U.S. patent application number 11/726168 was filed with the patent office on 2007-09-13 for balloon catheter with molded stepped balloon.
This patent application is currently assigned to BOSTON SCIENTIFIC SCIMED, INC.. Invention is credited to Lixiao Wang.
Application Number | 20070213663 11/726168 |
Document ID | / |
Family ID | 23571933 |
Filed Date | 2007-09-13 |
United States Patent
Application |
20070213663 |
Kind Code |
A1 |
Wang; Lixiao |
September 13, 2007 |
Balloon catheter with molded stepped balloon
Abstract
A balloon catheter suitable for deploying a stent utilizes a
balloon molded with a stepped diameter profile.
Inventors: |
Wang; Lixiao; (Maple Grove,
MN) |
Correspondence
Address: |
VIDAS, ARRETT & STEINKRAUS, P.A.
SUITE 400, 6640 SHADY OAK ROAD
EDEN PRAIRIE
MN
55344
US
|
Assignee: |
BOSTON SCIENTIFIC SCIMED,
INC.
Maple Grove
MN
55311
|
Family ID: |
23571933 |
Appl. No.: |
11/726168 |
Filed: |
March 21, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11181215 |
Jul 14, 2005 |
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11726168 |
Mar 21, 2007 |
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10153277 |
May 21, 2002 |
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11181215 |
Jul 14, 2005 |
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09774725 |
Jan 31, 2001 |
6402778 |
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10153277 |
May 21, 2002 |
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09396841 |
Sep 15, 1999 |
6290485 |
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09774725 |
Jan 31, 2001 |
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08931190 |
Sep 16, 1997 |
5980532 |
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09396841 |
Sep 15, 1999 |
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08397615 |
Mar 2, 1995 |
5749851 |
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08931190 |
Sep 16, 1997 |
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09709033 |
Nov 8, 2000 |
6352551 |
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11726168 |
Mar 21, 2007 |
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Current U.S.
Class: |
604/96.01 |
Current CPC
Class: |
A61M 25/10 20130101;
A61M 25/1002 20130101; A61F 2/958 20130101; A61M 25/104 20130101;
A61M 2025/1075 20130101; A61F 2250/0039 20130101; A61M 2025/1059
20130101; A61M 25/1029 20130101 |
Class at
Publication: |
604/096.01 |
International
Class: |
A61M 29/02 20060101
A61M029/02 |
Claims
1-10. (canceled)
11. A balloon catheter for use in vascular anatomy, the balloon
catheter comprising: a catheter body, the catheter body being
movably disposed about a guidewire; and a balloon positioned at a
distal portion of the catheter body, the balloon including a
balloon outer skin, the balloon having a first section with a first
average diameter, and second section with a second average diameter
that is smaller than the first average diameter, the first and
second sections being coupled by a transition section that has a
geometry and diameter transitioning between the first section and
the second section.
12. The catheter of claim 11, further comprising: a radiopaque
marker positioned at the balloon.
13. The balloon catheter of claim 11, wherein the balloon is made
of any suitable polymer, non-polymer or composite material
thereof.
14. The balloon catheter of claim 11, wherein the first average
diameter is substantially the same along an entire length of the
first section.
15. The balloon catheter of claim 11, wherein the second average
diameter is substantially the same along an entire length of the
second section.
16. The balloon catheter of claim 11, wherein at least a portion of
the first section is tapered.
17. The balloon catheter of claim 11, wherein at least a portion of
the second section is tapered.
18. The balloon catheter of claim 11, wherein a radiopaque marker
is positioned at a proximal section of the balloon.
19. The balloon catheter of claim 11, wherein a radiopaque marker
is positioned at a distal portion of the balloon.
20. The balloon catheter of claim 11, wherein the catheter body is
part of an over-the-wire catheter system.
21. The balloon catheter of claim 11, wherein the catheter body is
part of a rapid-exchange catheter system.
22. The balloon catheter of claim 11, wherein the balloon catheter
is configure for use in an angioplasty application in a vessel with
a stenting procedure.
23. The balloon catheter of claim 11, wherein the balloon catheter
is configure for use in an angioplasty application in a vessel
without a stenting procedure.
24. The balloon catheter of claim 11, wherein the balloon catheter
is configured for use with a stent for a stent delivery
application.
25. The balloon catheter of claim 11, wherein the balloon catheter
is used as a stent delivery system with a stent designed for any
vascular anatomy.
26. The balloon catheter of claim 11, wherein the first section has
a larger length than a length of the second section.
27. The balloon catheter of claim 11, wherein a length of the
second is greater than a length of the first section.
28. The balloon catheter of claim 11, wherein the lengths of the
first and second sections are about the same.
