U.S. patent application number 14/546696 was filed with the patent office on 2015-03-05 for side branch balloon.
The applicant listed for this patent is TriReme Medical, LLC. Invention is credited to Jayson DE LOS SANTOS, Tanhum FELD, Eitan KONSTANTINO, Nadia P. MATOV, Guillermo PIVA.
Application Number | 20150066070 14/546696 |
Document ID | / |
Family ID | 43309197 |
Filed Date | 2015-03-05 |
United States Patent
Application |
20150066070 |
Kind Code |
A1 |
MATOV; Nadia P. ; et
al. |
March 5, 2015 |
SIDE BRANCH BALLOON
Abstract
An improved balloon catheter structure includes a beveled distal
tip, a reinforced distal portion, and an elastic or split sleeve
over at least a portion of the balloon. The balloon may have a
short length and a marker at its midline. The catheters are
particularly useful for crossing through stent walls at vessel
bifurcations.
Inventors: |
MATOV; Nadia P.; (San Jose,
CA) ; DE LOS SANTOS; Jayson; (Union City, CA)
; PIVA; Guillermo; (San Ramon, CA) ; FELD;
Tanhum; (Moshav Merhavya, IL) ; KONSTANTINO;
Eitan; (Orinda, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TriReme Medical, LLC |
Pleasanton |
CA |
US |
|
|
Family ID: |
43309197 |
Appl. No.: |
14/546696 |
Filed: |
November 18, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12795911 |
Jun 8, 2010 |
|
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14546696 |
|
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|
61185124 |
Jun 8, 2009 |
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Current U.S.
Class: |
606/194 |
Current CPC
Class: |
A61M 2025/1093 20130101;
A61M 25/0108 20130101; A61M 2025/1045 20130101; A61M 2025/0059
20130101; A61F 2002/9583 20130101; A61M 2025/1079 20130101; A61M
25/0068 20130101; A61M 25/10 20130101; A61M 25/104 20130101; A61M
2025/1081 20130101; A61F 2/958 20130101; A61M 2025/1068 20130101;
A61F 2002/061 20130101 |
Class at
Publication: |
606/194 |
International
Class: |
A61M 25/10 20060101
A61M025/10 |
Claims
1. A balloon catheter having improved crossing characteristics,
said catheter comprising a catheter body having a distal end, a
proximal end, and an inflatable balloon near the distal end,
wherein a distal tip is asymmetrically beveled relative to a
longitudinal axis of the catheter body, and wherein the catheter
body comprises a braided shaft section to torsionally reinforce the
distal portion thereof, thereby improving rotation of the beveled
distal tip when the catheter body is placed in vasculature.
2. A balloon catheter as in claim 1, wherein at least a portion of
the balloon is covered with an expandable sleeve.
3. A balloon catheter as in claim 2, wherein the expandable sleeve
covers at least a distal region of the balloon to enhance column
strength of a distal region of the catheter shaft and to present a
smooth forward-facing surface as the catheter is advanced through
the vasculature.
4. A balloon catheter as in claim 2, wherein the expandable sleeve
covers at least a proximal portion of the balloon to enhance the
column strength of a proximal region of the catheter body and to
present a smooth proximal-facing surface as the catheter is
withdrawn through the vasculature.
5. A balloon catheter as in claim 2, wherein the sleeve is elastic
to expand and contract over the balloon as the balloon is inflated
and deflated.
6. A balloon catheter as in claim 2, wherein the sleeve splits as
the balloon is inflated.
7. A balloon catheter as in claim 1, wherein the balloon has a
length when inflated in the range from 3 mm to 6 mm and a
radiopaque marker at its middle.
8. A balloon catheter as in claim 7, wherein the balloon is
non-distensible and has a diameter in the range from 1 mm to 5 mm
when fully inflated.
9. A balloon catheter as in claim 1, wherein the braided shaft
section is attached to a proximal shaft section comprising a
hypotube.
10. A balloon catheter as in claim 1, wherein the braided shaft
section is attached to a proximal shaft section comprising a
polymeric balloon catheter shaft.
