Atherectomy catheter and RF cutting method

An atherectomy device includes a catheter with a window at its distal tip for admitting tissue into a catheter compartment. A cylindrical cartridge in the compartment has a cutting edge that supports an electrically conductive cutting element, e.g. a band or wire. The cutting element and adjacent tissue can be heated to a selected temperature by generating an electrical current through the cutting element. The catheter is maneuverable to position its distal end near a lesion in an artery. The catheter incorporates a dilatation balloon or other feature to urge the catheter against the lesion, so that at least part of the lesion enters the compartment through the window. Then, the cartridge is manipulated from the catheter's proximal end to move the cutting edge across the window, severing the acquired tissue. According to alternative embodiments, the cartridge is either rotated or moved axially relative to the catheter, in either event closing the catheter window when the cut is complete. Further alternatives involve either placing an indifferent electrode on the patient and providing an RF signal via a single conductor to the cutting element for ohmic heating, or providing an RF (or a DC) current through the cutting element and two separate conductors for direct resistive heating of the cutting element.

BACKGROUND OF THE INVENTION 
The present invention relates to devices for removing obstructions from 
body lumens, and more particularly to catheters for removing 
atherosclerotic plaque and thrombotic occlusions from blood vessels. 
Atherectomy catheters are known for their utility in removing 
atherosclerotic plaque and thrombotic occlusions from arteries. While 
intended mainly for use in the coronary arteries, such catheters may as 
well be used in peripheral vessels. Beyond coronary uses, such catheters 
can have neurological applications, e.g., removal of lesions in carotid 
arteries, gynecological use in recanalizing fallopian tubes, and a 
potential urological application for removal of benign prostate 
hyperplasia. 
Atherectomy catheters have a variety of designs. According to one design, 
the catheter has a rounded or bullet shaped tip with an abrasive surface. 
At the treatment site, the tip is rotated at high speed and burrows 
through the occlusion. The resulting debris, typically in particulate 
form, is not captured by the device. Rather, it is allowed to flow to the 
capillary bed where it is absorbed. The device is most effective in 
abrading hardened (calcified) occlusions, with the intent being to produce 
particulate debris no larger than about 7 microns in diameter. When 
encountering softer occlusions, however, the device presents the risk of 
an occlusion breaking off during the atherectomy procedure, causing an 
acute and potentially life-threatening reclosure of the artery. The 
abrasive tip may inadvertently remove endothelium cells during catheter 
insertion, use or removal, thereby creating sites for potential lesions. 
A second type of catheter employs a cartridge housed within the catheter, 
near the catheter distal tip. When the distal tip region is placed near 
the occlusion, plaque enters the cartridge through an opening or "cutting 
window". A cup-shaped blade then is rotated or oscillated at high speed, 
and advanced to cut and capture plaque that entered the cartridge. U.S. 
Pat. No. 5,312,425 (Evans); U.S. Pat. No. 5,087,265 (Summers); and U.S. 
Pat. No. 5,085,662 (Willard) disclose versions of atherectomy catheters 
with a movable blade or cartridge within a tissue collection volume near 
the catheter distal tip. 
An example of an atherectomy catheter that depends on vaporization of 
plaque is found in U.S. Pat. No. 5,087,256 (Taylor). A dome-shaped head on 
the tip can be heated to temperatures in the range of 300-400 degrees C., 
for disintegrating plaque. U.S. Pat. No. 5,098,431 (Rydell) discloses a 
catheter in which an RF discharge between two spaced apart annular 
electrodes, electrosurgically cuts tissue to remove a blockage. 
Conventional atherectomy catheters are limited principally to an axial 
cutting direction and subject to smooth cell muscle migration (restonosis) 
after treatment. Patients treated with conventional atherectomy devices 
have restonosis rates of 30-40 percent within the six months following 
treatment. 
Therefore, it is an object of the present invention to provide an 
atherectomy catheter with a cutting edge that achieves a finer, more 
accurate cutting of unwanted tissue, to reduce the risk of acute blockage 
due to the breaking off of an occlusion. 
Another object is to provide a tissue cutting element for an atherectomy 
catheter that is effective in severing calcified and soft occlusions. 
