WO1990005562A1

WO1990005562A1 - Angioplasty catheter with off-axis angled beam delivery fiber

Info

Publication number: WO1990005562A1
Application number: PCT/US1989/005127
Authority: WO
Inventors: Miles A. Finn
Original assignee: Medilase, Incorporated
Priority date: 1988-11-16
Filing date: 1989-11-16
Publication date: 1990-05-31
Also published as: AU4661489A; CA2003069A1

Abstract

A laser catheter (10) for angioplasty is disclosed which utilizes a rotatable and axially movable beveled optical fiber, (30) which is off-axis to the axis of the catheter, to fire a laser beam (52) at an angle, (42) allowing extremely precise aiming of the laser energy at any point within the cross-section of a vessel in which the catheter is located.

Description

AN6I0PLASTY CATHETER WITH OFF-AXIS ANGLED BEAM DELIVERY FIBER Background of the Invention 1. Field of the Invention This invention relates to catheters and similar devices having a mechanism for aiming light transmitting fibers. Although particularly described with reference to laser angioplasty, the invention has broad applicability to any medical instrument which fires a laser at a target. 2. Description of the Related Art This invention relates to medical instruments and in particular to devices for performing laser surgery e.g., angioplasty, the treatment of atherosclerosis and the like. Atherosclerosis is a disease which causes thickening and hardening of artery walls. It is characterized by lesions of raised atherosclerotic plaque which form within arterial lumens and occlude them partially or wholly. Coronary atherosclerosis is a leading cause of death in the United States. Atherosclerosis tends to increase progressively with age. The treatment of atherosclerosis typically consists of drug therapy, surgery or percutaneous balloon angioplasty. In percutaneous balloon angioplasty, small balloon tipped catheters were first developed which could be passed percutaneously into various arteries and then inflated to dilate areas of partial obstruction. While this procedure has gained a measure of acceptance as a less invasive alternative to surgery, in most cases balloon angioplasty simply redistributes the atherosclerotic plaque. Frequency of recurrence or restenosis of the plaque occlusions has caused some concern about the efficacy of this technique. Laser therapy has been suggested as another approach to percutaneous angioplasty. One such technique utilizes laser technology to emit radiation onto a light receiving surface of a heat generating element. The light is converted by the element to heat. The element can then be contacted against material in a patient's body, such as a clot, atherosclerotic deposit or tissue, to alter the same by melting, removing or destroying it. In another laser technique, laser radiation is appl ed directly to the plaque deposit, clot or the like to vaporize or ablate it. It is this second technique to which the subject invention is most particularly directed. This particular technique of laser angioplasty provides the ability to remove the atherosclerotic plaque and reopen even totally occluded vessels without significant trauma to the vessel wall. It also offers the potential of reduced restenosis rate. However, the current technology for impinging laser radiation directly on a selected discrete treatment area has its own problems. Most critical has been the lack of ability to precisely aim laser radiation to selected areas to be treated without accidental arterial perforation. Various attempts have been made to overcome the problem of aiming the laser at the target, while avoiding damage to the vessel wall. U.S. Patent No. 4,445,892 issued May 1, 1984 for a "Dual Balloon Catheter Device" discloses a tubular structure carried inside the catheter. Mounted on the outside of the tubular structure is the optic system which includes light transmitting fiberoptic bundles. The optic system is rotatably mounted on the tubular structure, and may be axially displaced as well. The laser beam is reflected using a prism, such that the beam is fired directly at the vessel wall. A major problem with this embodiment is in determining when the beam has penetrated the target and is firing on bare vessel wall. U.S. Patent No. 4,587,972 issued May 13, 1986 for a "Device for Diagnostic and Therapeutic Intravascular Intervention" discloses a device which contains a bundle of optic fibers in the center of a catheter. The device is capable of firing one or more of these laser fibers. However, the laser beam fires axially, which limits the precision with which the physician may aim the laser energy at targets close to the vessel wall. U.S. Patent No. 4,627,436 issued Dec. 9, 1986 for a "Angioplasty Catheter and Method For Use Thereof" discloses another device which fires a laser beam axially. An expansion balloon permits the distal end of the catheter to be tilted for more precise aiming. The problem with this design is that targets close to the vessel wall remain difficult to hit due to the axial firing of this design. U.S. Patent No. 4,648,892 issued Mar. 10, 1987 for a "Method For Making Optical Shield For A Laser Catheter" discloses a device which fires one or more laser beams axially. The device has a shield which allows the distal end of the catheter to be put into contact