"Modular stent system and delivery means"
Field of the Invention
The present invention relates to a stent for placement in a bodily vessel or cavity and a method of placement of such a stent.
Background of the Invention
Vascular occlusion and occlusion of other vessels is a common form of disease.
Such diseases include atherosclerosis which is characterised by an accumulation of plaque from cholesterol residues. The build up of plaque subsequently thickens and hardens the arterial wall to create an arterial stenosis. The resultant narrowing of the artery has adverse effects on blood flow through the vessel.
Current medical practices and techniques employ both invasive and non- invasive procedures to address stenosis of a vessel. One such procedure involves the delivery of an rahaϊυminal stent to the site of a stenotic lesion.
Conventional use of stents has involved inserting a stent percutaneously through a distal and connecting vessel to that in which the stent is to be used. The device can be inserted through the femoral artery in a catheter to the site in which the stent is to be used, for example for treatment of a stenotic lesion within the aorta. The device is then released f om the catheter and expanded to the required size, extending above and below the lesion to effectively bridge the lesion.
A procedure termed "balloon angioplasty" can also be used in the treatment of Stenotic disease. In this procedure, a deflated balloon is delivered to the site of a stenotic lesion. When in place, the balloon is inflated to break down the stenotic lesion.
Although both of the above procedures are commonly employed, the rate of re- stenosis is uriaceeptably high in both stent and balloon angioplasty procedures. Approximately 40% of patients treated with balloon angioplasty show restenosis of the ' vessel, whereas the vessels of patients treated by stent insertion are likely to restenose in 20% of cases.
The present invention is directed at overcoming problems encountered in the prior art.
Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of. these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed in Australia before the priority date of each claim of this application.
Summary of the Invention
Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
According to a first aspect, the present invention consists in an mtraluminal stent comprising: a first stent member comprising an elongate tubular body, said tubular body having a first cell structure; and a second stent member comprising an elongate tubular body, said tubular body having the same or a different cell structure to the cell structure of the tubular body of the first stent member; wherein the first stent member and the second stent member are capable of expanding or being expanded from a radially compressed state to a radially expanded state, at least a portion of the second stent member being positionable within the first stent member and wherein further said first stent member and said second stent member are rotatable relative to each other.
In a second aspect, the present invention provides a method of delivering and positioning the stent according to the first aspect of the invention in a vessel of a patient, the method comprising the steps of:
(i) introducing a catheter or other delivery device into a vein, artery or other vessel in the body of a patient when the tubular body of the first and the second stent members are in the radially compressed state;
(ii) causing the first stent member and the second stent member to be carried through the catheter or other delivery device to a target site of stenosis;
(iii) causing or allowing the first stent member to move from its radially compressed state to its radially expanded state; (iv) causing or allowing the second stent member to move from its radially compressed state to its radially expanded state such that it overlaps with at. least a portion of the first stent member; and
(v) withdrawing the catheter or other delivery device along with any other apparatus used to introduce the traluminal stent into the vessel from the body of the patient.
In a third aspect, the present invention provides a delivery system for the delivery of the intraluminal stent of the first aspect to a target vessel, said delivery system comprising an introducer catheter having an elongate tubular body to allow the passage therethrough of a placement catheter wherein said placement catheter has an elongate body adapted to carry both the first stent member and the second stent member at a position intermediate a proximal and a distal end of the elongate body.
Preferably, the second stent member is rotatable relative to the first stent member when the first stent member is in its radially expanded state and when the second stent member is in its radially compressed state.
Typically, the first stent member and the second stent member are connected to each other via a connecting means. Preferably, the connection is such that it still enables rotation of the second stent member relative to the first stent member, at least when the second stent member is in its radially compressed state. However, when both the first stent member and the second stent member are in their radially expanded states, the first stent member and the second stent member may be connected such that each stent member is prevented from rotating relative to each other.
The first and the second stent members may be of the same length or of differing lengths to each other.
While the tubular body of the first stent member and the tubular body of the second stent member may be formed of a thin biocompatible material such as Nitinol or stainless steel, other alloys such as tantalum or Elgiloy are also envisaged. The
tubular body of each stent member may be bare or may be coated with a material having an elastic property such that the coating material is capable of covering the tubular body in both the radially compressed state and the radially expanded state.
In a preferred embodiment of the invention, the tubular body of each stent, member may be formed from other suitable biocompatible materials, selected, for best results, on the basis of the material's capacity to withstand the compressive forces of a stenoti c lesion and maintain patency of a vessel throughout the life of the stent,
There are at least three preferred mechanisms whereby the tubular body of both stent members may change from the radially compressed state to the radially expanded state. For instance, the tubular body may be expanded by the force of an irrflating balloon within the tubular body or by some other.mechanically applied force.
Alternatively,, the tubular body of either stent member may be made from a shape memory material as mentioned above wherein the patient's body temperature causes the temperature of the tubular body to rise, thereby enabling the tubular body to self-expand and take on its "memorised" shape.
