US20020183780A1 - Stent installation method using balloon catheter having stepped compliance curve - Google Patents

Abstract

A balloon catheter suitable for deploying a stent utilizes a balloon molded with a stepped diameter profile.

Description

• This is a continuation of application Ser. No. 09/774,725, filed Jan. 31, 2001, which is a division of application Ser. No. 09/396,841, filed Sep. 15, 1999, now U.S. Pat. No. 6,290,485, which is a continuation of copending application Ser. No. 08/931,190, filed Sep. 16, 1997, now U.S. Pat. No. 5,980,532, which is a division of application Ser. No. 08/397,615, now U.S. Pat. No. 5,749,851, all incorporated herein by reference.[0001]
BACKGROUND OF THE INVENTION
• The present invention relates generally to a method of installing a stent utilizing a balloon catheter to perform an initial angioplasty and to seat the stent after it has been located in the vessel. The invention also relates to novel balloon structures which have particular use in the method of the invention.[0002]
• Angioplasty, an accepted and well known medical practice involves inserting a balloon catheter into the blood vessel of a patient, maneuvering and steering the catheter through the patient's vessels to the site of the lesion with the balloon in an uninflated form. The uninflated balloon portion of the catheter is located within the blood vessel such that it crosses the lesion or reduced area. Pressurized inflation fluid is metered to the inflatable balloon through a lumen formed in the catheter to thus dilate the restricted area. The inflation fluid is generally a liquid and is applied at relatively high pressures, usually in the area of six to twenty atmospheres. As the balloon is inflated it expands and forces open the previously closed area of the blood vessel. Balloons used in angioplasty procedures such as this are generally fabricated by molding and have predetermined design dimensions such as length, wall thickness and nominal diameter. Balloon catheters are also used in other systems of the body for example the prostate and the urethra. Balloon catheters come in a large range of sizes and must be suitably dimensioned for their intended use.[0003]
• Recently the use of a catheter delivered stent to prevent an opened lesion from reclosing or to reinforce a weakened vessel segment, such as an aneurism, has become a common procedure. A typical procedure for stent installation involves performing an initial angioplasty to open the vessel to a predetermined diameter sufficient to permit passage of a stent delivery catheter across the lesion, removal of the angioplasty balloon catheter, insertion of a delivery catheter carrying the stent and a stent deploying mechanism, deploying the stent across the opened lesion so as to separate the stent from the catheter and bring it into contact with the vessel wall, usually with dilation to a larger diameter using a balloon larger than the balloon of the predilation catheter, and then removing the delivery catheter (after deflating the balloon if used). In many cases it has become the practice to then “retouch” the dilation by deploying a third catheter carrying a balloon capable of dilating at a substantially higher pressure to drive the stent into the vessel wall, thereby to assure that there is no risk of the stent later shifting its position and to reduce occurrence of restenosis or thrombus formation. This third “retouch” dilation is often considered necessary when the balloon used to seat the stent is made of a compliant material because such balloons generally cannot be safely pressurized above 9-12 atm., and higher pressures are generally considered necessary to assure full uniform lesion dilation and seating of the stent.[0004]
• A wide variety of stent configurations and deployment methods are known. For instance, stent configurations include various forms of bent wire devices, self-expanding stents; stents which unroll from a wrapped configuration on the catheter; and stents which are made of a deformable material so that the device may be deformed on deployment from a small diameter to a larger diameter configuration. References disclosing stent devices and deployment catheters include:[0005]