with the target, allowing viewing of the target without the interference of any liquid, such as blood. Various types of elements may be placed within the shield to reflect the laser light. A problem with this design is that the distal end of the catheter must be manipulated such that the distal end comes into contact with the plaque. If the plaque is in a difficult to reach spot it may be difficult to ablate it. One advantage of the present single fiber invention over this multiple fiber device is that it allows for a smaller diameter device. Another approach was disclosed in U.S. Patent No. 4,672,961 issued June 16, 1987 for a "Retrolasing Catheter and Method". This patent discloses a device which fires a group of laser fiber bundles spaced around the perimeter of the catheter, reflecting the laser beams backward through a window portion in the catheter wall to aim at a target. The energy from each bundle of fibers is focused on a different point around the perimeter of the catheter. A problem with this design is that it is difficult to determine where each of the laser fibers is being aimed since no imaging technique is used. This device also cannot be used in vessels so severely occluded that the catheter cannot be advanced through the obstruction. Applicant's invention allows even totally occluded vessels to be unblocked by carving away the plaque with the laser beam. U.S. Patent No. 4,681,104 issued July 21, 1987 for an "Apparatus For Focusing An Intravascular Laser Catheter" discloses a device which fires an array of laser fibers spaced around the perimeter of the catheter, angling the beams such that they focus at a point on the longitudinal axis of the catheter. The problem with this device are that it is only useful for targets which almost totally clog the vessel, due to the location of the focal point of the laser beams. If the laser beams are allowed to fire through the focal point and spread in an attempt to reach a target off axis, the vessel wall opposite the target may be damaged. This is true even if a portion of the array of laser beams is in fact correctly aimed at the target. In addition, the multiple fiber configuration requires a larger diameter catheter than applicant's single fiber catheter. The invention disclosed herein overcomes these problems by providing a catheter device which may be aimed at any point within the cross-section of a vessel. The present invention fires a laser at an angle β at a target using a beveled optical fiber and the refractive indices of glass and water or air. Rotation of the optical fiber which carries the laser beam causes the laser beam to describe a cone. The optical fiber may also be moved axially within the catheter and may even extend beyond the distal end face of the catheter. Movement of the fiber axially within the vessel, and movement of the catheter, combined with the rotation of the fiber allows the physician to aim the laser at any point within the cross-section of the vessel. Placement of the laser fiber off-center within the distal end portion of the catheter, with respect to the longitudinal axis of the catheter, allows for the ablation of plaque which is on the axis. It also allows the imaging means (typically an optical fiber bundle) to be placed at the center axis of the catheter, which may facilitate the aiming of the catheter. Various types of lasers may be utilized in the context of the present invention. The pulsed dye laser is one that is often preferred for cardiovascular use due to its superior ability in avoiding damage to surrounding tissue. This is due in part because the plaque tends to absorb the particular wavelength of light used by pulsed dye lasers more readily than the surrounding tissue. Plaque is ablated by using pulsed energy as brief as about .5 to 50 microseconds, although the pulse time can vary. The pulsed dye laser is also preferred because more energy can be delivered through the relatively fragile fibers because of the longer pulse time. Excimer lasers as well as other types of lasers could also be used in the present invention. Optical fibers and fiber bundles have also been used in a variety of medical applications. An optical fiber is a relatively flexible clad plastic or glass core wherein the cladding is of a lower index of refraction than the core. When a plurality of such fibers are combined, a fiber optic bundle is produced. Optical fibers are flexible and are therefore capable of guiding light in a curved path defined by the placement of the fiber. Summary of the Invention The aiming arrangement of the invention is specifically described herein with reference to catheters for laser angioplasty but has broad applicability to any medical instrument which fires a laser at a target. The instrument may be used in both coronary and peripheral percutaneous angioplasty, but may also be used in intraoperative procedures, such as when the chest cavity or femoral artery are exposed incident to another procedure or as a primary procedure. In its most preferred form a device of the invention will comprise a fiber optic catheter suitable for performing medical procedures in a vascular lumen or other cavity within a patient. The catheter will have a distal end to be inserted into a patient and a proximal end including a control means for directing