Abstract:
A control device and mechanism for deploying a self-expanding medical device includes an actuating mechanism which allows the user to retract a restraining sheath from the self-expanding medical device by using a motion that is in angle to the line of motion of the restraining sheath, which helps prevent movement of the catheter portion of the control device within the patient. The control mechanism allows the physician to obtain a longer retracting stroke to the restraining sheath with a shorter actuating motion reducing the amount of manual actuation needed to be performed by the physician when retracting the sheath. The control mechanism can also reduce the amount of actuating force needed to retract the restraining sheath by utilizing springs or biasing members in connection with the actuating mechanism which combines with the actuating force supplied by the physician to cause the retraction of the restraining sheath.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to vascular catheters and devices, and more specifically to a control device for deploying self-expanding medical devices. Vascular catheters and devices are currently employed in a variety of medical procedures. These procedures often require manipulation (or actuation) of the vascular device by a mechanism located outside the patient&#39;s body. The present invention is specifically useful in deploying self-expanding medical devices, such as a self-expanding stent or graft, within a patient&#39;s vasculature.  
           [0002]    Catheters have long been used in intraluminal procedures for various medical needs. They generally are made from elongated tubes which may be placed within various body lumens. A common use for catheters is the treatment of vascular diseases. Such procedures usually involve the percutaneous introduction of an interventional device into the lumen of the artery, usually through the catheter. One widely known and medically accepted procedure is balloon angioplasty in which an inflatable balloon is introduced within the stenosed region of the blood vessel to dilate the occluded vessel. The uninflated balloon catheter is initially inserted into the patient&#39;s arterial system and is advanced and manipulated into the area of stenosis in the artery. The balloon is inflated to compress the plaque and press the vessel wall radially outward to increase the diameter of the vessel, resulting in increased blood flow. The balloon is then deflated to a small profile so that the dilatation catheter can be withdrawn from the patient&#39;s vasculature. Enhanced blood flow should now resume in the dilated artery. As should be appreciated by those skilled in the art, while the above-described procedure is typical, it is not the only method used in angioplasty.  
           [0003]    In the procedure of the kind referenced above, abrupt reclosure may occur or restenosis of the artery may develop over time, which may require another angioplasty procedure, a surgical bypass operation, or some other method of repairing or strengthening the injured area. To reduce the likelihood of the occurrence of abrupt reclosure and to strengthen the area, a physician can implant an intravascular prosthesis for maintaining vascular patency, commonly known as a stent, inside the artery across the lesion. The stent can be crimped onto the balloon portion of the catheter and transported in its delivery diameter through the patient&#39;s vasculature. At the deployment site, the stent is expanded to a larger diameter, often by inflating the balloon portion of the catheter.  
           [0004]    A variety of stent designs have been developed and include self-expanding stents insertable and deliverable through the patient&#39;s vasculature in a compressed state for deployment in a body. Unlike balloon expandable stents which rely on an external radial force to expand the stent at the area of treatment, self-expanding stents are made from materials which are self-expanding in order to move between a compressed or collapsed position to an expanded, implanted position. Stent delivery catheters used for implanting self-expanding stents usually include an inner member upon which the compressed or collapsed stent is mounted and an outer restraining sheath placed over the stent to maintain it in its compressed state prior to deployment. When the stent is to be deployed in the body vessel, the outer restraining sheath is retracted in relation to the inner member to uncover the compressed stent, allowing the stent to immediately move into its expanded condition for implantation in the patient.  
           [0005]    Vascular grafts also can be implanted within a body vessel utilizing a delivery catheter which is percutaneously introduced into the patient&#39;s vasculature system. These types of grafts may include a number of self-expanding rings, or small stents, placed along a flexible tubular member that forms a conduit once implanted in a body vessel. Vascular grafts are utilized to bypass diseased and weakened body vessels, such as when an artery experiences an aneurysm which weakens and abnormally expands the artery. In this manner, the vascular graft will act as a conduit for blood to flow freely there through, bypassing the diseased portion of the arterial wall caused by the aneurysm. As a result, the chances that the artery could possibly rupture due to pressure build-up in the artery is greatly reduced. Self-expanding vascular grafts also can be mounted onto a delivery catheter which includes a restraining sheath placed over the entire vascular graft, including the self-expanding rings, in order to maintain the graft in a collapsed position. Once the physician is able to manipulate the vascular graft into the desired location in the patient&#39;s vasculature, the simple retraction of the restraining sheath from the vascular graft will cause the self-expanding rings or stents to expand and contact the wall of the body lumen in which the graft is implanted.  
