Device for the Removal of Thrombi
The invention relates to a device provided with one or several distal elements (27), with the distal element (27) comprising at least two core wires (14) which are twisted around each other and between which fibers (6) are arranged transversely to the extension of the core wires (14), with said fibers (6) being twisted together with the core wires (14) so that the fibers (6) project radially outward from the distal element (27).
The invention relates to a device for the removal of foreign bodies and thrombi from body cavities and blood vessels using a guide wire provided with one or several distal elements.
Thromboembolic diseases such as cardiac infarction, pulmonary embolism, peripheral thrombosis, organ embolisms etc. are typically caused by a thromboembolism (hereinafter for short thromb or thrombus), i.e. a visco-elastic blood clot comprising platelets, fibrinogen, coagulation factors etc. forming in a blood vessel which it obstructs either wholly or in part. The obstruction of organ arteries also leads to the supply of oxygen and nutrients to the associated tissue being interrupted. The disorder of the functional metabolism linked with functional losses is closely followed by a failure of the structural metabolism resulting in the relevant tissue becoming destroyed (infarction). Organs most frequently affected in this way are the heart and the brain. Nevertheless, the arteries of the limbs as well as pulmonary arteries are also impaired. Venous thromboses and thromboembolic occlusions are frequently occurring in the leg and pelvic veins. The disease pattern of the thrombotic occlusion of an intracranial sinus may lead to severe intracerebral hemorrhage due to a failure of venous drainage of brain tissue.
In view of the severity of the disease patterns associated with thromboembolism and the prevalence rate of such diseases various techniques have been developed aimed at dissolving or removing thrombi.
It is known in this context to treat such patients with thrombolytic agents such as streptokinase or urokinase or anticoagulants intended to achieve thrombolysis or limit the growth of thrombi. Since treatment methods of this kind are usually very time consuming they are frequently combined with invasions aimed at reducing the size of or removing the thrombus or embolus mechanically.
Aside from open surgical operations prior art techniques more and more embrace the use of transluminal or endovascular, catheter-guided interventional therapy methods because these are of less invasive nature. It is thus known to remove the thrombus from the patient's body by means of vacuum producing suction catheters or mechanically using catheters provided with capturing cages, helixes, hooks or similar elements; refer to U.S. Pat. No. 6,245,089 B1, U.S. Pat. No. 5,171,233 A1, Thomas E. Mayer et al., Stroke 2002 (9), 2232.
Disadvantages associated with the known transluminal devices are that with said devices it is often impossible to remove the thromb completely and, moreover, there is a risk of the thromb or fragments of it being released into the blood stream thus passing on to vessels of smaller lumen which are more difficult to be reached and treated. Furthermore, due to their size and/or low flexibility the devices known from prior art are only inadequately suited for the removal of thrombi from greatly convoluted vessels or those of particularly small lumen such as those in the brain.
From US 2002/0049452 a device with a catheter is known for the removal of thrombi to which distal end capture arms made of shape-memory material are attached which in their compressed state rest against the catheter and when expanded extend radially from the catheter outwards. When in expanded position which is caused by the body temperature the capture arms are intended to get caught in the thrombus and then retract it out of the blood vessel as the catheter is pulled back into another catheter. The drawback associated with this device is, however, that in order to cool and thus keep the capture arms below trans-formation temperature before they are released into the blood stream it must either be moved past the thrombus in a secondary catheter which brings about the cooling effect, or a heating system has to be arranged inside the catheter provided with the capture arms that enables the transformation temperature to be attained when the thrombus has been reached. Not only are the design requirements of this configuration very high and thus prone to disturbances it is also the sheer physical size of this device that rules out a treatment of vessels having a particularly small lumen.
In view of the disadvantages of these prior art devices it is thus the object of the invention to provide a device for the removal of foreign bodies and thrombi from body cavities and blood vessels which alleviates the surgical risk existing when removing thrombi and allows the treatment of vessels of especially small lumen.
According to the invention this objective is reached by providing a device for the removal of foreign bodies and thrombi from body cavities and blood vessels using a guide wire and one or several distal elements that comprise at least two core wires which are twisted around each other and between which fibers are arranged transversely to the extension of the core wires, with said fibers being twisted together with the core wires, so that the fibers project radially outward from the distal element.
The distal element thus has the form of a brush provided with bristle-like outwardly projecting fibers. The fibers serve the purpose of capturing and stabilizing a thrombus in that they hook themselves into the thrombus and in this manner facilitate its retrieval. At the same time the fibers/bristles are designed so as to be flexible so that due to the mechanical resistance in proximal direction they press against the distal element when the device is moved forward. When the external strain caused by the micro-catheter is omitted the brush unfolds to assume its full brush structure. Accordingly, to fulfill their intended purpose of securing the thrombus the fibers must have adequate stiffness but at the same time must be sufficiently flexible and bendable so that they can be passed through a catheter and do not damage the vessel walls.
The fibers or bristles are suited to capture and stabilize a thrombus, especially if they are made of or finished with thrombogeneous materials.
The fibers/bristles may also consist of a natural substance, polymer material, metal, ceramic material, glass or combinations thereof. Especially preferred are polymer materials.
Suitable materials in this respect are primarily polyurethane, polyacrylics, polyester, polytetrafluoroethylene, polyamide or polyethylene and, due to its peptide-like bond structure, most notably polyurethane and polyamide, e.g. nylon, which enable the thrombus to excellently attach/adhere to the fibers.
