WO2005117750A1

WO2005117750A1 - A filter for blood vessels

Info

Publication number: WO2005117750A1
Application number: PCT/IB2005/001174
Authority: WO
Inventors: Stefano Montanari
Original assignee: G.A.M.A.-H.S. S.R.L.
Priority date: 2004-05-25
Filing date: 2005-04-27
Publication date: 2005-12-15
Also published as: ITMO20040129A1

Abstract

A wire element (2) is elastically-deformable between at least an inactive configuration in which is it straight and at least a working configuration, in which it exhibits at least an operative tract (3) formed as a conical spiral. The operative tract (3) is predisposed to be housed internally of a blood vessel in such a way that a geometrical axis (x) of the conical spiral is centred with respect to a longitudinal axis of a blood vessel.

Description

A Filter for Blood Vessels.

Technical Field

The invention relates to a filter for blood vessels, in particular for the vena cava.

Background Art

Filters of this type are predisposed to be inserted in a blood vessel in order to hold back migrating thromboid masses, i.e. moving clots of coagulated blood, which can form in the blood flow upstream of the filter location point. The majority of thrombi and venous embolisms (fragments of free thrombi in blood circulation) which form in the blood originate in the circulations of the lower limbs and the pelvis. For this reason the filters in question are typically inserted in the inferior vena cava, and are generally known as cava filters. The formation of thrombi in the blood can have various causes, known as Virchow's Triad: blood hypercoagulation, i.e. a particularity in the chemical nature of the blood meaning that coagulation occurs following stresses which are normally insufficient to provoke coagulation effects; a parietal lesion, i.e. where the internal wall of the vessel in a vein or artery suffers a lesion the blood coagulates in proximity of the lesion; and a slowing in blood flow, when, for some reason the blood flow is slowed or stopped. Once the blood coagulates internally of a vessel, especially a vein, the mass which is formed (thrombus) can grow in the direction of the flow (towards the heart in the case of a vein) and at a certain point it may break into small fragments, known as embolisms. For anatomical reasons all of the fragments (embolisms) end up in the pulmonary circuit, with the risk of obstructing it. This condition, which is known as pulmonary thrombo-embolism, is of various degrees of gravity, the least of which is not even noticed by the patient, one of the gravest being an amputation of a lung or lungs, the gravest of all being death. Some of the risk conditions which lead to deep venous thrombosis are surgical operations, obesity, trauma, immobility, the use of birth control pills, diabetes, lupus. The methods for preventing pulmonary thrombo-embolism are basically two: systematic use of anticoagulant pharmaceuticals or the introduction of filters of the type of the invention into the blood vessels.

Filters of known type exhibit a central zone having high filtering characteristics, as the embolisms are transported by the blood along the axis of the vein, and a peripheral zone which is rather permeable. The haematic embolism thus captured can be fragmented if it is of recent making, or if the embolism is old and has contracted and thus got more solid, it can be trapped in the filter for a few hours or even days until it is spontaneously dissolved. The filter is implanted percutaneously, through a small hole made in the neck, an arm or in the groin. A slim catheter, in which the filter is arranged, is introduced into the venous system to transport the filter into the desired position. Once the position has been reached, the catheter is removed while the filter remains in position, exiting from the catheter. Known-type filters are basically of two main types. A first of these types comprises filters which are constituted by a plurality of wires, usually metal, which joined one to another at an end and which progressively distance towards the other end, defining a sort of cone. All of these wires, or some of them, are provided at their free ends with hooks which hook into the walls of the blood vessel, anchoring the filter to the vessel.

The filter is arranged with the vertex, i.e. the part where the metal wires are joined to each other, facing in the direction of the blood flow, so that the flow enters the filter on the side of the free ends of the metal wires.

The filters of this type can be implanted through the jugular, brachial or femoral, but exhibit some drawbacks. The exhibits a certain tendency to thrombus, i.e. ability to induce formation of thrombi, caused by the impediment to flow provoked by the vertex of the filter. There is also a frequent tendency to cause perforations due to the presence of the anchors to the vessel wall. It is also extremely difficult to arranged the filter coaxially to the vena cava, i.e. with the vertex arranged on the axis of the vessel. Frequently the filter vertex inclines, coming to rest against the vessel wall. These two problems make it difficult or impossible to extract the filter percutaneously, which can in any case only be done through the jugular.

