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Description  |
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This invention generally relates to vascular catheters and particularly
low-profile steerable catheters for angioplasty procedures, such as
percutaneous transluminal coronary angioplasty (PTCA).
In PTCA procedures, a dilatation catheter having an inflated balloon on the
distal end thereof is advanced through a patient's arterial system until
the deflated balloon crosses the atherosclerotic lesion to be dilated. The
balloon is inflated to a predetermined size with radiopaque liquid at
relatively high pressures to compress the atherosclerotic plaque against
the inside of the artery wall and then the balloon is deflated so that the
catheter can be removed and blood flow resumed.
Typically, a guiding catheter having a pre-formed distal end is first
percutaneously introduced into the patient's arterial system with the
distal tip in the coronary artery. A guidewire is advanced through the
guiding catheter into the patient's coronary anatomy until the distal end
of the guidewire crosses the lesion to be dilated. The dilatation catheter
is then advanced over the guidewire, with the guidewire slidably disposed
within an inner lumen of the catheter, until the inflatable balloon is
positioned within the lesion. For a more detailed description of
angioplasty procedures and the devices used in such procedures, reference
is made to U.S. Pat. No. 4,332,254 (Lundquist); U.S. Pat. No. 4,323,071
(Simpson-Robert); U. S. Patent 4,439 185 (Lundquist); U.S. Pat. No.
4,468,224 (Enzmann et al.) U.S. Pat. No. 4,516,972 (Samson); U.S. Pat. No.
4,538,622 (Samson et al.); and U.S. Pat. No. 4,616,652 (Simpson) which are
hereby incorporated herein in their entirety.
Steerable dilatation catheters with built-in guidewires or guiding elements
are being used with greater frequency because the deflated profile of such
catheters are generally smaller than conventional dilatation catheters
having the same inflated balloon size. Further details of low-profile
steerable dilatation catheters may be found in U.S. Pat. No. 4,582,181
(Samson) which is hereby incorporated in its entirety by reference
thereto. The lower profile of these catheters allows the catheter to cross
tighter lesions and to be advanced much deeper into the patient's coronary
anatomy. Moreover, the use of steerable low-profile dilatation catheters
having a built-in guidewire or guiding element shortens considerably the
time for the angioplasty procedures because there is no need to first
insert a guidewire and then insert a conventional dilatation catheter over
the previously inserted guidewire.
However, it has been found that the balloon elements of commercially
available very low-profile steerable catheters tend to wrap on themselves
when the catheter is torqued so that the balloon frequently will not
completely inflate when positioned across a stenosis or if inflated to
deflate within a desired time period. Some suppliers of such catheters
recommend that the catheter be limited to one rotation to avoid such
balloon wrapping. However, such restrictions on rotations severely limit
the steerability of the catheter within a patient's vasculature.
What has been needed and heretofore unavailable is a steerable dilatation
catheter having a very low profile which can be torqued from the proximal
end thereof without wrapping the inflatable balloon element. The present
invention satisfies this and other needs.
SUMMARY OF THE INVENTION
This invention is directed to a steerable dilatation catheter having an
inflatable balloon which has a very low profile and which will not wrap on
itself upon torquing.
The steerable dilatation catheter in accordance with the present invention
generally comprises an elongated torquable member extending along the
length of the catheter and a balloon member secured at both ends thereof
to the distal portion of the torquable member so that no relative
rotational movement occurs therebetween as the catheter is advanced
through the patient's arterial system. The torquable member includes an
elongated tubular element having proximal and distal portions, an inner
lumen extending along the length thereof, and one or more inflation ports
in the distal portion thereof which are in fluid communication with the
inner lumen and the interior of the inflatable balloon on the distal end.