Description
CROSS-REFERENCE
[0001] This application is a continuation of U.S. patent
application Ser. No. 12/795,911 (Attorney Docket No. 32164-710.201,
previously 022246-001510US), filed on Jun. 8, 2010, which claimed
the benefit of Provisional Application No. 61/185,124 (Attorney
Docket No. 022246-001500US), filed on Jun. 8, 2009, the full
disclosure of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to medical methods and
devices, more specifically to medical dilatation balloon
catheters.
[0004] Balloon catheters often need to cross through luminal
obstructions, such as stent struts, occlusions, and tight turns.
One particular obstructions is encountered when treating stenosis
present at an arterial bifurcation. Treatment of a bifurcation site
is challenging since they are Y-shaped and require a different
approach from a simple lesion treated with a regular cylindrical
stent. When treating stenosis at bifurcation, it is common practice
to use a conventional cylindrical stent and, after implantation,
manipulate the stent's geometry using a balloon catheter to
accommodate the bifurcated anatomy.
[0005] The usual practice is to place a cylindrical stent in the
main vessel across the bifurcation ostium which typically results
in partially blocking ("jailing") the side branch ostium with stent
struts. The struts may be opened by advancing an angioplasty
balloon over a guide wire through the stent struts so that a distal
portion of the balloon is inside the side branch. If all goes well,
the balloon may then be inflated to open struts and clear the
ostium. Optionally, if the side branch is diseased or not expanded
widely enough, a second stent may be delivered into the side branch
and placed with its proximal end as close as possible to the main
vessel stent in an attempt to place the stents in a Y-pattern.
[0006] Crossing into the side branch with an angioplasty balloon,
however, can be difficult. The catheter tip and/or balloon that is
threaded on a guide wire is often caught by the stent struts and
the catheter cannot be advanced. This phenomenon is enhanced
because the guide wire always has bias and is leaning on the
nearest stent strut. The distal tips of balloon catheters are not
designed to pass obstructions such as stent struts. The tips are
usually soft and atraumatic to provide smooth passage without
scratching the artery walls during delivery. Soft tips are prone to
deformation and are more difficult to push past struts and other
obstructions. The clearance between the catheter tip and the
guidewire is usually large, again exacerbating the difficulty of
pushing the tip past obstructions.
[0007] Conventional balloon catheter shafts are not designed to
transmit torque, particularly over their distal segments near the
balloon. Often, the distal-most 25-30 cm of the shaft is made from
a soft, low profile and thin wall polymer material which is very
ineffective for torque transmission. In addition, the majority of
the torque is lost in the inflatable shell or the balloon which is
made of a thin polymer shell (typically nylon or pebax) and is
floating over the distal end of the catheter. Attempts to rotate
the catheter will result in twisting of the polymer shaft followed
by unfolding of the balloon pleats (referred to as the "candy
wrapper effect") and increasing profile and risk of damaging the
catheter without meaningful torque transmission to the tip.
Therefore, when the catheter tip is caught in a stent strut or
other obstruction, the operator can only move the catheter back and
forth, poking the strut and hoping that the catheter will somehow
be able to overcome and cross it. This process is unpredictable and
uncontrolled, both in terms of success and of the possible damage
caused. Inability to cross is documented in the literature and is a
common issue in bifurcations and other occlusions.
[0008] The outer surface of a conventional folded balloon can also
catch on stent struts. Angioplasty balloons are folded in order to
assume a small diameter for delivery. These folds or pleats often
catch on stent struts if advanced through a cell. The tendency of
the balloon to catch is worsened when the catheter turns from the
main vessel into the side branch, causing the balloon to bend and
partially unwrapping the pleats. In some cases the balloon tip may
also bend and twist, further hindering the progress of the
catheter.
[0009] When treating bifurcations, it is common practice to dilate
the side-branch ostium. Clinical studies have shown a high
correlation between post procedure (acute) ostium size and long
term patency of the side branch vessel. However, large ostium
dilations are not easily achieved. Measurements of human
bifurcation anatomy show that the ostium size is significantly
bigger than the side branch diameter. For side branch vessels
between 2.5 to 3.0 mm diameters, the ostium is usually about 0.5 mm
bigger. When using a regular sized balloon, the difference in
diameter between the side-branch ostium and the side-branch can
result in either over expansion in the side branch causing injury
to the side branch or under-deployment in the ostium. Often a
"kissing balloon" technique is performed where two balloons are
deployed in the main vessel. Two balloons, however, can cause
anatomical deformation and excessive pressure in the main vessel.
