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Description  |
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BACKGROUND OF THE INVENTION
This invention generally relates to vascular catheters and particularly
low-profile steerable catheters for angioplasty procedures, such as
percutaneous transluminal coronary angioplasty (PTCA).
In classic 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 preformed 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 across the lesion so that the balloon can dilate the lesion
when it is inflated. For a more detailed description of angioplasty
procedures and the devices used in such procedures, reference is made to
U.S. Pat. No. 4,323,071 (Simpson-Robert); U.S. Pat. No. 4,332,254
(Lundquist); U.S. Pat. No. 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 or fixed guidewires or guiding
elements are being used with greater frequency because the deflated
profile of such catheters are generally much 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
excellent pushability and a very low profile.
The steerable dilatation catheter in accordance with the present invention
includes a thin-walled, outer tubular member, a thin-walled inner tubular
member disposed within the outer tubular member, an inflatable balloon
member secured by the proximal end thereof to the distal end of the outer
member and by the distal end thereof to the distal end of the inner
tubular member, and a core member extending through the inner lumen of the
inner tubular member and out of the distal end thereof. An elongated
flexible body such as a helical coil is disposed about the distal portion
of the core member which extends out of the distal end of the inner
tubular member.
At least the distal portion of the inner tubular member is formed of
plastic material which provided longitudinal flexibility and diametric
rigidity and has a wall thickness less than 0.0015 inch, preferably less
than 0.00125 inch. The outer tubular member is also formed of plastic
material which provides longitudinal flexibility and diametric rigidity
and has a wall thickness less than 0.002 inch, preferably less than 0.0015
inch.
The distal portion of the inner tubular member which is disposed in that
portion of the catheter which extends out of the guiding catheter during
angioplasty procedures into the patient's coronary artery is preferably
formed of high strength plastic material such as polyimide. Wall
thicknesses less than 0.0006 inch generally do not provide sufficient
strength for use within a patient's vascular system. In a preferred
embodiment, the inner tubular member is formed of a hypotubing except for
the distal section formed of polyimide. Stainless steel, nitinol and other
hypotubing may be employed.
The structure of the catheter tip distally of the balloon may be of a
floppy design wherein the distal tip of the core member extends into a
coil or other elongated flexible body but terminates short of the distal
tip thereof. A shaping ribbon extends from the portion of the core member
extending out of the distal end of the inner tubular member to the distal
tip of the coil or flexible body where it is secured to a radiopaque plug.
Alternately, the structure of the distal tip of the catheter may be a
standard design, wherein the distal tip of the core member extends
distally through the interior of the coil and is secured to the radiopaque
plug in the distal tip thereof. The distal tip of the catheter is
preferably deflectable by means operable from the proximal end of the
catheter, such as described in copending application Ser. No. 199,099,
filed May 26, 1988, which is incorporated herein it its entirety by
reference thereto.
The proximal end of the catheter is provided with a multi-arm adapter
having means to introduce inflation fluid into the annular lumen disposed
between the inner and cuter tubular members and means to apply torque to
the core member disposed within the inner lumen of the inner tubular
member in order to provide steerability to the dilatation catheter. The
core member is free to rotate within the inner lumen of the inner tubular
member, but means are provided to prevent significant axial movement of
the core within the inner lumen of the inner tubular member.
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 steered through a patient's tortuous arterial system,
particularly the coronary anatomy thereof.