           [0006]    These various treatments at the intraluminal site typically require the manipulation of the catheter system, a portion of which remains external to the patient&#39;s body. The physician must actuate the catheter system to retract the restraining sheath in order to properly deploy the stent or vascular graft in the body vessel. Actuator mechanisms which can be located at the proximal end of the catherter system may be as simple as a control handle attached to the restraining sheath that can be manipulated by the physician to retract the restraining sheath from the self-expanding medical device. During the placement of a stent or graft, it is important that the retraction of the restraining sheath be performed while the main catheter, on which the stent or graft is mounted, remains stationery in the body lumen. Some control mechanisms for retracting the restraining sheath requires that some force be applied by the physician in the longitudinal direction of the delivery catheter (i.e., in an axial direction). This force, in turn, can be transmitted to the main catheter assembly which can cause the stent or graft to move from the desired location within the body lumen. As the physician retracts the sheath, if the main catheter holding the stent or graft moves proximally with the sheath out of the target area, precision placement of the medical device will not be accomplished. Therefore, when a physician uses this type of device, the mere act of retracting the restraining sheath can sometimes result in inaccurate placement of the medical device within the body vessel.  
           [0007]    Another problem exists when self-expanding stents or grafts which have an appreciable length (for example, 60 mm and longer) are to be deployed. These larger devices usually are more difficult to deploy accurately using existing catheter systems because a long retraction stroke is needed to retract the distal end of the restraining sheath from the medical device. In such cases, the physician may experience some difficulties in moving the proximal control device the required length to fully expose the self-expanding medical device. Moreover, the deployment of longer stents and grafts may require higher forces to retract the restraining sheath due to frictional forces which can be generated between the stent or graft and the restraining sheath as the sheath is being retracted. Therefore, the physician may have to apply more force to adequately retract the restraining sheath when a long stent or graft is being implanted. Thus, when a long stent or graft is being implanted, a physician may find it difficult to manipulate the proximalcontrol device while maintaining the remainder of the catheter system stationary to prevent the stent or graft from moving from the desired area of implantation.  
           [0008]    Thus, what has been needed is a control mechanism which helps to provide a more precise deployment of a self-expanding medical device within the body vessel to reduce the chances that the physician may inadvertently move the medical device from the intended area of treatment. An improved control device is also needed when a long stent or graft to be deployed to reduce the actuating force which is needed to retract the sheath the required distance. Such a device also should reduce the length of the actuating motion which must be applied to the control device when retracting the restraining sheath. The present invention satisfies these and other needs.  
         SUMMARY OF THE INVENTION  
         [0009]    The present invention provides a control device and mechanism for retracting a restraining sheath used in conjunction with self-expanding medical devices, such as self-expanding stents and vascular grafts, for implantation in a patient&#39;s vasculature.  
           [0010]    The control device and mechanism of the present invention are particularly advantageous since the actuating mechanism allows the physician to retract the restraining sheath from the self-expanding medical device by using a motion that is at an angle to the line of motion of the restraining sheath, which should help to prevent movement of the catheter portion of the control device within the patient In one particular aspect of the present invention, the actuating motion can be substantially perpendicular to the line of motion of the proximal end of the restraining sheath. As a result, the physician&#39;s manipulation of the control device, when retracting the restraining sheath, should not place a displacing force on the inner portion of the catheter which could otherwise cause the stent or graft to move from the target area. A more accurate placement of a stent or graft can thus be accomplished by the physician since the possibility of stent or graft movement is reduced when the restraining sheath is being retracted . The control mechanism also allows the physician to deploy a longer stent or graft with a shorter actuating motion to reduce the amount of manual actuation performed by the physician when retracting the restraining sheath. As a result, the physician only needs to push a thumb knob or trigger a short distance to cause the restraining sheath to retract a larger distance to fully expose the medical device for implantation. The present invention also can use springs or biasing members to reduce the amount of force needed to push the knob or trigger. As a result, a physician will find that it is much easier to manipulate a control device made in the present invention especially when longer stents or vascular grafts are being deployed in the patient&#39;s vasculature.  
