EP1404404A1

EP1404404A1 - Balloon catheter

Info

Publication number: EP1404404A1
Application number: EP02740750A
Authority: EP
Inventors: Erik Andersen
Original assignee: Cube Medical AS
Current assignee: Cube Medical AS
Priority date: 2001-06-25
Filing date: 2002-06-24
Publication date: 2004-04-07
Also published as: WO2003000332A1

Abstract

A balloon catheter having a catheter delivery tube on the distal end of which is fitted an inflatable balloon 4, optionally carrying a stent. The balloon 4 is formed of a central cylindrical section 13 reducing by concave tapering sections 12, 14 to respective proximal and distal end sections 11, 15 which are attached to the catheter delivery tube (not shown). The concave tapering sections 12, 14 reduce the incidence of 'dog-boning' during inflation of the balloon.

Description

BALLOON CATHETER

This invention relates to balloon catheters and particularly, but not exclusively, to balloon catheters incorporating stents. Balloon catheters are used in the treatment of various anatomical ducts in the body, such as blood vessels, the urinary ducts, or digestive ducts. A particular application is in the treatment of blood vessels exhibiting stenosis.

The conventional balloon catheter comprises a catheter delivery tube on the distal end of which is mounted a balloon of flexible material. During a balloon angioplasty procedure, the balloon is moved along blood vessels within the body to the site of the lesion and, when correctly positioned, is inflated, usually by means of fluid pressure supplied along the hollow interior of the catheter delivery tube. As the balloon inflates it expands against the vessel wall and thus applies outwards pressure to the wall tending to enlarge the vessel's lumen to remove or reduce the effect of a partly blocked vessel. Once the balloon has been inflated to the desired extent, the pressure is released, and the balloon deflates and is removed, leaving the vessel in its enlarged state. In order to avoid collapse of the vessel after treatment, a stent may optionally be carried by the balloon and left in place when the balloon is removed in order to act as a reinforcement for the vessel wall, thus maintaining the enlarged state of the lumen. There are many designs of stent available and their construction and deployment are both well known. A particular problem with balloon catheters arises as a result of overstretching during inflation of the balloon which not only damages the balloon, rendering it difficult to deflate and fold properly for removal, but more significantly can cause damage to the vessel being treated. This is a particular problem when a stent is fitted, and gives rise to a phenomena known as "dog-boning".

Reference is made to Figures 1 and 2 of the accompanying drawings which show diagrammatically and not to scale a balloon mounted with a stent both before inflation (Figure 1 ) and after inflation (Figure 2). Referring to Figure 1 there is illustrated the wall 1 of an artery to be treated, the artery exhibiting a lesion 2 such as a stenosis or cholesterol plaque. It will be seen that the lumen of the artery is partly blocked in the region of the lesion, and the purpose of the treatment is to restore the lumen to its original size, or something approaching this. To this end a balloon catheter is used. The balloon catheter comprises a catheter delivery tube (not shown) on which is mounted, at its distal end, a balloon 4. Crimped over the balloon 4 is a stent 5. During the surgical procedure, the balloon is moved to the site of the lesion, as shown in Figure 1. Radio-opaque marker bands, normally attached to the catheter delivery tube, may be used, in conjunction with external radiographic apparatus, to enable the surgeon to precisely position the balloon at the correct location. When the surgeon is satisfied that the balloon is correctly positioned, the balloon is inflated via the catheter delivery tube. Thus the balloon 4 and the stent 5 expand together in a radially outwards direction towards the interior of the artery wall. During inflation, two events occur, namely the balloon increases in length along its longitudinal axis while, at the same time, the stent decreases in length. This causes the proximal and distal ends of the balloon to become exposed and thus the expansion of the ends is no longer resisted by the stent. As a result, the ends of the balloon expand at a greater rate than those parts of the balloon surrounded by the stent, and a dog-bone shape, similar to that shown in Figure 2, results. Since the diseased artery wall is likely to be less flexible than the material of the balloon, this excess expansion at the ends of the balloon may cause damage to the artery wall at each end.

In Figures 1 and 2, it is assumed that the stent is positioned centrally over the balloon. However if the stent is incorrectly positioned in relation to the balloon the effect described above may take place to a greater degree at one end than the other, or even at one end only.