In a further embodiment, the tubular body of either stent member may self expand following deployment of the tubular body from an introducer catheter used to introduce the stent according to the present invention into the body of a patient This particular embodiment relies upon spring expansion of the material of the tubular body following release of the compressive force of the introducer catheter.
The first stent member and the second stent member may expand by different mechanisms relative to each other. For example, preferably the first stent member is made from a shape memory material as mentioned above wherein the patient's body temperature causes the temperature of the tubular body to rise, thereby enabling the tubular body to self-expand and take on its "memorised" shape.
The second stent member may be of the type which is balloon expandable and, accordingly, may be made from a material such as stainless steel or any other suitable material which is readily radially expanded upon exertion of pressure by a balloon.
Various combinations of the above mechanisms are envisaged, for example, both stent members may be spring expandable or self expandable. Alternatively, both stent members may be balloon expandable. The above examples are in no way lirmting to the various possible combinations of mechanisms to cause or allow the first and the second stent members to move from their radially compressed state to their radially expanded state.
As described in the Ihird aspect of the invention, the first and the second stent members are held on a placement catheter which is moved through the introducer catheter.
When the stent of the invention is appropriately positioned, the introducer catheter may be withdrawn. In this embodiment, it is preferred that the first stent member is self expandable and held in the radially compressed state due to the compression of the introducer catheter. Upon release of this compression, the first stent member moves to its radially expanded state within the vessel of the patient.
The second stent member is preferably balloon expandable such that it may be caused to move to its radially expanded state upon expansion of a balloon member on the placement catheter.
To ensure that both the first and the second stent members are appropriately positioned before me introducer catheter is withdrawn, each stent member may have radio-opaque markers incorporated in their structure. Accordingly, in this embodiment, the surgeon would be able to determine the exact positioning of the first and the second stent members within a vessel(s) of the pati ent before deployment.
The tubular body of the first stent member and the tubular body of the second stent member may have the same cell structure or different cell stractures. In this regard, the cell structure may include relatively large cells with large pores. While one stent member may have a tubular wall with such large pores, the other stent member may have a relatively tighter cell structure with each cell having a relatively smaller pore size. The present invention is in no way limited to particular combinations of cell size or configuration. Furthermore, the cell size and configuration of either stent member may vary along the length of each tubular body. For example it may be desirable to provide a region of the tubular body of either stent member which is made
up of a series of cells which have a smaller pore size relative to the remainder of the tubular body. Such a region provides an area of relatively good expansile strength.
When combined, the mechanical properties of the first stent member and the mechanical properties of the second stent member typically detemiine the overall mechanical properties of the stent of the invention. The first stent member and the second stent member may be rotated with respect to each other either before delivery to the bodily vessel or after delivery to the bodily vessel. The orientation of the cells of stent members relative to each other determines the overall surface area of the intraluminal stent of the invention and the amount of surface contact the stent has with a vessel wall.
Preferably, the first stent member is. made from a relatively thin material which has a relatively poor expansile strength. However, it is desirable that the second stent member has a good expansile strength relative to the first stent member. In this embodiment, the first stent member acts more like a sleeve to the second stent member, the latter providing the skeleton of the stent of the invention and which acts to bridge a stenotic plaque and to kee a diseased vessel open. The second stent member may, therefore, assist in maintaining the first stent member in a radially expanded state.
Additionally, it is preferred that the cells of the first stent member have a relatively smaller pore size than the cells of the second stent member. This is desirable when it is considered that the radial expansion of many stents causes disruption of the stenotic plaque it is designed to bridge. Such disruption may result in fragments of the plaque breaking off and being carried downstream whereupon they may lodge in a smaller vessel, occluding said vessel. Such an embolism is prevented by having the first stent member press against the plaque thereby holding the fragments of plaque^ which may be dislodged by the radial expansion of the second stent member, against the wall of the vessel.
Either, but preferably the first stent member may be used to deliver a treatment means to a vessel of a patient. Examples of treatment means include drugs and radiation emitting substances. Furthermore, the tubular body of the first stent member may be coated with materials to promote adhesion of cells or cell growth to assist in securing the tubular body in place in a vessel.
The first stent member and the second stent member may be interconnected such that the first stent member and the second stent member are delivered to the treatment site together. Alternatively, the first stent member may be delivered to the treatment site prior to the deli ery of the second stent member,
In either case, it is preferred that the first stent member and the second stent member are delivered through the same delivery catheter or other delivery device.
While the second stent member may be packaged substantially internal the first stent member during delivery, it is preferred that the first stent member and the second stent member are longitudinally interconnected such that fhe first stent member leads the second stent member along the delivery catheter. As the stent of the present invention is typically delivered to small vessels in the body, such longitudinal connection is advantageous as it avoids overlapping of the stent members during delivery. Overlapping increases the bulk of the stent and reduces the likelihood of delivering such a device to the smaller vessels of the body.
In the above aspects an embodiments of the invention, the term "cell size" defines the area of the perforations penetrating the wall of a stent. The degree or density of cells alters the mechanical properties and defines the amount of surface area contact a stent will have with an inner wall of a bodily vessel. The manner in which the cells are configured provides expansibility of the stents, arid can allow a stent to be self expandable.