29. An angioplasty balloon catheter for use in vascular anatomy,
comprising: an angioplasty catheter body, the catheter body being
movably disposed about a guidewire; and a tubular balloon coupled
to a distal end of the angioplasty catheter body and including, a
shaped balloon skin, the balloon having a shaped outer geometry and
size to reduce vessel damage when positioned at a point of a
vessel.
30. The balloon catheter of claim 29, further comprising: a
radiopaque marker positioned at the tubular balloon.
31. The balloon catheter of claim 29, wherein the balloon is made
of any suitable polymer, non-polymer or composite material
thereof.
32. The balloon catheter of claim 29, wherein the balloon includes
a first section with a first average diameter, and a second section
with a second average diameter.
33. The balloon catheter of claim 32, wherein the first average
diameter is substantially the same along an entire length of the
first section.
34. The balloon catheter of claim 32, wherein the second average
diameter is substantially the same along an entire length of the
second section.
35. The balloon catheter of claim 32, wherein at least a portion of
the first section is tapered.
36. The balloon catheter of claim 32, wherein at least a portion of
the second section is tapered.
37. The balloon catheter of claim 29, wherein a radiopaque marker
is positioned at a proximal section of the balloon.
38. The balloon catheter of claim 29, wherein a radiopaque marker
is positioned at a distal portion of the balloon.
39. The balloon catheter of claim 29, wherein the catheter body is
part of an over-the-wire catheter system.
40. The balloon catheter of claim 29, wherein the catheter body is
part of a rapid-exchange catheter system.
41. The balloon catheter of claim 29, wherein the balloon catheter
is configure for use in an angioplasty application in a vessel with
a stenting procedure.
42. The balloon catheter of claim 29, wherein the balloon catheter
is configure for use in an angioplasty application in a vessel
without a stenting procedure.
43. The balloon catheter of claim 29, wherein the balloon catheter
is configured for use with a stent for a stent delivery
application.
44. The balloon catheter of claim 29, wherein the balloon catheter
is used as a stent delivery system with a stent designed for any
vascular anatomy.
45. The balloon catheter of claim 32, wherein the first section has
a larger length than a length of the second section.
46. The balloon catheter of claim 32, wherein a length of the
second is greater than a length of the first section.
47. The balloon catheter of claim 32, wherein the lengths of the
first and second sections are about the same.
48. A stent delivery device, comprising: a catheter body, the
catheter body being movably disposed about a guidewire; a balloon
positioned at a distal portion of the catheter body, the balloon
including a balloon outer skin, the balloon having a first section
with a first average diameter, and second section with a second
average diameter that is smaller than the first average diameter,
the first and second sections being coupled by a transition section
that has a geometry and diameter transitioning between the first
section and the second section; and a vascular stent positioned on
an exterior of the balloon exterior.
49. The device of claim 48, further comprising: a radiopaque marker
positioned at the balloon.
50. The device of claim 48, wherein the balloon is made of any
suitable polymer, non-polymer or composite material thereof.
51. The device of claim 48, wherein the first average diameter is
substantially the same along an entire length of the first
section.
52. The device of claim 48, wherein the second average diameter is
substantially the same along an entire length of the second
section.
53. The device of claim 48, wherein at least a portion of the first
section is tapered.
54. The device of claim 48, wherein at least a portion of the
second section is tapered.
55. The device of claim 48, wherein a radiopaque marker is
positioned at a proximal section of the balloon.
56. The device of claim 48, wherein a radiopaque marker is
positioned at a distal portion of the balloon.
57. The device of claim 48, wherein the catheter body is part of an
over-the-wire catheter system.
58. The device of claim 48, wherein the catheter body is part of a
rapid-exchange catheter system.
59. The device of claim 48, wherein the device is used for any
vascular anatomy.
60. The device of claim 48, wherein the first section has a larger
length than a length of the second section.
61. The device of claim 48, wherein a length of the second is
greater than a length of the first section.
62. The device of claim 48, wherein the lengths of the first and
second sections are about the same.
63. A method of treating vascular anatomy, comprising: providing a
catheter that includes a balloon with a transition section that
couples a first section with a second section, the transition
section having a geometry and diameter transitioning from a greater
diameter of the first section to a lesser diameter the second
section; mounting a stent in a non-expanded state on an exterior of
the balloon; positioning the catheter with the stent in a
non-expanded state at a region of the vascular anatomy; inflating
the balloon and deploying the stent in an expanded state at the
region of vascular anatomy; and removing the catheter from the
vascular anatomy.
Description
[0001] This is a continuation of application Ser. No. 10/153,277,
filed May 21, 2002, incorporated herein by reference which 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 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.
