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Description  |
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BACKGROUND OF THE INVENTION
I. Field of the Invention
This invention relates generally to medical apparatus for removing plaque
and other deposits from the interior walls of a partially occluded blood
vessel, and more particularly to the design of an atherectomy catheter
whose cutting head exhibits a low profile to facilitate its being routed
through the vascular system but which expands in use to effect removal of
the atheroma.
II. Discussion of the Prior Art
The buildup of atheromas or the formation of thrombi in a blood vessel can
cause serious circulatory problems and when complete blockages occur,
distal tissues may be deprived of oxygen and nutrients leading to death of
those cells distally of the blockage. Thus, the formation of an atheroma
in a coronary artery can lead to a coronary infarction, especially when
the artery becomes so narrowed by the plaque build-up that a tiny clot or
thrombus cannot pass. Similarly, an atheroma or other type of stenotic
lesion in a peripheral vein or artery can have a corresponding affect on
tissue and cells supplied by the blocked blood vessel.
The treatment of such a condition naturally depends upon the location or
site of the blockage. In the case of a blocked or partially blocked
coronary artery, it has been the practice to conduct open-heart surgery
wherein the blocked vessel is by-passed with an autograft. Similarly,
blood vessel shunts have been installed in other body areas as well. Such
surgery, however, tends to be quite traumatic involving opening the
patient's chest and pericardium in the case of coronary by-pass surgery or
extensive excision and vessel replacement in the case of other peripheral
blockages.
More recently, following the technique created by A. Grunzig, a balloon
catheter may be used to restore patency to a blood vessel without
extensive surgery. A catheter having a small inflatable balloon on its
distal end may be routed through the vascular system to the site of the
constriction or blockage and when the deflated balloon is appropriately
positioned to span the blockage, a fluid may be introduced into the
proximal end of the catheter to inflate the balloon to a sufficiently high
pressure whereby the blockage may be spread open and patency restored.
As in pointed in the Auth U.S. Pat. No. 4,445,509, there are certain
deficiencies in the Grunzig procedure which render it ineffective in
certain applications. For example, the blockage may be such that it is not
possible to safely force the distal tip of the catheter through the
blockage prior to the inflation of the balloon. In such a situation, it
would be desirable if one could safely "tunnel" through the blockage using
an appropriate cutting tool. Once a passage has been formed during such
tunneling operation, a balloon can be advanced into the occlusion until it
is totally across it. Once so positioned, the balloon can be inflated and
the angioplasty procedure completed.
In U.S. Pat. No. 4,784,636 to Rydell and assigned to applicant's assignee,
there is described a balloon atherectomy catheter comprising three
concentrically disposed flexible plastic tubes. The innermost tube has an
annular cutter secured to its distal end and secured to the proximal end
of that catheter is a device which allows both rotational and
translational motion to be imparted to that innermost tube. The cutter
member is especially designed to preferentially remove tissue deposits
directly in line with the cutter without producing significant lateral
cutting.
SUMMARY OF THE INVENTION
The present invention provides an improved working catheter which may be
used in place of the innermost catheter illustrated and described in the
aforementioned Rydell U.S. Pat. No. 4,784,636. It includes an elongated
tubular flexible shaft made of stainless steel or a polymeric material
having a proximal end and distal end. The cutting head on the distal end
portion of the tubular body comprises a plurality of fibers which are
either integrally formed in the surface of the tube by slitting the tube
or, alternatively, may be separate elements which are bonded to the outer
periphery of the tube at one end only and arranged to lay flat along the
exterior wall of the innermost tube and thus present a low profile during
the catheterization process. When the working catheter is advanced in the
distal direction such that the distal end thereof projects outwardly
beyond the surrounding guide catheter, and when the shaft of the working
catheter is driven at high speeds, centrifugal force causes the fiber
elements at the distal end thereof to project radially outwardly to flail
and thereby pulverize the stenotic lesion. When the motor is again
stopped, the fibers will again lay down against the periphery of the
working catheter's shaft as the working catheter is pulled back into the
guide catheter.
OBJECTS
It is accordingly a principal object of the present invention to provide an
improved apparatus and technique for treating vascular atheromas.
Another object of the invention is to provide a working catheter for use in
a guide catheter having fiber elements at the tip thereof which are made
to project radially outward upon high speed rotation of the catheter
shaft.