A further object is to provide a flexible atherectomy catheter that 
incorporates means for capturing tissue being severed, to ensure against 
the escape of such tissue into the blood stream. 
Yet another object is to provide an atherectomy catheter with enhanced 
versatility, due to the incorporation of longitudinal and transverse 
(arcuate) tissue cutting motions. 
Further, it is an object of the present invention to provide an atherectomy 
catheter and procedure tending to seal the region of the cut, thus tending 
to reduce the incidence of restonosis. 
SUMMARY OF THE INVENTION 
To achieve these and other objects, there is provided a device for removing 
atheromas from a body lumen. The device includes an elongate catheter 
having a proximal end and a distal end. The catheter has a wall that 
defines a compartment within the catheter near its distal end, and a 
window is formed through the catheter wall to allow entry into the 
compartment. The catheter incorporates an electrically conductive tissue 
cutting element. A means is provided for generating an electrical current 
in the cutting element to heat the cutting element and adjacent tissue at 
least to a selected temperature above normal body temperature (i.e. 37 
degrees C.). A carrier is mounted movably relative to the catheter, for 
supporting the cutting element proximate the window and for a controlled 
movement of the cutting element along and adjacent the window. The 
catheter is flexible and maneuverable to locate its distal tip within a 
body lumen and to place the window against a tissue wall segment of the 
body lumen to acquire tissue within the compartment. The cutting element, 
when heated and when undergoing the controlled movement, severs the 
acquired tissue. 
There are several suitable approaches for generating the current necessary 
for cutting. At present, the most preferred approach involves a 
biocompatible cutting element (e.g. of platinum) subjected to RF energy in 
combination with an indifferent plate electrode on the patient's back. 
Application of the RF energy causes ohmic heating of tissue near the 
cutting element as current passes through the tissue. 
As an alternative, RF energy can be applied to heat an electrically 
resistive cutting element formed of nickel or a nickel chromium alloy. In 
this approach, the cutting element is heated to a temperature sufficient 
to sever a lesion that comes into contact with the element. As a third and 
presently least preferred alternative, DC power is applied to heat an 
electrically resistive cutting element, again of nickel or a nickel 
chromium alloy. For biocompatability, an insulative jacket or coating is 
applied to the nickel or nickel chromium cutting element. 
The preferred cutting element is a flat band, having a thickness of about 
0.015 inches and a substantially greater width. The band achieves a highly 
accurate and fine cut of the tissue, considerably reducing the pulling and 
tearing of tissue as compared to the conventional oscillating or rotating 
blades. Unwanted tissue is severed more cleanly, reducing patient risk. 
Further, it is believed that the elevated temperatures of the band and 
adjacent tissue have a sealing or cauterizing effect along the region of 
the cut. This is believed to result in a substantial reduction in 
restonosis in the treated artery. 
As an alternative to a flat band, the cutting element can be a fine wire 
having a diameter of about 0.030 inches or less to provide the cutting 
edge. 
The carrier preferably includes a cartridge contained within the 
compartment. The cartridge can have an axially extended cartridge wall, a 
cartridge opening and a cutting edge along the cartridge opening for 
supporting the cutting element. A control means is coupled to the 
cartridge proximal end, and operable to selectively position and move the 
cartridge within the compartment, to provide the controlled movement of 
the cutting element. Preferably the cartridge wall is longer axially than 
the window, so that the cartridge can be positioned to substantially close 
the window and thus capture severed tissue. With tissue secured in this 
manner, there is no need for a suction device or other means to withdraw 
tissue proximally through the catheter immediately after it is cut. With 
no need to pay attention to a vacuum or suction means, the physician is 
able to direct more attention to the atherectomy procedure at hand. 
Conversely, a vacuum means (or alternatively a plunger device and a 
diaphragm valve) may be provided if desired for removing severed tissue 
from the compartment, to allow cutting and removal of tissue at several 
locations during a single procedure. 
There are several alternatives for supporting the cutting element. For 
example, the cutting edge can be the leading or distal edge of the 
cartridge, preferably but not necessarily annular. In this event, the 
cartridge is moved distally to provide the necessary controlled movement 
of the cutting element. Alternatively, the cutting edge can be an axial 
edge of the cartridge opening, in which event the cartridge is rotated 
about a longitudinal axis to move the cutting element in an arcuate path. 