BACKGROUND OF THE INVENTION
[0002] 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.
[0003] 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.
[0004] 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.
[0005] 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: TABLE-US-00001 U.S. Pat. No. 4733665
Palmaz U.S. Pat. No. 4776337 Palmaz U.S. Pat. No. 5195984 Schatz
U.S. Pat. No. 5234457 Andersen U.S. Pat. No. 5116360 Pinchuck et al
U.S. Pat. No. 5116318 Hillstead U.S. Pat. No. 4649922 Wiktor U.S.
Pat. No. 4655771 Wallsten U.S. Pat. No. 5089006 Stiles U.S. Pat.
No. 5007926 Derbyshire U.S. Pat. No. 4705517 DiPisa, Jr. U.S. Pat.
No. 4740207 Kreamer U.S. Pat. No. 4877030 Beck et al U.S. Pat. No.
5108417 Sawyer U.S. Pat. No. 4923464 DiPisa, Jr U.S. Pat. No.
5078726 Kreamer U.S. Pat. No. 5171262 MacGregor U.S. Pat. No.
5059211 Stack et al U.S. Pat. No. 5104399 Lazarus U.S. Pat. No.
5104404 Wolff U.S. Pat. No. 5019090 Pinchuk U.S. Pat. No. 4954126
Wallsten U.S. Pat. No. 4994071 MacGregor U.S. Pat. No. 4580568
Gianturco U.S. Pat. No. 4681110 Wiktor U.S. Pat. No. 4800882
Gianturco U.S. Pat. No. 4830003 Wolff et al U.S. Pat. No. 4856516
Hillstead U.S. Pat. No. 4922905 Strecker U.S. Pat. No. 4886062
Wiktor U.S. Pat. No. 4907336 Gianturco U.S. Pat. No. 4913141
Hillstead U.S. Pat. No. 5092877 Pinchuk U.S. Pat. No. 5123917 Lee
U.S. Pat. No. 5116309 Coll U.S. Pat. No. 5122154 Rhodes U.S. Pat.
No. 5133732 Wiktor U.S. Pat. No. 5135536 Hillstead U.S. Pat. No.
5282824 Gianturco U.S. Pat. No. 5292331 Boneau U.S. Pat. No.
5035706 Gianturco et al U.S. Pat. No. 5041126 Gianturco U.S. Pat.
No. 5061275 Wallsten et al U.S. Pat. No. 5064435 Porter U.S. Pat.
No. 5092841 Spears U.S. Pat. No. 5108416 Ryan et al U.S. Pat. No.
4990151 Wallsten U.S. Pat. No. 4990155 Wilkoff U.S. Pat. No.
4969890 Sugita et al U.S. Pat. No. 4795458 Regan U.S. Pat. No.
4760849 Kropf U.S. Pat. No. 5192297 Hull U.S. Pat. No. 5147385 Beck
et al U.S. Pat. No. 5163952 Froix
[0006] 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.
[0007] 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.
[0008] 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."
SUMMARY OF THE INVENTION
[0009] 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.
[0010] 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.
[0011] 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.
[0012] 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.
BRIEF DESCRIPTION OF DRAWINGS
[0013] 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.
[0014] FIG. 2 is a view of a vessel as in FIG. 1 after installation
of a stent but before a "retouch" procedure.
[0015] 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.
[0016] FIG. 4 is a view as in FIG. 3 with the balloon expanded to
install the stent and further dilate the lesion.
[0017] FIG. 5 is a view as in FIG. 3 after completion of the
procedure of FIG. 3.
[0018] FIG. 6 is a side view the distal end of a catheter having an
alternate balloon of the invention, shown in hyper-extended
form.
[0019] FIG. 6a is a side distal view of a catheter as in FIG. 6,
but with the balloon mounted in reverse longitudinal
orientation.
[0020] FIG. 7 is a schematic illustration depicting the process
stages for preparing a balloon as in FIG. 6.
[0021] FIG. 8 is a view of a catheter as in FIG. 6 except that a
second alternate balloon of the invention is depicted.
[0022] FIG. 9 is a schematic illustration depicting the process
stages for preparing a balloon as in FIG. 8.
[0023] FIG. 10 is a graph showing the compliance curves of several
balloons of the type shown in FIGS. 1, 3 and 4 compared to a
conventional 3.5 mm angioplasty balloon of the same material.
[0024] FIG. 11 is a graph of the compliance curves of a balloon of
the type shown in FIG. 6.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0025] 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.