The tubular element is relatively flexible in the longitudinal direction
but diametrically relatively rigid, and it does not expand under internal
pressures normally experienced. A guide extension or element, which is
preferably tapered toward its distal end, is secured by suitable means at
its proximal end to the distal end of the elongated tubular element. Means
are provided to direct inflation fluid from the inner lumen of the tubular
member to the interior of the balloon through the inflation ports. In one
preferred embodiment the proximal end of the balloon is secured by
suitable means to the tubular member proximal to one or more of the
inflation ports therein so that the ports are in fluid communication with
the interior of the inflatable balloon to facilitate the inflation thereof
and the distal end of the balloon is sealingly secured about the distal
extremity of the tubular member or the guide extension. In another
preferred embodiment, an extension tube, which is radially relatively
rigid and non-inflatable is concentrically disposed about the core member
having the distal end thereof secured to the proximal end of the balloon
and the proximal end thereof secured to the distal end of the tubular
member proximal to the inflation ports. In this embodiment, inflation
fluid passageways are provided in the proximal end of the balloon so that
inflation fluid can flow from the inflation ports in the tubular member
through the annular lumen defined by the extension tube through the
passageways into the interior of the balloon. In both of these
embodiments, an elongated flexible member such as a helical coil or a
cylindrical plastic member (e.g., polyethylene) having a rounded plug on
the distal end is coaxially disposed about the guide extension and extends
distally of the balloon. It is joined by suitable means to the guide
extension at one or more locations along the length thereof.
The structure of the catheter tip distally of the balloon can be of
standard design wherein the distal tip of the guide extension is secured
to the rounded plug at the distal tip of the coil. Alternatively, it may
have a floppy design wherein the distal tip of the coil extends beyond the
distal tip of the guide extension and a safety ribbon extends from an
intermediate location to the rounded plug in the distal tip of the coil
where it is secured.
The proximal end of the elongated tubular member has an adapter with means
to introduce inflating liquid into the inner lumen of the tubular member
and also means to apply torque to the tubular member in order to provide
steerability to the dilatation catheter.
The low-profile steerable dilatation catheter of the invention can be used
by itself to dilate tight stenoses, or it can be used in conjunction with
a larger diameter conventional dilatation catheter as described in
copending application Ser. No. 760,636 filed July 30, 1985, which is
hereby incorporated in its entirety herein. As described in the above
copending application, when it is found during an angioplasty procedure
that the deflated balloon of a conventional dilatation catheter is too
large to cross a stenotic region to be dilated, the steerable low-profile
catheter of the invention is advanced through an inner lumen of the
conventional dilatation catheter until the balloon of the low-profile
catheter is in the stenotic region. The balloon is inflated to dilate the
stenosis sufficiently so that the conventional dilatation balloon can be
advanced over the low-profile dilatation catheter in place to position the
balloon of the conventional catheter across the stenosis so that upon
inflation thereof the dilation can be complete.
In a presently preferred embodiment, the elongated tubular member is a
hypotube formed of stainless steel (e.g., type 304) or other suitable
materials, such as nitinol, which is a nickel-titanium alloy having a
"memory" and superelastic properties. The use of hypotubes in such
instances allows the dilatation catheter to be made with profiles as low
as 0.010 inch (0.254 mm). Moreover, even though the hypotube is formed of
high-strength materials and is diametrically rather rigid, the
diameter-to-length ratio is sufficiently low that the elongated tubular
member made therefrom is relatively flexible. It can be easily advanced
through the tortuous arterial passages of a patient and it has excellent
pushability.
In one presently preferred embodiment, the distal end of the tubular member
terminates within the interior of the balloon. In this instance, the guide
element, which is secured to the distal end of the tubular member, extends
through the distal end of the balloon. In another presently preferred
embodiment, the tubular member extends through the interior of the
balloon. However, in this embodiment, a plurality of slots are formed in
the wall of the tubular member extending through the balloon to increase
the flexibility without significantly reducing the torquability thereof.
In accordance with the invention, both ends of the inflatable balloon are
fixed so there is little or no tendency for the balloon to wrap on itself
when the catheter is torqued from the proximal end during the advancement
of the catheter through the patient's arteries.
