Vascular catheter

Abstract: The invention is directed to a very low-profile dilatation catheter (10) having an inner tubular member (13) with an inner lumen (17) with a diameter of not more than 0.003 inch (0.076 mm) greater than the diameter of a guidewire (16) disposed therein. Preferably, the inner diameter of the tubular member is less than 0.015 inch (0.381 mm). the inner member may be formed of a thin-walled tubing such as polyimide tubing having a wall thickness less than 0.003 inch (0.076 mm). Polyimide tubing is also preferably employed as the tubular member in low-profile steerable dilatation catheters wherein the guide elements thereof are fixed within the catheter.

Description: This invention generally relates to vascular catheters and particularly to catheters for vascular procedures such as percutaneous transluminal coronary angioplasty (PTCA). In typical PTCA procedures, a guiding catheter having a preformed distal tip is percutaneously introduced into the cardiovascular system of a patient and advanced therein until the distal tip thereof is in the ostium of the desired coronary artery. A guidewire is introduced through the guiding catheter and advanced into the patient's coronary vasculature until the distal end of the guidewire crosses the lesion to be dilated. A dilatation catheter having an inflatable balloon on the distal portion thereof is advanced over the previously introduced guidewire, with the guidewire slidably disposed within an inner lumen of the dilatation catheter, until the dilatation balloon is properly positioned across the lesion. Once in position across the lesion, the flexible, relatively inelastic balloon is inflated to a predetermined size with radiopaque liquid at relatively high pressures to radially compress the atherosclerotic plaque of the lesion against the inside of the artery wall. The balloon is then deflated so that the dilatation catheter can be removed and blood flow resumed through the dilated artery. Further details of angioplasty procedures and the devices used in such procedures, can be found in U. S. Patent 4,332,254 (Lundquist); U. S. Patent 4,323,071 (Simpson-Robert); U. S. Patent 4,439,185 (Lundquist); U. S. Patent 4,468,224 (Enzmann et al.) U. S. Patent 4,516,972 (Samson); U. S. Patent 4,538,622 (Samson et al.); and U. S. Patent 4,616,652 (Simpson). It is generally desirable to make the deflated profile of the dilatation catheter as small as possible because a smaller profile allows a catheter to pass through tigher lesions and to be advanced much further into the patient's coronary anatomy. However, if the diameter of the guidewire is reduced to reduce the profile of the catheter, the ability of the guidewire to transmit torsional and axial forces is likewise reduced. Heretofore, movable guidewires utilized in coronary angioplasty typically have been on the order of 0.012-0.018 inch (0.305 - 0.457 mm) in diameter. Attempts have been made to use smaller diameter movable guidewires in angioplasty procedures, but such smaller diameter guidewires frequently were unable to effectively transmit torque for steering the guidewire from the proximal to the distal ends, and, in many instances, they did not have the pushability to be readily advanced through the tortuous coronary vasculature without buckling or kinking. Heretofore, attempts have also been made to reduce the profile of dilatation catheters by reducing the wall thickness of the tubular members which make up the catheters. However, as with reducing the diameter of the guidewire, there is a limit on how much the wall thickness of the tubular members can be reduced without detrimentally affecting the performance of the catheter. What has been needed and heretofore unavailable is a dilatation catheter assembly which has a substantial reduction in profile with essentially no loss in performance characteristics. The present invention satisfies that need. Two references of interest are AU-B 10067/88 and DE-A 35 23 615. In the first reference, a dilatation catheter for use with a thin guidewire is disclosed. In the second reference, a catheter of a polymeric material is described. The surface of the catheter is treated with gamma-globulin. According to the invention, there is provided a catheter as defined in claim 1. This invention is directed to an improved low-profile balloon dilatation catheter assembly in combination with a small diameter guidewire. A vascular catheter in accordance with the invention generally comprises