The dog-boning effect may be reduced or even eliminated by careful sizing of the stent in relation to the balloon, and by precise positioning of the stent on the balloon. However, due to the different tolerances of the stent, the balloon and marker bands, there is a risk of approximately 2-4 mm inaccuracy when placing the stent in relation to the balloon.

The present invention seeks to reduce or eliminate the dog-boning effect. This is achieved by making one, or preferably both, ends of the balloon concave whereby to better resist the outward force created by the inflation pressure applied to the balloon during its expansion.

Thus, in accordance with the invention, there is provided a balloon catheter comprising an expandable balloon made of flexible material, and mounted on the distal end of a catheter delivery tube, said balloon being made up of proximal and distal end sections which join to the catheter, a central section having a generally cylindrical shape, and proximal and distal intermediate sections joining the central section to the proximal and distal end sections respectively, the balloon catheter being characterised in that, in its unexpanded state, the central section has a greater diameter than the end sections and at least one of the intermediate sections has a concave profile. Preferably both intermediate sections have a concave profile.

In an embodiment of the invention an expandable stent is mounted over the central section of the stent. However the benefits of the invention will be felt in a balloon without a stent.

At least one of the intermediate sections has a continuous curved concave profile from the smaller diameter of the respective end sections to the larger diameter of the central section. It is possible that a small diameter step may be present at the smaller or larger diameter end of the intermediate section, but it will be understood that the majority of the step between the smaller and larger diameters is effected by the concave profile; otherwise the desirable advantages of the invention will not be realised.

The balloon is designed so that, as inflation pressure is applied, it is the central section which expands, whilst the end sections remain attached to the catheter. Thus it is the intermediate sections which act as the interface between those parts of the balloon which expand, and those which do not. To act in this way, the intermediate sections need to be flexible and since, even if a stent is fitted, they are not restrained on the exterior, there is always a danger that they will expand excessively on inflation of the balloon. The use of intermediate sections substantially of concave profile enables the inflation pressure to be resisted to a greater extent.

When a stent is fitted, problems can arise over the poor profile caused by the steps which are inevitably created at the ends of the stent. As discussed in more detail below, these steps can result in injury to the vessels through which the balloon catheter is passed.

In an embodiment of the invention a stiff ring, made for example of polymer material such as Pebax, is fitted over the catheter delivery tube at the distal end of the balloon. The ring is positioned within the balloon beyond the distal end of the stent and thus causes a local enlargement in the unexpanded balloon against which the stent may abut, thus limiting movement of the stent in the distal direction. The ring has an external diameter, when fitted, which is slightly less than that of the unexpanded stent so as to reduce the radial dimension of the step which is formed at the end of the stent. A similar ring can alternatively be fitted at the proximal end of the stent, or rings can be fitted at both ends of the stent, this latter arrangement thus having the effect of trapping the stent between the two local enlargements so formed. The distal and proximal rings may be positioned so as to prevent longitudinal movement of the stent altogether, or a limited degree of movement may be permitted. Conveniently, the distal ring (and proximal ring if fitted) may be positioned at least partially over the marker bands which happen also to be positioned just beyond the ends of the stent.

In order that the invention may be better understood two embodiments thereof will now be described by way of example only and with reference to the accompanying drawings in which:-

Figure 1 is a diagrammatic view of a balloon catheter with mounted stent positioned within an artery, and shown in its unexpanded state prior to inflation;

Figure 2 is a view similar to Figure 1 , but showing the arrangement after inflation;

Figures 3 and 4 are diagrammatic views of two alternative embodiments of balloon catheter according to the invention, shown in their unexpanded state, prior to inflation;

Figure 5 is a lengthwise cross sectional view of the balloon of a balloon catheter according to an embodiment of the invention;

Figures 6 and 7 are views similar to Figures 1 and 2 respectively, but showing the balloon catheter of Figure 4;

Figure 8 is a lateral sectional view showing how the balloon of Figure 5 is folded;

Figure 9 is a diagrammatic sketch showing the cross section of a conventional balloon, with stent, prior to inflation; Figure 10 is a view similar to Figure 9, but showing a ring attached about the catheter delivery tube;