[0026] Referring to FIGS. 1-5, the process of the invention is
illustrated by these Figures. In FIG. 1, a catheter 10 carrying a
balloon 12 on the distal end thereof has been inserted over guide
wire 13 into a vessel 14 and fed to a lesion 16 where it is used to
predilate the lesion to a predetermined diameter, typically about
2.5 mm. In the process of the invention, balloon 12 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 the
catheter 10 is removed from the vessel 14.
[0027] 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 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.
[0028] 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.
[0029] Alternatively, catheter 10 may be employed as a delivery
catheter. In the specific embodiment illustrated in FIGS. 3-4, an
unexpanded stent 18 has been mounted on the catheter 10 over
balloon 12 after catheter 10 has been used to predilate the lesion
and has been removed from the lesion. Catheter 10 is then
reinserted into the vessel 14 and located across the lesion (FIG.
3). Balloon 12 is then reinflated as shown in FIG. 4 to expand and
install the stent 18 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 the balloon 12 follows a low compliance
curve above the transition region, the pressure can safely be
increased above 12 atm so as to firmly seat stent 18 without having
to undergo "retouch." Typically the balloon 12 will be capable of
inflation to at least as high as 20 atm.
[0030] FIG. 5 depicts the stent 18 in place after high pressure
dilation. A similar result is obtained if the catheter 10 is used
for predilation and for "retouch" but not for stent installation.
It should be noted that the specific configuration of the stents 17
and 18 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.
[0031] 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.
[0032] 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.
[0033] 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.
[0034] 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.
[0035] In FIG. 6, the balloon 30 is shown in its fully expanded
high pressure configuration, mounted on a catheter 28. The balloon
is mounted on the catheter at balloon end regions 31, 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 the
enlarged portion 32 by dipping the balloon in the direction
indicated by arrows 36 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 that only portion 32 is
annealed. After annealing portion 32 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, the portion 34 of balloon 30 will continue to
expand along the same generally linear curve but portion 32 will
rapidly expand until the balloon configuration is restored to shape
shown in FIG. 6, after which the expansion profile of portion 32
will level out again to a non-compliant curve but at a substantial
increase in absolute diameter relative to the diameter of portion
34. Balloons of this configuration have been used to produce
compliance curves as shown in FIG. 11.
[0036] It should be understood that while FIG. 6 shows portion 32
of balloon 30 mounted distally on catheter 28, balloon 30 may
instead be mounted with portion 34 mounted distally without
departing from the invention hereof. This orientation is depicted
in FIG. 6a.
[0037] If the balloon of FIG. 6 is used to deliver and install the
stent, the catheter 28 will have to be backed up a short distance
to center portion 32 under the stent after expansion of balloon 30
sufficiently to bring it into contact with the lesion but before
the balloon portion 32 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 of portion
32.
[0038] In the alternate embodiment of FIG. 8, the balloon 40,
mounted on catheter 38, has a hyper-extensible portion 42 located
centrally on the balloon body. The balloon is mounted on the
catheter at balloon end regions 41, 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 shrink portion 42 to the diameter of portions
44, 46, heating during annealing may be confined to the central
portion 42, suitably by heating with a hot air stream, using
baffles to protect the end regions 44, 46 from the air stream.
Alternatively, as shown schematically in FIG. 9, the balloon 40 is
dipped in the direction of arrows 47 to level A in a heated bath to
fully immerse portions 42 and 46, until portion 42 has reached the
diameter of portion 44. At this point portion 46 will be shrunk to
a diameter less than portion 44. Balloon 40 is then dipped into a
heated bath in the direction of arrows 49 to level B so that only
portion 46 is immersed and then portion 46 is reblown to the
diameters of portion 44 and shrunken portion 42. This reblowing
step may be accomplished either with the aid of a mold or by
free-blowing.
[0039] 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.
[0040] FIG. 11 is a graph of the compliance curves of a balloon of
the type shown as balloon 30 in FIG. 6. Curve 11a is the compliance
curve of portion 32 of balloon 30 and curve 11b is the compliance
curve of the portion 34 of balloon 30. The balloon was made from
PET of 0.74 intrinsic viscosity and, after blowing had a body wall
thickness of 0.0013 inches. Portion 32 thereof was annealed by
dipping in a 95 C water bath for 5 seconds, while pressurized at 10
atm pressure, to shrink portion 32 to the diameter of portion 34.
The balloon was then mounted on a catheter and the compliance curve
obtained by incrementally inflating the balloon until burst,
measuring the diameter of both portions 32 and 34 at each
incremental pressure.
[0041] 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 11a between 3 and 10 atm and again between
about 13 and 26 atm. Curve 11b is 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. Curves 11a and 11b are "generally collinear" in the range
from 3 atm to about 10 atm.
[0042] 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.
[0043] 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.
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