GB2381457A

GB2381457A - Dilatation catheter system

Info

Publication number: GB2381457A
Application number: GB0126113A
Authority: GB
Inventors: Leonidas Diamantopoulos
Original assignee: Thermocore Medical Systems NV
Current assignee: Thermocore Medical Systems NV
Priority date: 2001-10-31
Filing date: 2001-10-31
Publication date: 2003-05-07
Also published as: GB0126113D0

Abstract

A dilatation catheter consists of a catheter body 1 comprising at least two expandable sections 2a, 2b capable of selective independent expansion to deliver stent(s) 3a, 3b to vascular site(s). The expandable sections 2a, 2b may be adjacent or remote from one another. Where a considerable length of vascular tissue is stenosed, a stent delivery catheter may be selected which has a number of adjacent expandable sections 2a, 2b, each carrying a stent 3a, 3b. The catheter may be inserted into the vascular tissue and the expandable section with the stent most closely matched to the stenosed region may be expanded to place the stent, in a tailored fashion, into the vascular tissue. The surgeon can establish whether a sufficient length of tissue has been stented. If not, an additional second expandable section may be positioned in the appropriate unstented region, expanded and a stent delivered accordingly.

Description

Dilatation Catheter System Field of the Invention The present invention relates to a dilatation catheter, more specifically, a catheter capable of delivering one or more stents to a vascular site.

Background to the Invention It is a well known medical practice to use balloon catheters for enlarging the luminal diameter of a blood vessel, for example, at a point of stenosis such as is produced by an accumulation of plaque. The vessel having a stenosis may be modelled as an inwardly protruding arcuate addition of hardened material to the cylindrical vessel wall, where the stenosed region presents a somewhat rigid body attached along, and to, the elastic wall. The stenosis prevents resistence to any expansion of the vessel in the region bridged by the stenosis. Stenoses vary in composition, for example, in the degree of calcification. Stenotic material may be deposited throughout the vascular system and is commonly found in coronary blood vessels that feed the heart but stenotic material may accumulate in localised regions, including the blood vessels and results in restricting blood flow. Restriction of blood flow in the coronary artery, for example, can cause severe health problems including heart attacks and strokes.

In one procedure, known as percutaneous transluminal coronary angioplasty, the patient is viewed on an x-ray imaging screen while a flexible guide catheter is first introduced through the skin an positioned at the ostium of the coronary artery. A guide wire is then fed along the guide catheter and into the coronary artery to a point in the artery which is just proximal of the occlusion. Finally, the dilatation catheter is sent along the guide wire, within the guide catheter, and into the artery of the patient to position the balloon portion of the catheter in the occluded portion of the artery.

Typical dilatation catheters have a flexible shaft which includes a flexible balloon portion at the distal end of the shaft. The balloon portion is capable of expansion when fluid under pressure is directed therein.

When the balloon portion of the catheter has been correctly positioned as seen on the x-ray imaging screen, a radiopaque, fluid contrast medium is introduced under pressure into the space between the inner and the outer tubes to expand the balloon portion which presses against the occluded matter on the inside of the artery. The

expansion of the balloon must be carefully controlled to prevent possible over-expansion and over-stressing of the wall of the catheter which might cause it to rupture, while putting sufficient force on the blood vessel to accomplish the objectives of the procedure. When the desired enlargement of the occluded portion of the artery is completed, the pressure on the fluid inside the catheter is relieved, the balloon shrinks, and the catheter is then removed.

PTCA has, however, two major shortcomings: first, in a proportion of patients treated with PTCA, the treated coronary artery re-occludes within the first 24-48 hours after the procedure, despite the use of anticoagulant drugs to deter the reformation of the occlusion (called "abrupt closure") ; second, in a proportion of patients treated with PTCA, the subsequent healing process in the treated coronary artery is associated with sufficient recoil, scarring and/or proliferation of smooth muscle cells to cause re-occlusion of the artery (catted"restenosis").

In hopes of preventing abrupt closure and restenosis, coronary artery stents were developed (Topol, 1994, N. Engl. J. Med. 331: 539-541). Such stents are tubular devices which provide structural support for maintaining an open vessel.

In order to provide the necessary structural functionality as well as a means for adequate anchoring, stents have been designed which enable the predictable increase or decrease of their radial diameter. Thus, the diameter of a stent may be decreased to permit its introduction into a blood vessel (or similar structure), and then expanded for placement at a desired location. A change in the diameter of such stents may be effected by means integral (self-expanding stents) or ancillary (non-self-expanding stents) to the stent itself.