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  US 5061275	Wallsten et al
  US 5064435	Porter
  US 5092841	Spears
  US 5108416	Ryan et al
  US 4990151	Wallsten
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• In U.S. Pat. No. 5,348,538, incorporated herein by reference, there is described a single layer balloon which follows a stepped compliance curve. The stepped compliance curves of these balloons has a lower pressure segment following a first generally linear profile, a transition region, typically in the 8-14 atm range, during which the balloon rapidly expands yielding inelastically, and a higher pressure region in which the balloon expands along a generally linear, low compliance curve. The stepped compliance curve allows a physician to dilate different sized lesions without using multiple balloon catheters.[0006]
• Stepped compliance curve catheter balloon devices using two different coextensively mounted balloon portions of different initial inflated diameter, are also described in co-pending U.S. application Ser. No. 08/243,473, filed May 16, 1994 as a continuation of now abandoned U.S. application Ser. No. 07/927,062, filed Aug. 8, 1992, and in U.S. Pat. No. 5,358,487 to Miller. These dual layer balloons are designed with the outer balloon portion larger than the inner portion so that the compliance curve follows the inner balloon portion until it reaches burst diameter and then, after the inner balloon bursts, the outer balloon becomes inflated and can be expanded to a larger diameter than the burst diameter of the inner balloon.[0007]
• A polyethylene ionomer balloon with a stepped compliance curve is disclosed in EP 540 858. The reference suggests that the balloon can be used on stent delivery catheters. The disclosed balloon material of this reference, however, yields a compliant balloon and therefore a stent delivered with such a balloon would typically require “retouch.”[0008]
SUMMARY OF THE INVENTION
• The invention in one aspect is directed to a method for method for installing a stent in a vessel utilizes a single balloon catheter for both low pressure predilation at a relatively small diameter to open the lesion sufficiently to allow insertion and deployment of the stent across the lesion and for subsequent high pressure embedding of the stent in the vessel wall. The same balloon catheter may also be employed to insert and deploy the stent. Thus at least one catheter may be eliminated from what has heretofore been a two or three catheter installation process. The balloons utilized in the method have a stepped compliance curve which allows for predilation at a low pressure and predetermined diameter and for high pressure embedding at a substantially larger diameter.[0009]
• In a further aspect of the invention novel balloon structures having high wall strengths, high burst pressures and low compliance are provided in which a first portion of the balloon body has a generally linear compliance curve and a second portion of the balloon body has a stepped compliance curve. Both portions of the balloon are configured to have essentially the same diameter at low pressure so that the entire balloon may be used to predilate a lesion. However at higher pressure the configuration of the balloon changes due to rapid expansion of the second balloon portion. At still higher pressures the compliance curve of the second portion levels off to a low compliance profile so that this portion of the balloon can be used for high pressure embedment of the stent without substantially increasing the stent size. With such balloons, exposure of the vessel wall areas which are not reinforced by the stent to high pressure can be avoided, despite the typically shorter length of conventional stents than the typical length of predilation balloons.[0010]
• The novel balloons of the invention are made by molding a balloon into a configuration in which the second portion has a larger diameter than the first portion and then shrinking the second portion to the diameter of the first portion. The method of making such balloons comprises yet another aspect of the invention.[0011]
• These and other aspects and advantages of the present invention will no doubt become apparent to those skilled in the art after having read the following detailed description of the invention as illustrated by the various drawing figures.[0012]
BRIEF DESCRIPTION OF DRAWINGS
• FIG. 1 is a longitudinal sectional view of a vessel showing an angioplasty catheter, not in section and having a stepped compliance curve balloon on the distal end thereof, inserted in the vessel and predilating a lesion in the vessel.[0013]
• FIG. 2 is a view of a vessel as in FIG. 1 after installation of a stent but before a “retouch” procedure.[0014]
• FIG. 3 is a view as in FIG. 1 in which after predilation and with the same catheter, now carrying a stent mounted over the balloon, reinserted to deliver the stent to the lesion.[0015]
• FIG. 4 is a view as in FIG. 3 with the balloon expanded to install the stent and further dilate the lesion.[0016]
• FIG. 5 is a view as in FIG. 3 after completion of the procedure of FIG. 3.[0017]
• FIG. 6 is a side view the distal end of a catheter having an alternate balloon of the invention, shown in hyper-extended form.[0018]
• FIG. 7 is a schematic illustration depicting the process stages for preparing a balloon as in FIG. 6.[0019]
• FIG. 8 is a view of a catheter as in FIG. 6 except that a second alternate balloon of the invention is depicted.[0020]
• FIG. 9 is a schematic illustration depicting the process stages for preparing a balloon as in FIG. 8.[0021]
• FIG. 10 is a graph showing the compliance curves of several balloons of the type shown in FIGS. 1, 3 and[0022]4 compared to a conventional 3.5 mm angioplasty balloon of the same material.
• FIG. 11 is a graph of the compliance curves of a balloon of the type shown in FIG. 6.[0023]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
• The catheters employed in the practice of the present invention are most conveniently constructed as over-the-wire balloon catheters of conventional form for use in angioplasty, except that the balloon has a stepped compliance curve. However it should be understood that the present invention can be applied, in addition to over-the-wire catheters, to fixed-wire catheters, to shortened guide wire lumens or single operator exchange catheters, and to non over-the-wire balloon catheters. Furthermore this invention can be used with balloon catheters intended for use in any and all vascular systems or cavities of the body.[0024]