These and other objects and advantages of the invention will become
apparent to those skilled in the art from the following detailed
description of the preferred embodiment, especially when considered in
conjunction with the accompanying drawings in which like numerals in the
several views refer to corresponding parts.
DESCRIPTION OF THE DRAWINGS
FIG. 1A illustrates by means of a partially sectioned view the preferred
embodiment of the invention with the cutter head in its retracted, stopped
position;
FIG. 1B is a partial view showing the cutter in its extended position while
being driven;
FIG. 1C is a partial view of the catheter of the present invention at a
further step in the process;
FIG. 2 is a side view of the distal end portion of the working catheter
when stationary;
FIG. 3 is a side view of the cutter tip when being driven;
FIG. 4 is an end view of FIG. 3; and
FIG. 5 illustrates the manner in which the cutting fibers may be integrally
formed with the shaft of the working catheter.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIG. 1A, the atherectomy catheter assembly of the present
invention is indicated generally by numeral 10 and is seen to include
three concentrically disposed elongated flexible tubular plastic members
12, 14 and 16. The outer tubular member 12 has a distal end portion 18 to
which is sealingly affixed an inflatable expander member 20 which may
preferably be formed from a thin biaxially oriented plastic such as
polyethylene terephthalate (PET) or another suitable plastic. As can be
seen in FIG. 1A, the distal end of the intermediate tubular member 14
projects beyond the distal end 18 of the outer tubular member 12 and the
distal end of the expander 20 is sealed to the outer periphery thereof. As
will be further explained, this will permit an inflation fluid to be
injected through the lumen of the outer tube 12 and into the confines of
the expander member 20. The expander 20 can subsequently be deflated by
aspirating the inflation fluid out from the proximal end of the catheter
assembly.
The innermost catheter 16, which is also referred to herein as the drive or
working catheter, is configured to pass over a guidewire and fits loosely
Within the lumen of the intermediate tube 14. Its distal end can be made
to extend outwardly beyond the distal end of the intermediate catheter,
all as shown in FIG. 1A.
As shown in FIGS. 2 through 4, the distal end portion 22 of the innermost
working catheter 16 disposed on a guidwire 15 is provided with a plurality
of elongated fibers as at 23, it being recognized that the views of FIGS.
2 through 5 are greatly enlarged to exhibit the features of the cutter
element.
With continued reference to FIG. 1A, there is illustrated a blood vessel
such as an artery or vein and it is indicated generally by number 24. The
blood vessel is shown as being occluded by a fatty deposit (atheroma) 26.
For applying the rotational and translational motion to the drive tube 16
and for inflating and deflating the balloon 20 while aspirating blood and
tissue deposits during the course of the atherectomy procedure, there is
connected to the proximal end of the catheter a generally tubular housing
28 which is dimensioned to be conveniently grasped in the palm of the
hand. Contained within the tubular housing 28 is a motor 30 which is
preferably air driven but which alternatively may be electrically powered.
The motor 30 has a shaft 32 which is keyed to a rotary union or valve
member 34 contained within a valve housing 36. An annular groove 38 is
formed in the rotatable union member 34 and disposed on opposed sides of
the annular groove 38 are air seals 40 and 42 in the form of O-rings. A
bore is formed through the side wall of the valve housing 36 and a fitting
44 fits within that bore for coupling it to a vacuum system (not shown).
The rotatable union member 34 is hollow and the annular recess 38 is ported
to the hollow interior thereof by a radial bore (not shown). A coupler 46
is used to join the rotatable union 34 to the drive tube 16. Thus, by this
arrangement, when the motor 30 is energized, the tubular drive member 16
is rotated within the lumen of the intermediate tube 14 and,
simultaneously, a suction may be applied to the lumen of the drive tube 16
to draw blood and any tissue debris back to the proximal end of the
assembly.
A fluid port 48 is also formed through the side wall of the tubular plastic
housing member 28 and it communicates with a chamber 49. This chamber is
adapted to be filled through port 48 with a suitable fluid such as saline
solution and provides the means whereby the balloon or expander member 20
may be inflated. More particularly, the lumen of the outer tube 12 is open
to the interior of the chamber 49 through compression fitting 50 and when
the hydraulic pressure is appropriately increased, the saline solution
flows into the expander member 20 to cause it to inflate to its maximum,
predetermined outside diameter. By applying a negative pressure to the
port 48 the inflation medium can be aspirated out from the proximal end of
the outer tubular member 12 causing the expander member 20 to assume its
low profile condition of being collapsed against the periphery of the
intermediate tube 14. Again, an O-ring seal 52 is used to preclude the
flow of liquid beyond the rotary union housing 36.