Self-expanding stents are, prior to placement, maintained in a restrained conformation, such that when the restraints are removed, the stent expands, like a released spring. A stent delivery system for a self-expanding stent typically provides a means for release of the stent after the stent is positioned in the desired location.

Examples of non-self-expanding stents are described in U. S. Pat. No.

4,733, 665 by Palmaz, and include, in particular, the Palmaz-Schatz stent, a single slotted tube of surgical grade stainless steel having multiple staggered slots and a central articulation. The staggered slots allow expansion of the inner diameter of the tube, the surface structure of which assumes a configuration resembling chicken-wire as the stent is stretched to wider diameters. For placement, the Palmaz-Schatz stent

is typically inserted, disposed upon an inflatable balloon at the tip of a catheter, into a stenotic artery, and the position of the stent is secured by inflating the balloon.

A problem associated with stent delivery is that stents are manufactured in predetermined lengths. A cardiac surgeon generally has to calculate how big a lesion is using fluoroscopic techniques and match the stent size to the lesion. This is inherently flawed as fluoroscopy does not present a reliable or accurate picture of the stenotic lesion's dimensions. This can lead to an insufficient sized stent being placed in the region being treated, thus leaving part of an occluded area untreated. Further, the technique may provide too large a stent for a particular region, thus risking damaging healthy tissue adjacent a stenosed region.

Additional, a patient suffering from atherosclerotic plaque may exhibit several dozen atherosclerotic plaques which are vulnerable to rupture. Thus, a number of catheters must be run in and out of the patients body, each one delivering a stent to a vulnerable site of plaque. This can lead to an increased treatment time, an increased risk of thrombogenic events occurring in the body, and thus, trauma to the patient's vascular system.

It would be desirable to provide a device capable of delivering a tailored length of stent to a particular region.

It would further be desirable to provide a device capable of minimising the time and extent of invasive procedure in treating sites of stenosis within a patient vasculature.

Summary of the Invention A first aspect of the present invention provides a dilatation catheter having a catheter body comprising at least two expandable sections capable of being selectively expanded to deliver a stent to a vascular site.

In a second aspect of the present invention, there is provided a method of delivering a stent to a vascular site comprising inserting a stent delivery catheter carrying a stent on a first expandable section and a stent on a second expandable section, expanding the first section to deliver the stent to a first site, and expanding the second section to deliver the second stent to a vascular site.

Generally, the stent delivery catheter comprises a plurality of co-axial lumen.

Preferably, the catheter comprises a central lumen adapted to be mounted on a standard angioplasty guide wire, suitable for vascular intervention. The catheter is

preferably based on a rapid-exchange or monorail system, although over-the-wire techniques are also envisaged. There may be a one or more lumen located coaxially about the central lumen. Additionally, there may be provided a sheath which covers at least part of the outer most lumen.

Preferably mounted on an outer most lumen, there are two or more expandable sections. The number of expandable sections is unlimited, although a range of 2 to 20, preferably 3 to 10, more preferably 4 to 6 expandable sections are provided.

Each expandable section preferably comprises a dilatation balloon, or part thereof. However, alternative expansion means are envisaged, such as cages, concertina type mechanisms and the like.

In the preferred balloon embodiment, the balloons are generally made from a wide variety of polymeric materials. Typically the balloon wall thickness are in the order of 0.0003 to 0.009 inches for most materials.

Preferably, the balloons are made from thermoplastic polymeric type materials and are preferably selected from the group consisting of polyethylenes, ionomers, ethylene-butylene-styrene block copolymers blended with molecular weight polystyrene and, optionally, polypropylene, and similar compositions substituting butadiene or isoprene in place of the ethylene and butylen. Particularly preferred polymers are poly (vinyl chloride), polyurethanes, copolyesters, thermoplastic rubbers, silicone-polycarbonate copolymers, polyamides, and ethylene-vinyl acetate copolymers and polyethylene therephthalate (PET).

The catheter body may be formed from standard catheter lumen materials. For example, nylon, PTFE, polyurethane, polycarbonate and silicones and mixtures thereof are preferred materials. Likewise, the sheath is manufactured from similar materials.

Where a sheath is provided, this is adapted to cover the expandable sections, at least during insertion of the catheter into the vascular tube.

The expandable sections may be expanded using any suitable means.

Preferably, pressure generating means commonly used in intravascular procedures are used. For example, a pump, whereby the pressure may be controlled, is particularly preferred. Such pressure generating means generally are provided with pressure monitoring means. The pressure monitoring means may be provided

integrally with the pressure generating means, or separately thereof. Commonly used pressure monitoring means, such as manometers, are preferred.