Figure 11 shows the arrangement of Figure 10, after inflation;

Figures 12 and 13 are views similar to Figures 10 and 11 respectively, but showing a ring positioned at both ends of the stent. Referring firstly to Figures 3 and 4 there are shown the two basic embodiments of the invention: one which is concave at one end, and one which is concave at both ends. It should be noted that Figures 3 and 4 are diagrammatic, and are not drawn to scale. In both cases the balloon 4 essentially comprises five sections joined together along a longitudinal axis 10. The five sections are, from left to right:-

1 ) a proximal end section II

2) a proximal intermediate section 12

3) a central section 13

4) a distal intermediate section 14 5) a distal end section 15

The sections are preferably joined together as an integral whole, and are made from flexible plastics material such as polyamide PA. Although the end sections 11 ,15 are not necessarily of the same diameter, they are both of lesser diameter than the central section 13. The intermediate sections 12,14 act to join the respective end sections 11 ,15 to the central section 13. The end sections 11 ,15 are joined to the exterior of a catheter delivery tube 3 which passes through the balloon coaxial with its longitudinal axis 10. Apertures in the wall of the tube as it passes through the balloon allow for inflation of the balloon. Formed on the tube 3 are proximal and distal marker bands 16,17 respectively which are positioned beyond the ends of the stent (not shown). The marker bands are formed as small metal bands mounted on the catheter delivery tube. The bands are radio-opaque so that, with the aid of suitable radiographic apparatus (not shown), the surgeon is able to effectively see the catheter on a display screen, but also make sure that the stent, usually also of metal, can be positioned accurately between the bands.

In Figure 3, the proximal intermediate section 12 is concave over the whole of its length from the reduced diameter of proximal end, section 11 to the larger diameter of central section 13. The distal intermediate section 14 is largely straight, sloping at an angle to the longitudinal axis from the reduced diameter of distal end section 15 to the larger diameter of central section 13.

In Figure 4, both intermediate sections 12 and 14 have a concave shape similar to that of section 12 of Figure 3. A more accurate drawing of the balloon only of Figure 4 is provided in Figure 5 in which typically the total length L1 of the two intermediate sections 12,14 and the central section 13 lies in the range 10 mm to 40 mm while the length L2 of each of the intermediate sections 12,14 lies in the range 2 mm to 5 mm.

The usual way of manufacturing balloons is by blow moulding, and Figure 5 shows the shape of the balloon as it emerges from the mould. The mould used is an external mould, with pressure applied from the interior to blow the balloon material outwards so that it takes up the shape of the mould - in other words, the exterior shape of the balloon corresponds to the interior shape of the mould. Thus, Figure 5 shows the balloon unfolded and in its unexpanded state prior to inflation. When in this state, the central section 10 is substantially cylindrical in shape and the intermediate sections are concave in shape. If required, a stent (not shown) may be fitted over the central section 10. Figure 6 shows diagrammatically the balloon of Figure 5 positioned within an artery 1 to be treated, and prior to inflation. Figure 7 shows the arrangement after inflation - it will be seen that the inflation pressure has caused the naturally concave intermediate sections 12,14 to become convex, but they have not expanded outwardly in the gross way illustrated in Figure 2. Obviously, if extreme inflation pressure were applied, then, dog-boning would occur even with the balloon of Figure 5, but it has been found that, with the pressures normally necessary to expand the balloon, and any stent mounted thereon, the dog-boning effect is substantially reduced or eliminated by the use of concave intermediate sections.

