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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to balloon angioplasty for dilating
obstructed blood vessels, and more particularly to an improved
balloon-tipped catheter which provides for convectively heating a gas
volume within the balloon to promote healing and sealing of damage which
may occur to the interior wall of the vessel.
Balloon angioplasty was first described by Andreas Gruntzig in 1977. Dr.
Gruntzig employed a balloon-tipped flexible catheter to percutaneously
dilate a region of stenosis within the coronary artery of a patient with
atherosclerotic coronary artery disease. Since the original work, the use
of percutaneous balloon angioplasty has become widespread, with treatment
of occluded peripheral blood vessels as well as coronary arteries.
Conventional balloon angioplasty compresses the plaque outwardly into the
vessel wall. Such outward compression results in stress on the vessel
wall, often causing cracking, tearing and stretching of the wall. In some
cases, after the balloon catheter is removed, torn plaque and tissue
become dislodged from the vessel wall resulting in abrupt reclosure of the
vessel. Even when such abrupt reclosure does not occur, it is thought that
the irregular inner surface of the vessel wall (which results from the
cracking and tearing) may contribute to restenosis at the same location
within the vessel. For these reasons, it would be desirable to provide a
method for sealing the torn tissue and plaque to the vessel wall to
provide a smooth interior surface which will not be subject to reclosure
or restenosis.
One approach for promoting the healing of blood vessels damaged by balloon
angioplasty has been proposed by Dr. Richard Spears and his colleagues at
the Beth Israel Hospital, Harvard Medical School, Boston, Massachusetts.
They proposed the use of dispersed laser radiation to promote healing and
sealing of the injured vessel wall. Specifically, their technique requires
that a dispersion lens be placed inside the dilation balloon, and that a
Nd-YAG laser be connected to the lens by a fiber optic waveguide extending
the length of the catheter. While the balloon is dilated, the laser source
is activated, resulting in direct irradiation of the interior wall of the
blood vessel through the balloon wall.
While Dr. Spears' technique offers many advantages, it also suffers from
certain drawbacks. First, the optics required to disperse the laser
radiation are only effective over relatively short distances on the order
of about 10 mm. Since the length of the angioplasty balloon can be as much
as 10 cm (in the case of some peripheral vessels), it becomes impractical
to treat the entire length of a damaged vessel wall in a single step.
Second, the outer surface of the dilation balloon is covered with blood
and often becomes clouded and opaque as the balloon is inserted in the
vessel and dilated to expand the stenosed region. Such obscuring of the
surface can limit the transmission of the laser radiation through the
balloon wall, reducing or preventing healing of the vessel wall. Third, it
appears that the laser radiation, which is of a relatively high energy,
has an effect on the nature of the interior of the vessel wall. The long
term significance of such effects are not yet known.
For the above reasons, it would be desirable to provide methods and
apparatus for promoting the healing and restoration of the interior wall
of blood vessels damaged by balloon angioplasty. In particular, it would
be desirable to provide such methods where the entire length of the vessel
contacted by the balloon can be treated in a single step, where the
treatment is unaffected by occlusion and obscuring of the outer surface of
the angioplasty balloon, and where treatment does not degrade or otherwise
affect the nature of the tissue on the interior of the vessel wall.
2. Description of the Prior Art
The basic technique of balloon angioplasty is taught in U.S. Pat. No.
4,195,637 to Gruntzig et al. Certain aspects of the use of Nd-YAG laser
radiation to promote healing and sealing of injured blood vessel walls, as
described hereinabove, are set forth in Hiehle, Jr., et al. (1985) Am. J.
Cardiol. 15:953-957. U.S. Pat. No. 4,470,407 to Hussein discloses an
endoscopic device having a laser beam terminating inside a balloon. The
laser beam, which is directed through the wall of the balloon, is intended
to illuminate and treat the interior of the wall of the vessel. The exact
nature of the treatment is not made clear. Sanborn et al. (1985) J. Am.