A preferred control means includes an elongate drive member, e.g. a rod, 
coil or tube, attached to the proximal end of the cartridge and extending 
proximally to a proximal end of the catheter. The member can be rotated, 
pushed or pulled at the catheter proximal end, to impart like motion to 
the cartridge. 
Another aspect of the invention is a process for removing tissue from a 
body lumen, according to the following steps: 
a. providing, near a distal end of an elongate catheter, a compartment and 
a window to the compartment through a catheter wall, and an electrically 
conductive tissue cutting element mounted to the catheter for a controlled 
movement of the cutting element adjacent and along the window; 
b. inserting the catheter into a body lumen, and guiding the catheter to 
position the window against a tissue wall segment of the body lumen, thus 
to cause tissue to enter the compartment via the window and occupy the 
compartment; 
c. generating an electrical current in the cutting element to heat the 
cutting element and adjacent tissue at least to a selected temperature 
above normal body temperature, while causing the cutting element to 
undergo the controlled movement, thereby to sever the tissue occupying the 
compartment. 
After the tissue is severed, the compartment can be closed to prevent 
egress of the severed tissue. The controlled movement of the cutting 
element can be one of two alternatives: substantially linear and axial 
with respect to the catheter, or arcuate about an axis running 
longitudinally of the catheter. 
Thus in accordance with the present invention, there is provided an 
atherectomy device and procedure suitable for treating soft occlusions and 
calcified occlusions alike, with clean and accurate cutting that reduces 
the risk of tissue tearing and escaping into the blood vessel under 
treatment. The catheter is versatile, due to its flexibility for 
traversing tortuous vessels and for the ability to cut in either an 
arcuate or axial path. The application of heat is concentrated along the 
region of the cut, i.e. the cutting element and adjacent tissue, reducing 
the required cutting force, increasing cutting accuracy and tending to 
cauterize or seal the region of the cut, thus tending to substantially 
prevent restonosis.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Turning now to the drawings, there is shown in FIG. 1 an atherectomy device 
16 for removing unwanted tissue from body lumens, more particularly blood 
vessels. The device includes a control housing or handle 18, and an 
elongate and pliable catheter 20 connected at its proximal end to the 
handle. 
Catheter 20 is formed of a biocompatible polymer such as Pebax (brand name) 
polyether block amides, Pellethane (brand name) polyurethane or polyimide, 
and can have an outside diameter in the range of 3 Fr. (1 mm) to 8 Fr. 
(2.7 mm) or larger. Catheter 20 includes several lumens that run axially 
from handle 18 to a distal end region 22. A guidewire 24, contained within 
one of the lumens, extends proximally beyond handle 18 and distally beyond 
a tapered distal tip 26 of the catheter. Further lumens are provided in 
the catheter, for delivery of contrast fluid or treatment fluid to the 
distal end region, and for balloon inflation. While not shown, a braided 
or other filament structure can be embedded into the catheter body to 
enhance torque transmission, if desired. 
A window 28 is formed through a wall 30 of the catheter along the distal 
end region. Window 28 is elongate in the axial direction and extends along 
about forty percent of the circumference of catheter wall 30. A cartridge 
or cutting sleeve 32 is contained within catheter 20. The cartridge is 
shown adjacent and along window 28, but is movable axially relative to the 
catheter. This enables a proximal retraction of the catheter from window 
28, to open the window whereby the catheter can acquire tissue. An 
elongate drive rod 34, contained within a lumen of catheter 20, is coupled 
to the proximal end of cartridge 32 and extends proximally through the 
catheter and into handle 18. 
Drive rod 34 is formed of an electrically insulative material, e.g. a PTFE 
coated wire coil or spiral wrapped polyimide. The drive rod has a high 
degree of bending elasticity to permit its movement (with the remainder of 
catheter 20) along serpentine passages toward an intended treatment site. 
At the same time, drive rod 34 is sufficiently rigid in the axial 
direction to permit controlling the cartridge axial position by 
manipulating the drive rod at its proximal end. Drive rod 34 is 
constructed of an electrically insulated material. A pair of conductors 36 
and 38, preferably polyimide jacketed copper or copper-clad steel wires, 
are bonded to the drive rod and electrically isolated from one another. 