the contemplated procedure. Such devices are typically constructed for disposal after a single use. More specifically, the catheter includes an elongated external tube containing a laser light transmitting means, such as an optical fiber. The catheter may also contain one or more fiber optic viewing bundles, one or more fiber optic illumination fibers and may also be provided with one or more fluid passageways through which gases or liquids may be evacuated or transmitted. The catheter may also include a balloon at the distal end to halt the flow of blood for the duration of the procedure. This balloon may not be needed for intraoperative procedures since the blood may have been removed from the vessel in question, or may not be flowing. A guide wire may also be inserted through one of these conduits or otherwise included in the catheter. The distal end of the catheter is advanced through a lumen to the area of the vessel where the procedure is to be performed. The fiber optic viewing bundles along with various other techniques such as fluoroscopy allow the physician to see what the laser is aimed at. The laser beam is situated such that it fires at an angle β. The angle β is determined by the bevel angle α of the optical fiber as well as the refractive indices of glass and water or air. Angle α may vary among catheter designs to provide the physician flexibility for the various procedures which must be performed. Rotation of the optical fiber around its own axis causes the laser beam to describe a conic section, where the conic section is the projection of a circle or ellipse onto the surface of the plaque. By a combination of rotation of the catheter, axial movement of the catheter, and rotation of the optical fiber around its own axis, any point within the entire cross-section of the vessel can be precisely aimed at by the laser. Brief Description of the Drawings Fig. 1 is an elevational view of a preferred embodiment of the medical device of the invention; Fig.2 is an enlarged detail view of the distal end of the device shown in Fig. 1; Fig. 3 is an end elevational view of Fig. 2; Fig. 4 shows simplified schematics of various stages of the procedure; Fig. 5 shows simplified schematics of how the laser spot is kept in the field of view, and Fig. 6 shows simplified schematics of how rotating the catheter may result in a higher amount of energy being directed at the target. Description of the Preferred Embodiments While this invention can be embodied in many different forms, there are shown in the drawings and described in detail herein specific preferred embodiments of the invention. The present disclosure is an exemplification of the principles of the invention and is not intended to limit the invention to the particular embodiments illustrated. The present invention in preferred form comprises a medical device for delivering and applying laser radiation to a site in a vessel lumen of a patient. The radiation may be used to vaporize atherosclerotic plaque. Such instruments oftentimes take the form of icrocatheters of extremely small diameter. Such instruments are usually readily available in various diameter sizes to suit the particular work site in the particular lumen in which they are to be located and used. Thus a physician will have a number of various sized catheters at his disposal during any given procedure. This may include a number of catheters which will fire the laser beam at various angles. In some such devices, an elongated guide wire (not shown) may be selectively positioned within the lumen of the patient in association with the catheter. To this end, the catheter may include an elongated channel such as a slot, bore or conduit through which an external guide wire may slide longitudinally. The catheter can then be slid along the guide wire until a selected position in close proximity to a lesion which partially or totally occludes a vessel is reached. The aiming mechanism can be manipulated as desired and the laser radiation can then be selectively impinged on any area selected for treatment within the cross-section of the vessel . Some versions of such catheters are desirably constructed with at least a tip portion thereof including radio-opaque material (not shown). The radio-opaque material can then be used to locate the catheter under fluoroscopy which in combination with the image bundle aids in determining the location of the catheter tip relative to the plaque and aids in verifying the aiming. Referring now particularly to Figure 1 of the drawings, a catheter device of the present invention in one embodiment comprises an elongated catheter, generally designated 10, having a working distal end generally designated 12. The device is adapted to be inserted into a patient and remote control means 14 is attached^' at a proximal end 13 for manipulation and control by a physician. The catheter is flexible and generally comprises an extruded solid plastic body 15. Body 15 may consist of a single, soft, solid, extruded plastic material or it may consist of a plastic composite reinforced with plastic or metal braided filaments, such as Dacron^® polyester fiber or stainless steel. Plastics such as polytetrafluoroethylene, polyester, polyethylene and silicone may be used. When using the catheter in a vessel which