Abstract:
A high pressure dilation medical device delivery catheter having a proximal and distal end comprising two tubes mounted generally concentrically about an inner tube. The balloons being characterized as a relatively short inner tube which is inflated with high pressure and a longer outer tube which is inflated with low pressure. The balloons have independent inflation lumens which extend toward the proximal end of the inner tube. A medical device mounting region is disposed about at least a portion of the outer balloon and may have a stent or other medical device mounted thereupon. A retractable outer sheath is further disposed about the medical device mounting region and is operatively connected near the proximal end of the catheter.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Not Applicable 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
     Not Applicable 
     BACKGROUND OF THE INVENTION 
     The present invention relates to medical device delivery systems, particularly dilation balloon catheters employed in applications such as percutaneous transluminal angioplasty (PTA), percutaneous transluminal coronary angioplasty (PTCA) procedures, and more particularly to the utilization of a catheter having multiple inflation balloons for the delivery of medical devices, namely stents. 
     Balloon catheters, are a highly developed and well known field of medical technology. Balloon catheters are typically used to occlude and seal bodily spaces, expand blood vessels, and deliver a variety of medical devices. 
     Stents are medical devices that are commonly placed into a body vessel by way of a balloon catheter delivery system. A stent is a prosthesis which is generally tubular and which is expanded radially in a vessel or lumen to maintain its patency. Stents are widely used in body vessels, body canals, ducts or other body lumens. 
     In many stent delivery applications, the stent is often designed to be self-expanding. When these self-expanding stents are utilized, balloon catheters are typically designed to mount the stent upon the deflated balloon and further surround the stent with a retractable sheath. To actually deliver the stent the sheath is retracted thereby allowing the stent to expand away from the balloon. The balloon is then inflated to seat the stent in place. Stent delivery catheters which utilize a single balloon and a sheath can be seen in U.S. Pat. No. 5,192,297 to Hull, U.S. Pat. No. 5,360,401 to Turnland et al. and U.S. Pat. No. 5,453,090 to Martinez et al. 
     In the case of a non-self expanding stent, to deploy the stent the catheter must have a means to initially expand the stent from about the catheter and into the target vessel. Typically a balloon is inflated to expand the stent a sufficient diameter about the catheter and then deflated to release the stent. Subsequent to expanding the stent, in many applications the catheter must be completely removed to replace this first balloon with a second balloon more suitable for seating the stent in place, or alternatively an entirely new balloon catheter is used to seat the stent. 
     In some other applications the laborious and time consuming task of balloon or catheter changeover is avoided by utilizing a catheter which has multiple balloons mounted adjacently to one another. In these applications after an initial balloon expands the stent, the catheter is moved forward in the vessel to put the seating balloon into position under the now expanded stent. While these systems save time by avoiding the extra step of removing the catheter and replacing the balloon, they remain less than ideal as often the balloons are easily ruptured by the edges of the stent and the effect of the entire catheter being moved back and forth in the vessel, in order to properly position the stent, places additional unwanted friction and stress upon the vessel walls. 
     In many operations which utilize stents, the stent and catheter must often pass through a variety of interferences such as a build up of arterial plaque, hardened calcified legions, or other known medical conditions. The typical low pressure balloon used to expand the stent lacks the required strength, pressure, diameter and compliance characteristics to properly inflate the balloon through these anomalies without risk of rupture or vessel damage. As a result numerous catheter configurations have been developed to address the problems associated with these conditions. 
     U.S. Pat. No. 5,810,871 to Tuckey et al. discloses a stent delivery system which addresses the stent mounting and balloon puncture problems associated with previous catheters such as those described above, by providing an expandable sheath to be placed between the balloon and stent. Moreover, to protect the vessel from possible tearing as the stent is moved therethrough, the Tuckey catheter employs two end caps which contain the ends of the stent while the stent is compressed prior to expansion. Although Tuckey addresses some of the problems as stated above, Tuckey fails to provide a balloon with compliance, pressure and diameter characteristics for proper seating of the stent as may be required in many applications. 
