FIELD OF THE INVENTION

The present invention relates to an endovascular catheter, in particular a flexible catheter tip for use, for example, for stent delivery and percutaneous angioplasty. The catheter tip of the invention is specially designed to have features especially useful in percutaneous procedures in which the catheter must traverse stenotic blood vessels, tortuous vessels, or vessels containing previously deployed stents.

BACKGROUND

In standard stent delivery systems, the proximal portion of the catheter is manufactured from materials that make it relatively stiff or inflexible, which endows the catheter with adequate pushability. By contrast, the distal portion of the catheter is manufactured to be rather flexible to allow adequate deliverability of the stent through tortuous vessels to the desired target.

In the case of a balloon catheter, the balloon, which is located at the distal portion of the catheter, is delivered in a deflated state, wrapped around the catheter's inner inflation tube and covered by a crimped stent. The balloon distal shoulder may be fused to the catheter's inner inflation tube. The whole catheter is designed to glide on a guide wire, with the catheter tip serving as the leading part of the catheter to, for example, penetrate a lesion, navigate through a curved vessel, or pass through an already deployed stent within the vessel.

The properties of the catheter tip determine to a large extent whether or not the catheter will catch on the rough surface of the vessel, the surface of vessel lesion or obstruction, or the struts of a previously deployed stent.

Current catheter tips of stent delivery systems and on angioplasty balloon systems are made of plastic material and have a tip shape that is aimed to provide deliverability of the catheter through challenging anatomies. Two parameters may be adjusted to improve deliverability. The catheter tip may be designed to have longitudinal flexibility to accommodate tortuous vessels, and/or the tip shape and its radial rigidity may be modified to avoid collapse of the distal edge of the tip and/or kinking of the proximal neck of the catheter tip when obstacles are encountered. Optimizing both parameters simultaneously in a catheter tip is problematic, as longitudinal flexibility requires a very thin or flexible material, while pushability and radial rigidity require a thick or stiff material.

Therefore, there is a need in the art for an endovascular catheter tip that is longitudinally flexible and pushable and has radial rigidity at its distal end—in particular at the distal edge, to optimize deliverability of the catheter.

SUMMARY OF THE INVENTION

The present invention provides an endovascular catheter tip having longitudinal flexibility, pushability and radial rigidity at its distal end. By longitudinal flexibility is meant an ability to bend along the longitudinal axis (e.g., to facilitate navigation through tortuous vessels). The catheter tip of the invention includes two features. The first feature of the catheter tip includes a spring-like structure, a spring element, that endows the catheter tip with the desired longitudinal flexibility and pushability. The spring element may be made from any suitable material, for example, metal or plastic, and may be manufactured by any of the methods known in the art. In particular, the spring element may have an external diameter that tapers distally, i.e., the diameter decreases from the proximal end to the distal end. Such tapering may decrease the crossing profile of the spring element thereby improving the catheter's deliverability. When tapered, the spring element may further have an inner diameter (lumen diameter) that is constant from the proximal to distal end or tapers at a lesser rate than the outer diameter. The second feature of the catheter tip—the distal end—provides radial rigidity and is rounded and tapered to prevent the distal edge from flaring and catching on, for example, plaque or the strut of a previously implanted stent as the catheter is moved through the vessel. The spring element may act as the second “distal end” feature of the catheter tip. Thus, the spring element provides longitudinal flexibility, radial rigidity, and pushability in the distal-most portion of the catheter tip. By so combining these two features in one catheter tip, the present invention provides a device having otherwise conflicting structural and functional parameters to facilitate deliverability of the catheter.

In one embodiment, the catheter tip further includes a flexible spacer portion, contiguous with the distal end of the balloon and attached to or integrated with the spring element that, in conjunction with the spring element, confers longitudinal flexibility to the catheter tip.

In another embodiment, the spring element may be partially covered by a jacket that connects the balloon shoulder and the spring itself. The jacket may help maintain the natural properties of the spring. In one aspect, the spring element may be embedded in the jacket. Embedding the spring element in the jacket may improve the bond between the spring and the distal fuse section, where the catheter tip connects with the balloon. In a preferred aspect of this embodiment, the jacket covers or embeds a proximal region of the spring element, leaving a distal region, and in particular the distal end, exposed, i.e., uncovered or unembedded. In another aspect of this embodiment the jacket may include a mediating portion similar to the spacer portion that extends proximal of the spring element.

In yet another embodiment, the spring element comprises coils that are tightly packed in a distal section while in a proximal section the spring element includes coils that are spaced apart from each other.

In still another embodiment, the spring element is a wire coil extending to the distal edge of the catheter tip and the distal edge of the coil is smoothed, for example to minimize damage to the vessel wall. In one aspect of this embodiment the distal edge of the coil is smoothed by having a laser polish/weld applied to it. In another aspect of this embodiment, the distal edge of the coil is smoothed by having a bond applied to it.

Thus, the presently claimed catheter tip comprises a differentially tapering spring element, the differentially tapering spring element having an outer diameter that tapers distally at a first rate to a distal edge of a distal end of said catheter tip, and an inner luminal diameter that does not taper at the first rate. The inner luminal diameter may taper at a second rate or may have a constant diameter. The differentially tapering spring element further may be partially covered by a jacket. The jacket may cover a proximal region of the spring element and not a distal region of the spring element, leaving the distal end of the spring element bare, i.e., exposed. The differentially tapering spring element further may be a wire coil having a pitch space between 2 or more coils in a proximal region and/or a middle region of the spring element and tightly packed coils in a more distal region of the spring element.

The presently claimed catheter tip also comprises a combination spring element, the combination including two or more of the following properties: tapering distally, a wire coil having pitch space between 2 or more coils in a proximal region and tightly spaced coils in a distal region, and partially covered by a jacket. In any of these combination spring element embodiments comprising a jacket, the jacket may cover a proximal region of the spring element and not a distal region of the spring element, leaving the distal end of the spring element bare, i.e., exposed. In any of these combination spring element embodiments in which the spring tapers distally, the spring element may have an outer diameter that tapers at a first rate and an inner diameter that does not taper at the first rate. The inner luminal diameter may taper at a second rate or may have a constant diameter.

The apparatus of the invention may be used, for example, for intravascular delivery of prosthetic devices, such as a stent, or for balloon angioplasty. Where a balloon catheter is used, the catheter tip constitutes the portion of the catheter distal to the balloon. In embodiments where the catheter does not have a balloon mounted on it, for example in biliary stent systems where the catheter itself may be expandable, the catheter tip of the invention may be mounted at the end of the expandable catheter to lead the catheter through the biliary duct. Generally, the catheter tip may extend a few millimeters beyond the distal edge of such a catheter.

In addition to the advantage of enhanced deliverability parameters, another desirable effect of the catheter tip of the invention is higher radio-opacity, which may provide the operator with valuable feedback regarding position of the catheter tip during insertion of the catheter into the anatomy to be treated.

