a second position in which first sheath control  550  is disengaged with sheath  170  and the sheath stop is engaged. Another will be a third position in which first sheath control  550  is engaged with sheath  170  and the sheath stop is disengaged. As will be appreciated by one of skill in the art, more or fewer than three positions are possible for combination stop control and sheath engagement control  156 , and combinations of first sheath control  550  and sheath stop states other than those described are possible. 
     In some exemplary embodiments, combination stop control and sheath engagement control  556  can be spring-loaded so as to naturally tend to remain in a neutral position. The neutral position can correspond to the middle position. In such an exemplary embodiment, the portions of combination stop control and sheath engagement control  556  that extend on either side of housing  520  can each correspond independently to one of a stop control and a sheath engagement control. For example, a user can depress and release the left side of combination stop control and sheath engagement control  556  in order to engage or disengage the sheath stop, regardless of the state of engagement of the first sheath control  550  with the sheath  170 . Correspondingly, the user can depress and release the right side of combination stop control and sheath engagement control  556  in order to engage or disengage first sheath control  550  with the sheath  170 , regardless of the state of the sheath stop. Alternatively, rather than a single member protruding from opposing sides of housing  520 , combination stop control and sheath engagement control  556  can include two separate protrusions, acting as buttons extending from either side of housing  520 , each independently performing the functions of either a stop control or a sheath engagement control. 
     It should be noted that although the terms “left” and “right” are used above in relation to the position of combination stop control and sheath engagement control  556 , these terms are used for convenience of description only, and are not meant to be limiting. As one of skill in the art would appreciate, the described positions can be oriented other than left and right, for example “top” and “bottom”, “proximal” and “distal”, and the like. 
       FIG. 6  is a perspective view of a delivery system  600  according to an exemplary embodiment of the present invention. Description of elements of the exemplary embodiment depicted in  FIG. 6  that are the same or operate similarly as those described above may be omitted or abbreviated. 
     In an exemplary embodiment of the present invention, a delivery system  600  includes a first sheath control  650  that includes a lever-based control member mounted to a housing  620  (housing  620  including a proximal portion  610  and a distal portion  630 ) such that the lever extends in a substantially axial direction with respect to housing  620 , albeit angled thereto, depending on its state. First sheath control  650  is shown in  FIG. 6  as being mounted near a midpoint of housing  620 , with its lever extending in a distal direction with respect to housing  620 . The lever of first sheath control  650  can be moved toward or away from housing  620 . Movement of the lever in one direction will cause the sheath to move proximally with respect to the housing, thereby at least partially releasing the prosthesis. Movement of the lever in the other direction will cause the sheath to move distally with respect to the housing, thereby recapturing at least a portion of the prosthesis, if the prosthesis has not already been fully released. 
     Because of the location of first sheath control  650  on housing  620 , as well as the mechanical advantage and precision control provided by first sheath control  650 , the user can operate first sheath control  650  using his or her thumb and index finger while holding housing  620  with the palm and remaining fingers. to release or recapture the prosthesis with the fingers of the user&#39;s hand that is grasping  620 , without the need to employ the user&#39;s other hand. In order to facilitate such operation, first sheath control  650  can be provided with grip enhancers  654 , which, in the embodiment of  FIG. 6 , are grooves extending across the lever of first sheath control  650 . 
     It should be noted that although the lever of first sheath control  650  is shown in  FIG. 6  as being mounted near a midpoint of housing  620 , with its lever extending in a distal direction with respect to housing  620 , this configuration is exemplary, and is not meant to be limiting. As one of skill in the art would appreciate, sheath control  650  can be positioned in a variety of configurations with respect to housing  620 . For example, first sheath control  650  could be mounted near a midpoint of housing  620  with its lever extending in a proximal direction with respect to housing  620 , or it could be mounted near an endpoint (either proximal or distal) of housing  620  with its lever extending toward the opposing endpoint of housing  620 . 