The extraction of the filters of this first type requires the use of a special catheter provided at one end with pliers which can be retracted internally of the catheter itself. The catheter is introduced into the blood vessel and is positioned in such as way as to grip, with the pliers, the vertex of the filter. Once the vertex has been gripped, the external catheter is advanced, closing the conical filter and sheathing it. If the vertex of the filter is not in the correct position the extraction becomes impossible as it does if the anchoring hooks penetrated too deeply, faultily internally of the blood vessel wall. A second type of known-type filter comprises filters formed by two filtering cones joined at the base and arranged symmetrically to one another. One filtering cone is oriented according to the direction of the blood flow, while the other cone, upstream with respect to the flow, is oriented in the opposite direction. The symmetry of the design with respect to a transversal plane to the direction of the blood flow enables a single kit to be used both for the jugular-entry plants (from the neck), and for high-entry plants in general (e.g. brachial), and for femoral-entry plants (in the groin). In any case, the filters are not highly effective as the cone upstream deviates the embolisms from their trajectories, obstructing entry into the vertex of the downstream cone; also, they exhibit a certain thrombus favourability, as the inside of the vertex of the inverted upstream cone constitutes a point where the flow is stagnant. A further drawback is that a thrombus forming internally of the inverted cone distances the embolisms from the axial path more than does the inverted cone itself, thus further weakening the downstream cone's ability to capture clots. Also, the inside of the inverted cone is potentially the seat of intergranular corrosion since it is not crossed by an adequate blood flow. A further drawback of double-cone filters is the poor efficiency of their hooks, which frequently lead to displacements of the filters.

The main aim of the invention is to provide a filter for blood vessels which enables the drawbacks in the known-type filters to be overcome. An advantage of the filter of the present invention is that it is constituted by a single piece, as it is more resistant to fatigue and corrosion. A further advantage of the filter of the invention is that is can be implanted and extracted through the jugular, brachial and femoral by means of a catheter which is very much slimmer than those in the prior art. A further advantage of the filter is that it does not cause any perforations on the walls of the vessel it is positioned in. A further advantage is that the filter positioning can be repeated several times until an absolutely satisfactory position is achieved. A still further advantage of the filter is that it does not exhibit any point at which blood flow is zero; thus it is not liable to cause clotting. A further advantage of the filter is that it is absolutely self-centring and considerably simplifies the filter implanting operation. Disclosure of Invention Further characteristics and advantages will better emerge from the detailed description that follows of a filter for blood vessels, made with reference to the accompanying figures of the drawings, provided by way of a non-limiting example, and in which: Figure 1 is a schematic view of a filter of the invention, illustrated in a working configuration internally of a blood vessel;

Figures 2 and 3 show two alternative embodiments of the filter of figure 1; Figure 4 is a plan view of the filter of figure 1 ; Figure 5 is the filter of figure 1 in an extraction or insertion configuration in a blood vessel.

With reference to the figures of the drawings, the filter of the invention comprises a wire-shaped element 2, elastically deformable between at least a working configuration, at which it is housable internally of a blood vessel. In this configuration the wire element 2 is suitable for functioning as a filter, while in the inactive configuration it is suitable for introducing or extracting into or from a blood vessel. In the working configuration at least one operative tract 3 of the wire element 2 is conformed in a conical spiral. The operative tract 3 is predisposed to be housed internally of a blood vessel so that the geometrical axis x of the conical spiral is about parallel to the longitudinal axis of the vessel.

The operative tract 3 is conformed as a conical helix spring which winds in progressively increasing or decreasing coils about a geometrical axis x thereof. At one end of the spring is a maximum-radius coil, while at another end thereof there is at least one minimum-radius coil. In the working condition, i.e. the configuration assumed when arranged in the blood vessel, the wire element 2 defines, with its coils, a sort of conical filtering surface the vertex of which is positioned at the minimum-radius coil, while the base is defined by the maximum-radius coil. As will be described herein below, the wire element 2 is positioned in such a way that the blood penetrates into the filter through the maximum-radius coil and flows in the direction of the minimum-radius coil. The wire element 2, if not subjected to external forces, assumes and maintains a free configuration in which it exhibits at least a maximum-radius coil, a diameter of which is greater than a diameter of the blood vessel in which it is inserted. The free configuration of the wire element 2 coincides with the working configuration thereof, with the difference that in the free configuration at least the maximum-diameter coil exhibits a greater diameter than the diameter of the blood vessel. When the wire element 2 is introduced into a blood vessel, the maximum-diameter coil is disposed in contact with the internal wall of the blood vessel, exerting thereon a predetermined pressure. This pressure is sufficient to maintain the wire element 2 in position.