The expandable sections are expanded using a fluid, preferably a liquid.

Preferred liquids include blood, saline, water, contrast media and other biocompatible liquids commonly used in interventional cardiology.

The stents delivered by the above-mentioned system, are generally those commercially provided. These vary in both diameter and length, and by method of expansion. The type of stent may be selected by the surgeon and matched to the type of procedure and vascular tissue being treated.

The stents are preferably pre-loaded onto the catheter body, most preferably each stent being loaded exclusively over a respective expandable section. The stents may be retained in place by any suitable means, for example, anchoring, by the sheath where employed, and other methods commonly used in intravascular procedures.

The expandable sections may be adjacent one another, or remote from one another. Thus, where a considerable length of vascular tissue is found to be stenosed, a stent delivery catheter may be selected which has a number of adjacent expandable sections, each provided with a stent. The catheter may be inserted into the vascular tissue and the expandable section with the stent most closely matched to the stenosed region may be expanded to place the stent, in a tailored fashion, into the vascular tissues. The surgeon can then establish whether a sufficient length of tissue has been stented. If this is not the case, a second expandable section may be positioned in the appropriate unstented region, expanded, and a stent delivered accordingly.

Altematively, where a patients vascular system has a number of stenotic lesions, a catheter having the appropriate number of expandable sections, matched to the number of legions to be treated, may be selected and inserted into the vascular tissue. The surgeon may then work through the vascular system, selectively expanding the expandable sections, in order to place a stent in the correct regions. This way, a single catheter insertion is necessary in order to deliver a number of stents, thus reducing the risk of adverse conditions in the patient.

An auxiliary balloon may be provided either adjacent, or remote from the expandable sections. This may be used to fix a stent in place after initial delivery by a given expandable section.

Where the expandable section comprises an angioplasty balloon, each balloon may be fed by the same pressure generating means, or by separate pressure generating means. Preferably, the same pressure generating means is used to feed all expandable sections.

Where the same pressure generating means is used to feed all expandable sections, each section may be fed via a separate, or interconnected conduit.

In a particularly preferred embodiment, a valve system is provided. Such a valve system may be provided within the catheter body. In this embodiment, a first expandable section is expanded by the pressure generating means at a predetermined pressure. Once the predetermined pressure is reached, the valve system may be manually operated or may be operated upon attaining the predetermined pressure, in order to expand a second, preferably adjacent expandable section. Where more than two expandable sections exist, a series of valves may be provided, each of which may be selectively manually operated, or having a range of predetermined valve-operating pressures. Thus, the first expandable section may be expanded at a pressure P, a second expandable section may be expanded at a pressure P+x, a third expandable section may be expanded at a pressure P+x+y, where x and y are individually smaller than P.

Altematively, the valve system may be provided within the expandable sections themselves. In such an embodiment, a multi-celled balloon may be provided, a valve being provided between each cell. This valve system operates in a similar way to that described above.

In an alternative embodiment, a variable compliance balloon may be provided.

In this embodiment, a single balloon is provided on the outer most lumen on the catheter body. The balloon has a variable pressure compliance along the length of its body. Thus, at a first pressure P, a first section of the balloon IS expanded. Upon increasing the pressure further, a second expandable section is expanded at the higher pressure P+x and so on.

The variable pressure compliance balloon may be provided by any suitable means. Preferably, the variable compliance is provided by a technique selected from moulding, orienting and laminating of the balloon materials and mixtures of these techniques. Thus, a moulding or lamination technique could be used to provide variable balloon thickness along the length of the balloon, thus providing the variable pressure compliance. Orientation of the polymer may provide a similar effect.

Additionally or alternatively, chemical modification of the balloon materials may be used to effect the variable pressure compliance. Thus, chemical modification, such as increased cross linking of polymers in a certain region, provide a region which expands at a higher pressure than a less cross-linked region. Such chemical modification may be effected by any of the usual techniques. These include regiospecific light activated (usually UV activated) cross-linking, the regiospecific addition of cross linking catalysts, regiospecific heat treatment and the like.

Brief Description of the Drawings Examples of the present invention will now be described in detail with reference to the accompanying drawings, in which :- Figure 1 shows a cutaway diagram of the catheter body in the region of the expandable sections; Figure 2 shows a variable pressure compliant balloon embodiment; Figure 3 shows a multi-celled balloon embodiment.