Aside from polymer materials metals also well suited for the intended purpose. Suitable metallic materials for treatment purposes are all metals that do not have detrimental effects on the patients. Especially suited for the described purpose are stainless steel fibers made of metal alloys having shape-memory properties such as for example nitinol fibers. Fibers made of shape-memory materials offer the advantage that when under the external strain exerted by a micro-catheter they are initially shaped to fit closely and after having been released from the micro-catheter assume a second orthogonal shape allowing them to stick out freely. Furthermore, gold and platinum are suitable materials as well. Also suited are ceramic materials, fiber glass and carbon fibers.
Particularly suitable for the treatment of vessels of especially small lumen are fibers having a length of 0.5 to 6 mm and preferably 0.5 to 3 mm so that an outer diameter of 1 to maximum 12 mm of the fiber-carrying part of the distal element is attained even when the fibers are arranged radially. For a particularly atraumatic treatment such outer diameter should be sized slightly smaller than the inner diameter of the relevant blood vessel.
Expediently, the fibers extend over a length of the distal element which ranges between 0.5 and 5 cm. To make sure the thrombus is sufficiently anchored it is expedient if the fibers are arranged on the distal element of the guide wire with a density ranging between 20 and 100 per cm.
The fibers or bristles to be used according to the invention preferably project at an angle ranging between 70° and 110°, preferably at an angle of between 80° and 90° from the longitudinal axis of the device. These angle indications are to be understood such that angles<90° characterize a proximal orientation of the fibers whereas angles>90° signify a distal orientation of the fibers. Embodiments providing for an angle which is slightly smaller than 90° are particularly atraumatic when being moved into the vessel or through the thrombus and at the same time result in an especially effective anchoring within the thrombus when being pulled out of the blood vessel.
Expediently, the guide wire is made of a medical stainless steel or shape-memory material, preferably nitinol. It is expedient in this case to provide a guide wire having an outer diameter ranging between 0.2 and 0.4, preferably 0.22 and 0.27 mm. A typical guide wire length ranges between 50 and 180 cm, but may as well amount to several meters.
As per a particularly preferred embodiment of the device the fibers are coated. For example, this coating may be a neutral one consisting of Parylene or polytetrafluoroethylene (Teflon), but may also be comprised of collagen or may be a coating of a material conducive to blood coagulation, preferably having one or several coagulation factors. This embodiment serves to strengthen the anchorage of the fibers inside the thrombus and alleviates the risk of the thrombus disintegrating to such an extent that fragments of it remain in the blood vessel or may be allowed to be released in the blood stream.
Surprisingly, it has been found that a thrombogeneous finishing of the fibers/bristles resulted in a significant stabilization of the thrombus at the device according to the invention. In this context it is left to the surgeon to bring the inventive device into contact with the thrombus and maintain this contact for a certain period of time thus allowing the thrombogeneous elements to promote an “adherence” of the thrombus to the device. Such an adherence to thrombogeneous fibers/bristles is achieved after a relatively short period, even within a few minutes at times. Not only does this preclude the disintegration of the thrombus as it is encountered with many commercially available devices, also the retraction of the thrombus into the catheter and its extraction from the vascular system is facilitated in this manner. Especially suited thrombogeneous materials and coatings for this purpose are known from literature to those skilled in the art. Especially suitable to this end are, for example, one or several of the factors fibrin, thrombin, factor XIII and/or factor VIII.
The following procedure is to be adopted when using the invention: The device is transferred to the application site with the aid of a small-lumen micro-catheter. The device situated inside the micro-catheter may either be 1) initially maneuvered to the distal location of the thrombus and then retracted, 2) released from the micro-catheter in the area of the thrombus, or 3) pushed out of the micro-catheter at a point proximal to the thrombus and then penetrate the thrombus anterogradedly. When moving the device forward the flexible fibers are pressed onto the distal element in proximal direction due to the mechanical resistance encountered, and when the device is retracted they assume an upright position, hook themselves into the thrombus and thus aid the retraction into a micro-catheter larger than the one originally used. Said larger catheter is usually a guide catheter by means of which a micro-catheter can be introduced coaxially which in turn is used to bring the device to the target area. The thrombus thus secured via the device will then preferably be retracted into the guide catheter and contained in this catheter eliminated from the body.
In the context of this invention the terms “distal” and “proximal” are to be understood as viewed from the direction of the attending physician. The distal end is thus the end situated away from the attending physician which relates to the components of the device advanced farther into the blood vessel system whereas proximal means facing towards the attending physician, i.e. the proximally arranged components of the device are introduced less far into the blood vessel system.
If the phrase ‘longitudinal direction’ is used in this document it is to be understood as denoting the direction into which the device is advanced, i.e. the longitudinal axis of the device also coincides with the longitudinal axis of the blood vessel along which the device is moved forward.
The inventive device is manufactured in such a way that the fibers ultimately forming the brush are placed adjacent to each other and, if so desired, also superimposed on each other between two core wires, with said fibers extending orthogonally to the core wires. It is to be noted in this context that according to the invention an orthogonal extension shall not exclusively mean an angle of exactly 90° but rather any transverse configuration of the fibers in relation to the core wires, i.e. the fibers primarily extend transversely to the core wires, not in parallel. Accordingly, also angles of for instance 700 may be viewed as being orthogonal in the framework of the invention. After the fibers have been placed between the core wires, said wires are twisted together, for example in that one end is fixed while the other one is turned or twisted around the other to bring about a plastic deformation of the core wires thus forming into a spiral structure. After the core wires have been twisted together the fibers project outwardly from the twisted core wires virtually in the form of a helical line. A significant advantage of such a device is that relatively little core wire is required to achieve a very high fiber coverage of the distal element serving as brush. Having to use only a little amount of core wire also offers benefits in that the system retains high flexibility. Moreover, fixing the fibers at the core wires in this embodiment is particularly simple and results in the fibers to be distributed over the brush in very uniform manner.