Brief Description of the Drawings
By way of example only, a preferred embodiment of the present invention is now described with reference to the accompanying drawings:
Figure 1 shows an example of a first stent and a second stent;
Figure 2 shows examples of configurations of a first stent member and at least a second stent member;
Figure 3 shows examples of mesh orientation, configuration and cell size;
Figure 4 shows an example of a second stent member internal of a first stent member;
Figure 5 shows an example of the relationship of meshes of a first stent member and a second stent member throughout relative rotation between the first stent member and the second stent member;
Figure 6 shows an example of a stent being delivered to and implanted, within a bodily vessel;
Figure 7 shows a further example of a stent system being delivered to and implanted within a bodily vessel by a delivery means; and
Figure 8 is a perspective view of the second stent member when placed internal the first stent member of the invention.
Detailed Description of the Invention
A stent according to the present invention is depicted in Figs 1 and 8 and comprises a first stent member 10 and a second stent member 20. As depicted in Figure 1 first stent member 10 has a cell size 1, and second stent member has a cell size 2. .
Figure 2 shows examples o configurations in which the first stent member 10 and the second stent member 20 can be assembled with respect to each other. The second stent 20 can protrude from the lumen of the first stent member 10 at one end, both ends or not protrude at all. There can be more than one second stent member 20. Two second stent members 20 can be located within the lumen of the first stent member 10, or a second stent member 20 can be located within the lumen of another second stent member 20. Again, various configurations and combinations of more than one second stent member 20 are possible.
Depending upon the treatment requirements, different stent member combinations can be used. Different combinations of first stent member 10 and second stent member 20 change the mechanical and flexural properties of the composite stent
system. Stents system of different lengths and diameters can be configured depending upon application requirements.
Figure 3 shows examples of different cell densities and orientations. The geometric and material properties of the stent, including cell size, cell orientation, stent inner and outer diameter, cell wall size and material from which the stent is made of, deteπnine the flexibility, strength and behavioural characteristics of the stent.
Figure 4 shows a second stent member 20 within the lumen of a first stent member 10. The stent member 20 can rotate with respect to stent member 10 prior to it being expanded. The mechanical properties of the stent system are determined by the individual mechanical properties of the first stent member 10 and the second stent member 20.
Figure 5 shows an example of a first stent member 10 having a cell wall 3 and a second stent member having a cell wall 4, throughout stages of rotation with respect to each other. The first stent member cell wall 3 and the second stent member cell wall 4 provide an effective combined cell geometry and size for contact with the inner wall of a bodily vessel. Depending upon the phase of rotation and cell size of the stents, the amount of contact area between the outer surface of the stent members and the internal surface of the bodily vessel can be predetermined. This stent system provides adjustable cell size.
Figure 6 illustrates an example of delivery and deployment of a stent system in a bodily vessel 5. A first stent member 10 and a second stent member 20 are contained within the lumen of a stent system delivery means 30. In this example, the stent system delivery means is a catheter. The first stent 10 and the second stent are in a radially όompressed state.
As shown in Figure 6(a), the delivery means 30 containing the first stent member 1 and the second stent member 20, is within a bodily vessel 5. In Figure 6(b), the catheter of the delivery means 30 is partially retracted from the stent system allowing the first stent member 10 and the second stent member 20 to expand so that the outer surface of fhe first stent member is engaged with the inner wall of the bodily vessel 5.
Figure 6(c) shows the catheter of the delivery means 30 fully retracted from the stent system and the first stent member 10 and the second stent member 20 fully expanded such that the outer surface of the first stent member 10 is engaged with the inner surface of the bodily vessel 5.
Figure 7 shows an example of delivery and deployment of a stent system within a bodily vessel 5. In Figure 7(a), the stent system having a first stent member and a second stent member is delivered by a delivery means 30 to a predetermined site within the lumen of a bodily vessel 5.
The delivery means includes a catheter 31 and an inflatable balloon expansion means 32. The first stent member 10 is self expandable and contained within the lumen of the catheter 31 in a compressed state. The second stent member 20 is balloon expandable,
In Figure 7(a), the stent system is partially deployed. The catheter 31 is retracted and the first stent member 10 allowed to partially expand such that it engages with the inner surface of the bodily vessel 5. As shown in Figure 7(b), the second stent member 20 can be expanded by the inflatable balloon expansion means 32 during the expansion of the first stent member 10 as in this example, or after complete expansion of the first stent member 10.
In Figure 7(c), the catheter 31 is fully retracted such that the outer surface of the first stent member 10 engages with the inner surface of the bodily vessel 5 fully, The second stent member 20 is fully expanded during the retraction of the catheter 31 as in this example, or can be fully expanded after the first stent member 10 has fully expanded and engages with the inner surface of the bodily vessel 5.
Figure 7(d) shows the first stent member 10 engaged with the inner surface of the bodily vessel 5, and the second stent member 20 expanded such that the outer surface of the second stent member 20 is engaged with the inner surface of fhe first stent member such that the first stent member 10 and the second stent member 20 cannot rotate with respect to each other.
It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific
embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.