           [0011]    In one aspect of the present invention, the control device utilizes a movable rack and pinion mechanism for retracting the proximal end of the restraining sheath while maintaining the inner catheter portion, on which the self-expanding medical device is mounted, stationary. The physician can grasp the control device and utilize his/her thumb to push a control knob attached to the moveable rack which causes rotation of a pinion and an attached pulley. Rotation of the pulley causes a timing belt to translate along the housing of the control device to move a slider member towards the pulley. The slider is attached to the proximal end of the restraining sheath so that when the slider is retracted proximally by the control mechanism, the distal end of the restraining sheath also will be retracted proximally the same distance to expose the stent or vascular graft. The moveable rack is designed to translate in a direction set at an angle, usually between 30° to 90°, to the line of motion defined by the slider/restraining sheath. As a result, when utilizing this type of mechanism, the physician does not have to move the control device in the same axial direction as the motion of the restraining sheath to retract the sheath for deployment purposes. Thus, the chances of the stent or vascular graft becoming displaced from the desired area of implantation in the body vessel is greatly reduced.  
           [0012]    In another aspect of the present invention, the ratio of the pulley pitch diameter to the pinion pitch diameter can be increased to allow the physician to retract the restraining sheath a longer distance with only a minimal amount of actuating distance when manipulating the control knob. As a result, a long stent or graft can be more easily deployed with a minimal amount of actuating movement required by the physician. The moveable rack also can be spring loaded in order to reduce the amount of force needed to move the control knob when retracting the restraining sheath. In this manner, the physician does not need to use as much strength when using the actuating mechanism, which is especially useful when a long stent or vascular graft is being deployed. In this manner, the spring or biasing element utilized in conjunction with the moveable rack assists in pushing the movable rack along with the actuating motion provided by the physician.  
           [0013]    It is to be understood that the present invention is not limited by the embodiments described herein. Other features and advantages of the present invention will become more apparent from the following detailed description of the invention, when taken in conjunction with the accompanying exemplary drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    [0014]FIG. 1 is a perspective view of a control device and control mechanism embodying features of the present invention.  
         [0015]    [0015]FIG. 2 is a perspective view of the control device and control mechanism of FIG. 1 with the top plate removed to better show the particular control mechanism embodying features of the present invention.  
         [0016]    [0016]FIG. 3 is another perspective view showing the particular control mechanism of FIGS. 1 and 2.  
         [0017]    [0017]FIG. 4 is a plane view of the control device and control mechanism of FIGS. 1 and 2.  
         [0018]    [0018]FIG. 5 is a side elevational view of the control device and control mechanism of FIGS. 1 and 2.  
         [0019]    [0019]FIG. 6 is a side elevational view of the distal end of the catheter portion of the control device which shows a self-expanding stent being maneuvered into a diseased portion of a body vessel.  
         [0020]    [0020]FIG. 7 is an elevational view similar to FIG. 6 which shows the distal end of the restraining sheath being retracted to deploy the self-expanding stent in the area of treatment in the body vessel.  
         [0021]    [0021]FIG. 8 is a side elevational view, partially in cross-section, of the slider member and timing belt which forms part of the control mechanism of FIGS. 1 and 2.  
         [0022]    [0022]FIG. 9 is a side elevational view, partially in cross-section, taken along line  9 - 9  showing the moveable rack and pinion system used in accordance with the present invention.  
         [0023]    [0023]FIG. 10 is a side elevational view, partially in cross-section, showing the control knob and moveable rack which forms part of the control mechanism shown in FIGS. 1 and 2.  
         [0024]    [0024]FIG. 11 is a side elevational view, partially in cross-section, showing the control knob of FIG. 10 as it is pushed down to contact the moveable rack when an actuating motion is to be applied to the control knob.  