an elongated tubular member having an inner lumen extending therethrough which is adapted to receive a guidewire and which has an inner diameter of not more than 0.003 inch (0.076mm) greater than the outside diameter of the guidewire over a substantial portion of the lumen length. The inner lumen has a diameter of less than 0.015 inch (0.381 mm). In this manner, the inside surface of the inner lumen is close enough to a guidewire disposed therein to provide support to the guidewire and to prevent the buckling thereof when the guidewire is subjected to axial forces, such as when the guidewire is advanced through a patient's vasculature. Moreover, by maintaining a lubricious surface on the inner wall of the tubular member which defines the inner lumen, contact friction between the lumen surface and the guidewire can be reduced substantially and thereby allow a more effective transmission of steering torque from the proximal to the distal extremities of the guidewire. The invention is particularly directed to dilatation catheters having inflatable balloons on the distal ends thereof. In accordance with the invention, the inner tubular member is a longitudinally flexible but diametrically rigid tubular element formed of polyimide. This polymeric material provides a tubular member having the strength and flexibility of prior tubular members formed from materials such as polyethylene, polyvinylchloride and polyurethane but with substantially smaller wall thickness. For example, the polyethylene tubing typically used for dilatation catheters has a nominal wall thickness of about 0.005 inch (0.127 mm). Polyimide tubing having a nominal wall thickness of about 0.001 inch (0.025 mm) will provide essentially the same strength and flexibility as the typical polyethylene tubing, but the thin wall thereof provides for a reduction of 0.008 inch (0.203 mm) in profile, which can amount to a reduction up to 40% or more in the outer diameter of the polyethylene tubing. Further details of low-profile steerable dilatation catheters can be found in U.S. Patent No. 4,582,181 and European Patent Application EP-A-0 274 130 filed December 29, 1987. The present invention provides for a substantial reduction in the profiles of a wide variety of dilatation catheters with no loss in steering capabilities or catheter performance. Moreover, the invention allows for the use of guide wires with much smaller diameters. These and other advantages of the invention will become more apparent from the following detailed description of the invention when taken in conjunction with the accompanying exemplary drawings. FIG. 1 is a side elevational view, partially in section, of a dilatation catheter assembly embodying features of the invention; FIG. 2 is an enlarged cross-sectional view taken along line 2-2 of FIG. 1; FIG. 3 is an enlarged cross-sectional view taken along line 3-3 of FIG. 1; and FIG. 4 is a longitudinal cross-sectional view of a low-profile steerable dilatation catheter embodying features of the invention. FIG. 1 illustrates a catheter 10 embodying features of the invention which has an axially extending outer tubular member 11 with a flexible, relatively inelastic inflatable balloon element 12 near the distal end thereof. An inner tubular membe 13 extends coaxially within the outer tubular member 11 and defines an annular passageway 14 therebetween which connects in fluid communication the interior of balloon 12 with a source of inflation fluid at the proximal end of the catheter 10. The distal end portions of the tubular members 11 and 13 are joined together at location 15 by suitable means such as heat sealing or by adhesive to seal the distal end of the balloon 12 and prevent the loss of inflation fluid therefrom. A passageway or other suitable means (not shown) is provided which is in fluid communication with the interior of balloon 12 to allow the passage of air out of the distal portion of the catheter but will prevent the passage of inflating liquid. This allows trapped air to be vented from the balloon 12 as it is filled with inflating liquid. A guidewire 16 extends through an inner lumen 17 in the inner tubular member 13. The diameter of inner lumen 17 is slightly larger than the diameter of the guidewire 16 over a substantial portion of the length thereof. A two-arm adapter 20 is secured to the proximal end of the catheter 10. Guidewire 16 passes through arm 21, and arm 22 is adapted to be connected in fluid communication with annular passageway 