In a preferred embodiment, the operative tract 3 exhibits at an end thereof two adjacent maximum-diameter coils. In this case too, when the wire element 2 is introduced into a blood vessel, the maximum-diameter coils are arranged in contact with the internal wall of the blood vessel and exert thereon a predetermined pressure. The pressure exerted by the coils on the vessel wall is sufficient to keep the wire element 2 in position, and is also sufficient to centre the geometrical axis x of the conical coil with respect to the blood vessel.

In a first preferred embodiment the operative tract 3 exhibits a first portion 3a, arranged in a conical coil, and at least a second portion 3b, also arranged in a conical coil. The two portions are consecutively arranged, so that the minimum-diameter coil (i.e. the vertex) of the second portion 3b is adjacent to the maximum-diameter coil (i.e. the base coil) of the first portion 3a. The maximum-diameter coils of both portions have the function of stabilising and centring the filter with respect to the blood vessel. In a second embodiment, the operative tract 3 of the wire element 2 is provided at each end with a maximum-diameter coil. One of the maximum- diameter coils is adjacent to the minimum-diameter coils, in order to guarantee a perfect centring of the filter internally of the blood vessel. The wire element 2, at ends thereof, is provided with hooking element 2a predisposed to engage with means for extraction and/or insertion of the filter which will not be fully described herein as they are not part of the present invention. The operative tract 3 of the wire element 2 is comprised between two end tracts 4 having a straight development, aligned with the geometrical axis x of the conical coil. The hooking elements 2a are arranged at free ends of the end tracts 4 and are defined by the free hooked ends of the end tracts 4. Thanks to the conformation and arrangement of the end tracts 4 of the wire element 2, the hooking elements 2a are arranged along the longitudinal axis of the blood vessel they are inserted in. The filter is inserted and extracted into and from the blood vessel by the means for insertion/extraction which comprise a catheter internally of which the wire element 2 is sheathed in its inactive configuration. An elongate element is slidably predisposed in the catheter to engage at and end to one of the hooking elements 2a. The elongate element is caused to projected from the catheter, is constrained to a hooking element 2a and is retracted into the catheter. The wire element 2 is then pulled internally of the catheter, and goes into the inactive configuration. Once the wire element has been completely inserted, the catheter can be introduced into a blood vessel to bring the filter into a desired position. When the wire element 2 reaches the desired position, the catheter is pulled away, with the elongate element in position. This operation causes the wire element 2 to exit from the catheter, freeing itself from the constricted and inactive position. The wire element 2 is arranged elastically in its working position in which the maximum-diameter coils of the operative tract 3, which as has been described exhibit a diameter when freed from constriction which is greater than the diameter of the blood vessel, become arranged in contact with the walls of the vessel and exert thereon a pressure which brings the filter to centre optimally in the section of blood vessel. The maximum-diameter coils are made of such a size that the pressure they exert on the vessel walls is sufficient to keep the filter in position, preventing all lesions on the walls due to contact with the filter itself. When the filter is in position, the elongate element disengages from the hooking element 2a and is retracted from the blood vessel together with the catheter.

The extraction of the filter is done with the same operations, performed in inverse sequence. The catheter is introduced into the blood vessel and brought up to close to the filter, after which the elongate external element is pushed until it engages with a hooking element 2a of the wire element 2 and both are retracted into the catheter, which can then be extracted from the blood vessel. The wire element 2 is made of Nitinol, a very elastic alloy made of nickel and titanium in almost equal parts, giving it extreme elasticity and its pre- sprung "memory".

In the working configuration, the wire element 2 exhibits, on a perpendicular plane to the longitudinal axis x, a coil shape in which proximity of the coils is greatest towards the centre of the spring, while at the ends the coils are more spaced out. In this configuration the operative tract 3 is arranged in such a way that the radius of the coils decreases in the direction of the blood flow. Thanks to the working conformation the filter element 2 assumes, the filtering surface defined by the operative tract 3, which as has been mentioned is overall conical in shape, is rather selective in the central zone, i.e. in the zone which is close to the longitudinal axis of the blood vessels, while it is very permeable in the lateral zones. This guarantees excellent filter efficiency in relation to the entrapping of embolisms which, as is known, travel at the centre of blood vessels, while the filter itself is overall very permeable to the blood flow.