Coll. Cardiol. 5:934-938 discloses the use of a laser-heated metallic cap
on a fiber optic tube, where the heated cap is used to destroy stenotic
obstructions in blood vessels.
SUMMARY OF THE INVENTION
Apparatus and methods are provided for performing balloon angioplasty under
conditions which promote restoration and healing of the treated region of
the blood vessel. An improved balloon-tipped catheter includes means for
convectively heating the volume inside the inflated balloon as the balloon
is dilating the stenosis within the artery. The resulting convective heat
transfer to the interior artery wall seals the plaque and endothelium to
the intima of the vessel without the tissue denaturation which accompanies
the use of direct laser irradiation. Moreover, the area of convective
heating is not limited, and even very long balloons on the order of 10 cm
or longer may be heated, allowing treatment of very large areas of
stenosis. Finally, convective heat transfer is not impeded by occlusion on
the surface of the balloon as is the case with direct laser irradiation.
In the preferred embodiment, the catheter comprises a flexible tube having
an inflatable balloon at one end. A radiant heating block, typically a
metal block having heat transfer fins, is mounted within the balloon, and
a means for heating the block is provided. Conveniently, the block may be
heated by a fiber optic waveguide which extends the length of the catheter
and is connected at one end to an external laser light source. Other
heating means, such as electrical resistance heaters, may also find use.
According to a second aspect of the present invention, a means is provided
on the catheter forward of the balloon for injecting a plurality of
perfusate streams into the blood vessel being treated. At least some of
the streams will be directed at angles which are oblique to the axis of
the catheter. Such oblique perfusate streams are particularly effective at
loosening and clearing adhering platelets and clots prior to dilation of
the stenosed region.
In operation, the catheter is inserted into the stenosed blood vessel by
conventional techniques, typically employing a guiding catheter or sheath
and a guidewire. The catheter is initially placed adjacent to the
stenosis, and a pulsatile stream of perfusate is injected to clear the
stenosed region of loose clots and platelets. The catheter is then moved
forward so that the deflated balloon lies within the stenosed region.
After inflation of the balloon, the inflation medium, typically a highly
conductive liquid, is heated for a preselected time period or periods. The
balloon is then deflated, the treated area having been sealed and smoothed
to lessen the chance of abrupt reclosure and restenosis.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates a catheter constructed in accordance with the concept of
the present invention.
FIG. 2 is a detail view of the balloon tip of the catheter, shown in
section.
FIG. 3 is a sectional view taken along line 3--3 of FIG. 2.
FIG. 4 is a sectional view taken along line 4--4 of FIG. 2.
FIG. 5 is a block diagram illustrating the control system of the present
invention.
FIGS. 6A-6C illustrate the method of the present invention as applied to
clearing the stenosed region of the profunda femoral artery in a leg.
DESCRIPTION OF THE SPECIFIC EMBODIMENTS
Referring now to FIG. 1, a vascular catheter 10 constructed in accordance
with the principles of the present invention will be described. The
catheter 10 includes a balloon tip 12 at its distal end and a manifold
connector 14 at its proximate end. The manifold connector 14 includes
ports for optical fibers 16 and 18 for connection of heating and Doppler
lasers 77 and 78, respectively, as will be described in greater detail
hereinafter. The manifold 14 also has ports 20 and 22 which are connected
to sources for perfusate and a balloon inflation solution, respectively.
Finally, the manifold 14 includes a port 23 for thermister wires 24 and 26
which are connected to balloon and perfusate thermisters, respectively.
Each of these connections will be discussed in greater detail in reference
to FIG. 5, hereinbelow.