Furthermore, struts and other stent components are not
advantageously placed. While short balloons could alleviate these
problems, a short balloon would have a tendency to slip and lose
its longitudinal position in the vessel. Therefore, dilation
balloons are typically at least 8 mm in length or are provided with
external blades or cages to prevent slippage.
[0010] A balloon catheter addressing some of the issues noted above
will be desirable. In particular, it would be desirable to provide
a balloon catheter with improved crossability achieved through
adding another degree of control to the operator and a new
dimension to the procedure by adding asymmetric tip design such as
skived, beveled or similar configuration that can be re-oriented by
rotation when facing an obstacle. Enhanced torqueability is a key
element of such balloon catheter.
[0011] 2. Description of the Background Art
[0012] Catheters having beveled or chamfered distal tips are
described in U.S. Pat. Nos. 3,884,242; 5,967,988; 6,010,449;
6,206,852; 6,966,902; and 7,306,575 and in U.S. Publ. Application
No. 2009/024212. Balloon and other catheters having torsionally
reinforced distal ends are described in U.S. Pat. Nos. 4,994,032;
5,827,231; 5,997,487; 6,994,687; and 7,022,106. Catheters having
"short" balloons and having balloons with mid-line markers are
described in U.S. Pat. Nos. 5,295,962; 5,324,261; 5,669,932;
6,692,483; and 6,884,258; and in U.S. Publ. Application Nos.
2004/186560; 2006/100694; 2008/045896; and 2009/048655. Catheters
having sleeves over at least a portion of an angioplasty or other
balloon are described in U.S. Pat. Nos. 5,628,755; 6,068,634;
6,679,900; 6,695,863; 6,699,273; and 6,830,575; and U.S. Publ.
Application Nos. 2005/203463 and 2009/112159.
SUMMARY OF THE INVENTION
[0013] This invention provides balloon catheters having improved
"pushability" (column strength and asymmetric tip design) and
torqueability (torsional stiffness), particularly through the
distal balloon section. The balloon catheters of the present
invention have an improved ability to cross obstacles and
obstructions, such as stent struts and tight turns with improved
physician control, improved ostium expansion, and reduced injury to
the vasculature using the benefits of asymmetric tip design coupled
with torque transmission properties. Such balloon catheters are
useful for a variety of cardiology procedures, including
angioplasty, drug delivery, stent deployment, and the like, and
have particular advantages when employed vascular bifurcations.
[0014] In one embodiment, the balloon catheter tip is formed in
asymmetric manner (e.g. beveled, asymmetrically tapered,
differential stiffness across the circumference of the tip) to
allow improved crossability overcoming obstacles, such as stent
struts, by rotating and realigning the asymmetric tip relative to
the obstruction. By "beveled", it is meant that the distal tip of
the catheter has a at least one planar or non-planar surface at its
leading end, where at least a portion of the surface is at a
non-perpendicular angle relative to the axis of the catheter body
typically from 30.degree. to 70.degree.. Usually, the leading end
is formed by a planar "cut" across the distal tip. In other cases
there may be two or more planar cuts to form facets, each of which
is at an angle relative to the axis of the catheter body. In other
instances, the beveled end could have one or more non-planar
surfaces or facets, at least some of which are inclined relative to
the catheter body axis.
[0015] In one embodiment, the balloon catheter shaft is designed to
transmit torque applied by an operator so that the distal tip can
be rotated. Combination of the beveled tip and improved torsional
stiffness (torque transmission) improves the crossing properties
more than either feature alone.
[0016] In one embodiment, the balloon catheter comprises a "torque
bridge" to allow torque delivery through the balloon region of the
catheter body. The torque bridge can be in a form of cylindrical
polymer sleeve disposed over or attached to at least a portion of
the balloon and covering the balloon taper and all or part of the
balloon working length. Such sleeves can cause the balloon to
progressively inflate from the proximal end toward the distal end,
which can be advantageous in opening stent cells. Such torque
bridge can take other forms, as well, such as metal reinforcement
for the proximal balloon segment or welding of the inner member to
the balloon proximal leg to improve structural stability during
rotation.