Quantity as well as density of the fibers can be controlled via the number of core wire twistings or windings so that different hardness characteristics can be produced with respect to the radial force exerted by the brush because the higher the number of windings the more fibers can be arranged per unit of brush length. Moreover, the bending stiffness of the core can be adjusted, inter alia, via the number of core wires and twistings provided. For example, by providing for a great number of twistings or windings of two or more core wires a double helix of these two core wires is formed that is less rigid than with a design wherein fewer windings are provided.
If thought expedient, the at least two core wires may be connected with each other at the distal end and thus form a loop. In this case only a single core wire is used that first extends up to the distal end and then leads back in such a manner that it twists together the two parallelly arranged lines of the core wire with the fibers arranged in between.
At the proximal end the core wires may be connected by means of a coil to additional components of the device located in proximal direction. Such proximally arranged additional components may, in particular, consist of a guide wire or another distal element designed in the form of a brush. A connection with the help of coils of this nature is sufficiently known in the field of medical technology, particularly when occlusion helixes are employed to treat aneurysms. Connecting the coil with the core wires may be brought about in this case by welding, bonding, soldering or mechanical (i.e. force- and/or form-closed) joining methods.
The core wires may consist of platinum or its alloys, in particular of a platinum-iridium alloy, stainless steel, nickel-titanium alloys such as nitinol, or of tungsten and tungsten alloys as well as of combinations of the materials named here.
The core wires and thus the entire brush may have a straight configuration or form into a secondary structure, for example be shaped in the form of a wave or helix, i.e. the core wires themselves which are twisted together are designed such that the core itself has a wave or helix form. It is to be understood in this context that the difference between a wave and a helix is that the geometry of a wave is merely two-dimensional whereas a helix has a three-dimensional configuration. Brushes having a wave or helix form offer advantages in terms of an improved cleaning efficiency. In this context the diameter of the helix may increase either from proximal to distal or from distal to proximal.
In the case of a secondary structure formed by twisted core wires an elongation preventing filament may additionally be run through the inner space of the secondary structure or external to it, with said filament ruling out an axial extension of the device beyond the nominal length. Elongation preventing filaments of this nature may be made of polymer materials (e.g. nylon) or metal, such as, for example, nickel-titanium alloys (nitinol). The filaments in this case are connected both distally and proximally to the secondary structure formed by the core wires. The elongation preventing filament itself may have a straight, wave-like or helix-shaped geometry, with the two latter variants allowing for a certain tolerance or play in longitudinal direction with respect to a possible axial extension. However, to achieve a still sufficient protection against elongation such a helix should have a very high pitch resulting in the tolerance or play with respect to axial extension to be kept within certain limits.
The core wires mentioned above must not necessarily be conventional wires having a round cross section but may be provided in the form of cut or shaped form elements, for example if the core wires are cut from a plate. In this case the cross section of the core wires is not round but quadratic or foursquare.
In accordance with another advantageous embodiment the device is provided with several distal elements from which fibers stick out radially. Such a system consisting of several brushes may, for example, offer benefits if particularly large thrombi or, as the case may be, several thrombi have to be eliminated from the blood vessel system. Furthermore, a brush located farther distally may serve, if need be, to intercept and remove fragments of a thrombus that detach from the proximally arranged brush.
To enable an adequate flexibility to be achieved despite the length of such a system comprising several brush portions it is considered expedient to interconnect the individual distal elements by means of connecting elements, especially articulated joints. Such an articulated joint makes it possible for the device to perform within certain limits bending movements and thus follow the configuration of the blood vessels.
As the case may be, several distal elements forming a brush, preferably two or three brushes, may be arranged side by side as viewed in the cross section of the device, preferably in parallel. These brushes are in turn interconnected proximally and distally, for example in that the core wires of the brushes again converge centrally on the proximal and distal sides. Such an embodiment offers the advantage that each individual brush may be provided with shorter fibers because the fibers need not extend from the center of the device to the inner wall of the vessel but merely from the individual distal elements that are near the vessel walls in the event they are arranged side by side. Since fibers that are shorter or stick less far out of the distal element are in any case harder the cleaning efficiency may be improved even more in this way. If thought expedient, the individual brushes may also be twisted further so as to form a helix. Furthermore, the distal elements may be provided with braces (expediently at least 3) that start out from the distal end of the distal element, extend radially outward and again converge centrally at the proximal end of the distal element. The radial extension of the braces preferably corresponds roughly to the radial extension of the fibers. Throughout the middle area the braces thus extend for the main part in parallel with the inner core of the distal element. The provision of braces on the distal element serves as additional guide for the system in the blood vessel. To a certain extent the braces impart a resemblance to cage structures, but the braces in this case need not be arranged such closely so that it cannot be said in any circumstance that a true cage structure exists.
In cases where the device is provided with several distal elements having outwardly projecting fibers the braces may span in each case over one distal element or over several distal elements. In the event of two distal elements the braces may, for example, extend from the distal end of the distal element located farthest away in distal direction and only converge at the proximal end of the proximal brush. In this case it is expedient to arrange additional intermediate braces between the braces and the centrally extending core wires and in this way enhance the stability of the structure formed by the braces.