Detailed Description A first embodiment of the invention is shown in figure 1. This shows a cutaway of the catheter body 1 bearing two expandable balloon sections 2a and 2b. Two stents 3a and 3b are in place over the expandable balloon sections. A central lumen 4 is provided which allows mounting of the catheter on a standard angioplasty guide wire 5. A conduit 6 allowing fluid communication between a pressure generating means and the expandable balloon sections is provided. This incorporates a valve 7.

In the embodiment shown, this is placed in the region of the conduit that runs longitudinally along the body of the catheter. The valve may also be placed in the necks 8 which connect the longitudinal section of the conduit with the expandable balloon sections. Where the valve is placed in the longitudinal section of the conduit, this provides for ramping of the pressure in series along the length of the catheter. Where the valve is placed in the neck, this allows any predetermined series of pressure compliant valves to be chosen along the length of the catheter.

Figure 2 shows a cross-sectional view of a catheter according to the present invention, wherein the expandable balloon section exhibits variable pressure compliance along its length. A stent is not shown. The catheter body 1, central lumen 4, and guide wire 5 are similar to those presented in figure 1. Similarly, the conduit

6 IS of a similar construction, except that no valving system is present therein. The variable compliance balloon 2 is fed by the conduit through the neck portion 8. The balloon construction shown exhibits a gradation of balloon thickness along the length of the balloon. Thus, in the embodiment shown, the balloon 9 is divided into five regions, 9a, 9b, 9c, 9d and 9e, each exhibiting a predetermined expansion pressure. Thus, the pressure required to expand section 9a will be smaller than that required to expand section 9b which will be smaller than that required to expand section 9c etc. This is achieved in the present embodiment by providing a variable wall thickness of the balloon. Thus, when the fluid pressure is increased to a predetermined level Q, section 9a selectively expands, while sections 9b, 9c, 9d and 9e remain unexpanded.

When the pressure is increased to Q + a, section 9b is expanded, while section 9c, 9d and 9e remain unexpanded. The pressure is incrementally increased until each of the sections 9a-9e are expanded as required. In this embodiment, a series of stents is preferably used. Thus, a first stent would be placed over section 9a, a second over section 9b, a third stent over 9c etc. In the embodiment shown, sections 9a-9e are equidistant. It should be understood that each section may be of different lengths.

Figure 3 shows a cross-section of a third embodiment of the invention. This comprises a multi-celled balloon. The catheter body 1, central lumen 4, and guide wire 5 are similar to those presented in figure 1. Similarly, the conduit 6 is of a similar construction, except that no valving system is present therein. The balloon 10 is fed by the conduit through the neck portion 8.

The expandable sections comprise a multi-celled balloon. The multi-celled balloon 10 may be divided into the four expandable sections shown, denoted 10a, 1 Ob, 1 Oc, 1 Od. Section 1 Oa is expanded when a predetermined pressure is reached.

Section 10a is fed by the conduit through the neck portion. If the pressure is increased, the valve 11, bordering sections 10a and 10b is opened, and section 10b is pressurised. Section 10b will inflate at a second higher predetermined pressure.

The pressure is increased until the number of sections which require expansion in order to treat a stenosis are reached. Each section 10a-10d may bear a stent (not shown).

Claims

CLAIMS 1. A dilatation catheter comprises a catheter body having two expandable sections capable of being selectively expanded to deliver a stent to a vascular site.
2. A catheter according to claim 1, wherein the number of expandable sections is in the range of 2 to 20, preferably 3 to 10, most preferably 4 to 6.
3. A catheter according to claim 1 or claim 2, wherein the expandable sections are balloons.
4. A catheter according to any preceding claim, wherein the expandable sections are discrete from one another.
5. A catheter according to any of claims 1 to 4, wherein the balloon is a multi- celled balloon comprising a valve between each cell.
6. A catheter according to any of claims 1 to 4, wherein the balloon is a variable pressure compliant balloon, wherein the compliance varies along the length of the balloon.
7. A catheter according to any preceding claim, wherein the catheter is a rapidexchange type catheter.
8. A stent delivery catheter, comprising a catheter according to any preceding claim, and at least one stent mounted thereon.
9. A catheter according to claim 8, wherein the catheter comprises an auxiliary balloon which may be located adjacent or remote from stent mounted expandable sections.
10. A method of delivering a stent to a vascular site comprising inserting a stent delivery catheter carrying a stent on a first expandable section and a stent on a

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second expandable section, expanding the first section to deliver the stent to a first site, and expanding the section to deliver the second stent to a vascular site.