Figure 5 shows the balloon in its unstressed or natural state, prior to the application of inflation pressure. Thus the diameter of the balloon is at its minimum. However, even this diameter is too large to comfortably enable the balloon to be moved to the site of the lesion. For this purpose, the balloon is folded to a smaller diameter and the use of concave ends has been found to assist the folding possibilities. There are various possible folding techniques, one of which is shown in Figure 8 in which the material of the central section of the balloon is folded to form three longitudinally extending "arms" 20 which are circumferentially evenly spaced (i.e. 120° apart). After being folded, the arms are themselves folded around the catheter delivery tube 3 in the clockwise or anticlockwise direction, as illustrated by the clockwise arrows in Figure 8. The result of this is that the balloon can be folded so that its final diameter is substantially constant around the circumference, at around 6 material thicknesses above the diameter of the catheter delivery tube 3. If a stent is fitted, this may be crimped about the folded balloon and carried to the lesion site with the balloon. Thus the inflation of the balloon proceeds in two stages: a first stage in which the balloon unfolds from the folded position shown in Figure 8 to the unstressed position shown in Figure 5, and a second stage in which the balloon material stretches to further expand the diameter of the central section, and any stent mounted thereon. Reference is now made to Figure 9 which shows a conventional balloon catheter 4 prior to inflation, on which is crimped a stent 5. The purpose of this is to illustrate more clearly the steps 6,7 which are created by the proximal and distal ends of stent 5 mounted on the exterior of the balloon. The uneven profile created by the stent can give rise to various problems, particularly bearing in mind that the artery wall 1 in general is not straight, but curved, as the catheter is moved into position:

1 ) damage to the artery wall

2) deformation of the catheter/stent

3) dislodgement of the stent from the balloon catheter All of these problems can, of course, cause harm to the patient. In an embodiment of the invention, shown in Figure 11 , a ring 30 of stiff polymer material, such as Pebax, is mounted on the catheter delivery tube 3, partly over marker band 17 at the distal end of the balloon, and abutting the distal end of the stent 5. It will be noted that the ring 30 is situated within the balloon 4 and the balloon material thus passes over the outer circumference of the ring. The ring 30 will be seen to reduce the relatively large step 6 at the distal end of the stent to two smaller steps, thus improving the profile presented by the combination of the balloon and the mounted stent. Preferably, in fact, the outer diameter of the ring 30 is sufficiently large that the outer diameter of the balloon, as it passes over the ring 30, approximately matches that of the stent so that the stent in fact does not present an edge at all. In a still further embodiment (not shown) the outer diameter of ring 30 is such that the outer diameter of the balloon as it passes over the ring is greater than that of the stent. The presence of the ring 30 prevents the stent from coming into contact with the lesion 2 during angioplasty.

As shown in Figure 12, a similar ring 31 of polymer material may also be added at the proximal end of the stent. The ring 31 is positioned partly over the proximal marker band 16.

Although the rings 30,31 are shown positioned over the respective marker bands 17,16, this is not essential; it is just that the normal positioning of marker bands is immediately adjacent the ends of the stent, and this is the position which the rings 30,31 also best occupy. Since the rings 30,31 are of plastics material, they do not affect the ability of the marker bands 16,17 to be "seen" by the radiographic equipment.

Claims

1. A balloon catheter comprising an expandable balloon made of flexible material, and mounted on the distal end of a catheter delivery tube, said balloon being made up of proximal and distal end sections which join to the catheter, a central section having a generally cylindrical shape, and proximal and distal intermediate sections joining the central section to the proximal and distal end sections respectively, the balloon catheter being characterised in that, in its unexpanded state, the central section has a greater diameter than the end sections and at least one of the intermediate sections has a concave profile.

2. A balloon catheter as claimed in claim 1 wherein both intermediate sections have a concave profile.

3. A balloon catheter as claimed in either one of claims 1 or 2 wherein the concave profile is substantially continuous from the smaller diameter of the respective end section to the larger diameter of the central section.

4. A balloon catheter as claimed in any one of the preceding claims including an expandable stent mounted on the central section of the balloon catheter.

5. A balloon catheter as claimed in claim 4 wherein a ring is mounted within the balloon, on the catheter delivery tube at the distal end of the stent, said ring having an external diameter which is less than that of the stent so as to reduce the step formed at the distal end of the stent.

6. A balloon catheter as claimed in claim 5 wherein a further ring is mounted within the balloon, on the catheter delivery tube at the proximal end of the stent, said further ring having an external diameter which is less than that of the stent so as to reduce the step formed at the proximal end of the stent.

7. A balloon catheter as claimed in either one of claims 5 or 6 wherein the ring at the or each end of the stent is of sufficient external diameter to reduce the step at one or both ends of the stent to zero.