[0017] The torque bridge of the present invention increases
rotational accuracy and stent deployment precision by minimizing
uncontrolled rotation resulting from "unwinding" of the catheter or
portions thereof during balloon inflation and stent deployment. The
torque bridge of the present invention enhances the ability of the
stent to rotate since the system does not absorb torque. Torque
absorption in the prior art is sometimes caused by windup of
catheter components such as balloon folds, distal shaft and, for
catheters having two guidewires side branch wire lumen wrap on the
main vessel wire lumen and others. In one embodiment of the present
invention, the torque bridge is used to enhance rotation and/or
self rotation of bifurcation stents and stent delivery systems by
minimizing torque storage and by minimizing wire wrap which is a
well known limitation of bifurcation delivery systems.
[0018] The torque bridge improves torque transmission and
crossability by covering the balloon folds and applying elastic
pressure to enhance column strength in this area of the balloon.
The structural integrity of the balloon, which otherwise would have
a limited ability to resist forces in circumferential direction,
increases significantly and torque can be delivered through the
balloon segment. Without the sleeve, the balloon (or inflatable
shell) is virtually floating on the catheter attached to the distal
shaft in one end and to the inner member at the distal tip.
Therefore, torque cannot be efficiently delivered through this
segment of the catheter. The sleeve is designed to compress the
folds while still allowing the balloon to inflate and deflate
during the deployment of the balloon and optionally to carry stents
or other components or devices during the deployment. The sleeve
will also reinforce the catheter shaft to improve axial force
transmission and allow push forces to be transmitted all the way to
the balloon to assist in overcoming obstacles. Such improved column
strength and pushability is beneficial for the delivery of all
types of stents including bifurcation stents which requires
rotational alignment. In another embodiment the torque bridge is
used for a stent delivery system of bifurcation stent with side
branch apparatus or hole or crown that needs to be aligned to the
side branch.
[0019] In one embodiment, the balloon catheter comprises a thin
wall cylindrical polymer sleeve attached to the balloon's distal
end and covers the balloon's distal taper and at least part of the
balloon's working length, thus covering the balloon folds creating
a smooth passage through difficult obstacles further improving
crossability and handling. The sleeve can be made of elastic
polymer such as pebax or polyurethane or nylon or alike and can be
coated with lubricious coating to improve crossing. Furthermore,
this polymer sleeve controls balloon inflation by creating an axial
expansion movement in addition to the conventional radial
expansion. This is particularly beneficial in treating side branch
ostiums.
[0020] In one embodiment the balloon catheter comprises a thin wall
polymer sleeve attached to the balloon's proximal end and covers
the balloon's proximal taper and at least part of the balloon's
working length. This "torque bridge" allows improved torque
delivery all the way to the balloon by elastically constraining the
proximal balloon pleats and eliminating the "candy wrap` effect
thus enhancing the control of the operator. This novel design of
the "torque bridge" enabling rotation of the beveled tip offers
enhanced crossing abilities and overcoming obstacles.
[0021] In one embodiment of this invention, the balloon catheter
comprises of a small ("football shaped") balloon typically with a
working length of 3 to 6 mm sometimes with total lengths of 10 mm,
15 mm, or longer. In specific examples, the balloon will have
distal and proximal tapers having lengths of 2.5 mm to 4 mm on
either side of the working length in the middle. This balloon can
be used to dilate a bifurcation ostium without slipping due to
axial reinforcement of the torqueable catheter shaft. A middle or
mid-line radiopaque marker will usually be provided on the balloon
or shaft underlying the balloon to permit alignment of the balloon
with the ostium and/or the stent wall prior to balloon
inflation.
[0022] In another embodiment the combination of beveled tip and
torque bridge is used for long balloons for peripheral applications
to improve crossing through diffused and calcified lesions by
allowing the operator to torque the catheter and navigate the
asymmetric tip through the lesion(s).