• Referring to FIGS.[0025]1-5, the process of the invention is illustrated by these Figures. In FIG. 1, acatheter10 carrying aballoon12 on the distal end thereof has been inserted overguide wire13 into avessel14 and fed to alesion16 where it is used to predilate the lesion to a predetermined diameter, typically about 2.5 mm. In the process of the invention,balloon12 is made of a high strength polymer, such as PET and has a stepped compliance curve, the predilation diameter is below the transition region on that curve and the desired final dilated diameter, typically 2.75-4.0 mm, lies on the portion of the curve above the transition region. After the predilation the balloon is deflated and thecatheter10 is removed from thevessel14.
• The next step is to deliver the stent to the lesion. In a first embodiment of the process, a separate stent delivery catheter of any conventional type is used to deliver the stent to the lesion, install the stent in place across the lesion, and further dilate the lesion to a larger diameter, typically 2.75-4.0 mm. The delivery catheter is then withdrawn to leave the[0026]stent17 in place across the dilated lesion, as shown in FIG. 2. Occasionally as indicated in FIG. 2 the stent is not fully seated or can move somewhat after installation if the installation process is discontinued at this point.
• To assure that the stent is firmly seated in the lesion so that it cannot move and to additionally reduce occurrences of restenosis and thrombus formation, in this embodiment of the inventive process, after the delivery catheter has been removed,[0027]catheter10 is reinserted and expanded to a retouch pressure, typically above 9 atm and preferably in the range of 12-20 atm.
• Alternatively,[0028]catheter10 may be employed as a delivery catheter. In the specific embodiment illustrated in FIGS.3-4, anunexpanded stent18 has been mounted on thecatheter10 overballoon12 aftercatheter10 has been used to predilate the lesion and has been removed from the lesion.Catheter10 is then reinserted into thevessel14 and located across the lesion (FIG. 3).Balloon12 is then reinflated as shown in FIG. 4 to expand and install thestent18 and to dilate the lesion. The pressure employed is one which inflates the balloon to a diameter above the transition region and therefore the same balloon as used in predilation can be used to deliver the catheter and dilate the lesion. Further, because theballoon12 follows a low compliance curve above the transition region, the pressure can safely be increased above 12 atm so as to firmly seatstent18 without having to undergo “retouch.” Typically theballoon12 will be capable of inflation to at least as high as 20 atm.
• FIG. 5 depicts the[0029]stent18 in place after high pressure dilation. A similar result is obtained if thecatheter10 is used for predilation and for “retouch” but not for stent installation. It should be noted that the specific configuration of thestents17 and18 is not critical and two different configurations have been depicted merely to indicate that different configurations may be employed in either embodiment of the inventive installation process. The particular configurations employed may be reversed or another stent configuration, including balloon expandable stents and self-expandable stents, may be substituted without departing from the invention hereof.
• Thus unlike the prior art methods for accomplishing the same sequences of predilation, stent delivery/dilation and high pressure seating or “retouch,” a separate catheter is not required to be used in the final high pressure seating step from the catheter used in the predilation step. This significantly reduces the cost of the procedure, since the catheter costs are a significant part of the overall cost of the procedure.[0030]
• The stepped compliance curve balloons should be made of a thermoplastic polymer material which has a high strength, and gives a low compliance balloon at pressures above about 15 atmospheres. For purposes of this application “low compliance” is considered to correspond to a diameter increase of no more than 0.1 mm per increased atmosphere of pressure, preferably less than 0.06 mm/atm. Suitably the balloon polymer is poly(ethylene terephthalate) (PET) of initial intrinsic viscosity of at least 0.5, more preferably 0.7-0.9. Other high strength polyester materials, such as poly(ethylene napthalenedicarboxylate) (PEN), nylons such as nylon 11 or[0031]nylon 12, thermoplastic polyimides and high strength engineering thermoplastic polyurethanes such as Isoplast 301 sold by Dow Chemical Co., are considered suitable alternative materials. Desirably the balloon is blown in a way which will give a wall strength of at least 18,000 psi, preferably 20 greater than 20,000 psi. Techniques for manufacturing balloons with such wall strengths are well known.
• After being blown, the balloon is provided with a stepped compliance curve by annealing the balloon for a short time after blowing at a pressure at or only slightly above ambient and at a temperature which causes the blown balloon to shrink. The process is described in U.S. Pat. No. 5,348,538. However, the balloons of the invention are desirably constructed with a greater difference between the low pressure and high pressure linear regions of the compliance curve so that the transition between the two regions results in a step-up of diameter of the balloon of at least 0.4 mm. This is accomplished by blowing the balloon to the larger diameter and then shrinking to a greater extent than was done in the specific illustrative examples of U.S. Pat. No. 5,348,538. The amount of shrinkage is controlled by the pressure maintained in the balloon during annealing and the temperature and time of the annealing. For a balloon made from 0.74 intrinsic viscosity PET, the blowing pressure is suitably in the range 200-400 psi, and temperature is suitably in the range of 90-100C, and the annealing pressure is in the range of 0-20, preferably 5-10 psi at 90-100C for 3-10 5 seconds.[0032]
• In a further aspect of the invention, the balloons employed in the inventive process are configured so that a first portion of the body of the balloon has a stepped compliance curve and the remainder of the balloon has an unstepped compliance curve, the low pressure regions of the compliance curves of both the first portion and the remainder portion(s) being generally collinear. By this means the length of the balloon which will expand and seat the stent will be smaller than the length which is used to accomplish predilation. Since many stents are in the 7-10 mm length range whereas predilation balloons are desirably 15-20 mm or even longer, this shorter configuration for the portion which will step-up to a larger diameter (“hyper-extend”) is desirable so that the hyper-extension will not overlap tissue which is unreinforced by the stent. Two balloons of this preferred configuration are shown, mounted on catheters, in FIGS. 6 and 8.[0033]