         [0025]    [0025]FIG. 12 is a perspective view of another embodiment of a control device and control mechanism made in accordance with the present invention.  
         [0026]    [0026]FIG. 13 is an exploded perspective view of the control device and control mechanism of FIG. 12.  
         [0027]    [0027]FIG. 14 is a plan view showing the control mechanism located in the control device of FIGS. 12 and 13.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0028]    Turning now to the drawings, in which like reference numerals represent like or corresponding elements in the drawings, FIGS.  1 - 4  illustrate a control device  20  incorporating features of the present invention. This control device  20  is adapted for use with a medical device, such as a self-expanding stent or vascular graft. FIGS.  1 - 4  show a particular embodiment of a control device  20  incorporating features of the present invention which includes a housing  22  in which a control mechanism  24  (see FIGS.  2 - 4 ) is mounted. The control device  20  includes a catheter portion including a restraining sheath  26  which extends out from the housing  22  and extends to a distal end  28  where a self-expanding medical device, such as a stent  30  (see FIGS. 6 and 7) is maintained in a collapsed state ready for delivery into the patient&#39;s vasculature. The control device  20  includes a control knob  32  (FIG. 1) which can be manipulated by the physician to retract the restraining sheath  26  to deploy the stent  30  in the body vessel. This control knob  32  moves along a slot  34  in a top plate  36  which forms part of the housing  22 . A bottom plate  38 , shown better in FIGS. 2 and 3, forms the lower part of the housing  22  upon which the control mechanism  24  is mounted.  
         [0029]    In use, the physician grasps the hand portion  40  of the control device and utilizes his/her thumb or index finger to move the control knob  32  in an upward motion to retract the restraining sheath  26  in order to deploy the stent  30 . This control knob  32  is connected to a moveable rack  42  which remains in contact with a pinion gear  44  that is mounted onto a hub  46  formed on the bottom plate  38 . The translation of the moveable rack  42  causes the pinion gear  44  to rotate which in turn rotates another gear or pulley  48  attached to the pinion gear  44 . This pulley  48  is in turn connected to a timing belt  50  connected to a slider  52  that translates in a channel  54  formed on the bottom plate  38 . This slider  52  is connected to the proximal end  56  of the restraining sheath  26  and causes the proximal end  56  to retract back in a linear motion within the housing  22  as the timing belt  50  moves the slider  52  proximally towards the pulley  48 . In this manner, the distal end  28  of the restraining sheath  26  is retracted back to deploy the self-expanding stent  30 .  
         [0030]    As can be seen by the particular construction of this control mechanism  24 , the travel of the slider  52  on the control device  20  is made in a line of motion which is accordingly parallel to the line of travel of the proximal end of the restraining sheath  26 . The moveable rack  42 , which is manipulated by the physician via the control knob  32 , also translates in a linear motion that is substantially perpendicular to the line of motion of the slider  52  and, hence, the restraining sheath. In this manner, the physician can manipulate the proximal end  56  of the restraining sheath  26  with a hand motion which should not cause the stent  30  to move longitudinally within the body vessel once positioned in the patient&#39;s vasculature. Thus, a more precision placement of the medical device can be made by the physician since the risk of moving the self-expanding device with the retraction of the sheath is greatly reduced.  
         [0031]    Referring specifically to FIG. 4, the hand portion  40  and moveable rack (not shown in FIG. 4) are substantially perpendicular to the line of motion of the slider  52  within the channel  54  formed on the bottom plate  36  of the housing  22 . A dotted line designated “A” in FIG. 4 shows the substantial 90° angle which the hand portion  40  and moveable rack  42  makes with the line of motion for the slider  52  and restraining sheath  26 . Also, as is shown in FIG. 4, the hand portion  40  and moveable rack  42  could be placed at other angles besides 90° to the line of motion for the slider/sheath. For example, dotted lines “B” and “C” in FIG. 4 show the locations where the hand portion  40  and movable rack  42  could be positioned from the line of motion of the slider/sheath as well. This angle is shown to be about 30.° The position of the hand portion  40  and moveable rack  42  could be anywhere between these dotted lines “B” and “C” if desired. If an angle of less than about 30° is utilized, there still exists the possibility that the actuation of the control knob by the physician may cause some longitudinal movement to the catheter portion which will in turn move the placement of the stent or graft within the patient&#39;s vasculature. However, if the hand portion  40  and moveable rack  42  are located somewhere between dotted lines “B” and “C”, there should be a minimal chance of catheter movement when the control knob is manipulated by the physician.  