These and other advantages of the dilatation catheter of the invention will
become more apparent from the following detailed discussion thereof when
taken in conjunction with the accompanying exemplary drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an elevational view, partially in section, of a steerable
dilatation catheter embodying features of the invention;
FIG. 2 is a sectional view of the distal portion of an alternate embodiment
having a floppy tip;
FIG. 3 is an elevational view, partially in section, of another alternative
steerable dilatation catheter embodying features of the invention;
FIG. 4 is an elevational view partially in section of a preferred
alternative embodiment of the invention; and
FIG. 5 is an elevational view partially in section of another preferred
embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 illustrates a steerable dilatation catheter assembly 10 embodying
features of the invention. As shown, the catheter assembly 10 generally
comprises an elongated tubular member 11, a guide extension 12 joined by
soldering or brazing 13 at the proximal end 14 thereof to the distal end
15 of the tubular member 11, a balloon element 16 secured by suitable
adhesive 17 at the proximal end 18 thereof to distal end 15 of the tubular
member 11 and by adhesive 19 at the distal end 20 to the guide extension
12, and a flexible coil 21 secured to the guide extension 12 at a suitable
location distally of the balloon 16. A removable hub 23 such, as the Luer
lock shown, is connected to the proximal end of the elongated tubular
member 11 to facilitate connection to a source for radiopaque inflation
fluid. The hub 23 when tightened against tubular member 11 permits
torquing of the proximal end of the tubular member 11 which extends
therethrough to steer the catheter when it is advanced through a patient's
vasculature.
The elongated tubular member 11 is preferably a hypotube formed from
stainless steel, such as type 304 stainless steel, or other suitable
materials such as nitinol, and has an inner lumen 25 extending along the
length thereof. It has one or more inflation ports 28 in the distal
portion 15 thereof to discharge inflation fluid from the inner lumen 25
into the interior of the balloon element 16 for the inflation thereof.
Inflation fluid is introduced into the inner lumen 25 through hub 23.
Typical dimensions of the tubular member include a length of about 150 cm,
an outside diameter of 0.018 inch (0.457 mm), and an inside diameter of
0.012 inch (0.305 mm) in the proximal portion which tapers to an outside
diameter of 0.01 inch (0.254 mm) in the distal portion. The tubular member
can be tapered in steps along its length. These steps can be formed by
drawing the tubing or by joining sections of tubing having sequentially
smaller diameters by brazing, soldering, welding and the like.
The proximal end 14 of the guide extension 12 is suitable secured to the
distal end 15 of the tubular member 11 such as by soldering, brazing, or
welding as shown at 13. Preferably, the proximal end 14 of the guide
extension 12 is sized to fit within the distal end 15 of tubular member
11. The guide element 12 tapers in the distal direction to smaller
diameters to provide greater flexibility to the distal end of the catheter
assembly 10. The most distal portion 34 of guide extension 12 is
preferably flattened to provide even greater flexibility in a single plane
and also to facilitate its manual shaping. The guide element 12 may be
made of stainless steel or other suitable materials, such as nitinol.
Moreover, it can be in the form of a solid rod or a helical coil or wire
or combination thereof. The length of the guide element may generally
range from about 2 to about 6 cm depending upon tip design. The most
distal flattened portion 34 of guide element 12 typically has a transverse
cross section of 0.001 by 0.003 inch (0.025 by 0.076 mm).
The proximal end of inflatable balloon element 16 is secured by adhesive 17
to the distal extremity 15 of the tubular element 11 so that one or more
of the discharge ports 28 are disposed within the interior of the balloon
element 16. The distal end 20 of the balloon 16 is sealingly secured by
adhesive 19 either directly to the guide extension 12 or indirectly
through porous plastic element 35 to seal the interior of the balloon
element 16 and prevent the escape of inflation liquid when the balloon is
inflated. The balloon element 16 is preferably formed from flexible but
relatively inelastic materials such as irradiated polyethylene or
polyethylene terephthalate. The proximal and distal ends 18 and 20,
respectively, of the balloon 16 may also be heat shrunk onto the tubular
member 11 and extension 12 if the balloon is made from heat shrinkable
material. Preferably, a porous plastic sheath 35, formed of material such
as porous polypropylene, is positioned between the distal end 20 of the
balloon 16 and the guide element 12 to allow for the escape of air (as
shown by the arrows) but not liquid when the balloon is filled with
inflation liquid. Other suitable means for venting air when the balloon is
filled with liquid include a small conduit, such as described in U.S. Pat.
No. 4,638,805 (Powell). Alternatively, microscopic holes may be drilled in
the balloon element as described in copending application Ser. No.