Conductors 36 and 38 extend along the entire catheter length to control 
housing 18. 
A dilatation balloon 40 is formed to extend axially along distal end region 
22, axially aligned with window 28 but also spaced apart angularly 180 
degrees, i.e. on the opposite side of the catheter from the window. 
Balloon 40 is inflated using a fluid supplied to the balloon under 
pressure via a lumen of catheter 20. 
A fluid port 42 admits contrast or treatment fluids in the region just 
proximally of window 28, while such fluids can be administered distally of 
the window via the guidewire lumen. 
Control housing 18 includes three branches for coupling two sources of 
fluid (not shown): a branch 44 for balloon inflation, and two branches 46 
and 48 for delivery of contrast fluids or treatment fluids such as 
heparin. At the proximal end of the control housing is a connector 50 with 
two electrically independent paths coupled to conductors 36 and 38, 
respectively. A line 52 (e.g. coaxial) removably electrically couples 
connector 50 to a power supply 54. Power supply 54 preferably is an RF 
source, but can be a DC source as well. Also mounted at the housing 
proximal end are a fitting 56 and a control knob 58. Knob 58, coupled to 
the proximal end of drive rod 34, is movable axially relative to fitting 
56, to control the axial position of cartridge 32. 
A display 60 (e.g. LED) indicates the temperature of a cutting element 
mounted to the cartridge. A temperature control 62 adjusts the current 
through the cutting element, thus to set the cutting element temperature. 
FIG. 2 shows several lumens running through the catheter, including a 
guidewire lumen 64 that also can be used to administer contrast and 
treatment fluids. A control lumen 66 accommodates drive rod 34. Further 
lumens include a balloon inflation lumen 68 and an upper infusion lumen 70 
for providing fluids to fluid port 42. 
As seen in FIGS. 3 and 4, control lumen 66 along the distal end region 
forms a compartment 72 to accommodate cartridge 32. The compartment 
extends distally beyond window 28 a slight distance, and extends 
proximally of the window a sufficient amount to allow cartridge 
retraction, i.e. placing the complete cartridge proximally of the window. 
Cartridge 32 is cylindrical, having an axial wall 74 and a disk-shaped 
proximal wall 76. As seen in FIG. 5, cartridge 32 is open at its distal 
end to provide a circular cutting edge 78. A tissue cutting element, more 
particularly a fine, flat band 80, is mounted to the cutting edge to form 
an arc. Band 80 need not circumscribe the cutting edge, but should extend 
a sufficient amount to span window 28. Band 80 has a thickness of about 
0.015 inches, and is formed of nickel or a nickel chromium alloy coated 
for biocompatability. Alternatively (in an indifferent electrode approach 
discussed below) the band can be formed of platinum or another 
electrically conductive and body compatible material. The band is heated 
when subject to an electrical current. As an alternative to the band, the 
cutting element can be a wire with a diameter of at most 0.030 inches. 
The polymer forming cartridge 32 can be blended with barium sulphate, 
bismuth trioxide or another suitable radiopaque material to facilitate 
fluoroscopic observation of the cartridge position before and during 
tissue removal. Radiopaque markers also may be placed along the cartridge 
cutting edge and on corresponding (distal and proximal, or intermediate) 
edges of the window. Along with aiding accurate positioning, these markers 
are useful in confirming when the cartridge is closed after cutting. 
Conductors 36 and 38 are coupled to opposite ends of cutting element 80. As 
indicated in broken lines, conductors 36 and 38 are embedded in axial wall 
74 which, like the drive rod, is electrically insulative. A thermocouple 
82 can be mounted to the cartridge near cutting edge 78 and preferably 
bonded to cutting element 80, to monitor the cutting element temperature. 
Conductors 84, embedded in the cartridge and the drive rod, permit the 
cutting element temperature to be monitored from control housing 18. 
Alternatively, thermistors can be used to sense temperature. Further, for 
a resistive cutting element (i.e. nickel or nickel chromium) a 
characteristic dependence of resistance upon temperature can be used to 
monitor the cutting element temperature. 