[0023] Thus, in a first aspect of the present invention, a balloon
catheter with improved crossing characteristics comprises a
catheter body having a distal end, a proximal end, and an
inflatable lumen near the distal end. A distal tip of the catheter
body is asymmetrically beveled relative to an axis of the catheter
body and at least a distal portion of the catheter body is
torsionally reinforced to improve the ability to rotate the beveled
tip by torquing a proximal end of the catheter body when the
catheter is present in the vasculature. The beveled tip may be a
simple planar bevel at an angle relative to the axis of the
catheter in the range from 25.degree. to 75.degree., usually at an
angle in the range from 30.degree. to 60.degree.. Optionally, the
catheter tip may be tapered one or more times between the maximum
diameter region of the catheter body and the distal tip which is
beveled. The distal tip may be beveled along two, three, four or
more surfaces so that the tip resembles a diamond or trocar tip.
The beveled tip without torque reinforcement is not functional in
crossing lesions and may even be inferior to regular tip since its
structural integrity is lower than regular tip (less materials and
the distal end of the tip) and it may deform. Coupling this tip
with torque reinforcement allows new way of crossing obstacles that
was never used with balloon catheters due to the inability of the
inflatable shell to deliver torque.
[0024] Torsional reinforcement of the catheter may include a
variety of structures. In a first exemplary structure, a distal
region of the catheter, typically at least over or within the
balloon, may comprise a reinforcement sleeve. For example, an
elastic reinforcement sleeve may cover a distal region of the
balloon, a proximal region of the balloon, or in some cases the
entire balloon. The elastic sleeve will not only provide additional
column strength, thus increasing the torsional rigidity of the
distal region of the catheter, it will also smooth the exterior
surface of the catheter presented to the blood vessel and stent or
other obstructions as the catheter is being advanced. In this way,
the folds and discontinuous surface of the balloon may be covered
and protected against engaging the stent struts or other
obstructions. Alternatively or additionally, the stent body within
the balloon may be reinforced by conventional structures, such as
braids, coils, axial reinforcement elements, or the like. As an
alternative to the elastic sleeves, the sleeves may be non-elastic
or non-distensible but frangible so that they split, fracture or
rupture as the balloon is inflated. In some instances, the balloon
will have a particularly short length, typically from 3 mm to 6 mm,
so that it may be inflated within a stent wall (typically within a
single stent cell) to open the stent cell, while only a short
portion of the balloon extends into the side branch and a similarly
short portion of the balloon remains within the lumen of the stent
in the main vessel. Such short stents have greatly improved the
ability to dilate the ostium at the bifurcation. Preferably, the
short balloons will have a radiopaque marker at or near their
midsections so that the balloon can be aligned with the stent wall
and/or the side vessel ostium prior to inflation.
[0025] In another aspect of the present invention, the catheters
described above may be used for advancing the catheter tip past
obstructions present within a patient's vasculature. The distal end
of the catheter may be observed fluoroscopically as it is being
advanced through the vasculature. If the stent encounters an
obstruction, such as a stent strut, when attempting to enter a side
branch vessel from a main branch vessel, the user may torque the
stent from the proximal end, causing the beveled distal end to
rotate and change its orientation relative to the obstruction. By
continuing to rotate the stent and gently advance the stent, an
orientation which allows the stent to atraumatically pass the
obstruction will usually be found, and the catheter can be advanced
forward. In some instances, after the balloon on the catheter is
disposed within the cell of the stent, the balloon may be expanded
to expand the stent cell.
[0026] In yet another aspect of the present invention, a balloon
catheter having improved stent crossing characteristics comprises a
catheter body having a distal end, a proximal end, and an
inflatable balloon near the distal end. The balloon will have a
short length, typically in the range from 3 mm to 6 mm, and a
radiopaque marker at its middle. The balloon is preferably
non-distensible and has a diameter in the range from 1 mm to 5 mm
when fully inflated. This balloon may be used in methods for
opening a cell in a stent deployed in a main branch vessel of a
patient's vasculature. The method comprises advancing the short
balloon into a cell adjacent to a side branch vessel so that the
radiopaque marker is aligned with the cell or the ostium and a
distal half of the balloon is advanced into the branch vessel and a
proximal half of the balloon remains within a central lumen of the
stent. After properly positioning the balloon, the balloon is
inflated to open the stent cell.
