Note: Descriptions are shown in the official language in which they were submitted.
CA 02213571 2006-03-08
CATHETER FOR DETACHING ABNORMAL DEPOSITS
FROM BLOOD VESSELS IN HUMANS
The invention relates to a catheter of the type
known as a rotary catheter. Rotary catheters for
detaching abnormal deposits from blood vessels in humans,
such as arteries or veins, generally consist of a cutting
tool which is arranged at its front end, and a rotor
connected via a flexible drive shaft arranged in a
tubular sheath, to a rotary drive mechanism which can be
attached at the rear end of the catheter. The flexible
drive shaft is designed as a conveyor screw and is wound
helically in such a way that when it is being driven, it
conveys the dislodged deposits in the direction of the
rotary drive mechanism.
A catheter of this kind is used in particular
for treating occlusive diseases of the arteries by
dislodging stenoses and breaking up blood clots. It is
introduced into the artery and is advanced as far as the
stenosed area which is to be treated. A cutting tool
which can be driven in rotation is arranged at its front
or leading end.
In the case of a catheter known from US-A
5269751 and along the lines of that described above, the
flexible helical drive shaft, also designed as a conveyor
screw, serves as a guide which is introduced into the
artery before the catheter and over which the catheter is
guided. If this helical drive shaft is introduced into
the artery without the protective catheter tube, then it
is not possible to rule out the risk of the artery being
damaged in the process.
A further known catheter, for example the one
from EP-B1-0,267,539, has as its cutting tool a
substantially elliptical milling cutter which is provided
with abrasive material on its surface and is driven at a
speed of up to 160,000 rpm. The milling cutter is
connected via a flexible drive shaft to a rotary drive
mechanism which is arranged at the other end of the
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catheter. The drive shaft runs inside a tubular sheath
which serves as a catheter tube. A guide wire extending
right through the drive shaft is introduced into the
artery before introduction of the catheter and is
advanced right through the stenosis.
In this known rotary catheter, the particles
which are dislodged by the milling cutter are not removed
from the body, since they should normally be smaller than
the red blood cells by about 7 Vim. If, however, some of
the particles which have been dislodged are larger than
red blood cells, then there is a considerable risk of
their blocking the bloodstream at another location and
thereby causing an embolism.
From the literature, it is also known for the
particles which have been dislodged to be drawn off
through the catheter by suction. Here, however, there is
the risk that too many particles will fail to be caught
and that these will thus pass into the bloodstream.
The invention is therefore based on the object
of providing a catheter which is of the type mentioned at
the outset and in which the particles which have been
dislodged are removed from the circulation almost in
their entirety.
According to the invention, the object set is
accomplished by means of a catheter for detaching
abnormal deposits from blood vessels in humans, such as
arteries or veins, with a cutting tool which is arranged
at its front end, has a rotor and can be connected, via a
flexible drive shaft arranged in a tubular sheath, to a
rotary drive mechanism which can be attached at the rear
end of the catheter, the flexible drive shaft being
designed as a conveyor screw and being wound helically in
such a way that when it is being driven, it conveys the
dislodged deposits in the direction of the rotary drive
mechanism, characterized in that a guide wire which can
be moved independently of the flexible drive shaft and
the tubular sheath extends coaxially right through the
flexible drive shaft designed as a conveyor screw.
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The catheter according to the invention has a
conveyor screw with considerably improved efficacy and
therefore ensures an immediate and continuous withdrawal
of the dislodged or detached particles, so as to reliably
prevent these particles from being able to pass into the
circulation.
An embodiment having a drive shaft designed as
a conveyor screw consisting of a helically wound wire,
represents a particularly simple solution from the
constructional point of view.
The efficacy can be enhanced still further by
use of a helically wound wire that is substantially
rectangular in cross-section, since the surface area of a
square cross-section affords a higher conveying capacity
than, for example, a round wire cross-section.
The use of a coated wire makes it possible, on
the one hand, to choose freely a material which is
particularly suitable as regards strength, and, on the
other hand, to provide an appropriate protection against
corrosion and satisfy corresponding requirements in
respect of hygiene and tribology.
In a particularly preferred embodiment the
cutting tool has at least one slot through which the
deposits are conveyed into the inside of the cutting tool
when dislodged, and in that the drive shaft extends into
the inside of the cutting tool. With this arrangement
the particles, immediately after they have been detached,
pass through the slot and onto the conveyor screw. This
largely avoids detached particles being able to pass into
the bloodstream.
In an embodiment of the invention the cutting
tool has a stator with a stator portion, and the cutting
edges are arranged on the stator portion and on the rotor
to interact in a shearing action. The shearing action,
in contrast to the use of freely cutting blades, ensures
improved control of the dislodging of the deposits and in
so doing also reduces the risk of damage to the blood
vessel walls. In particular, with such an embodiment it
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is also easier to ensure that the particles which have
been dislodged will in all probability pass through the
slot or slots into the region of the conveyor screw and
are thus kept from entering the bloodstream.
In a preferred embodiment the stator portion
and the rotor are designed at least substantially
cylindrical, at least in the region of the cutting edges,
in that the rotor surrounds the stator portion as
external rotor, and in that the cutting edges are
arranged in the circumferential surfaces of the rotor and
of the stator portion. In such a configuration, the
rotor attacks the deposits radially. This ensures that
it is not possible, for example in the area of curves, to
drill straight into the vessel wall.