The main body of the catheter comprises an elongate flexible tube 30
extending between the connector manifold 14 and the balloon tip 12. The
tube 30 may be composed of a wide variety of biologically compatible
elastomers, including silicone rubber, natural rubber, polyvinylchloride,
polyurethanes, polyesters, and the like. The exact dimensions of the
catheter 10 will vary depending on the particular use. For peripheral
arteries, the catheters 10 will generally have a length in the range from
about 30 to 60 cm, while for coronary arteries, the length will generally
range from about 100 to 150 cm. The diameter of the catheter will
generally vary from about 1 to 2 mm, with the catheters for peripheral
arteries generally being larger.
Referring now to FIG. 2, the balloon tip 12 comprises a cylindrical metal
block 40 mounted at the distal end of the flexible catheter tube 30. The
cylindrical block 40 will typically be composed of a heat-radiating metal,
such as aluminum, copper, or brass, and will include a plurality of fins
42 formed on its outer surface to enhance heat transfer to the balloon
inflation medium.
A distal tip 44 is joined to the other end of the heating block 40, and the
tube 30, block 40, and distal tip 44 are generally axially aligned. The
distal tip 44 will usually be composed of the same flexible material as
the tube 30, and each of the tube 30, block 40 and distal tip 44 include a
common central lumen 50 passing therethrough. As will be described in
greater detail hereinafter, the central lumen 50 allows for delivery of
perfusate from the manifold 14 to the distal tip 44 of the catheter 10.
Referring now to FIGS. 2 and 3, in addition to the central lumen 50, the
flexible tube 30 includes three additional lumens 52, 54, and 56,
respectively. Each of the lumens is isolated from the other, and each
serves to connect a different port on the manifold 14 to the catheter tip
12. Lumen 52 is connected to the balloon inflation port 22 on manifold 14,
and serves to transport the balloon inflation medium to and from the
interior of balloon 60.
Lumen 54 carries the optical waveguide 16 which is attached to the laser
heating source 72, as will be described in more detail hereinafter. The
waveguide 16 terminates in the interior of heating block 40, so that the
radiation carried by the waveguide will heat the block. Usually, the
waveguide will be clad along its entire length, except at the end within
the heating block so that the radiation may penetrate into the block.
Finally, lumen 56 carries the laser Doppler waveguide 18. The lumen 56
extends through the metal block 40 and through a portion of the distal tip
44, as illustrated in FIG. 2. Within the distal tip 44, the waveguide 18
is exposed to the central lumen through a lateral passage 62. In this way,
the waveguide 18 can measure the flow rate of perfusate being pumped
through the central lumen 50.
The balloon 60 is of conventional construction, having a length in the
range from about 2 to 10 cm, and a diameter when fully inflated in the
range from about 4 to 8 mm. The balloon may be constructed of the same
elastomers described for the flexible tube 30 and distal tip 44.
The distal tip 44 includes a plurality of oblique perfusion ports 68, as
well as an axial port 70 at its distal tip. As perfusate is pumped through
the central lumen 50, it is injected in oblique or inclined streams
through the port 68, as well as an axially aligned stream through the
distal port 70. The angle of inclination of port 68 is not critical,
although they will usually lie within the range of from about 30.degree.
to 60.degree. relative to the axial direction through the catheter. In the
preferred construction, the tip 44 will include from about 4 to 24
perfusion ports 68, usually from about 8 to 16 perfusion ports, with about
half the ports directed forwardly and half directed rearwardly.
Referring now to FIG. 5, the catheter 10 will be connected to a laser
heating source 72 by means of the optical waveguide 16. The laser heating
source 72 suitable laser heating sources include argon lasers, Nd-Yag
lasers, and the like usually having a power in the range from about 5 to
40 watts.
Control of the perfusate flow through the central lumen 50 is provided by a
Doppler laser controller 74 connected to the catheter through optical
waveguide 18. The use of laser Doppler flow control is well known in the
art and described in detail in U.S. Pat. No. 4,538,613, the contents of
which are incorporated herein by reference.