000,651, filed Jan. 6, 1987.
Flexible coil 21 is coaxially disposed about the guide extension 12 and is
directly or indirectly secured thereto by at least the proximal end 36
thereof. Suitable joining means include brazing, soldering, or adhesives.
A smooth round plug 37 of solder or brazement is provided at the distal
tip 38 to reduce the trauma to the interior of the patient's vascular
system when the catheter is advanced therein. Preferably, the entire coil
section is formed of radiopaque metal, such as platinum, tungsten,
irridium, rhenium, gold and alloys thereof to permit observation thereof
under fluoroscopic examination. The plug 37 may be similarly formed of
radiopaque materials. The distal coil section 40 is given a small stretch
(e.g., 10%) to provide a greater degree of flexibility to the tip. If
desired, the proximal coil section 41 may be formed from stainless steel
(e.g., type 304) or other suitable materials. Radiopaque marker coils 42
and 43 may be also provided about the guide element 12 and about the
tubular member 11, respectively, to aid in locating the proximal and
central portions of the balloon 16 during fluoroscopic examination.
An alternate embodiment, commonly termed a floppy design, is shown in FIG.
2 wherein the distal end 34 of the guide element 12 does not extend to the
distal end 38 of the coil 21 but instead is joined to the coil by brazing
or soldering at an intermediate location 45. A safety or shaping ribbon 46
extends from the brazement at location 45 to the plug 37. The ribbon 46
can be manually bent or curved to facilitate the entry of the distal end
of the catheter into a desired blood vessel during angioplasty procedures.
In a presently preferred embodiment, the safety ribbon 46 is formed of
material stronger than the material of the guide extension such as
tungsten or tungsten alloys and has typical transverse cross-sectional
dimensions of 0.001.times.0.003 inch (0.025.times.0.076 mm).
Another alternate embodiment is shown in FIG. 3 wherein a flexible plastic
tubular element 48 is disposed concentrically about the tubular member 11
and wherein the plastic tubular element is sealingly secured about the
periphery of the tubular member 11 at a location 49 by suitable means such
as adhesive proximally of the balloon 16. This construction directs
inflation fluid passing within the annular passageway 50 between the outer
tubular member 48 and the inner tubular member 11 into the interior of the
latter through inlet ports 51. The inflation fluid passes through the
inner lumen 25 of the tubular member 11 and flows out of inflation ports
28 into the interior of the balloon element 16 as described in the
previous embodiment.
FIG. 4 represents an alternate embodiment of the invention wherein tubular
member 11 extends through the interior of the balloon 16 and guiding
element 12 is secured to the distal portion of the tubular member 11 which
extends through the distal end of balloon 16. To provide additional
flexibility to the portion of the tubular member 11 which extends through
the balloon, a plurality of slots 48 are formed in the wall of the tubular
member 11, preferably with each slot axially set off from the adjacent
slot by at least 45.degree.. The slots can be formed by any suitable means
such as by cutting with blade or laser, etching, and the like. The width
and depth of the slots, the distance between the slots, the angular
disposition about the perimeter of the tubular member and the angular
orientation with respect to the longitudinal axis can be adjusted to vary
the flexibility and torquing characteristics of the tubular member.
Preferably, the width of the slots ranges from about 0.01 to about 0.034
inch (0.254 to 1.02 mm) and the distance between slots ranges from about
0.02 to about 0.08 inch (0.508 to 0.203 mm). The slots should extend more
than halfway through the diameter of the tubular member 11. A similar
structure can be obtained by replacing the slotted tubular section with a
helical coil.
Reference is made to FIG. 5 which illustrates a preferred embodiment of the
invention. This embodiment is directed to a catheter assembly 60 which
includes elongated tubular element 11, guide extension 12 suitably joined
as in the previously discussed embodiments. The balloon element 16 is
secured to the guidewire extension 12 at the proximal end 18 by suitable
adhesive 17 and at the distal end 20 by adhesive 19. In this embodiment,
extension member 61, which is longitudinally flexible, but radially rigid
is concentrically disposed about the guide extension 12, the distal
portion of the tubular element 11, and the proximal end 18 of the balloon
16. The proximal end of the extension tube 61 is secured by suitable
means, such as adhesive 63, to a cylindically shaped spacer member 64
which is in turn secured by suitable means such as adhesive 65 to the
distal portion of tubular element 11 proximal to the inflation ports 28.
