This invention generally relates to intraluminal catheters, and particularly to balloon catheters used for stent delivery and percutaneous transluminal coronary angioplasty (PTCA).
PTCA is a widely used procedure for the treatment of coronary heart disease. In this procedure, a balloon dilatation catheter is advanced into the patient""s coronary artery and the balloon on the catheter is inflated within the stenotic region of the patient""s artery to open up the arterial passageway and thereby increase the blood flow there through. To facilitate the advancement of the dilatation catheter into the patient""s coronary artery, a guiding catheter having a preshaped distal tip is first percutaneously introduced into the cardiovascular system of a patient by the Seldinger technique through the brachial or femoral arteries. The catheter is advanced until the preshaped distal tip of the guiding catheter is disposed within the aorta adjacent the ostium of the desired coronary artery, and the distal tip of the guiding catheter is then maneuvered into the ostium. A balloon dilatation catheter may then be advanced through the guiding catheter into the patient""s coronary artery until the balloon on the catheter is disposed within the stenotic region of the patient""s artery. The balloon is inflated to open up the arterial passageway and increase the blood flow through the artery. Generally, the inflated diameter of the balloon is approximately the same diameter as the native diameter of the body lumen being dilated so as to complete the dilatation but not over expand the artery wall. After the balloon is finally deflated, blood flow resumes through the dilated artery and the dilatation catheter can be removed therefrom.
To reduce the restenosis rate and to strengthen the dilated area, physicians frequently implant an intravascular prosthesis, generally called a stent, inside the artery at the site of the lesion. Stents may also be used to repair vessels having an intimal flap or dissection or to generally strengthen a weakened section of a vessel. Stents are usually delivered to a desired location within a coronary artery in a contracted condition on a balloon of a catheter which is similar in many respects to a balloon angioplasty catheter, and expanded to a larger diameter by expansion of the balloon. The balloon is deflated to remove the catheter and the stent left in place within the artery at the site of the dilated lesion. See for example, U.S. Pat. No. 5,507,768 (Lau et al.) and U.S. Pat. No. 5,458,615 (Klemm et al.), which are incorporated herein by reference in their entireties. The implantation of a stent at the site of the dilatation can significantly reduce the restenosis rate.
One difficulty has been retention of the stent on the catheter balloon. The balloon must retain the stent during advancement of the catheter within the patient""s vasculature, and yet still provide for expansion and release of the stent once the balloon is positioned at the desired location. It would be a significant advance to provide a catheter balloon having improved stent retention, and without inhibiting balloon or catheter function. The present invention satisfies these and other needs.
The invention is directed to an intraluminal balloon catheter with an elongated shaft, and an inflatable balloon on the shaft which has an inner layer and a discontinuous outer layer. The discontinuous outer layer is formed at least in part of an elastomeric polymeric material. In a presently preferred embodiment, the catheter is a stent delivery catheter with a stent disposed on the balloon in contact with at least a section of the discontinuous outer layer of the balloon.
In one embodiment, the discontinuous outer layer of the balloon comprises woven fibers, or strands, of the elastomeric material. The term woven should be understood to include a variety of arrangements of fibers including a fiber braided, webbed, meshed, wrapped or wound to form the outer layer of the balloon. The fibers may be tightly or loosely woven with openings or spaces between adjacent fibers of a mesh or adjacent sections of a wound fiber of about 0.01 mm to about 0.10 mm, preferably about 0.03 mm to about 0.07 mm. Because the outer layer is discontinuous, it improves stent retention while minimizing the disadvantageous effects, such as increased bulk and stiffness, of providing a continuous outer layer on the balloon.
The outer layer of the balloon extends along at least a section of the working length of the balloon, to provide for improved stent retention thereon. In a presently preferred embodiment, the length of the outer layer is about equal to the length of the inner layer of the balloon. Alternatively, the outer layer may have a length less than the length of the inner layer of the balloon, as for example when the length of the outer layer is equal to or less than the working length of the balloon. Additionally, the outer layer of the balloon may have a length greater than the length of the inner layer of the balloon, so that the outer layer extends beyond the balloon and onto at least a section of the catheter shaft. In the embodiments in which the outer layer extends over the tapered sections of the balloon, the outer layer reduces longitudinal elongation of the balloon when it is expanded under pressure.
The elastomeric outer layer of the balloon is preferably formed of thermoplastic elastomers, including polyesters such as HYTREL or LOMOD, polyamides, polyether block amides such as PEBAX, polyurethane and polyurethane block copolymers such as PELLETHANE. In a presently preferred embodiment, the thermoplastic elastomer is in the same family of materials as the material used to form the inner layer of the balloon, so that the materials are compatible and, consequently, heat fusible together. The elastomeric material provides an outer layer which is somewhat tacky. Consequently, the outer layer improves stent retention on the balloon by frictionally engaging the stent.
The inner layer of the balloon may be formed of a variety of polymeric materials used for forming catheter balloons. The inner layer is preferably formed of a polymeric material which produces a noncompliant or semicompliant inner layer to provide controlled expansion. However, a compliant inner layer may also be used. The compliance of a balloon is a measure of the ease with which a balloon expands under pressure. Noncompliant and semicompliant balloons require relatively higher pressures to expand than do compliant balloons formed from materials such as elastomers. Typically, noncompliant balloons have a compliance of less than about 0.025 mm/atm, semicompliant balloons have a compliance of about 0.025 to about 0.045 mm/atm, and compliant balloons have a compliance of greater than about 0.045 mm/atm. In a presently preferred embodiment, the inner layer is formed of high molecular weight orientable semicrystalline materials such as polyolefin, polyethyleneterephthalate (PET), nylon, polybutyleneterephthalate (PBT), polyethylene napthalate (PEN), and polyetheretherketone (PEEK), providing a noncompliant or semicompliant balloon. In a presently preferred embodiment, the inner layer of the balloon is a single polymeric layer. However, the inner layer may also be multilayered, as for example where the inner layer is formed by coextruding two or more layers of different polymeric materials.
Various designs for balloon catheters well known in the art may be used in the catheter of the invention. For example, the catheter may be a conventional over-the-wire dilatation catheter for angioplasty or stent delivery having a guidewire receiving lumen extending the length of the catheter shaft from a guidewire port in the proximal end of the shaft, or a rapid exchange catheter having a short guidewire lumen extending to the distal end of the shaft from a guidewire port located distal to the proximal end of the shaft.
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