US 20050251195 A1
A balloon catheter suitable for deploying a stent utilizes a balloon molded with a stepped diameter profile.
11. An assembly comprising
a balloon catheter having a balloon mounted thereon near the distal end, and
a stent mounted over at least a portion of the balloon,
wherein the balloon comprises a structural layer formed of a polyurethane.
12. An assembly as in
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 step segment being 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 step 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.
13. The assembly of
14. The assembly of
15. An assembly comprising
a balloon catheter having an elongate tubular body, a distal end and a balloon mounted thereon near the distal end, and
a stent mounted over at least a portion of the balloon,
wherein the balloon is formed of material consisting essentially of a polyurethane.
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.
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.
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.
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.
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:
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.
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.
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.”
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.
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.
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.
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.
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.
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 stent 17 in place across the dilated lesion, as shown in
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, catheter 10 is reinserted and expanded to a retouch pressure, typically above 9 atm and preferably in the range of 12-20 atm.
Alternatively, catheter 10 may be employed as a delivery catheter. In the specific embodiment illustrated in
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.
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 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 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 90-100 C, and the annealing pressure is in the range of 0-20, preferably 5-10 psi at 90-100 C for 3-10 seconds.
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
It should be understood that while
If the balloon of
In the alternate embodiment of
Referring now to the graph shown in
With regard to definitions,
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.
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.