The further dependent claims characterize
further preferred embodiments of the invention.
An illustrative embodiment of the invention is
explained in greater detail with reference to the
drawings, in which:
Figure 1 shows a rotary catheter in a general
view, with drive mechanism, guide wire and collection
container for the deposit fragments detached from the
blood vessel,
Figure 2 shows a plan view of the head part of
the rotary catheter according to Figure 1, but on a
larger scale,
Figure 3 shows a longitudinal section through
the head part of the rotary catheter according to Figure
2, and
Figure 4 shows the guide wire and conveyor
screw on a still larger scale.
The catheter 12 shown in Figure 1 has, at its
front end 12a, a cutting tool which consists of a stator
14 and rotor 16. At its rear end 12b, the catheter 12 is
connected to a rotary drive mechanism 20 via a discharge
chamber 18. A flexible drive shaft is mounted in a
tubular sheath 22 which serves as catheter tube, said
drive shaft connecting the rotor 16 to the rotary drive
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mechanism 20. A guide wire 24 extends right through the
entire length of the catheter 12, and its front e:nd 24a
protrudes from the rotor 16 and its rear end 24b from the
rotary drive mechanism 20. The guide wire 24 has a nib
point 24c at its front end 24a. A collection container
28 is linked to the discharge chamber 18 in the radial
direction via a tube or a pipe 26.
When using the catheter 12, the guide wire 24
is introduced, with its front end 24a leading, into the
artery or vein which is to be treated, and it is then
advanced as far as the stenosed area and manoeuvred
through the latter, with radiographic monitoring. The
catheter 12 is then passed along the guide wire 2~4. As
soon as the front end 12a has reached the area which is
to be treated, the rotary drive mechanism 20 is switched
on in order to detach the undesired deposits by means of
the cutting tool 14, 16 and to convey them out of the
bloodstream. The speed of rotation of the rotor 16
preferably lies in the range between 30,000 and 40,000
rpm. The catheter 12 is advanced slowly as the operation
proceeds. The deposits which have been dislodged and
broken up are carried off through the tubular sheath 22
as far as the discharge chamber 18 and they pass from
there into the collection container 28.
Figures 2 and 3 show the front end 12a of the
catheter 12 with its stator 14, its rotor 16 designed as
external rotor, its tubular sheath 22, and the front end
24a of the guide wire 24. The tubular sheath 22 is shown
cut away at 30 in order to reveal the flexible drive
shaft 32 whose front end 32a is fixed to the rotor 16 in
terms of rotation and tensioning. The guide wire 24 runs
through the inside of the drive shaft 32. The drive
shaft 32 is designed as a conveyor screw in order to
convey the deposits, which have been dislodged by the
cutting tool 14, 16, through the tubular sheath 22 to the
discharge chamber 18 (Figure 1).
A portion 14a of the stator 14 extends into the
rotor 16. It can be seen that the stator portion 14a and
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the rotor 16 engage one within the other like a bushing.
The stator portion 14a has two shearing slots 14b, 14c
which are offset 180° to each other about the
circumference. The rotor 16 likewise has two shearing
slots 16b, 16c which are offset 180° to each other about
the circumference.
The slot 14b of the stator portion 14a is
narrower than that 16b of the rotor 16 in the circum-
ferential direction. One margin of the rotor slot 16b is
designed as cutting edge 16d. The opposite margin of the
stator slot 14b is designed as opposite cutting edge 14d.
This opposite cutting edge 14d runs, in the axial
direction, in an at least approximately undulating
configuration relative to a cylindrical surface.
The cutting edge 16d and the opposite cutting
edge 14d interact in a shearing action. Cutting edges of
this type are in each case arranged offset 180° t:o one
another about the circumference in both slots 14c, 16c
which are also referred to as shearing slots.
Towards its tip, the rotor 16 has a front end
16a of diminishing diameter. In this way, the stenosed
area of the artery or vein to be treated is widened upon
insertion of the catheter 12.
The rotor 16 and stator 14 are preferably made
of metal. The guide wire 24 with the nib tip 24c is a
steel wire. The drive shaft 32 serving as conveyor screw
consists of a coated steel wire, for example. The
tubular sheath 22 is made of plastic.
For connecting the stator 14 to the tubular
sheath 22 in a rotationally fixed manner, the end 22a of
the latter is press-fitted into the stator 14. For
securing purposes, holes 14e are arranged in the
circumferential surface of the stator 14, and the
pressed-in tube material 22b swells with a positive fit
into said holes 14e.
Figure 3 shows in particular that the drive
shaft 32 extends into the front end 16a of the rotar 16,
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and its front end 32a is fixed to the rotor 16 in terms
of rotation and tensioning, for example press-fitted into
the latter. The figure also shows how the tubular sheath
22 is secured with a positive fit in the stator 14 by
means of the holes 14e.
Figure 4 shows the rectangular cross-section of
the wire 32c of the helical drive shaft 32 serv_~ng as
conveyor screw. The arrangement of the guide wire 24
coaxially inside the drive shaft 32 results in a
particularly high degree of efficacy as conveyor screw.
The dislodged fragments of the deposits are conveyed in a
virtually linear manner inside the catheter tube 22.