In accordance with another advantageous embodiment of the invention the brushes have a tapered structure, i.e. the radial extension of the fibers which eventually corresponds to the brush diameter increases from proximal to distal. The main advantage of such a tapered brush form is that irrespective of the width of the blood vessel to be cleaned at a time there are always at least some brush portions the fibers of which are of optimum length. Fibers have an optimum length for a given blood vessel especially if the fibers contact the walls of the blood vessel in such a way that they are not bent in distal direction when the device is moved proximally. In this case the cleaning efficiency of the fibers is particularly good. Longer fibers, on the other hand, are bent distally during the return movement in proximal direction so that their cleaning efficiency diminishes whereas short fibers may not even reach the inner wall of the vessel and are thus incapable of providing a cleaning effect anyway. Due to the fact that with a tapered brush shape not all fibers are of equal length there are even in the case of varying blood vessels always at least some fibers that have an optimum cleaning efficiency.
Preferred is a tapered distal element (brush) wherein the radial extension of the fibers increases from proximal to distal. This can be achieved in that fibers of increasing length are placed from proximal to distal between the core wires. Such a brush offers the advantage that should the situation arise the distally arranged longer fibers are capable of also capturing individual thrombus fragments if the device is retracted in proximal direction. However, tapered brushes are also conceivable wherein the radial extension of the fibers increases from distal to proximal.
In this case the tapered brushes may be of different shape, and it will basically be adequate of they are of tapered configuration. However, also several tapered brushes may be provided which are interconnected by means of an articulated joint, or many short tapered segments on a single distal element.
Additionally or alternatively the fibers in the proximal area of a distal element may also be designed to be harder than in the distal area. The harder fibers in the proximal area in this case mainly serve to scrape off a thrombus adhering to the vessel wall while the softer fibers in the distal area primarily serve to secure or retain the thrombus or fragments of a thrombus. Another possibility warranting that fibers of different length are provided so that at least some fibers always have an optimum length is to arrange the individual fibers in such a way that they have a shorter and a longer side when sticking out on both sides of the core wires twisted around each other. This can be brought about by placing the fibers, before the core wires are twisted around each other, not exactly centered between the core wires but in an irregular fashion.
Further possibilities of producing on the distal element fibers of different length are to use even at the time of twisting differently long fibers so that an irregular brush structure is arrived at in this way or to produce tapered brushes the diameter of which increases from distal to proximal. However, more advantageous is the variant described heretofore wherein the radial extension of the fibers increases from proximal to distal because the longer fibers in this case are situated to the rear when the device is retracted in proximal direction so that thrombus fragments may be intercepted in this way.
To facilitate the capture of a clot (thrombus) the brush of the distal element may be differently designed along its core. Some areas, for example, especially the area in the middle of a brush may be provided with softer fibers, with these fibers serving to retain the clot. Areas located further proximally or distally provided with harder fibers on the other hand are rather intended to produced a more intense cleaning effect.
A similar effect is achieved if the density of the fiber coverage in some areas is lower, especially in the middle area of the distal element, than in other areas. This as well produces the effect that the proximal and distal areas of the brush where the fibers are more densely arranged primarily serve to enhance the cleaning effect on the walls of the vessel whereas the less densely covered middle area is intended to capture the clot.
The fibers placed between the twisted core wires are primarily secured in that they are clamped in place when twisting is carried out. However, further fixation can be achieved additionally or alternatively by bonding, knotting and/or fusing methods.
The fiber ends located radially outward beneficially are provided with slubs or thicker nubs, for example of spherical shape, so that increased surface is available for better clot mass retention. Another advantage of this embodiment makes it possible in this way to provide fiber ends that have an atraumatic effect. The thicker nubs at the ends of the fibers may for example be produced by cutting the fibers with the aid of methods like micro-laser cutting, electron beam cutting etc.
In accordance with another embodiment the fiber ends located radially outward are at least partially connected with each other via loops. The fibers connected in this manner thus comprise or are made up by a single fiber and not two fibers with the single fiber having a loop-shaped configuration. The fiber emerges from the core, extends to the outer rim of the brush where it forms into a loop and then runs back to the core. The fiber in this case extends such that an elliptical shape is formed. This embodiment offers advantages in that, similar to the thicker nubs at the end of the fiber, there is a larger surface available for clot mass retention which results in the thrombus capturing effect being improved. Furthermore, the roundness of the loop makes it atraumatic. Also beneficial is that the fibers have increased stiffness due to the loop-shaped fiber configuration exhibiting a behavior similar to that of two fibers arranged side by side.
As per a further embodiment the core wires in the cross section of the distal element extend outside the center, i.e. have eccentric extension. Such a brush with an eccentrically arranged core has the effect that on one side of the brush relatively short fibers are located while long ones exist on the other side of the core. As a result of their short distance to the core the short ends of the fibers have significantly harder characteristic and the long fiber ends are significantly softer so that in this case as well the harder fibers rather improve the cleaning effect whereas the softer fibers enable a better retention of the captured thrombus. A brush with eccentrically arranged core offers still another advantage in that such a brush can be maneuvered past the side of a clot more easily and then be retracted so that while the brush moves back in proximal direction the thrombus is captured.
The brush-shaped devices described hereinbefore may basically be used for the filling of aneurysms as well. In such cases the brushes should be designed in the form of a helix which are relatively short in comparison to brushes that serve the purpose of eliminating thrombi. To be able to place the brushes into aneurysms the distal element(s) have to be designed so as to be detachable from the guide wire. To be able to fill the aneurysm more completely the bristles may also be provided with an adhesive or a thrombogeneous coating.