Tissue is cut by advancing cartridge 32 distally from the retracted 
position, with cutting element 80 and adjacent tissue maintained at at 
least a predetermined temperature above body temperature. A circuit for 
heating the cutting element and tissue is schematically illustrated in 
FIG. 6. A controller 86 adjusts power from supply 54 as required, for 
generating current through cutting element 80 in an amount selected to 
heat the cutting element to the predetermined temperature. Thermocouple 82 
senses the temperature and provides the corresponding temperature reading 
at display 60. If the display indicates a need to increase or reduce the 
temperature, controller 86 is adjusted to alter the current accordingly. A 
broken line at 88 indicates that if desired, the output of thermocouple 82 
can be employed to automatically adjust the cutting element current. 
The use of device 16 to remove unwanted tissue is shown in FIGS. 7-9, where 
catheter 20 has been either steered or moved over guidewire 24 to a 
treatment position near a lesion 90 in a coronary artery. Catheter 20 is 
manipulated from housing 18 to axially and angularly align the catheter 
and lesion 90, so that window 28 faces the lesion (FIG. 7). At this point, 
dilatation fluid is supplied to expand balloon 40 against an arterial wall 
92 opposite the lesion (e.g. as in aforementioned U.S. Pat. No. 
5,085,662). Balloon dilatation drives the catheter distal end upward as 
viewed in FIGS. 7-9, forcing the catheter against the arterial wall about 
lesion 90 and causing at least a portion of the lesion to enter 
compartment 72 through window 28. 
With tissue thus acquired, cartridge 32 is advanced distally from the 
retracted position, while cutting element 80 is maintained at the selected 
temperature, from 50-600 degrees C. and more preferably 50-400 degrees C. 
This heating of the wire and adjacent tissue considerably enhances the 
cutting of tissue. Moreover, the heating has a cauterizing effect at the 
region of the cut and thus tends to seal the wound almost immediately 
after cutting, to significantly reduce smooth cell muscle migration or 
restonosis after treatment. The minute filament results in a precise, well 
defined cutting path that minimizes stretching and tearing of tissue. 
Accordingly, cutting element is effective in severing soft tissue as well 
as calcified or hardened tissue. This minimizes the risk of tissue 
fragmenting into particles or pieces that escape into the bloodstream. 
Cartridge 32 is advanced until cutting edge 78 is distally of window 28 
(FIG. 9), to completely acquire severed tissue within the cartridge. 
During or following the cut, a treatment fluid may be administered through 
lumens 64 and 70. After balloon deflation, the cartridge can be proximally 
withdrawn to remove the severed tissue. 
In addition to the cauterizing/sealing effect, a salient feature of the 
invention is the continuity of axial wall 74, which closes window 28 when 
the cartridge is completely advanced. This insures that severed tissue 
remains captured within compartment 72 as the catheter is withdrawn, thus 
to eliminate the risk that severed tissue will enter the bloodstream. 
FIG. 10 illustrates, in axial (longitudinal) section, the distal end region 
of an alternative device 96. This device differs from device 16 in several 
respects concerning primarily the catheter distal end, but also as to the 
manner of controlling the cartridge. A catheter 98 of device 96 has 
flexible band 100 along its distal end in lieu of a dilatation balloon. 
Band 100 can be flexed radially away from the catheter and, upon 
contacting an artery, drives the catheter toward the opposite end of the 
artery. An example of such band and its control is found in U.S. Pat. No. 
5,087,265 (Summers). 
A single, central lumen 102 accommodates the guidewire and is enlarged to 
provide a compartment 104. The compartment accommodates a cartridge 106 
having an axially extended wall 108, a proximal end wall 110 and a distal 
end wall 112. A drive tube 114, connected to the proximal end wall, is 
manipulated at the housing to selectively position cartridge 106. 
Drive tube 114 is used to rotate cartridge 106 about a longitudinal axis, 
rather than to move the cartridge axially. Consequently, while it requires 
less axial stiffness than drive rod 34, drive tube 114 must be resistant 
to torsional bending to apply the necessary torque to rotate cartridge 
106. Also because of the lack of axial movement, compartment 104 need not 
extend proximally beyond window 116 to accommodate the cartridge length. 