contains an opaque fluid such as blood, it is often necessary to remove the opaque fluid and flush the area with a clear fluid such as saline solution to provide a viewable work area. To accomplish this, catheter body 15 may include conduits 18 and 19 (shown in Fig. 3), which open at distal end 12 and which are respectively connected to tubes 20 and 21 at the proximal end. Conduits 18 and 19 may be formed during extrusion of body 15. Tubes 20 and 21 include appropriate connector fittings 22 and 23, which will be familiar to those of ordinary skill in the art. Conduits 18 and 19 may thus . function as suction tubes, fluid flushing tubes, supply tubes or for receiving a guide wire, in the already known manner. Referring now to Figures 1 and 2 together, provision is made for delivering laser radiation to the distal end 12 of catheter 10 by providing a laser light source, (not shown). The laser may be coupled as is known in the art to control means 14 through an optical coupling fitting 29. This arrangement in turn directs laser radiation through control means 14 and through a laser radiation transmitting fiber 30, which may be located within an internal conduit 31 in body 15. Preferably, a single glass or fused silica fiber 30 or other optical fiber with a core diameter of about 50 to about 600 microns is utilized for the laser radiation transmitting fiber 30. These are typical sizes presently available and are not critical; the smaller the fiber the better, as long as enough energy can be transmitted through the fiber without damage to the fiber. Such fibers are known in the art. However, other fiber arrangements may be used as they become available. Additionally, a bundle of very flexible and very small diameter optical fibers or imaging bundle 32 including a lens as well as illumination fibers 33 (shown in Fig. 3) may be included and will also extend through catheter 15. In the preferred embodiment bundle 32 runs down the center of catheter 15. The proximal end thereof is appropriately connected to a fitting 33 to provide imaging or viewing in the known manner. Imaging bundle 32 is coherently packed, such that light at the proximal end is in the same relationship to the fibers in the bundle as when the light enters the imaging bundle 32 at the distal end. The illumination fibers 33 are not arranged in a coherent bundle like the imaging bundle. This is because the illumination fibers need only transmit white light to allow the physician to see inside the vessel, and not receive and transmit an image in a coherent manner for viewing. Placing the imaging bundle 32 in the center of the catheter aids in the viewing of the vessel and in aiming the laser energy. However, it is to be understood that the viewing bundle 32 could be placed anywhere within catheter 15. Referring now specifically to Figures 2 and 3 together, it can be seen that laser transmitting fiber 30 running through conduit 31 terminates near or at the distal end of the catheter 12. The optical fiber 30 terminates in a bevel angle α which may be adjusted along with the refractive indices of the silica fiber 30 and the water or air near the distal end of the catheter to control the angle β at which the laser beam is fired. This type of arrangement is well known in the art. It is contemplated that other arrangements which result in the laser being fired at an angle β could be used also, such as using a mirror to reflect the beam, or other arrangements. The laser beam is directed out through opening 38 in distal end 12 of the catheter. The laser energy emerges from opening 38 at a predetermined angle β shown at 40. Angle β shown at 40 is determined by the formula β = Sin^"1 (n, / n₂ Cos α) + o - 90" where α is the bevel angle shown at 42, n, is the refractive index of glass or fused silica shown at 44, and n₂ is the refractive index of water or air shown at 46. Angle β is determined by the longitudinal axis 48 of laser fiber 30 and the longitudinal axis 50 of the laser cone 52. The laser beam spreads out into a cone 52 as the beam moves further from the distal end of the catheter. Reference numerals 54, 56, 58 and 60 represent conic sections of the cone shaped laser beam 52. The corresponding distances O_v D₂, D₃, and D_n show the various locations of plaque which would be ablated if the plaque intersects the laser beam at various distances from the distal end 12. As the optical fiber 30 is rotated within conduit 31 the cone 52 will rotate around the longitudinal axis 48 of the optical fiber 30, always at an angle β. By moving the catheter axially along the vessel the catheter may be placed the exact distance from the target such that the diameter of the cone at that point will include the target, and the laser radiation will strike it. The conic sections also demonstrate that the diameter of the cone may exceed the diameter of the catheter if the vessel is large enough to allow the laser radiation to travel far enough. With axially firing prior art arrangements it was difficult to aim at a target which was outside the diameter of the catheter. By a combination of rotation of the catheter 10, axial movement of the catheter 10, and rotation of the optical fiber 30 around its own axis 48, any point within the entire cross-section of the vessel can be precisely aimed at by the laser.