The tapered form of a brush as described earlier where the diameter of the distal element increases from proximal to distal has turned out to be especially advantageous. Aside from a device providing for the above described arrangement of fixing the fibers between two core wires another device is as well basically conceivable for the removal of foreign objects and thrombi from body cavities and blood vessel wherein the distal element has a tapered form, the diameter of the distal element thus increasing from proximal to distal or vice versa. Preferred is a tapered form wherein the distal element has a diameter that distally is greater than proximally.
In accordance with an alternative embodiment (irrespective of the brush structure described above) a device with guide wire is provided for the elimination of foreign objects and thrombi from body cavities and blood vessels, wherein said device is provided with a cage structure at the distal end of the guide wire which is composed of individual braces and suited to be flatly collapsible under the external strain exerted by a micro-catheter and capable of being transported inside the micro-catheter and unfolding to its full cage structure as soon as the external strain caused by the micro-catheter is omitted, with said cage structure comprising at least two cages arranged in longitudinal direction one behind the other.
Such a device with cage structure for the removal of thrombi is in principle intended to accommodate thrombi in its interior and in this way enable thrombi to be eliminated. The cage structure in collapsed condition is transported inside a micro-catheter through the blood vessels to the target site where it is then pushed out of the micro-catheter distally of the thrombus to be removed whereupon the device unfolds and assumes its full cage structure. The cage structure may accommodate the thrombi to be removed either completely or in fragmented form. Subsequently, the device is retracted through the blood system and, after it has been pulled into a catheter which may be provided in the form of an additional guide catheter having a greater inner diameter than the micro-catheter within which the cage structure was brought to the target site, finally and completely removed from the blood vessel system together with the thrombus.
Generally, the cage structure has an oblong, ship-like structure of a length ranging between 5 and 50 mm with a diameter of between 2 and 6 mm in expanded state. The cage structure is composed of peripheral, in particular longitudinally extending braces which as a rule are regularly spaced over the circumference.
According to the invention this cage structure comprises at least two cages arranged in longitudinal direction one after the other so that a double-cage structure is formed. Two or more successively arranged cages offer the advantage that the cages may serve different purposes. For example, the proximally arranged cage may serve as cutting tool for the thrombus or clot that has formed within the vessel whereas the distal cage serves to accommodate the thrombus or the fragments of it. Such a fragmentation of the clot is of special significance if the clot in its entirety is too big to be accommodated entirely within the cage structure or has hardened to such an extent that it is very difficult to maneuver it into the cage structure. It is to be assumed that especially older thrombi show such hardening tendencies.
As mentioned earlier, the cage structure is composed of braces which preferably extend at least partially in longitudinal direction. It is to be noted in this respect that by ‘braces extending in longitudinal direction’ not only braces are meant that are running exactly parallelly to the longitudinal axis but also those extending at a certain degree of <90° to the longitudinal axis in distal or proximal direction. It is to be noted further that in order to form a true cage structure it must preferably be composed of at least three, but even better of four to eight braces. It is also considered expedient for the cage structure and thus the braces to be made of shape-memory material, preferably nitinol, which enables said structure to be transported in folded-up condition in a micro-catheter and unfold automatically when released from the micro-catheter.
The process of unfolding to the full cage structure upon omission of the external strain exerted by the micro-catheter must not necessarily take place automatically but may also be effected manually. For example, an additional guide wire may be attached to the cage structure which causes the cage structure to unfold when being advanced.
Expediently, a core filament extends centrally through the cage structure. This core filament constitutes the distal segment of the guide wire or is a separate core filament serving as continuation of the guide wire in distal direction.
Folding up of the cage structure under the influence of the external constraint caused by a catheter is normally associated with a stretching of the cage structure. To counteract this stretching or facilitate radial expansion associated with a longitudinal contraction when the cage structure is released from the catheter it will be expedient for the cage structure to be movably designed allowing it to follow these stretching/contraction movements. Therefore, the cage structure should be movable relative to the core filament at least at its proximal end. This can be achieved in such a manner that the cage structure terminates in a sleeve at its proximal end through which the core filament movably extends in longitudinal direction.
Since with the inventive double-cage structure the cage arranged further distally shall primarily serve as cutting tool for the clot to be removed whereas the distal cage is intended to accommodate the clot, it is considered expedient to appropriately design the cages such that they can fulfill their duty optimally. To this end the distally located cage may thus be designed to be longer for instance to make available sufficient space for the thrombus to be taken in. On the other hand, the proximal cage intended to fragment the thrombus may be designed to be shorter in longitudinal direction.
Considering the necessity that the proximally arranged cage must exert such forces on the thrombus that are necessary to fragment it, it is moreover deemed expedient to design this cage so as to be harder than the distally arranged cage. A harder design in this context is to be understood such that the radial forces required to bring about deformation are higher than the radial forces necessary to deform the distally arranged cage. By providing an appropriately hard design for the proximally arranged cage even very old and already severely hardened thrombi can be scraped off the vessel wall or fragmented to such an extent that after they have been accommodated in the distally arranged cage they may be eliminated from the blood vessel.
To enable the proximally and distally arranged cages to fulfill their duty they can be manufactured of different materials, and for this purpose a harder material should be used for the proximal cage as mentioned above. For example, different nitinol materials may be used here, i.e. especially different alloys. Alternatively or additionally also the braces of which the proximally arranged cage is formed may have a greater diameter than the braces of which the distally arranged cage is composed. In this way it is ensured as well that the proximal cage not only is harder but also capable of withstanding higher radial forces.