A source of inflation medium 76 is connected to the catheter by conduit 22,
which in turn is connected to the interior of balloon 60 by means of the
lumen 52. Suitable inflation mediums include liquids having relatively
high heat transfer coefficients, including water and saline. Inflation
solution will be under a pressure in the range from about 50 to 150 psi.
Perfusate, typically saline, is heated to a preselected temperature,
typically in the range from about 34.degree. to 35.degree. C. in perfusate
heater 78. The perfusate is then pumped to the catheter 10 through conduit
20 where it enters the central lumen 50. The perfusate pump provides for
pulsatile flow, typically with pressure peaks in the range from about 100
to 150 mmHg. The pulse cycle will be in the range from about 20 to 100
cps.
The heating laser 72, Doppler laser 74, inflation medium source 76, and
perfusate heater and pump 78 and 80, are controlled by a central
controller 82, which receives input from the balloon thermister 24,
perfusate thermister 26, and laser Doppler system 74. The controller 82,
which is typically a microprocessor-based controller, varies the output
power of the heating laser 72 in order to control the temperature of the
inflation medium based on the output of the balloon thermister 24.
Similarly, the controller 82 controls the perfusate flow rate by varying
the output of perfusate pump 80 based on the Doppler controller 74. The
perfusate heater is controlled based on the perfusate thermister 26. In
this way, the various parameters of the catheter 10 may be controlled
based on preselected criteria.
Referring now to FIGS. 6A-6C, use of the catheter 10 of the present
invention in clearing a restriction present in the femoral artery will be
described. A sheath 90 inserted into the patient's leg L into the common
femoral artery CFA, according to conventional techniques such as the
Seldinger technique. After administering heparin, a guidewire (not
illustrated) is inserted in through the sheath 90 and guided to the region
of stenosis S under fluoroscopic guidance. The catheter 10 is then
inserted on the guidewire until the balloon tip 12 reaches the area
immediately adjacent to the region of stenosis S. After withdrawing the
guidewire, perfusate is introduced through the catheter 10 in order to
remove loose platelets and clots which may be present in the region of
stenosis S. The use of inclined perfusion ports 68 enhances the cleaning
action of the perfusate.
After clearing the stenosed region S with the perfusate, the catheter 10 is
moved forward so that the balloon 60 lies within the remaining lumen of
the senoses, under fluoroscopic guidance. The heating block 40 allows
fluoroscopic observation, and additional radio opaque markers may be
provided as desired. Once the balloon 60 is in position, as illustrated in
FIG. 6B, the source of inflation medium is activated, pressurizing the
balloon with the medium to a pressure in the range from about 50 to 150
psi. The pressure dilates the region of stenosis, simultaneously causing
tearing, cracking, and stretching of the surrounding arterial wall. In
order to restore and rehabilitate the arterial wall, as well as seal the
plaque onto the wall, the inflation medium is convectively heated by
radiant heating block 40. The block 40, in turn, is heated by the laser
light source 72, where the laser light is transmitted by fiber optics
waveguide 16.
The degree and length of the heating will depend on the particular
application. Typically, the temperature will be raised to a final
temperature in the range from about 40.degree. to 80.degree. C., above
normal body temperature, more typically from about 40.degree. to
60.degree. C. above body temperature. The duration of heating will
typically last through the entire period of inflation, although the heat
may be cycled up and down during the period. A period of inflation will
typically last from about 30 to 45 seconds. Frequently, it will be
desirable to disinflate the balloon in order to allow restored flow of
blood through the artery. This is particularly necessary with the coronary
artery, where the flow of blood may not be stopped for more than about 10
to 12 seconds without causing irreversible damage to the heart. In such
cases, it may be desirable to repeat the balloon dilation and heating
several times in order to affect the desired permanent dilation of the
stenosed region.
Although the foregoing invention has been described in some detail by way
of illustration and example for purposes of clarity of understanding, it
will be obvious that certain changes and modifications may be practiced
within the scope of the appended claims.
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