     Unlike the catheters discussed above many of the catheters developed for use in PTA procedures utilize complex multiple balloon configurations in order to properly dilate a vessel and clear blockages. U.S. Pat. No. 4,744,366 to Jang is one such PTA catheter. 
     Although the Jang reference provides a catheter with a dilation region with multiple compliances, it does not provide an easy or atraumatic means to position the balloon in selected regions of the stent. 
     The Jang catheter uses a plurality of independently controlled balloons having the ability to be inflated over a range of pressures and diameters. As a PTA catheter, the Jang catheter is not designed to mount and deliver a stent. Even if Jang could be modified to deliver a stent, it is unclear from the disclosure if the balloons described by Jang would have the strength and puncture resistance necessary to expand and set a stent. 
     In order to address the problems described above and to overcome the continued shortcomings suffered by previous balloon catheters, it is an object of the present invention to provide for a medical device delivery catheter capable of inflating and setting the medical device in a vessel without a catheter or balloon exchange, while reducing the possibility of damage to the vessel by the stent or balloons. 
     A further object is to provide for a multiple balloon catheter capable of expanding a stent with low pressure and seating the stent into place using high pressure. 
     Yet another object is to provide for multiple balloon catheter capable of expanding a body lumen with low pressure and subsequently seating a medical device into the expanded body lumen using high pressure. 
     BRIEF SUMMARY OF THE INVENTION 
     To achieve these and other objects, there is provided a medical device delivery catheter that has multiple inflation balloons. Preferably a catheter having two balloons, an outer balloon and an inner balloon mounted in an essentially concentric manner on the distal end of the inner tube of the catheter. The outer balloon and the inner balloon being used respectively to expand a medical device with low pressure and to then properly seat the medical device in a vessel with high pressure. The inner balloon being capable of motion inside the outer balloon on the catheter shaft. The inventive catheter may have a retractable outer sheath which surrounds the distal end of the catheter prior to delivery of the medical device. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     A detailed description of the invention is hereafter described with specific reference being made to the drawings in which: 
     FIG. 1 is an elongated cross sectional view of an embodiment of the medical device delivery catheter showing the balloons in their inflated posture; 
     FIG. 2 is an elongated cross sectional view of another embodiment of the medical device delivery catheter; 
     FIG. 3 is an elongated cross sectional view of an embodiment of the medical device delivery catheter including a retractable sheath; 
     FIG. 4 is elongated cross sectional view of an embodiment of the medical device delivery catheter including only a single mobile balloon and a retractable sheath; 
     FIG. 5 shows an additional embodiment of the invention wherein the mobile inner balloon is positioned distally relative to the mobile outer balloon; 
     FIG. 6 shows an additional embodiment of the invention wherein the mobile inner balloon is positioned proximally relative to a stationary outer balloon; 
     FIG. 7 show an additional embodiment of the invention which illustrates the affect of expanding an inner balloon which has a length less than that of the stent; 
     FIG. 8 is close up view of a mobile inner balloon which includes a slidable seal; and 
     FIG. 9 shows yet another embodiment of the invention wherein two balloons are utilized to inflate different portions of a stent in an adjacent arrangement on the catheter. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following detailed description should be read with reference to the drawings in which similar parts in different figures are numbered the same. The drawings, which are not necessarily to scale, depict exemplary embodiments and are not intended to limit the scope of the invention. Those skilled in the art will recognize that many of the examples provided have suitable alternatives which may also be utilized. 
     It is well known in the stent delivery art that an entire catheter may be repositioned within a vessel to properly position and seat a stent. However, moving the entire catheter places unwanted strain along the entire length of the vessel. In order to ensure that the inner balloon may be repositioned to properly seat the stent, without requiring that the entire catheter be repositioned, the present invention provides for a stent delivery system having an independently moveable inner balloon for stent seating. 
     The present invention relates to a high pressure medical device deployment catheter. FIG. 1 illustrates a catheter, indicated generally at  20 , for deploying a stent  24 . As shown, catheter  20  has two balloons, a shorter mobile high pressure inner balloon  30  within a longer low pressure outer balloon  40  distally mounted upon an inner tube or shaft  32 . The inner balloon  30  is capable of independent movement relative the inner tube  32 . In an alternative embodiment, the outer balloon  40  may be capable of independent motion as well. 