It is also possible in this context to select a suitable angle determining the position of the braces in relation to the longitudinal axis. The braces of which the proximally arranged cage is made may thus extend in relation to the longitudinal axis at least partially at an angle greater than that of the braces of the distally arranged cage which results in the proximally arranged cage to be less easily collapsible by radial forces. The distally arranged cage thus has a somewhat flatter structure which will be noticeable particularly if the distal cage is designed to be longer than the proximal cage.
In cases where on account of extraordinarily big thrombi the amount of clot material to be taken in is particularly great cage structures may be employed that comprise more than two cages. All the cages thus provided distally of the proximally arranged cage will then serve to accommodate clot material.
As mentioned above, the cages may be composed of braces of different number with the highest cage density being achieved of course in the cage that has been provided with the greatest number of braces. It has turned out, however, that depending on application it may be expedient not to provide too many braces lest the proximal opening of the cage structure through which the thrombus shall enter the cage structure may be too small. Viewed in the proximal cross section of the cage structure the partial openings between the braces will be all the greater the fewer braces are provided. This is of special significance if the thrombus is rather old and thus firm and coherent and creates problems when it is attempted to capture it through the openings in the cage structure. To handle thrombi of this type it has turned out to be especially advantageous to provide for a number of braces ranging between four and six.
Conceivable are of course also combinations configured in such a way that the proximal cage which the thrombus must first enter when the cage structure is retracted within the blood vessel system is provided with fewer braces than the distally arranged cage which is designed to accommodate the thrombus already fragmented by the proximal cage.
The braces of each cage usually meet at the distal and at the proximal end of the cage each in a point which is preferably arranged centrally. At the points where the braces converge the braces may be connected with each other directly or indirectly by means of a connecting element. If thought expedient the connecting element may be designed in the form of a sleeve which in relation to a centrally extending core filament is longitudinally movable so as to facilitate in this way stretching and contraction of the cage structure when moved into or out of the catheter.
Besides the above described approach of reducing the number of braces there is another method by means of which the proximal opening of the cage structure can be made larger, said method providing for the partial openings existing between the braces to be enlarged at least partially, so that in this manner a strongly coherent thrombus is allowed to enter more easily. For this purpose the large partial openings existing between the braces are enlarged which in turn causes the size of small partial openings to reduce. This can be brought about by arranging the braces of at least one cage, preferably the proximally arranged cage, such that they extend, with the cage structure unfolded, from the point where the braces at the proximal cage end converge, in groups along a first section, e.g. in pairs close to each other in distal direction, then diverge distally to this first section, and in a second section distally to the first section extend equally distributed in distal direction over the circumference of the cage. In other words, the braces do not uniformly extend along the entire cage equally spaced over the circumference but such an equal distribution is provided in distal direction only some distance away from the proximal opening. Due to the fact that the braces at the proximal end of the cage initially are grouped close to each other, partial openings are created the size of which giving the impression as if only half or a third of the number of braces were used. In case a total of four braces are provided two pairs of braces each run together for example at the proximal opening so that two significantly enlarged partial openings are created which are almost semicircular whereas the remaining small partial openings left between the braces closely adjacent to each other can be neglected. Similarly, if a total of six braces are provided with said braces initially extending in pairs, partial openings almost the size of a third of a circle would be produced. If along the first section three braces each are arranged close to each other in distal direction, two almost semicircular openings are even created if six braces are provided. Basically, such an approach providing for the partial openings to be enlarged in part is of course also conceivable in the event of cage structures that merely consist of a single cage.
The braces forming the cages may be of identical design for the proximal and distal cage. In this case the braces will extend from the proximal end of the proximally arranged cage to the distal end of the distally located cage. To make sure that the braces form a double-cage structure and do not merely build up a greatly extended cage they will preferably cross each other at least partially so that the junction point where the braces meet constitutes the distal end of the proximally arranged cage and at the same time the proximal end of the distally located cage. Such an embodiment offers the advantage that the radial forces being exerted on the distal cage and on the proximal cage will influence each other because the radial forces in the braces are transmitted to the other cage. In this manner the device may retain its unfolded shape even if the nominal diameter cannot be realized in a given vessel. This is particularly true if the measures for a length adjustment of the cage structure as described hereinbefore have been provided.
At the junction point the braces may be interconnected and/or attached to the core filament. Preferably, no connection will be provided, however, because the radial forces effect will not be disturbed in this manner.
Furthermore, the radial forces may also be influenced by not entirely pushing the device out of the micro-catheter. For example, if only the distal cage is moved out whereas the proximal one is kept within the micro-catheter the radial force of the distally arranged cage increases. This may be advantageous in the event especially firm clots/thrombi have to be retrieved.
The radial forces will influence each other particularly well if from the proximally arranged cage to the next distally located cage the braces are run to the opposite side of the cage structure, i.e. if there is an offset by 180° from one cage to the next.
The cage arranged farthest in distal direction may expediently be designed to have a net structure at least distally so as to provide increased safety against losing thrombus fragments that may slip out of the cage when the device is retracted out of the blood vessel. This net structure may in particular be composed of braided wire for which, same as for the braces, nitinol can be used. Expediently, such a net structure of a cage is arranged especially at the distal end because for the removal of the thrombus the cage structure after all is moved in proximal direction so that a net structure located at the proximal end of the cage would be less desirable as it could in fact prevent the thrombus from entering the cage. Accordingly, the net structure should only be located at the distal end of the cage or should become more fine-meshed from proximal to distal. Moreover, a greater mesh size in the proximal area of the cage facilitates the retraction of the cage into the catheter with the structures collapsing and containing the thrombus.