INCORPORATION BY REFERENCE
[0027] All publications, patents, and patent applications mentioned
in this specification are herein incorporated by reference to the
same extent as if each individual publication, patent, or patent
application was specifically and individually indicated to be
incorporated by reference.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] The novel features of the invention are set forth with
particularity in the appended claims. A better understanding of the
features and advantages of the present invention will be obtained
by reference to the following detailed description that sets forth
illustrative embodiments, in which the principles of the invention
are utilized, and the accompanying drawings of which:
[0029] FIGS. 1A to 1D show catheter tips approaching a stent strut.
FIG. 1A shows a prior art catheter. FIGS. 1B to 1C show a catheter
according to the present invention, comprising a beveled or skived
catheter tip, approaching the stent strut.
[0030] FIG. 2 shows a catheter of the present invention with a
polymer sleeve that is attached over a distal portion of the
balloon.
[0031] FIGS. 3A to 3B show an axially progressive expansion of the
balloon catheter of FIG. 2.
[0032] FIGS. 4A to 4B show a catheter of the present invention
having a polymer sleeve attached over a proximal portion of the
balloon in accordance with the present invention.
[0033] FIGS. 5A and 5B show expansion of a short balloon with a
stent cell at a vascular bifurcation in accordance with the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0034] The present invention provides catheters and methods for
their use with the improved ability to cross obstructions as they
are advanced through a patient's vasculature, particularly the
coronary vasculature. Obstructions which can be overcome by the
catheters and methods of the present invention include tight turns,
eccentric occlusions, and most particularly, stent struts present
at a bifurcation. As discussed earlier, one or more struts which
form part of a main vessel stent placed at a vessel bifurcation
will often be located across the ostium leading into the side or
branch vessel. The catheters and methods of the present invention
are able to advance past such jailing stent struts in at least most
cases.
[0035] The catheters and methods of the present invention may
comprise and utilize various design elements which facilitate the
catheter passage through obstructions. A first design element
includes a beveled distal tip at a leading end of the catheter. The
bevel will generally include at least one planar surface or face
disposed at an angle in the range from 30.degree. to 60.degree.
relative to a central longitudinal axis of the catheter, usually in
the range from 40.degree. to 50.degree. relative to the axis.
Optionally, the distal tip may include two or more of such inclined
or beveled surfaces. A second design element of the catheter
comprises torsional reinforcement over at least a distal portion of
the catheter, typically over at least a distal or proximal portion
of the balloon of the catheter. A third design element of the
catheter is the use of a short balloon, typically in the range from
3 mm to 6 mm, which is particularly useful for expanding a cell or
other aperture and its stent which is aligned with the ostium of a
bifurcation. Such short balloons will preferably have a middle or a
mid-line marker, typically a radiopaque marker on the catheter
shaft, to facilitate positioning the short catheter at the ostium
or within the struts of a stent adjacent the ostium.
[0036] Referring to FIG. 1A, a prior art balloon catheter 10 would
typically have a distal end or tip 12 with a blunt leading edge 14
which is oriented at 90.degree. relative to the longitudinal axis
15 of the catheter. In order to facilitate advancement, such
catheters would often have a distally converging taper 16,
typically a conical section, but because of the limitations of
catheter fabrication described above, the blunt leading edge 14
would still present a square as shoulder the catheter is advanced
over the guidewire GW. The shoulder would create a substantial risk
of catching or engaging a stent strut SS or other luminal
obstruction, thus compromising the ability to advance the catheter
through the vasculature or other body lumen, and particularly
through side branch ostia covered by stents.
[0037] Referring now to FIGS. 1B and 1C, a catheter 20 constructed
in accordance with the principles of the present invention will
have a distal tip 22 having a beveled leading edge 24. The beveled
leading edge is typically formed at the distal end of a tapered or
conical section 26 located distal to the main body 28 and balloon
42 (shown schematically) of the catheter.