• -

1 Referring now to Figure 4, reference line 64 shows the

2 relative position of the distal end 12 of the catheter to the plaque

3 target shown at 66. The first portion of figure 4, shown generally

4 at 68, shows the laser beam 52 directed through opening 38 at an

5 angle β towards plaque target 66. The laser beam, as shown, would

6 strike the vessel wall 70, which is undesirable. The second portion

7 of figure 4, shown generally at 72, shows how advancing the distal

8 end 12 of catheter 10 forward will enable the laser beam 52 to

9 strike the plaque target 66 without damaging the vessel wall 70. 0 The last portion of figure 4, shown generally at 74, shows how the 1 same laser beam placement on plaque target 66 may be achieved by 2 advancing the laser fiber 30 out of opening 38 of the catheter's 3 distal end 12. Some of the advantages of moving the fiber 30 4 forward rather than moving the entire catheter forward include less 5 wear and tear on the vessel wall and the ability to keep the distal 6 end of the optical fiber 30 in view of the viewing bundle 32 7 (discussed in figure 5 below). 8 Referring now to Figure 5, reference line 64 shows the 9 relative position of the distal end 12 of the catheter to the plaque 0 target shown at 66. The viewing bundle 32 (shown in figure 3) 1 provides a field of view shown generally at 76 bounded by lines 78 2 and 80. In the first portion of figure 5, shown generally at 82, 3 the distal end of the catheter must be moved up to the reference 4 line 64 to allow the laser beam 52 to strike the target 66. The 5 closeness of the catheter to the target however, causes the laser 6 beam 52 and the target 66 to be outside the field of view 76. The 7 second portion of figure 5, shown generally at 84, shows that by 8 advancing the laser fiber 30 instead of the distal end 12 of the 9 catheter the laser beam 52 still strikes the plaque target 66, with 0 both being in the field of view 76. 1 Referring now to Figures 6, reference line 64 shows the 2 relative position of the distal end 12 of the catheter to a target 3 point shown at 86. The first portion of figure 6, shown generally 4 at 88, shows laser beam 52 striking point 86. The second portion of 5 figure 6, shown generally at 90, shows that the same point 86 may be 6 reached with the laser beam 52 traveling less distance by advancing the catheter 10 and rotating it so the laser beam originates on the same side of the vessel as the target point 86. The closer the laser fiber 30 to the plaque the less beam spread (the conic section diameter of the cone is less) therefore focusing more laser energy on the target point 86. Also there is less attenuation in the laser beam 52 caused by the beam moving through the medium in the artery. This completes the description of the preferred and alternate embodiments of the invention. Those skilled in the art will recognize other equivalents to the specific embodiments described herein which equivalents are intended to be encompassed by the claims attached hereto.

Claims

WHAT IS CLAIMED IS: 1. A catheter comprising: an elongate catheter body constructed and arranged for insertion and axial movement within a vessel whereby the catheter may be placed in selected positions therein, and further being constructed and arranged for rotation about the longitudinal axis when in the vessel, the body having proximal and distal end portions; laser beam transmitting fiber means carried interiorly of and off-axis to the longitudinal axis of said body, said fiber means being constructed and arranged to rotate about the longitudinal axis of the fiber means and to direct a laser beam at a predetermined angle from the distal end of the catheter, whereby the laser beam may be directed to a target forward of the distal end of the catheter. 2. The catheter of claim 1 wherein the laser beam fiber means has proximal and distal ends and wherein the distal end of said fiber means is beveled so as to cause the laser beam to be directed at said predetermined angle. 3. The catheter of claim 2 wherein the laser beam fiber means may be moved along the longitudinal axis of the fiber means. 4. The catheter of claim 3 wherein the fiber means may be extended beyond the end of the distal end of the catheter. 5. A catheter for laser angioplasty comprising: an elongate catheter body constructed and arranged for insertion and axial movement within a vessel whereby the catheter may be placed in selected positions therein, and further being constructed and arranged for rotation about the longitudinal axis when in the vessel, the body having proximal and distal end portions; laser beam transmitting fiber means carried interiorly of said body and off-axis with respect to the longitudinal axis of said body, said fiber means being constructed and arranged to direct a laser beam at a predetermined angle, wherein said laser beam fiber means is rotatable around the longitudinal axis of the fiber means, and wherein the laser beam describes a cone as the laser beam fiber means is rotated about the longitudinal axis of the fiber means, whereby the beam may be directed anywhere within the entire cross-section of the vessel by the combination of laser beam fiber means rotation and axial movement of the catheter body. 6. The catheter of claim 5 wherein the laser beam fiber means has proximal and distal ends and wherein the distal end of said fiber means is beveled so as to cause the laser beam to be directed at said predetermined angle. 7. The catheter of claim 6 wherein the laser beam fiber means may be moved along the longitudinal axis of the fiber means. 8. The- catheter of claim 7 wherein the fiber means may be extended beyond the end of the distal end of the catheter, whereby the beam may be directed anywhere within the entire cross-section of the vessel by a combination of rotation of the catheter, axial movement of the catheter, axial movement of the fiber means, and rotation of the fiber means around the axis of the fiber means. 9. A method of maximizing the beam strength of a laser beam in a catheter of the type having a rotatable laser beam transmitting fiber which is constructed to direct the laser beam at a predetermined angle with respect to the distal end of the catheter, comprising the steps of: a) rotating the catheter until the laser beam fiber means is on the same side of a vessel as a target to be fired at by said fiber means; b) advancing said laser beam fiber means until the laser beam is aimed at the target, and c) firing the laser beam at said predetermined angle. 10. A method of keeping a laser beam and a target within a field of view in a catheter of the type having a rotatable laser beam transmitting fiber which is constructed to direct the laser beam at a predetermined angle with respect to the distal end of the catheter, comprising the steps of: a) advancing the distal end of the catheter until a target is included in the field of view; b) advancing the laser beam fiber means past the distal end of the catheter until the laser beam fiber means is aimed at the target, and c) firing the laser beam at said predetermined angle.