         [0032]    As can be seen in FIGS. 6 and 7, the stent  30  is mounted onto a mounting component  58  located at the distal end  28  of the restraining sheath  26 . This mounting component  58  is in turn attached to an inner member  60  which extends coaxially with the restraining sheath  26  and is mounted within the control device  20 . This inner member  60  and mounting component  58  also form a part of the catheter portion of the device  20 . This inner member  60  extends through an opening  62  in the housing  22  to a leur fitting  64  which connects to the proximal end  66  of the inner member  60 . This inner member  60  serves as a conduit for receiving a guide wire  68  (see FIGS. 6 and 7) utilized to deliver the medical device into the patient&#39;s artery, as will be explained in greater detail below. This inner member  60  can be made from a hypotube or other similar materials which provides axial strength to the catheter system. In use, this inner member  60  and the mounting component  58  must remain relatively stationary during the deployment of the stent otherwise the stent may be improperly implanted in the patient&#39;s vasculature. An obturator  70  creates an atraumatic tip for the catheter portion of the control device to prevent snowplowing of the distal end of the restraining sheath  26  as it moves through the patient&#39;s vasculature in an over-the-wire fashion along the guide wire  68 . As can be seen in FIG. 6, this obturator is coned-shaped and is flush with the outer surface of the restraining sheath  26  to create a relatively smooth surface that helps to prevent snowplowing from occurring in the patient&#39;s vasculature.  
         [0033]    In use, the self-expanding stent  30  would be delivered within a body vessel of the patient, such as an artery  72 , as shown in FIGS. 6 and 7. The delivery of the stent  30  can be accomplished in the following manner. The stent  30  is first mounted onto the mounting component  58  of the inner catheter member  60  with the restraining sheath  26  being placed over the contracted stent. The catheter/stent assembly can then be introduced within the patient&#39;s vasculature in a conventional Seldinger technique through a guiding catheter (not shown). The guide wire  68  would be initially steered into the area of treatment where a stenosis  74  is located. The catheter/stent would then be advanced over the guide wire  68  until the stent  30  is directly under the stenosis  74 . The restraining sheath  26  can then be retracted, allowing the stent  30  to expand to its larger diameter to press upward against the artherosclerosic plaque which has built up on the vessel wall, as illustrated in FIG. 6. While not shown in the drawing, the artery  72  is preferably expanded slightly by the expansion of the stent  30  to seat or otherwise fix the stent  30  to prevent movement. In some circumstances during the treatment of the stenoic portions of an artery, the artery may have to be expanded considerably in order to facilitate passage of blood or other fluid therethrough. Once the restraining sheath  26  is retracted to expose the stent, as shown in FIG. 7, the stent will expand and compress the stenosis somewhat to enlarge the lumen through which blood flows.  
         [0034]    It should be appreciated that although the stent  30  is shown being utilized to treat an area in which artherosclerosic plaque has built up against the wall of an artery, it could also be used to hold up a detached lining, or other abnormality, of the patient. Moreover, the stent  30  can be utilized in any one of a number of different body vessels, including but not limited to carotid arteries, coronary arteries and renal arteries. The stent could be used for primary stenting purposes, i.e., to directly enlarge the opening in the artery, or it could be utilized in conjunction with predilitation in which the stenoic plaque is initially expanded in the area of treatment by a balloon dilitation catheter. Thereafter, the stent  30  could be placed in the predilitated area of treatment to help restenosis and to maintain this diseased portion of the artery in an open position. As indicated above, the present invention can also be utilized in conjunction with other self-expanding medical devices, for example, a self-expanding graft which could be delivered to a particular area in the patient&#39;s vasculature for providing a fluid conduit that bypasses a diseased portion of a vessel wall to prevent the vessel wall from rupturing.  