     In an embodiment where the respective balloons  30  and  40  are individually or both capable of independent movement, the balloons  30  and  40  will respectively include proximal extensions  51  and  53 . Where the inner balloon  30  is capable of independent motion the inner balloon  30  may be manipulated as well as inflated from the proximal end of the catheter  20  through proximal extension  51 . Likewise, where the outer balloon  40  is independently mobile, the outer balloon  40  may be manipulated and inflated at the proximal end of the catheter  20  through proximal extension  53 . 
     In order for either the inner balloon  30  or outer balloon  40  to be capable of independent motion relative to the inner tube  32 , the balloons must respectively be equipped with a sliding seal  60 . Slidable seal  60  forms a fluid-tight seal against the inner tube  32  during balloon inflation. The slidable seal  60  will be discussed in greater detail below. 
     Disposed about inner tube  32 , and located proximal of the catheter tip  28  is a medical device mounting region upon which a medical device such as a stent  24  is mounted. 
     In operation catheter  20  is inserted into a vessel and advanced to a treatment site. Once properly in position, the outer balloon  40  may be inflated under low pressure to initially expand stent  24  and/or dilitate the vessel walls. In an embodiment where outer balloon  40  is not independently mobile, outer balloon  40  may be inflated from within inner tube  32  through low pressure inflation lumen  50 . Similarly, in an embodiment where the inner balloon  30  is not independently mobile, the inner balloon may be inflated via internal lumen  54 . 
     Because the low-pressure outer balloon  40  is designed to initially expand stent  24  and to pre dilate a vessel, the balloon will typically be constructed to be highly compliant and readily expandable. The low-pressure balloon  40  is designed to readily expand to a predetermined diameter when inflated with low pressure. An example of some appropriate low pressure volumes may be within the range between 4 and 12 atmospheres, however the required low-pressure values may vary greatly depending on several factors. 
     In order to ensure proper seating of stent  24  into the vessel, inner balloon  30  is positioned under stent  24  and inflated. Inner balloon  30  may be inflated with a relatively high pressure fluid, from within inner tube  32 , through the high pressure inflation lumen  54  or where the inner balloon is mobile through proximal extension  51  as previously discussed. Actual pressure values may vary greatly in actual use, however an example of an appropriate range of values for high pressure inflation may be between 10 and 20 atmospheres. 
     In a preferred embodiment shown in FIG. 2, both the inner balloon  30  and outer balloon  40  are longitudinally independently mobile relative to the inner tube  32 . Inner balloon  30  includes proximal extension  51  which extends all the way to the proximal end of the catheter  20  where the proximal extension  51  and eventually the balloon  30  may be directly inflated and manipulated. By effectively extending the balloon  30  all the way to the proximal end of the catheter, the proximal extension  51  provides a user with the ability to independently position balloon  30  by manipulating the proximal extension  51  while holding the inner tube  32  stationary. Outer balloon  40  is also capable of independent movement and inflation via proximal extension  53 . 
     In contrast to outer balloon  40 , inner balloon  30  is preferably designed to continue to expand only marginally when inflated at high pressure. The construction and manufacture of inner balloon  30  provides the inner balloon with sufficient strength to gradually push against and possibly through plaque buildups and other interferences when inflated at high pressure. 
     In the embodiment shown in FIG. 3 the catheter may be configured with a retractable outer sheath  48 , and a retraction member  49 . In this embodiment retractable outer sheath  48  surrounds the outer balloon  40  and stent  24 . In an embodiment where the inner balloon  30  is located distally or proximally of the outer balloon  40 , as best shown by FIGS. 5 and 6, the stent  24  and outer sheath  48  would be disposed about the outer balloon  40 . 
     In an alternative embodiment of the invention as shown in FIG. 4, the catheter  20  may avoid the requirement of a low pressure balloon and employ only a single moveable high pressure balloon  30  to seat a self-expanding stent after the stent  24  is freed by the retraction of sheath  48 . 