14 and a source of inflation fluid (not shown). Outer tubular member 11 may be fabricated of a relatively flexible material such as a low-density polyethylene. However, to facilitate advancement over guidewire 16 in a patient's vasculature, the proximal end portion of tubular member 13 may be provided with a stiffener sleeve (not shown) formed of a more rigid material such as a higher density polyethylene, such as is described in U.S. Patent No. 4,775,371, assigned to the present assignee. The outer tubular member 12 and the tubular stiffener sleeve may be secured together by heat sealing or other suitable means to form a laminated tubular structure which has a relatively flexible distal portion and a relatively stiff proximal portion. The inner tubular member 13, which is shown in FIGS. 1-3, has an inner lumen 17 extending therethrough which is adapted to receive a guidewire 16 therein. The inner lumen 17 has a diameter which is not more than about 0.003 inch (0.076 mm) greater than the outer diameter of guidewire 16 over a substantial portion of the lumen length in order to provide support to the guidewire, particularly when the guidewire has a relatively small diameter, i.e., less than 0.012 inch (0.305 mm). Preferably, the diametric size differential between inner lumen 17 and the guidewire 16 ranges from about 0.0005 to about 0.003 inch (0.013 mm to 0.076 mm) to provide maximum support to the relatively thin guidewire 16 to facilitate the transmission of both torsional and axial forces through the guidewire to enhance its steerability and pushability without buckling of the wire. The diameter of the inner lumen 17 is less than 0.015 inch (0.38 mm) and in a preferred embodiment the guidewire disposed therein has a diameter from about 0.006 to less than 0.012 inch (0.152 - 0.305 mm). The smaller diameter guidewires are useful in small arteries in the coronary and cerebral area. The inner tubular member 13 is provided with a lubricous inner coating or layer 23 such as polytetrafluoroethylene to reduce the friction with the guidewire. The outer surface of the guidewire 16 may also be provided with a similar lubricous coating. The polytetrafluoroethylene (Teflon) layer or coating provides an additional advantage of providing increased lubricity with increased pressure. Thus, when the guidewire 16 moves within the lumen 17, it presses against the Teflon lining of the inner lumen 17 which increases the lubricity of the material, thereby reducing the chances of binding the guidewire within inner lumen 17. Further, while the inner lumen 17 of inner tubular member 13 supports the guidewire 16, the guidewire in turn also supports the inner tubular member 13 and the rest of the catheter assembly 10. Thus, when the catheter 10 is advanced across a lesion, most of the axial force applied to the proximal end of the catheter goes into pushing the distal end across the lesion and not into the buckling or crumpling of the catheter or to overcome the contact friction within the lumen 17. The inner tubular member 13 is formed from relatively thin-walled tubing of polyimide. One presently preferred thin-walled polyimide tubing is the MicroBore™ tubing manufactured by PolyMicro Technologies in Phoenix, Arizona. Another desirable tubing is manufactured from Matrimid™ 5218 from Ciba-Geigy Corp. of Hawthorn, New York. The polyimide tubing may be formed with an inner lubricious lining of polytetrafluoroethylene which may be formed integral therewith or formed as a lining within the tubing. Further information regarding polyimide material may be found in A. Landis, "Commercial Polyimides", Handbook of Thermoset Plastics , Chapter 8, Edited by Sidney H. Goodman (1986), and E. Sacher, "A Reexamination of Polyimide Formation," J. of Macromolecular Science - Physics , Vol. B25, No. 4 (1986) pp 405-418. The polyimide tubing has a wall thickness of about less than 0.003 inch (0.076 mm), preferably within the range of about 0.00075 to about 0.0015 inch (0.0191 mm to 0.0381 mm), to provide mechanical and physical properties comparable to the conventionally used polyethylene and polyvinylchloride tubular products which have wall thicknesses many times thicker (e.g., 0.005 inch (.13 mm)). FIG. 4 illustrates guidewire 16 which is suitable for use with the catheter 10. The guidewire 16 generally comprises a relatively thin stainless steel wire with a short tapered distal portion 26 and a relatively long proximal portion 27, the latter longer portion having a