A function similar to that of the net structure just described can also be achieved by providing a cover on the distal side of the distally arranged cage in the form of a polymer skin. Providing such a polymer skin which may for example consist of expanded PTFE (polytetrafluoroethylene) results in the distal end of the cage forming a bag-like structure. The polymer skin in this case extends from the distal tip of the cage along the braces on to a desired position, for example to roughly the middle of the cage. At the distal end of the cage the polymer skin may be provided with one or several openings of a size big enough to allow liquid, especially blood, to pass through without difficulty whereas the thrombus or fragments of a thrombus captured by means of the cage structure are retained. This is advantageous, in particular, when the cage structure is retracted because such a configuration will in fact not impair the flow of blood while the thrombus itself can be completely eliminated from the blood vessel system.
As per another beneficial embodiment the braces of the cage structure are arranged in a helical fashion, i.e. the distal end and the proximal end are offset against each other by an angle ranging between 45° and 180°, preferably by approx. 90°. Such a helical line arrangement allows a thrombus adhering to a vessel wall to be sheared or cut off when the cage structure is moved forward without the necessity of having to turn to device.
In accordance with another variant the braces extend along a wave line with a lateral deflection of between 45° and 90°, i.e. the braces at first extend in lateral direction until they have reached for instance a point offset by 90° to the starting point and then along the second half of their length extend back to the starting point. In this case the proximal end and the distal end are not offset against each other.
In accordance with an especially preferred embodiment the device not only comprises a cage structure arranged at the distal end of the guide wire but in the area of the cage structure has additionally been provided with fibers or bristles projecting radially outward, with said fibers or bristles being arranged individually or in bundles.
The fibers or bristles are connected with a distal element of the guide wire in a manner known per se, for example, as is known from the fabrication of fiber-equipped embolization spirals. This may be achieved through entwinement with the distal element, by gluing, welding or any other suitable fastening method.
Advantageously, the device is provided with one or several radiopaque markers. These may, for example, be made of platinum or a platinum alloy. Radiopaque markers of this kind may be located both in areas from which the fibers or bristles emanate and as well on the cage structure to enable the attending physician to monitor the treatment with the help of image-forming methods conducive to the purpose.
Moreover, it is considered advantageous if the tip of the entire device is designed so as to be atraumatic, i.e. is rounded off for example.
The distal element of the device which is provided with fibers expediently extends centrally in the cage structure, i.e. the fiber-covered element is in fact located in the center of the cages. In this manner, the beneficial effect of the cage structure on the one hand and those of the fibers arranged on the distal element on the other are combined with each other. This design enables the captured thrombus to be secured and retained most safely both by means of the cage structure and the fibers so that the thrombus can be retrieved and drawn into a catheter.
The fibers or bristles may be arranged on and attached to in particularly one or several movable filaments located on the core filament extending through the cage structure so that the fibers/bristles virtually stick out radially from the cage structure in radiated form. The movable filament may, for example, consist of a helically wound wire. Alternatively or additionally, fibers or bristles may also be secured to the braces of the cage structure.
It shall, furthermore, be observed also with respect to the embodiment of the invention relating to a cage structure that with respect to the fibers all comments made hereinbefore in the context of the brush-like distal element shall apply as well, in particular regarding the material used for the fibers, the angular alignment, the length of the fibers, the coating of the fibers, the use of radiopaque markers etc.
Moreover, all the described embodiments of the invention may be combined with each other. Especially, the embodiment providing for a double-cage structure may have additional fibers, whereas, on the other hand the embodiment providing for fibers emanating from the distal element may additionally have a cage structure. In particular, a combination of double-structure and distal element composed of core wires twisted around each other with outwardly protruding fibers is also possible.
Eventually, the invention also relates to the combination of the device with a guide and/or micro-catheter in which the device is maneuvered to the application site and when filled with the thrombus removed from the blood vessel system. It may be expedient to additionally design the catheter in the form of an aspiration catheter capable of accommodating micro-catheters.
The above described invention is of special significance to the removal of thrombi from vessels of especially small lumen, in particular intracranial. The invention may of course be used also for the elimination of thrombi from other parts of the body, for example the heart, lungs, legs etc. However, the invention may also be used for the removal of other foreign objects from blood vessels, for example removing embolization spirals and stents.
Further elucidation of the invention is provided by way of examples through the enclosed figures, where
The invention is elucidated by way of
When core wires 14 have been twisted around each other the distal element 27 appears as shown in
It is also evident from
Another representation of a helical distal element can be seen from
Another embodiment is shown in
Another embodiment with braces can be seen from
Likewise, the embodiment shown in
As per an alternative embodiment of the invention
Since both cages 2, 3 are formed by the same braces 4 it is ensured that radial forces are transmitted from one cage to the next, and, for example, radial forces acting on the proximal cage 2 increase the outwardly acting radial forces exerted by the distal cage 3. For example, for the retrieval of particularly firm thrombi only the distal cage 3 may be pushed out of a micro-catheter while the proximal cage 2 is left inside the micro-catheter so that as a result of the external constraint the micro-catheter exerts on the proximal cage 2 the outwardly acting radial force of distal cage 3 is significantly increased.
It must be pointed out in this context that
1. Device for the removal of foreign objects and thrombi from body cavities and blood vessels comprising a guide wire (18) provided with one or several distal elements (27), characterized in that the distal element (27) consists of at least two core wires (14) which are twisted around each other and between which fibers (6) are arranged transversely to the extension of the core wires (14), with said fibers (6) being twisted together with the core wires (14) so that the fibers (6) project radially outward from the distal element (27).
2. Device according to claim 1, characterized in that the core wires (14) are connected with each other at the distal end in such a way that they form a loop (16).