         [0035]    As is shown in FIGS. 6 and 7, as the restraining sheath  26  is retracted past the self-expanding stent, the proximal end  76  of the stent  30  may come in contact with a radiopaque marker  78  located on the mounting component  58  to provide a source of visualization for the physician during placement of the stent in the patient&#39;s vasculature. This radiopaque marker  78  serves as an abutting shoulder to help prevent the stent  30  from moving back with the restraining sheath as it is being retracted due to the frictional forces which may be generated between the moving sheath and outer surface of the stent. In this manner, the possibility that the stent can be pulled back along with the restraining sheath is reduced.  
         [0036]    Referring specifically now to FIG. 8, the particular attachment utilized to connect the proximal end  56  of the restraining sheath  26  to the slider  52  is shown in greater detail. As can be seen in FIG. 8, the slider  52  translates within a channel  54  formed in the bottom plate  38  of the control handle  20  which follows the line of travel of the restraining sheath. The slider  52  includes an opening  80  through which the inner catheter member  60  and the proximal end  56  of the restraining sheath  28  extend through. However, the proximal end  56  of the restraining sheath  26  would be bonded within this opening  80  utilizing adhesives or other attachment techniques well-known in the art. As such, it would be securely affixed to the slider  52  and will move with the slider as it moves proximally towards the pulley  48  in the direction of the arrow  81  shown in FIG. 4. It should be appreciated that the restraining sheath  26  remains in a coaxial arrangement with the inner catheter member  60  as the restraining sheath  26  moves along the length of the inner catheter member  60  during deployment. The control mechanism  24  also helps to prevent the restraining sheath  26  from retracting prematurely since the slider  52  will remain at its position as shown in FIG. 4 until the pulley  48  is rotated via the action of the moveable rack  42 . It should be appreciated by those skilled in the art that although a timing belt  50  is shown attached to the slider  52 , the control mechanism could also utilize cables, pulleys and movable racks, and the like, to accomplish this same motion. Again, the deployment motion could be at an angle other than 90° to the line of motion of the retraining sheath. It also should be appreciated that the configuration of the hand portion could be altered to allow deployment of the stent by a whole hand motion, or by use of an individual finger, such as the thumb. Although a control knob  32  is shown and described as providing the mechanism for providing an upward motion to the moveable rack  42 , the direction of this actuating motion could be in a opposite direction without departing from the spirit and scope of the present invention.  
         [0037]    The control device  20  also may include a distal hub  82  at which a strain relief member  84  is located. This strain relief member  84  helps to prevent unwanted bending of the restraining sheath  26  at the distal end of the control device. Conventional strain relief components could be utilized in accordance with the present control device as illustrated in FIGS.  1 - 4 .  
         [0038]    Referring now to FIGS. 4 and 9- 11 , the moveable rack  42  and control knob  32  are shown in greater detail. As can be seen in FIG. 9, the moveable rack  42  also translates within a channel  86  formed in the bottom plate  38  of the control handle  20 . In this particular embodiment, the moveable rack  42  is designed to translate in a direction substantially perpendicular to the line of travel of the slider  52  and restraining sheath  26 . The control knob  32  can be mounted onto the top plate  36  which forms part of the housing  22  in such a manner that the control knob will not engage the moveable rack  42  (as is shown in FIG. 10) until the physician is ready to retract the sheath  26 . In this regard, a biasing element such as a spring (not shown) can be utilized to maintain the control knob  32  in an upright position (as shown in FIG. 10) until the physician desires to retract the restraining sheath  26 . Thereafter, a slight downward push of the control knob  32  will engage the top portion of the moveable rack (as is shown in FIG. 11) to allow the physician to move the control knob  32  and movable rack  42  to retract the restraining sheath  26 . Again, it should be appreciated that this is just one form of a control knob which can be utilized in accordance with the present invention and other variations of this actuating mechanism can be utilized without departing from the spirit and scope of the present invention.  