As seen in FIGS. 11 and 12, cartridge wall 108 is open along a portion of 
its circumference, to provide an arcuate cartridge opening 118 defined by 
end walls 110 and 112 and axial edges 120 and 122. Axial edge 120 provides 
the cutting edge, and supports a linear cutting element 124. Cutting 
element 124 is flat and thin (e.g. 0.015 inches thick), with a rectangular 
profile, to provide a lower profile cutting edge as compared to a wire. 
FIGS. 13 and 14 illustrate the use of catheter 98 to remove a lesion 126 
from an artery 128. The catheter is positioned to axially align window 116 
with lesion 126, and further to angularly align the window and lesion. A 
control knob (not shown but similar to knob 58) is turned rather than 
pushed or pulled, to angularly align cartridge 106 such that opening 118 
coincides with window 116 (FIG. 13). At this point, band 100 is flexed to 
urge the catheter upwardly against the arterial wall whereby a portion of 
lesion 126 enters compartment 104. 
At this point, the knob is turned to rotate cartridge 106 clockwise as 
viewed in FIG. 13 while cutting element 124 is heated, thus to 
progressively cut the lesion. Cartridge rotation continues until cutting 
edge 120 is carried beyond the clockwise edge of window 116, which closes 
the window and captures acquired tissue. Then, catheter 98 is proximally 
withdrawn to remove captured tissue, or a plunger is used to remove tissue 
from the cartridge. 
FIG. 15 illustrates an alternative embodiment cartridge 130 having an axial 
wall that is open at the distal end and along part of its circumference to 
define two cutting edges 132 and 134. A continuous wire 136 (0.030 inch 
diameter) is mounted to the cartridge and shaped to provide an arcuate 
segment 138 mounted to cutting edge 132, and a linear segment 140 along 
axial cutting edge 134. Accordingly, cartridge 130 can be used to effect 
axial cutting and arcuate cutting. Cartridge wall 142 is continuous over 
at least sixty percent of its circumference to enable axial and angular 
positioning that closes the associated catheter window, to insure capture 
of severed tissue. Drive member 144 can be a tube, rod or coil and has 
sufficient axial and torsional rigidity to impart axial and rotational 
movement to the cartridge. 
FIG. 16 illustrates an alternative circuit for heating an arcuate cutting 
element 146. A conductor 148 connects the cutting element with an RF power 
supply 150. A second conductor 152 couples the power supply and an 
indifferent electrode 154. The indifferent electrode preferably is an 
electrode plate, typically applied to the back of the patient. The power 
supply provides an RF signal to the cutting element via conductor 148. The 
signal returns to the power supply via conductor 152. Between cutting 
element 146 and indifferent electrode 154, current flows through body 
tissue. Consequently, ohmic heating of tissue is the primary factor in 
raising the temperature of tissue adjacent the cutting element to the 
predetermined or desired level. Cutting element 146 preferably is 
platinum, for high biocompatability and electrical conductivity. 
Accordingly cutting element heating from the current, while present to a 
degree, is slight compared to the ohmic heating effect. A controller 156 
governs power supply 150 to provide the appropriate current in cutting 
element 146. While not shown in FIG. 16, a thermocouple or other sensing 
element can be mounted at the cutting element, to sense the temperature of 
the cutting element and adjacent tissue, and provide feedback to 
controller 156. As noted above, this approach (highly conductive cutting 
element and indifferent electrode) is presently the most preferred. 
While the disclosure has focused on the treatment of coronary arteries, it 
is to be appreciated that devices in accordance with the present invention 
can be used to treat peripheral arteries and other vessels. These 
principles further can be applied in constructing and utilizing devices in 
neurology for removal of lesions in the carotid arteries, in gynecology 
for recanalization of Fallopian tubes, and in urology for removal of 
benign prostrate hyperplasia. The heating of the cutting element and 
adjacent tissue provides a fine, accurate cut to sever tissue at minimal 
risk of forming fragments, and provides a sealing action believed to 
reduce the incidence of restonosis. The cartridge can be either rotated or 
moved axially of the catheter, for greater versatility in severing 
unwanted tissue. After the cut, the cartridge completely closes the 
tissue-admitting window of the catheter, to insure complete capture of 
severed tissue.