3. Device according to claims 1 or 2, characterized in that the core wires (14) are connected at their proximal end via a coil (17) with other, proximally arranged components of the device.
4. Device according any one of claims 1 to 3, characterized in that the core wires (14) are made of platinum or a platinum alloy, platinum-iridium, a nickel-titanium alloy, tungsten, a tungsten alloy, stainless steel or a combination thereof.
5. Device according to any one of the claims 1 to 4, characterized in that the twisted core wires (14) extend in a straight line.
6. Device according to any one of the claims 1 to 4, characterized in that the twisted core wires (14) form a secondary structure.
7. Device according to claim 6, characterized in that an elongation preventing filament extends through the inner space of the secondary structure or external to the secondary structure.
8. Device according to claim 7, characterized in that the elongation preventing filament is designed in the form of a straight, wave-like or helical wire.
9. Device according to claim 7, characterized in that the elongation preventing filament consists of a polymer material.
10. Device according to any one of the claims 6 to 9, characterized in that the twisted core wires (14) have a wave-like configuration.
11. Device according to any one of the claims 6 to 9, characterized in that the twisted core wires (14) are designed in the form of a helix.
12. Device according to claim 11, characterized in that the diameter of the helix increases from distal to proximal or from proximal to distal.
13. Device according to any one of the claims 1 to 12, characterized by several distal elements (27) from which fibers (6) protrude radially outward.
14. Device according to claim 13, characterized in that the distal elements (27) are connected with each other by articulated joints (20).
15. Device according to claim 13, characterized in that the distal elements (27) are arranged side by side viewed in a cross-sectional representation.
16. Device according to claim 15, characterized in that the distal elements (27) are twisted around each other to form a helix.
17. Device according to any one of the claims 1 to 16, characterized in that the distal elements (27) are provided with braces (21) starting out from the distal end of the distal element (27), extend radially outward and again converge centrally at the proximal end of the distal element (27).
18. Device according to claim 17, characterized in that the braces (21) span over several distal elements (27).
19. Device according to claim 17 or 18, characterized in that additional intermediate braces (22) are arranged between braces (21) and the centrally extending core wires (14) of the distal element (27).
20. Device according to any one of the claims 1 to 19, characterized in that the radial extension of the fibers (6) of the distal element (27) increases from proximal to distal.
21. Device according to any one of the claims 1 to 20, characterized in that the fibers (6) in the proximal area of the distal element (27) are harder than in the distal area of the distal element (27).
22. Device according to any one of the claims 1 to 20, characterized in that the fibers (6) in the middle area of the distal element (27) are softer than in the proximal and distal area of the distal element (27).
23. Device according to any one of the claims 1 to 22, characterized in that the density of the fiber coverage in the middle area of the distal element (27) is lower than in the proximal and distal area of the distal element (27).
24. Device according to any one of the claims 1 to 23, characterized in that the fibers (6) are secured or attached to the core wires (14) by clamping, bonding, knotting and/or fusing.
25. Device according to any one of the claims 1 to 24, characterized in that the ends of the fibers (6) located radially outward are provided with slubs or nubs.
26. Device according to any one of the claims 1 to 25, characterized in that the ends of the fibers (6) located radially outward are at least in part connected with each other by means of loops.
27. Device according to any one of the claims 1 to 26, characterized in that the fibers (6), at least partially, protrude differently far radially outward at both sides of the distal element (27).
28. Device according to any one of the claims 1 to 27, characterized in that the core wires (14) in the cross sectional area of the distal element (27) are arranged and extend eccentrically.
29. Device according to any one of the claims 1 to 28, characterized in that the brush structure formed by one or several distal elements is suitable to be flatly collapsible under the external strain exerted by a micro-catheter and transported inside the micro-catheter and unfolds to its full brush structure when said external strain caused by the micro-catheter is omitted.
30. Device according to any one of the claims 1 to 29, characterized in that the distal elements (27) are designed so as to be detachable from the guide wire (18).
31. Device according to any one of the claims 1 to 30, characterized in that the device additionally is provided with an elongated cage structure which is suitable to be flatly collapsible under the external strain exerted by a micro-catheter and transported inside the micro-catheter and unfolds to its full cage structure when said external strain caused by the micro-catheter is omitted.
32. Device according to any one of the claims 1 to 31, characterized in that the fibers (6) form an angle with longitudinal axis of the device that ranges between 70° and 110°, preferably between 80° and 90°.
33. Device according to any one of the claims 1 to 32, characterized in that the fibers (6) have been provided with a coating.
34. Device according to any one of the claims 1 to 31, characterized by one or several radiopaque markers (9).
35. Device according to any one of the claims 1 to 34 in combination with a guide catheter and/or micro-catheter.
36. Device according to claim 35, characterized in that the guide or micro-catheter is designed as aspiration catheter.
37. Method for the manufacture of a distal element (27) forming part of a device according to claim 1, characterized in that at least two core wires (14) are arranged parallel to each other, between which fibers (6) are arranged transversely to the extension of the core wires (14), with said core wires (14) being twisted around each other.
38. Device for the removal of foreign objects and thrombi from body cavities and blood vessels comprising a guide wire (18) provided with one or several distal elements (27), with the distal element (27) being provided with fibers (6) projecting radially outward, characterized in that the distal element (27) has a tapered shape.
39. Device according to claim 38, characterized in that the diameter of the distal element (27) increases from proximal to distal.
40. Device according to claim 38, characterized in that the diameter of the distal element (27) increases from distal to proximal.
International Classification: A61M 29/00 (20060101); A61M 25/00 (20060101);