• In FIG. 6, the[0034]balloon30 is shown in its filly expanded high pressure configuration, mounted on acatheter28. The balloon is mounted on the catheter at balloon end regions31,33, located on opposite ends of the balloon body. As shown schematically in FIG. 7, this balloon is blown in a mold of the general shape of the balloon in FIG. 6 and then the annealing step is performed on theenlarged portion32 by dipping the balloon in the direction indicated byarrows36 to level A in a bath of heated water or other suitable heated fluid while the balloon is pressurized at low pressure, for instance 0-10 psi, so thatonly portion32 is annealed. After annealingportion32 will be shrunken so that, the configuration of the balloon will be substantially linear and will expand generally linearly until pressurized above about 8-12 atm. At higher pressures, theportion34 ofballoon30 will continue to expand along the same generally linear curve butportion32 will rapidly expand until the balloon configuration is restored to shape shown in FIG. 6, after which the expansion profile ofportion32 will level out again to a non-compliant curve but at a substantial increase in absolute diameter relative to the diameter ofportion34. Balloons of this configuration, have been used to produce compliance curves as shown in FIG. 11.
• It should be understood that while FIG. 6 shows[0035]portion32 ofballoon30 mounted distally oncatheter28,balloon30 may instead be mounted withportion34 mounted distally without departing from the invention hereof.
• If the balloon of FIG. 6 is used to deliver and install the stent, the[0036]catheter28 will have to be backed up a short distance to centerportion32 under the stent after expansion ofballoon30 sufficiently to bring it into contact with the lesion but before theballoon portion32 is fully expanded to fully dilate the lesion and set the stent. This can be accomplished by providing marker bands (not shown) on the portion of the catheter shaft under the balloon to indicate the proximal and distal boundaries ofportion32.
• In the alternate embodiment of FIG. 8, the[0037]balloon40, mounted oncatheter38, has a hyper-extensible portion42 located centrally on the balloon body. The balloon is mounted on the catheter atballoon end regions41,43, located on opposite ends of the balloon body. Therefore, after installation of the stent, the high pressure stent setting step can be performed immediately without repositioning the catheter and without risking damage to tissue unreinforced by the stent. This balloon is blown in a mold having a configuration which is substantially the shape shown in FIG. 8. To anneal and shrinkportion42 to the diameter ofportions44,46, heating during annealing may be confined to thecentral portion42, suitably by heating with a hot air stream, using baffles to protect theend regions44,46 from the air stream. Alternatively, as shown schematically in FIG. 9, theballoon40 is dipped in the direction ofarrows47 to level A in a heated bath to fully immerseportions42 and46, untilportion42 has reached the diameter ofportion44. At thispoint portion46 will be shrunk to a diameter less thanportion44.Balloon40 is then dipped into a heated bath in the direction ofarrows49 to level B so thatonly portion46 is immersed and thenportion46 is reblown to the diameters ofportion44 andshrunken portion42. This reblowing step may be accomplished either with the aid of a mold or by free-blowing.
• Referring now to the graph shown in FIG. 10, in which pressure in atmospheres is plotted on the x-axis and balloon diameter in millimeters is plotted on the y-axis. The compliance curves of several balloons have been manufactured in accordance with U.S. Pat. No. 5,348,538 and useful in the practice of this invention have been plotted on this graph and compared to a conventional 3.5 mm angioplasty balloon Q of the same PET material. The stepped compliance curve balloons, X, Y and Z, plotted on this graph had nominal diameters prior to being shrunk of 3.0, 3.5 and 4.0 millimeters, respectively.[0038]
• FIG. 11 is a graph of the compliance curves of a balloon of the type shown as[0039]balloon30 in FIG. 6. Curve11ais the compliance curve ofportion32 ofballoon30 and curve11bis the compliance curve of theportion34 ofballoon30. The balloon was made from PET of 0.74 intrinsic viscosity and, after blowing had a body wall thickness of 0.0013 inches.Portion32 thereof was annealed by dipping in a 95C water bath for 5 seconds, while pressurized at 10 atm pressure, to shrinkportion32 to the diameter ofportion34. The balloon was then mounted on a catheter and the compliance curve obtained by incrementally inflating the balloon until burst, measuring the diameter of bothportions32 and34 at each incremental pressure.
• With regard to definitions, FIG. 11 can be referred to for illustration of what is meant by “generally linear” with reference to the portions of curve[0040]11abetween 3 and 10 atm and again between about 13 and 26 atm. Curve11bis considered generally linear through out its entire length. “Generally collinear” is considered to encompass divergences between two curves of no more than about 0.2 atm, preferably less than 0.15 mm divergence between the two curves. Curves11aand11bare “generally collinear” in the range from 3 atm to about 10 atm.
• The invention may also be practiced by use of dual layer balloons such as described in co-pending U.S. application Ser. No. 08/243,473, filed May 16, 1994 as a continuation of now abandoned U.S. application Ser. No. 07/927,062, filed Aug. 8, 1992, incorporated herein by reference, and in U.S. Pat. No. 5,358,487, incorporated herein by reference. Suitably both balloons of the dual layer balloons are low compliance balloons designed with the outer balloon portion larger by at least 0.25 mm than the inner portion and the inner balloon designed to burst at a pressure below about 15 atm so that the compliance curve follows the inner balloon portion until it reaches burst diameter and then, after the inner balloon bursts, the outer balloon becomes inflated and can be expanded to a larger diameter than the burst diameter of the inner balloon.[0041]
• Although the present invention has been described in terms of specific embodiments, it is anticipated that alterations and modifications thereof will no doubt be come apparent to those skilled in the art. It is therefore intended that the following claims be interpreted as covering all such alterations and modifications as fall within the true spirit and scope of the invention.[0042]