To effect translational or longitudinal movement of the cutter 22 relative
to the distal end of the intermediate tube 14, there is provided on the
housing 28 a thumb grip 54 having a stem 56 passing through an elongated
slot 58 formed in the tubular housing 28. The stem 56 may be affixed to
the motor assembly 30 which slidingly fits within the lumen of the tubular
housing 28 or alternatively to the rotary union housing 36. Thus, by
pushing on the thumb grip 54, the motor 30 and the rotary union 36 can be
moved back and forth within the bore of the tubular housing 28.
Referring to FIGS. 2 through 4, there is shown an enlarged view of the
distal end portion of the working catheter 16. As can be seen, it includes
a plurality of fibers 23 anchored to the exterior of the tube 16 at one
end only thereof. More particularly, the fibers 23 are shown as being
adhesively or thermally bonded at 25 to the exterior of the tube 16. While
in FIG. 2 it is the distal end of each of the fibers 23 that is bonded to
the exterior of the tube 16, it is to be understood that the invention
will work just as well when the opposed end of each of the fibers is the
bonded end.
The connection between the individual fibers 23 and the outer surface of
the working catheter 16 is such that the fibers tend to lay flat against
the side wall of the catheter. However, when the drive motor assembly 30
is energized to rotate the drive or working catheter 16 at a high
rotational velocity, centrifugal force causes the individual fibers 23 to
stand erect as shown in FIG. 3 to flail and pulverize the stenotic lesion
26.
FIG. 5 shows an alternative arrangement for the cutting tip in accordance
with the present invention. Here, rather than having discrete monofilament
fibers bonded to the exterior of the tube as in the embodiment shown in
FIGS. 2 through 4, the flailing fingers are integrally formed in the wall
of the tube 16 by creating a series of U-shaped slits 60 to define fingers
62. As with the embodiment of FIG. 2, when the working catheter 16 is spun
at high speed, centrifugal force will cause the fingers 62 to project
radially out forming tiny whips which flail and disintegrate the stenotic
lesion.
OPERATION
FIGS. 1A, 1B and 1C are included to illustrate the preferred mode of
operation of the atherectomy catheter of the present invention. As
indicated in FIG. 1A, the catheter assembly with the cutter 22 retracted
is advanced up over a guidewire to the occlusion 26 within the blood
vessel 24. At this point, saline or other suitable inflation fluid is
injected through the port 48 into the chamber 49 and, thence, through the
lumen of the outermost tube 12 to inflate the expander member 20. This
action stabilizes the tip end of the catheter assembly and inhibits
relative movement between the outer tubular member 12 and the blood vessel
24. Next, and as represented by FIG. 1B, the motor 30 is energized to
drive the cutter tube 16, and at the same time, the surgeon may, by
pressing on the thumb grip 54, advance the rotating cutter tip over the
guidewire and into the lesion 26. While this procedure is taking place, a
vacuum is preferably applied, via port 44 and the rotary valve member 34,
to the lumen of the drive tube 16 whereby blood and other debris cut loose
during the procedure is sucked back through the lumen of the drive tube
and into a suitable receptacle (not shown).
Once a path has been cut into the lesion 26, the expander member 20 may be
evacuated to collapse it to its smallest diameter and then by advancing
the entire catheter assembly 10 further in the distal direction, the
expander 20 is made to enter the previously cut opening in the lesion.
Following that, the expander may again be inflated and the steps repeated
until such time as the balloon is made to pass completely through the
occlusion to spread it open and to restore patency to the blood vessel 24.
The invention has been described herein in considerable detail in order to
comply with the Patent Statutes and to provide those skilled in the art
with the information needed to apply the novel principles and to construct
and use such specialized components as are required. However, it is to be
understood that the invention can be carried out by specifically different
equipment and devices, and that various modifications, both as to
equipment details and operating procedures, can be accomplished without
departing from the scope of the invention itself.
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