[0038] The beveled leading edge 24 of catheter 20 can still engage
or catch stent struts SS as the catheter is advanced through the
wall of a stent disposed at a side branch ostium, particularly if
the distalmost tip 30 is rotationally aligned engage the stent
strut, as shown in FIG. 1B. In contrast to the prior art catheter
10, however, the catheter 20 of the present invention allows the
user to rotate the catheter body about the guidewire GW so that
another portion of the leading edge 24, such as the trailing
surface 32 of the leading edge engages the stent strut SS, as shown
in FIG. 1C. The trailing edge, which trails away from the direction
of advancement, allows the stent to easily move past the stent
strut SS and into the branch vessel.
[0039] Although the beveled leading edge 24 will preferably consist
of a single surface having generally planar geometry (other than
the aperture or opening for passing the guidewire) as illustrated
in FIGS. 1B and 1C, it is also possible to provide a catheter 20
having a plurality of beveled or inclined surfaces 34, 36, and 38,
as illustrated in FIG. 1D. The distal tip, which then resembles a
trocar cutting element having a plurality of facets, is even less
likely to engage and interfere with the stent strut SS, although it
is still possible to rotate the catheter should any difficulty be
encountered in moving the catheter past the stent strut.
[0040] The balloon tip can be beveled at various angles, preferable
lower than 65 degrees and optimally at about 45-30 degrees. Bevel
angle is measured between the beveled surface and the longitudinal
axis of the catheter. It can be done on one side or both sides
(FIG. 1D) to prevent bias of the tip. If the angle is too steep
(e.g., lower than 30 degree) the unbeveled area is too long and can
bend out when interfering with obstacles thereby creating risk of
tip deformation, dislodgment and patient safety. If the angle is
not steep enough (e.g. less than 75 degree) the advantage of the
bevel is insignificant as the front tip cross section will
interfere with the obstacle similar to conventional tip design.
[0041] The catheter 20 will preferably have torsional reinforcement
over at least a distal region of the catheter body. As shown in
FIG. 2, an exemplary form of torsional reinforcement comprises a
sleeve 40 formed over at least a distal portion of expandable
balloon 42. The sleeve 40, which is typically elastic and has a
smooth exterior surface, optionally having a lubricious film or
coating disposed over the surface, will significantly reduce the
risk that the folds of the balloon may interfere with or be
captured by a stent strut or other obstruction as the catheter is
advanced.
[0042] Inflation of the balloon 42 is illustrated in FIGS. 3A and
3B, where the balloon first expands in a proximal portion not
covered by the sleeve 40. As the proximal portion fully inflates,
the inflation "front" reaches the sleeve, which then inflates from
its proximal end, as shown in FIG. 3B, toward the distal end. Upon
deflation, the elastic sleeve 40 helps close and deflate the
balloon. Thus, not only does the sleeve 40 help with introducing
the balloon catheter, it can also facilitate with removing the
balloon catheter.
[0043] The sleeve 40 need not be elastic, and in other embodiments
could be inelastic or non-distensible. In such cases, the inelastic
sleeve will typically have a frangible line or portion which
permits it to split, rupture, or fracture upon balloon inflation.
In order to facilitate withdrawal, the split sections could be
adhered to the balloon surface so that they close with deflation of
the balloon. In other instances, it may be desirable to cover the
entire balloon with an elastic or inelastic sleeve, and in all
cases, the sleeve will add to the column strength and torsional
stiffness of the distal portion of the balloon section of the
catheter. Such increased strength and stiffness combined to enhance
the resistance to bending and to torsional buildup. Together,
increased resistance to bending and torsional buildup will increase
the efficiency of delivering the axial forces from a proximal end
of the catheter to the distal end to overcome the obstruction of
the stent strut or other materials.
[0044] The ability to progressively inflate the balloon from a
proximal end toward a distal end can have particular advantage,
when opening a stent or otherwise treating a side branch ostium.
When treating a bifurcated lesion, it is common to dilate the
ostium after stent deployment by positioning a distal end of the
balloon in the side branch and a proximal end of the balloon in the
main vessel. The balloon is inflated to dilate the ostium and
position the stent struts outwardly toward the side branch in order
to cover and "scaffold" the ostium. In practice, however, this
procedure often pushes struts which are located distally to the
balloon back into the main vessel rather than into the side branch.