Claims (10)

We claim:

1. A balloon for a medical catheter, the balloon having a molded configuration with a longitudinal axis, the balloon configuration, when viewed in longitudinal quarter section, comprises:

first and second waist segments spaced longitudinally apart from each other and defining a longitudinally intermediate region therebetween, each waist segment being bonded to the catheter,

first and second step segments within said intermediate region and spaced longitudinally apart from each other, each being and spaced radially from the longitudinal axis and from said waist segments, the second step segment being spaced radially from the longitudinal axis a greater distance than the first segment,

a first diverging portion extending between the first waist segment and the first step segment,

a second diverging portion extending between the first step segment and the second step segment, and

a transition portion extending between the second step segment and the second waist segment.

2. A balloon as inclaim 1 wherein said balloon transition portion comprises

a third step segment, within said intermediate region and spaced longitudinally apart from the second step segment and from the second waist segment in a region therebetween,

a third diverging portion extending between the second step segment and the third step segment, and

a fourth diverging portion extending between the third step segment and the second waist segment.

3. A balloon as inclaim 1 wherein said balloon transition portion consists of a third diverging portion extending between the second step segment and the second waist segment and which, when moving from the second step segment to the second waist portion, continuously decreases in distance from the longitudinal axis.

4. A balloon as inclaim 1 wherein said step portions extend generally parallel to the longitudinal axis.

5. A balloon catheter assembly comprising a an elongate tubular body, a distal end and a balloon as inclaim 1 mounted thereon near the distal end thereof.

6. A balloon catheter as inclaim 5 wherein the balloon is mounted on the catheter with the first step segment located proximally along the catheter relative to the second step segment.

7. A balloon catheter assembly as inclaim 5 wherein the balloon is mounted on the catheter with the first step segment located distally along the catheter relative to the second step segment.

8. A balloon catheter as inclaim 5 wherein said balloon transition portion consists of a third diverging portion extending between the second step segment and the second waist segment and which, when moving from the second step segment to the second waist portion, continuously decreases in distance from the longitudinal axis.

9. A balloon catheter assembly as inclaim 5 wherein said balloon transition portion comprises

a third step segment, within said intermediate region and spaced longitudinally apart from the second step segment and from the second waist segment in a region therebetween,

a third diverging portion extending between the second step segment and the third step segment, and

a fourth diverging portion extending between the third step segment and the second waist segment.

10. A balloon catheter assembly as inclaim 5 further comprising an expandable stent mounted on the catheter over the balloon.

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