     As may been seen in FIGS. 1-3 and  5 - 9 , inner balloon  30  will typically be shorter than outer balloon  40 . This design feature provides significant benefits when seating the stent in place. Stent  24  will normally be the same or similar in length to the longer outer balloon  40 . Inner balloon  30  may be positioned centrally relative to stent  24 . As the shorter inner balloon  30  is inflated inner balloon  30  will generally impinge only a central portion of the stent as dictated by the inner balloon&#39;s shorter length and position. As shown in FIG. 7, the resulting central expansion of the stent  24  will cause the edges of the stent to have reduced contact with a vessel wall. The extent of the contact is dependant on the design and construction of the stent. By minimizing the contact of the vessel wall and the edges of the stent during the stent seating process, the present high pressure dilation balloon protects the patient from edge dissections which would otherwise be more likely to occur. 
     As best shown in FIG.8, inner balloon  30  may be slidably sealed to the inner tube  32 . The slidable seal  60  allows the inner balloon  30  to be positioned with great accuracy directly under the stent  24 . Slidable seal  60  is essentially a fold of inner balloon  30  that rests against inner tube  32 . Slidable seal  60  forms a fluid-tight seal as the pressure being exerted upon the seal during inflation of inner balloon  30  forces the slidable seal  60  against the inner tube  32 . As shown in FIGS. 2,  3 ,  5  and  7  outer balloon  40  may also be equipped with a slidable seal  60 . As should be obvious from such an embodiment the slidable seal  60  as applied to the outer balloon may be a fold of the outer balloon material which rest against the inner tube  32 . 
     Regardless of the specific embodiment, once the stent  24  is properly set into position both outer balloon  40  and inner balloon  30  are deflated and the entire catheter  20  is withdrawn from the vessel. 
     As mentioned above, the inventive catheter may contain the stent and balloons in a variety of spatial relationships. In additional embodiments the inner balloon  30  is initially positioned further distally (see FIG. 5) or proximally (see FIG. 6) relative to the stent  24  and outer balloon  40 . Where inner balloon  30  is located outside of outer balloon  40 , inner balloon  30  remains capable of independent movement along the inner shaft  32 . Depending on the specific embodiment desired outer balloon  40  may also be capable of independent movement relative to the inner balloon  30  such as in the embodiment shown in FIG. 5 or the outer balloon may be secured to the inner tube  32  as shown in FIG.  6 . 
     In yet another embodiment of the present invention shown in FIG. 9, stent  24  may be disposed about one or more inflation balloons  70  and  72 . In the embodiment shown only balloon  70  is capable of independent motion however multiple balloons could be mobile relative to the inner tube  32 . The proximal end of balloon  70  is equipped with a sliding seal  60  to allow the proximal extension  51  of balloon  70  to be drawn or advanced as desired without disturbing balloon  72 . Balloon  72  may be inflated via lumen  50 . Balloons  70  and  72  may be inflated at the same time to provide uniform initial expansion of stent  24 . In an embodiment where stent  24  is self expanding retractable sheath  48  may be included to retain the stent on the balloons prior to delivery. Once stent  24  is expanded balloon  70  may be moved to specific areas of the stent and inflated thereby providing the stent with increased pressure for seating the stent or for compressing plaque or other interferences between the stent and vessel wall. 
     In all of the embodiments described above, the balloon may be composed of suitable materials which include polyolefin copolymer, polyester, polyethylene terephthalate, polyethylene, polyether block amide, polyamide, polyimide, nylon, latex and urethane as well as other suitable balloon materials as are known in the art. 
     In addition to being directed to the embodiments described above and claimed below, the present invention is further directed to embodiments having different combinations of the features described above and claimed below. As such, the invention is also directed to other embodiments having any other possible combination of the dependent features claimed below. 
     The above examples and disclosure are intended to be illustrative and not exhaustive. These examples and description will suggest many variations and alternatives to one of ordinary skill in this art. All these alternatives and variations are intended to be included within the scope of the attached claims. Those familiar with the art may recognize other equivalents to the specific embodiments described herein which equivalents are also intended to be encompassed by the claims attached hereto.