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Description  |
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FIELD OF INVENTION
Surgery, Cannula, Catheter.
OBJECTS
It is the purpose of this invention to provide a new and effective means of
removing organized, cross-linked blood clots (thrombi) from the human
vascular system. It is a further object of this invention to provide a
tool for the physician which is relatively safe, reliable, and simple to
operate and which can be operated in such manner that surgery may be
unnecessary for thrombectomy, endarterectomy, and similar procedures.
A particularly useful application of this invention is in the removal of
fibrin clots formed as a consequence of vascular prostheses such as the
arterio-venous shunt used with hemodialysis and other procedures.
Furthermore, this invention may help to prevent the recurrence of such
thrombi.
At present, thrombosis is conventionally treated by surgical intervention
if the affected vessel is a very large or important one, or if vital
circulation is affected. If the thrombosed vessel is a small one, it is
usually sacrificed, leaving the circulation to other vessels. With the
arterio-venous shunt and many other conditions, however, the auxiliary
vessels soon become exhausted and no more shunt sites or auxiliary vessels
are available. With the chronic renal patient, this quickly becomes a very
serious problem.
If the thrombus is very recent, it can sometimes be partly removed by a
balloon catheter. However, at present, surgery will eventually be
required, because the balloon catheter cannot effectively remove firmly
attached clots, or prevent their recurrence. Further, because the balloon
catheter must be inflated, there is the danger that a foreign medium used
to inflate the balloon may be introduced into the vascular system, which
may cause infection, tissue reaction, or air-embolism. By contrast, the
present invention is operated by direct mechanical linkage and introduces
nothing into the vascular system but the catheter itself. The mechanical
linkage also offers valuable sensory feedback to the physician's fingers
which assists precise operation of the instrument.
These and other objects will be apparent from the following drawing, in
which:
FIG. 1 is an elevational view of the catheter in the position in which it
is inserted into a vessel;
FIG. 2 is a view similar to FIG. 1, but showing the catheter with the mesh
expanded;
FIG. 3 is a fragmentary cross section showing the details of the distal
end; and,
FIG. 4 is a fragmentary elevational view of the distal end of a modified
form of the catheter shown in FIGS. 1-3.
Referring now to the drawing in which like reference numerals denote
similar elements, the catheter 2 is comprised of a guide tube 4 having a
barrel portion 6 with finger rings 8 secured thereto and an elongate
flexible portion 10 preferably, although not necessarily, formed of
tightly wound spring wire. A flexible plunger wire 12 slidably extending
through tube 4 has on its outer end a thumb ring 14, and on the other end,
which is the distal end of the catheter, there is secured a round ended
tip 16, which is generally of bullet shape. Between the tip 16 and the end
of the flexible portion 10 of the guide tube is a mesh sleeve 18. The ends
of the sleeve 18 are secured to the round ended tip 16 and the flexible
portion 10 of the guide tube so that the mesh cannot be accidently
dislodged during use, and likewise the round ended tip 16 is secured to
the end of the flexible plunger wire 12. The mesh sleeve 18 is preferably
a tubular braid of, for example, tinned copper, stainless steel, or
silver. It is normally tubular as shown in FIG. 1, but when the thumb ring
14 is pulled back so as to draw the flexible plunger wire 12 back, the
mesh is pressed between its ends so that it assumes an expanded condition,
as in FIG. 2. The catheter 2A fragmentarily illustrated in FIG. 4 is the
same as that illustrated in FIGS. 1-3, except in that the mesh in sleeve
18A is a finer weave than that of sleeve 18. It has been found that a mesh
of relatively course weave will expand more whereas the finer weave meshes
are more dimensionally stable. In either case, the mesh sleeve may be
removable and replaceable, but, in any event, its ends should be securely
fastened to the rounded tip end 16 and the end of the flexible portion 10
of the guide tube 4.
In operation, the catheter enters the vessel in its FIG. 1 condition below
the clot with the mesh extended to its contracted position. The catheter
passes through or around the clot following the path of least resistance.
At a point above the clot or a narrowed part of the vessel, the mesh is
then expanded to maintain approximate contact with the clot or vessel
wall. The catheter is then withdrawn, carrying the clot with it. At the
same time, the mesh cleans and smooths irregularities on the vessel wall,
thereby helping prevent the recurrence of thrombosis.
The materials used to construct the catheter should be readily
sterilizable, non-pyrogenic, and free of tissue reaction. Stainless steel
and silver have been found particularly suitable, as they can be
autoclaved. However, many other materials, including plastics inert to
body fluids, will also be found suitable.
The construction of the instrument is determined by its intended use and
the size of the vessels. For example, a convenient size for
shunt-declotting in the limbs would have a mean diameter of approximately
one-sixteenth inch. A tubular mesh of one hundred wires of 0.004 inch
diameter woven to a tube of one-sixteenth inch will expand to one-quarter
inch. Of course, many types of expandable mesh may be used; tubular braid
has been found particularly suitable. Biased woven cloth may be used.
Physiological-inert polymers may also be employed, such as woven polyester
mesh or sterilizable reticulated polymer foam. Other modifications can be
made without departing from the principle of the invention. For example,
the flexible portion 10 of the guide tube, instead of being formed of
wound spring wire, could be replaced by a flexible-polymer tube. Likewise,
although the catheter as illustrated is designed for finger operation, it
could be readily designed for hand operation. It is desirable that the
entire instrument be radiopaque.
This invention has been extensively clinically tested, and can affectively
remove blood clots which are completely resistant to the balloon catheter,
thereby frequently eliminating the need for surgery.
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