By progressively inflating the balloon from proximal to distal, as
illustrated in FIGS. 3A and 3B, the distally advancing inflation of
the balloon will push all the struts distally into the side branch,
thus decreasing the risk that struts will protrude into the main
vessel when the procedure is over.
[0045] As illustrated in FIGS. 4A and 4B, the present invention
also provides for placing a constraining sleeve over a proximal
portion of the balloon. In particular, a sleeve 50 which may be
elastic or inelastic as described above, covers a proximal taper of
the balloon 52 of catheter 48 in order to cover the pleats of the
folded balloon and inhibit the balloon from catching on the struts
of a stent, particularly as the catheter is withdrawn through the
stent. The sleeve 50 is preferably formed from an elastic material
which can recover to close a balloon and the balloon is deflated.
Thus, when the procedure is over, the proximal region of the
balloon will be constrained and a smooth surface presented as the
catheter is withdrawn. The proximal balloon 50 also enhances both
torsional stiffness and column strength, a feature which is
particularly useful when the balloon is adapted to deliver stents.
In preferred embodiments, catheter 48 of FIGS. 4A and 4B will be
combined with a beveled distal tip 54 and optionally a braided
proximal shaft portion 56 in order to further enhance torsional
stiffness and column strength. In the exemplary embodiments, the
braided shaft section 56 may be attached to a proximal shaft 58
which may be a hypotube, conventional polymeric balloon catheter
shaft, or the like.
[0046] Referring now to FIGS. 5A and 5B, a balloon catheter 70
carries a short balloon 72 having a length less than 12 mm, usually
less than 8 mm, and typically in the range from 3 mm to 6 mm. The
balloon catheter 70 usually carries a radiopaque marker 74 at the
approximate middle or mid-line of the balloon (middle of the axial
dimension of the inflated balloon). Typically, the marker 74 is
carried on the shaft within the balloon and will be visible under
fluoroscopy to allow the middle of the balloon, i.e. the marker, to
be positioned at the ostium or stent wall before inflation. When
thus positioned, a distal half of the balloon is positioned largely
within the side branch vessel lumen SBL, while a proximal half of
the balloon remains largely in the main branch vessel lumen MBL. As
the ostium is usually larger than the side branch vessel diameter,
typically by about 0.5 mm, long balloons will generally enter the
side branch increasing the risk of overdilation when the user is
attempting to dilate stenotic material located at the ostium (which
is a very typical occurrence). Use of the short balloons of the
present invention minimizes the risk of overinflation of the side
branch vessel.
[0047] While short balloons have been proposed in the past for a
variety of purposes, their use in dilating the ostium of a
bifurcation was hindered by their tendency to slip from the ostium
back into the larger main vessel lumen. By inflating the short
balloons of the present invention so that the midsection is in the
ostium and preferably located within the stent structure, the
balloon will be stabilized and held in place by the stent.
[0048] A further advantage of the short balloon is that it does not
extend far into either the main branch vessel lumen MBL or side
branch vessel lumen SBL. Longer balloons which extend proximally
back into the main branch will tend to straighten as they are
inflated. As the proximal end of a long balloon can be anchored
within the main branch vessel, such straightening will then deflect
the distal end of the balloon downward, thus preferentially opening
struts on one side of the ostium and potentially causing an uneven
dilatation.
[0049] While the above is a complete description of the preferred
embodiments of the invention, various alternatives, modifications,
and equivalents may be used. Therefore, the above description
should not be taken as limiting the scope of the invention which is
defined by the appended claims.
[0050] While preferred embodiments of the present invention have
been shown and described herein, it will be obvious to those
skilled in the art that such embodiments are provided by way of
example only. Numerous variations, changes, and substitutions will
now occur to those skilled in the art without departing from the
invention. It should be understood that various alternatives to the
embodiments of the invention described herein may be employed in
practicing the invention. It is intended that the following claims
define the scope of the invention and that methods and structures
within the scope of these claims and their equivalents be covered
thereby.
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