diameter preferably of about 0.006 to about 0.010 inch (0.152 mm - 0.254 mm). The guidewire 16 may also be provided with a thin Teflon coating (not shown) or about 0.0005 to about 0.001 inch (0.013 to 0.025 mm). The tapered distal portion 26 has four sections 30-33 of progressively smaller cross-sectional dimensions with gentle tapers 34-36 between the progressively smaller sections. The last section 33 is preferably flattened. In a typical embodiment, the guidewire 16 has an overall length of about 175 cm. The proximal portion 25 has a length of about 140 cm and an outer diameter of about .010 inch (0.254 mm), section 30 has a length of about 7 cm and a diameter of about .008 inch (0.203 mm), section 31 has a length of about 18 cm and a diameter of about .006 inch (0.152 mm), section 33 has a length of about 1 cm and a diameter of about .004 inch (0.102 mm), and the flattened section 35 has a length of about 0.75 cm and a thickness of about .0008 inch (0.02 mm). Each of the tapered sections 34-36 is about 3 cm in length and provides a reduction in diameter of about .002 inch (0.051 mm) over this length. This guidewire is particularly suitable for use in accordance with the invention with a dilatation catheter having an inner lumen of less than about 0.013 inch (0.330 mm). Helical coil 40 is coaxially disposed about the distal portion 24 of the guidewire 16 with the distal tip of flattened section 33 being secured to plug 41 which is preferably made of radiopaque material. The proximal end of the coil 40 is secured to the tapered section 36 by brazing, soldering, or other suitable means. The coil 40 typically has a length of about 1.5 cm and in one presently preferred embodiment, is fabricated from a platinum wire having a diameter on the order of .0025 inch (0.064 mm) to make the tip of the coil visible under fluoroscopic examination. The use of the dilatation catheter described herein generally may follow conventional procedures, with the added advantage of being able to be advanced much further into a patient's vasculature and to cross much tighter lesions than prior dilatation catheters.

Claims: A dilatation catheter in combination with a thin guidewire of a diameter less than 0.012 inches (0.305 mm) comprising: a) an outer tubular member (11) having an inflatable balloon (12) on the distal portion thereof; b) an inner tubular member (13) disposed within the outer tubular member and defining an annular passageway (14) therebetween which connects in fluid communication with the interior of the inflatable balloon and a source of inflation fluid (22); c) an inner lumen (17) extending longitudinally through the inner tubular member (13) having a diameter which is not more than about 0.003 inch (0.076 mm) greater than the outer diameter of the guidewire slidably disposed therein; and d) means to seal the distal end of the balloon (12) about the distal end of the inner tubular member (13) to prevent loss of inflation fluid from the interior of the balloon (12), said catheter being characterized in that the inner tubular member (13) is formed of polyimide. The dilatation catheter of claim 1 further characterized in that the diameter of the inner lumen within the inner tubular member is less than 0.015 inch (0.38 mm) and said guidewire (16) has a diameter of 0.006 to 0.01 inch (0.15 to 0.25 mm) over a substantial portion of its length. The dilatation catheter of any one of the preceding claims further characterized in that the inner tubular member (13) has a wall thickness of less than about 0.003 inch (0.076 mm). The dilatation catheter of claim 3 further characterized in that the wall thickness is less than 0.0015 inch (0.038 mm). The dilatation catheter of any one of the preceding claims further characterized in that the inner lumen (17) of the inner tubular member (13) has a lubricous surface. The dilatation catheter of claim 5 further characterized in that the lubricous surface is formed with polytetrafluoroethylene. The dilatation catheter of claim 6 further characterized in that the guidewire (16) has a coating of polytetrafluoroethylene of about 0.0005 to about 0.001 inch (0.013 to about 0.025 mm) in thickness.

Inventors: MACHOLD TIMOTHY R, MAR CRAIG E, MUELLER RICHARD L JR, SHANAHAN JOHN P, MACHOLD, TIMOTHY R., MAR, CRAIG E., MUELLER, RICHARD L., JR., SHANAHAN, JOHN P.
Applicants: ADVANCED CARDIOVASCULAR SYSTEM, ADVANCED CARDIOVASCULAR SYSTEMS, INC.
Application year: 1989
Main classification: A61M25
IPC codes: A61M25, A61M29