         [0039]    Referring now specifically to FIG. 4, the diameters of the pinion gear  44  and pulley  48  can be seen. The upper pinion gear  44  has a smaller diameter than the pulley  48  utilized to translate the slider  52  within the channel  54 . As a result, a particular ratio can be achieved which will result in a longer retracting stroke being applied to the restraining sheath  26  as the physician moves the control knob  32  to translate the moveable rack  42 . In this manner, a greater retraction stroke can be achieved on the restraining sheath  26  by a smaller hand motion provided by the physician. This feature is certainly beneficial to the physician since less hand actuating would be required on his/her part in order to translate the restraining sheath a longer distance. This is particularly advantageous when a long stent is being deployed in the patient&#39;s vasculature which usually requires a long retracting stroke to fully retract the restraining sheath. This particular feature can be advantageous when a self-expanding vascular graft is the component to be deployed since vascular grafts are usually longer than self-expanding stents. It should be appreciate that any number of different gear ratios can be achieved in order to reduce the amount of hand motion needed by the physician to actuate the device while still achieving the desired retraction stroke to the sheath.  
         [0040]    Although it is not shown in FIGS.  1 - 4 , this moveable rack  42  can also be spring loaded to lower the force needed to be supplied by the physician when moving the control knob  32  to retract the restraining sheath  26 . Such a spring could be located at the end of the moveable rack  42  to provide an external force to the moveable rack  42  as the control knob  32  is being manipulated by the physician. As a result, the physician need not apply as much force to move the control knob. Again, this feature can be useful when long stents or vascular grafts are being deployed since greater force is usually needed due to the increased amount of frictional contact created between the moving inner surface of the restraining sheath and the outer surface of the stent or graft.  
         [0041]    Referring now to FIGS.  12 - 14 , another embodiment of a control device  100  and control mechanism  102  made in accordance with the present invention is shown. In this particular embodiment, the control device  100  includes a housing  22  which include a bottom plate  38  and a top plate  36 . This particular control device  100  and control mechanism  102  operates substantially as the previously described control device  20  in that the physician applies an actuating motion to the trigger  104  in a direction which is at an angle to the linear motion of the slider/restraining sheath in the housing. This angle can be between 30° and 150° with 90° being and optional angle when deploying the medical device. Referring specifically to FIGS. 13 and 14, the control device  100  includes a trigger  104  connected to a moveable rack  42  which contacts a pinion gear  44 . A second moveable rack  106  which is attached to the proximal end of the restraining sheath  26  is in contact with this gear  44  or a second pulley or gear (not shown). As a result, the second moveable rack  106  moves in a linear motion that is at a substantially 90° angle to the motion of the first moveable rack  42 . The trigger  104  of the control device  100  is designed with several openings  108  and  110  which are adapted to fit different sized hands of the physician using the control handle. In this manner, the movement of the trigger  104  by the physician should not cause the self-expanding medical device to move from the target in the patient&#39;s vasculature.  
         [0042]    Referring specifically to FIG. 14, the second moveable rack  106  is shown as it is placed within a channel  112  formed in the bottom plate  38 . The moveable rack  42  is also contained within a channel  54  and is, of course, attached to the trigger  104 . In this particular embodiment, the gear ratio between the pinion gear  44  and the second gear also can be set so that only a small amount of actuating motion of the trigger will produce a long retraction stroke to the restraining sheath. The control device can be equipped with a spring loaded mechanism  114  which contacts the moveable rack  42  to provide a force which lowers the force which would be required by the physician when moving the trigger  104 . For example, a spring  116  can be located in the channel  54  to contact one end of the moveable rack  42  to apply external force to the rack which again will help to reduce the amount of force needed when actuating the trigger.  
         [0043]    The components of the present invention can be made from conventional plastics and polymeric materials known in the art. The lengths of the various components can vary depending upon the particular uses intended. For example, the length of the catheter portion of the control device can vary depending on the particular type of medical device to be implanted, the target location and the type of procedure to be administered.  
         [0044]    Further modifications and improvements may additionally be made to the device and method disclosed herein without departing from the scope of the present invention. Accordingly, it is not intended that the invention be limited, except as by the appended claims.