     Delivery system  600  can also include a sheath stop that, when engaged, limits the axial motion of sheath  170  with respect to housing  620 . A stop control  652  can be actuated to disengage the sheath stop, thereby allowing axial motion of sheath  170  beyond the limits imposed when the sheath stop is engaged (e.g., allowing axial motion of sheath  170  to its full proximal position). Typically a user would operate stop control  652  to release the sheath stop once the user is certain of proper placement of the prosthesis. Thereafter, the user can operate first sheath control  650  to advance and fully release the prosthesis. As shown in  FIG. 6 , in an exemplary embodiment stop control  652  is a slidable control member disposed on the exterior surface of housing  620 . Stop control  652  can be located on housing  620  under or proximate to the lever of first sheath control  650 . This positioning facilitates easy single-handed access by a user. As described above, a user can grasp delivery system  600  with one hand such that his or her fingers wrap around housing  620  and are positioned on or proximate to the lever of first sheath control  650 . In such a position, the user&#39;s fingers would be positioned proximate to stop control  652 . Stop control  652  is slidable in an axial direction with respect to housing  620  between a proximal position and a distal position. Sliding stop control  652  from one position to the other disengages or engages the sheath stop. For example, sliding sheath stop control  652  from the distal position to the proximal position can cause sheath stop control  652  to disengage, at which point a user can continue to operate first sheath control  650  to move sheath  170  beyond the limits otherwise imposed by the sheath stop. 
     Delivery system  600  can also include a sheath engagement control  618  that is separate from second sheath control  112  and is slidably disposed on the exterior surface of housing  620 . Sheath engagement control  618  can be located on a side of housing  620  opposite to that of first sheath control  650 . This positioning facilitates single-handed access by a user. Sliding sheath engagement control  618  from one position to the other disengages or engages first sheath control  650  from sheath  170 . For example, sliding sheath engagement control  618  from the proximal position to the distal position can cause sheath engagement control  618  to disengage first sheath control  650  with sheath  170 , at which point a user can slide second sheath control  112  to control movement of sheath  170 . The user can slide sheath engagement control  618  from the distal position to the proximal position in order to re-engage first sheath control  650  with sheath  170 . In some exemplary embodiments, sheath engagement control  618  is spring-loaded such that it resists sliding from the proximal position to the distal position. In such an exemplary embodiment, a user who has slid sheath engagement control  618  to a distal position in order to disengage first sheath control  450  with sheath  170  need only release sheath engagement control  618  in order to allow sheath engagement control  618  to return to the proximal position and re-engage first sheath control  650  with sheath  170 . 
       FIG. 7  is a perspective view of a delivery system  700  according to an exemplary embodiment of the present invention. Description of elements of the exemplary embodiment depicted in  FIG. 7  that are the same or operate similarly as those described above may be omitted or abbreviated. 
     In an exemplary embodiment of the present invention, a delivery system  700  can include a first sheath control  750  aligned coaxially with respect to a housing  720 . First sheath control  750  includes gripping enhancements  754 . First sheath control  720  will operate similarly to first sheath control  150 , described above with reference to  FIGS. 1-3 . Delivery system  700  can also include a combination stop control and sheath engagement control  756  positioned near a distal end of housing  720 . Such combination stop control and sheath engagement control  756  will operate similarly to combination stop control and sheath engagement control  556 , described above with reference to  FIG. 5 . 
     Delivery system  700  can also include a second sheath control  712  extending longitudinally from a proximal end of housing  720 . Second sheath control  712  can be fixed to sheath  170  and axially slidable with respect to housing  720 . Second sheath control  712  can move proximally or distally with respect to housing  720  during operation of first sheath control  750  as a consequence of first sheath control  750  moving sheath  170 . Because second sheath control  712  extends from the proximal end of housing  720 , it can be viewed by a user, thereby providing to the user an indication of the extent of movement of sheath  170 . As an alternative to moving sheath  170  by way of first sheath control  750 , a user can choose instead to move sheath  170  by way of second sheath control  712 . As the user grips housing  720 , the user can position a rear portion of his or her hand on second sheath control  712 , and can slide second sheath control  712  proximally or distally with respect to housing  720 , thereby causing a corresponding movement of sheath  170  and at least partial release or recapture of the prosthesis. 
     While various exemplary embodiments of the present invention have been described above, they have been presented by way of example only, and not limitation. The elements of the exemplary embodiments presented above are not necessarily mutually exclusive, but can be interchanged to meet various needs as would be appreciated by one of skill in the art. Although the exemplary embodiments presented above allow a user to operate the delivery devices with one hand, it would be appreciated by one of skill in the art that the exemplary embodiments can also be operated with multiple hands, or with a single hand and another body part or implement. 
     It therefore will be apparent to one skilled in the art that various changes in form and detail can be made to the exemplary embodiments disclosed herein without departing from the spirit and scope of the present invention. The phraseology or terminology herein is used for description and not for limitation. Thus, it is intended that the present invention cover modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.