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 the steerable
dilatation catheter embodying features of the invention;
FIG. 2 is a transverse cross-sectional view of the catheter shown in FIG. 1
taken along the line 2--2; and
FIG. 3 is a transverse cross-sectional view of the catheter shown in FIG. 1
taken along the lines of 3--3.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 illustrates a steerable dilatation catheter assembly 10 generally
comprising a thin-walled, outer tubular member 11, a thin-walled inner
tubular member 12, a core wire or member 13 disposed within the inner
lumen 14 of inner tubular member 12 with a flexible coil 15 on the distal
portion thereof and inflatable relatively inelastic balloon member 16
which is secured by suitable adhesives at the proximal end 17 thereof to
the distal end of the outer tubular member 11 and at the distal end 18
thereof to the distal end 20 of the inner tubular member 12. A multi-arm
adapter 21 is provided on the proximal end of the catheter assembly 10 and
is secured to the proximal ends of both the outer tubular member 11 and
the inner tubular member 12. Arm 22 of adapter 21 is in fluid
communication with the annular lumen 23 disposed between the outer and
inner tubular members 11 and 12, respectively, and is adapted to direct
inflation fluid therethrough to the interior of balloon member 16. Arm 24
is adapted to receive the proximal end (not shown) of the core wire 13 and
has a torquing knob 25 secured to the end of the core wire 13 in order to
rotate the core wire within the inner lumen 14 of the inner tubular member
12 and thereby rotate the distal portion thereof having flexible core 15
secured thereto. In this manner, the catheter assembly 10 can be steered
through the patient's tortuous coronary anatomy.
In the presently preferred embodiment shown in FIG. 1, the portion of the
catheter assembly 10 distal to the balloon member 16 is provided with a
floppy construction wherein the distal end of the core member 13
terminates short of the distal tip of the coil 15 and a shaping ribbon 28
extends to the plug 27 in the distal tip of the flexible coil 15 and is
secured thereto. The proximal end of the shaping ribbon 28 is secured to
the distal portion of the core member 13 by suitable means, such as
brazing, soldering, welding, or adhesives at location 29.
At least those portions of the outer and inner tubular members 11 and 12,
respectively, which are disposed in that portion of the catheter assembly
10 which extends out of the distal end of a guiding catheter into a
patient's coronary arteries during angioplasty procedures are formed of
suitable high-strength plastic material, such as polyimide which provides
a thin-walled construction with diametric rigidity to avoid kinking or
buckling of the tubular members but with sufficient longitudinal
flexibility to pass through a patient's tortuous coronary anatomy.
Generally, the wall thickness of both the outer and inner tubular members
11 and 12 are less than about 0.002 inch, preferably less than about
0.0015 inch. In the portions of the inner member 12 within the interior of
the balloon member 16 and distal thereto, the wall thickness is preferably
less than about 0.001 inch. At least the most distal 20 cm, preferably 30
cm, of the outer and inner tubular members 11 and 12, respectively, has
the thin-walled construction of the invention.
The inner tubular member 12 preferably has a proximal section 30 formed of
a hypotubing from material such as stainless steel, nitinol and the like
to provide pushability and an intermediate section 31 and a distal section
32 are formed of polyimide tubing. The proximal end of the intermediate
member 31 interfits with the open distal end of the proximal section 30
and the proximal end of distal section 32 interfits with the open distal
end of the intermediate section 31. The interfitting ends of sections 30,
31, and 32 are secured together by adhesives or other suitable means. The
intermediate and distal sections 31 and 32 of the inner tubular member 12
are in that section of the catheter assembly 10 which extends out of the
guiding catheter. Therefore, the combined length of sections 31 and 32
should be greater than about 20 cm, preferably greater than about 30 cm.
As shown in FIG. 1, the transition section 33 between the intermediate
section 31 and the distal section 32 is followed distally by a radiopaque
marker coil 34 which preferably has a thickness the same as or slightly
less than the wall of the intermediate section and the same length as the
operative portion of the balloon member 16.
The outer tubular member 11 is preferably formed of polyimide over
essentially its entire length. Thin-walled sections of other materials can
also be included.