Preferably, as shown, the tubular element 11 has a small diameter
extension 66 which contains the inflation ports 28 so that there can be a
smooth transition on the exterior of the catheter One or more inflation
fluid passageways 67 about 0.001-0.0025 inch in diameter are provided in
the proximal end 18 of the balloon 16 to direct inflation fluid into the
interior of the balloon, as shown. Marker coil 68 of suitable radiopaque
material is provided between the distal end of the extension member 61 and
the proximal end 18 of the balloon 16. The distal end of extension member
61 is secured by suitable means such as adhesive 69 to the proximal end 18
of the balloon 18 distally of the inflation ports 67. The coil section of
catheter assembly 60 is shown in a floppy construction wherein the coil 21
is secured by suitable means, such as solder 45 and the like, to the guide
extension 12 at the proximal end thereof and to radiopaque plug 37 at the
distal end thereof. The distal end 34 of the guide extension 12 does not
extend to the plug 37. A shaping ribbon 46 extends from solder joint 45 to
the plug 37.
The proximal end of catheter assembly 60 is provided with a torque knob 20,
a detachable Luer adapter 71, and a Luer connection 72 for connection to
an inflation device (not shown).
The materials of construction of this embodiment generally may be those of
the previously discussed embodiment. The extension tube 61 is preferably
thin-walled polyimide tubing which is described in copending application
Ser. No. 220,563 filed July 18, 1988, which is hereby incorporated herein
by reference thereto. The tubular extension 61 is longitudinally flexible
and radially relatively rigid. It does not expand upon inflation of the
balloon 16 during angioplasty procedures. The shaping ribbon 46 is
preferably gold plated tungsten-rhenium alloy and the coil 21 is
preferably a gold plated palladium-platinum molybdenum alloy.
The balloon is preferably biaxially oriented polyethylene terephthalate
formed from polymer material having an intrinsic viscosity of less than
1.0. The wall thickness of the balloon in the cylindrical section ranges
from about 0.0002 to about 0.0005 inch whereas in the proximal and distal
ends thereof the thickness ranges from about 0.0008 to about 0.002 inch.
Preferably the balloon has a lubricious coating of polysiloxane bonded to
the surface thereof.
Typical dimensions of the steerable, low-profile dilatation catheter of the
invention include an overall length of approximately 150 to about 200 cm,
a tip coil length from about 1 to 3 cm, a balloon length of about 1 to 3
cm, and inflated balloon diameters from about 1 to about 5 mm. Deflated
profiles for the balloon range from about 0.01 to about 0.025 inch (0.254
mm-0.635 mm), preferably less than about 0.02 (0.508 mm) inch, so that the
dilatation catheter can be inserted through an inner lumen of a standard
dilatation catheter as disclosed in U.S. patent application Ser. No.
760,636, filed July 30, 1985.
The low-profile steerable dilatation catheter of the invention can be used
in the same manner as prior low-profile steerable dilatation catheters.
However, because of the smaller profiles available with the dilatation
catheters of the present invention, much tighter stenoses can be crossed
than with prior devices. Moreover, the dilatation catheter of the
invention can be readily advanced through very tortuous arterial
passageways with little risk of wrapping the balloon on itself thus
ensuring complete inflation and deflation when it is positioned within a
stenosis to be dilated. Additionally, the dilatation catheter can be used
as described in copending application Ser. No. 760,636 to be disposed
within the inner lumen of a standard dilatation catheter in order to first
dilate a stenosis so that the larger profile standard dilatation catheter
can then be inserted therein to complete the dilatation. The Luer lock
connection on the proximal end of the tubular member in accordance with
the invention provides the further advantage that the Luer connection can
be removed, an exchange wire inserted into the proximal end of the tubular
member and a standard dilatation catheter can be advanced over the
low-profile steerable catheter of the invention. Other uses of the
invention will become apparent.
While the above description of the invention is directed to presently
preferred embodiments, various modifications and improvements can be made
without departing from the scope of the invention.
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