The core member 13 which is disposed within the inner lumen 14 of inner
tubular member 12 has a diameter over most of its length which is just
slightly less than the diameter of the inner lumen 14 in order to reduce
the profile of the catheter as much as possible. In addition, the small
differential between the OD of the core member 13 and the ID of the inner
tubular member 12 allows for common support therebetween. Differentials
between the ID and the OD should be less than about 0.0025 inch,
preferably less than about 0.0015 inch. The diameter of the core member 13
is less than about 0.012 inch over most of its length. Typically, the core
member has a plurality of sections of various diameters, e.g., a proximal
section having a diameter of about 0.008 to about 0.012 inch and a length
of about 120 to about 160 cm; an intermediate section having a diameter of
about 0.004 to about 0.008 inch and a length of about 8 to about 20 cm;
and a distal section having a diameter of about 0.002 to about 0.004 and a
length of about 4 to about 10 cm. Generally tapers of about 1 to about 4
cm in length are provided between the core member sections. The distal tip
of the distal section of core member 13 may be flattened to a thickness of
about 0.001 inch if it is to extend to the distal tip of plug 27 as is
characteristic of standard or non-floppy construction. While the presently
preferred embodiment of the core member 13 is a solid member of stainless
steel, all or part of the core member 13 may be formed of material such as
nitinol and the like. Moreover, the core member may be formed as a tubular
member with one or more openings within the coil member to take pressure
measurements therein and to deliver fluids, including drugs.
The balloon member 16 is preferably a thin-walled, flexible but relatively
inelastic member which is secured at the proximal end 17 to the distal end
of the outer tubular member 11 by a suitable adhesive 35 (e.g., a UV cured
epoxy or cyanoacrylate) and the distal end 18 of balloon 16 is secured by
the same or similar adhesive 36 to the distal end of inner member 12. The
balloon may be made of a wide variety of flexible, relatively inelastic
biaxially oriented plastic materials such as polyolefins, including
polyethylene and polyethylene terephthalate. The thickness of the balloon
wall in the operative or cylindrical portion thereof should be less than
about 0.0015 inch, preferably less than 0.0015 inch.
The flexible coil 15 on the distal portion of the catheter assembly 10 is
secured to the freely rotating core member 13 so as not to restrict the
rotation thereof. However, the outer diameter of the flexible coil 15 is
usually larger than the ID of the inner tubular member 12 in order to
restrict axial movement of the core member 13 and the flexible coil member
15 secured thereto in the proximal direction. The torque knob 25 on the
proximal end of the core member 13 restricts axial movement thereof in the
distal direction, but it does not restrict the number of turns which may
be given to the core member 13 secured thereto.
The flexible coil 15 may be formed from a stainless steel wire or other
suitable wire product, such as palladium, platinum, and alloys thereof
including small quantities of molybdenum. The shaping ribbon 28 is
preferably a cold worked ribbon of tungsten-rhenium alloy.
The catheter assembly of the present invention has excellent flexibility in
at least the distal portion thereof which extends out of the guiding
catheter and into a patient's coronary arteries during angioplasty
procedures. However, notwithstanding this flexibility, the catheter has
excellent pushability so that it can be readily advanced across tight
stenoses. The inflation and deflation of the balloon is rapid to enhance
safety during the dilatation process.
The presently preferred thin-walled polyimide tubing is the MICRO-BORE.TM.
tubing manufactured by PolyMicro Technologies of Phoenix, Ariz. Another
desirable tubing is manufactured by H.V. Technologies of Trenton, Ga.
Further information regarding polyimide material may be found in THE
HANDBOOK OF THERMOSET PLASTICS, Chapter 8, "Commercial Polyimides," edited
by Sidney H. Goodman (1986), and an article by E. Sacher entitled "A
Reexamination of Polyimide Formation," J. MACROMOLECULAR SCIENCE-PHYSICS,
Vol. B25, No. 4 (1986) pp 405-418 which are hereby incorporated by
reference thereto. Polyimide tubing having a wall thickness of less than
about 0.002 inch preferably within the range of 0.0006 to about 0.0015
inch provides the mechanical and physical properties comparable to a
conventionally used polyethylene and polyvinylchloride products which have
wall thicknesses many times greater, e.g., 0.005 inch. Preferably,
suitable means to vent air from the interior of the balloon member are
provided such as described in U.S. Pat. No. 4,692,200; U.S. Pat. No.
4,638,805; and copending application Ser. No. 000,651 filed Jan. 6, 1987,
all of which are incorporated herein by reference thereto.
While the description of the present invention is directed herein to
certain preferred embodiments, it is obvious that various modifications
and improvements can be made thereto without departing from the scope
thereof.
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