The filter for blood vessels of the invention exhibits important advantages. Firstly it is constituted by a single piece, the wire element 2, which is thus extremely resistant to fatigue and corrosion. Almost all of the known-type filters exhibit at least one welding seam at the vertex, which is easily attacked by the blood, which has a very aggressive chemical nature. The filter of the invention has no weld seams and thus no points at which it is susceptible to corrosion. This characteristic makes it decidedly more resistant to breakage through fatigue. The blood vessels, especially the vena cava, are subject to continual section variations, mainly due to movement and respiration. The filter of the present invention absorbs these variations, broadening and tightening its coils and thus changing its axial dimension inside the vessel without being subject to the concentrated flexion that the known-type filters are subject to. In these filters each metal wire is subject to flexion at each deformation of the blood vessel, a flexion which occurs at the point at which the meal wire connects to the vertex of the filter, and which leads very frequently to the actual detachment of the wire. The double-cone filters, even where made in a single piece, concentrate fatigue at the points at which the leg adhering to the wall detaches from the wall itself.

A further advantage of the filter according to the invention is that it is implantable and extractable through the jugular, brachial and femoral, using a very much slimmer catheter than those at present in use by the competition. As the filter, in the inactive configuration of the wire element 2, can be reduced to the size and shape of a straight metal wire, it can be conveyed to the place of application in a very slim catheter. The special conformation of the wire element 2, both in the inactive configuration and the working configuration, makes bi-direction manoeuvres, those of insertion and extraction to and from the blood vessel, very much possible and what is more very adaptable to various working conditions. Furthermore, since the anchoring of the filter does not require the use of hooks, it causes no perforation of the walls of the blood vessel it is inserted in, and is thus stably positioned. This last characteristic, together with the ease of manoeuvring described above, means that the positioning of the filter can be repeated several times up until an absolutely satisfactory positioning is obtained. The filter can be positioned and removed from the same side of the vessel and using the same instrument, and can thus be positioned several times without any risk of damage to the blood vessel walls.

A further advantage of the filter is that it does not present any point at which it can slow down or stop blood flow, and is therefore not liable to creation of thrombosis. The filter section is defined by a spiral which is very narrow and selective in the central zone, the most important zone for capturing clots, while it is wide and permeably in the lateral zone, where it creates no obstacle to blood flow. The filtering section has no points of arrest of the blood flow, as happens in known filters at their vertices, and thus does not exhibit points at which clots might form.

A further important advantage of the filtering characteristic is that it is entirely self-centring. The centring of the filter is done by means of the pressure exerted by the maximum-diameter coils of the operative tract 3 on the walls of the vessel, and it is geometrical, i.e. it does not depend on special manoeuvres or treatments required by the person introducing filter into the blood vessel. The plant of the filter is thus considerably precise and accurate, but also simpler than the plant of a filter of known type which on the contrary is extremely difficult to centre.

Claims

Claims.

1). A filter for blood vessels, wherein it comprises a wire element (2) which is elastically deformable between at least a straight inactive configuration and at least a working configuration, in which at least a working configuration it exhibits at least one operative tract (3) conformed as a conical spiral; the at least one operative tract (3) being predisposed to be housed internally of a blood vessel in such a way that the geometric axis (x) of the conical spiral is about parallel to a longitudinal axis of the blood vessel.

2). The filter of claim 1, wherein the operative tract (3), in a free configuration of the wire element (2), exhibits at least a coil a diameter of which is greater than a diameter of the blood vessel in which the filter is inserted, the at least a coil having a greatest diameter of the operative tract (3) when the filter is in an operative configuration.

3). The filter of claim 2, wherein the operative tract (3) exhibits a first portion

(3a) which is arranged in a conical spiral, and at least a second portion (3b) which is arranged in a conical spiral, a coil having a smallest radius of the at least a second portion (3b) being adjacent to a coil having a largest radius of the first portion (3 a).

4). The filter of claim 2, wherein the operative tract (3) of the wire element

(2) is provided at each end thereof with a maximum radius coil.

5). The filter of claim 2, where the wire element (2) is provided at each end thereof with hooking elements (2a) which are predisposed to engage to means for extraction and/or insertion.

6). The filter of claim 5, wherein the operative tract (3) of the wire element

(2) is comprised between two end tracts (4) having straight development and being aligned with a geometric longitudinal axis (x) of the operative tract (3), the hooking elements (2a) being arranged at free ends of the end tracts (4). 7). The filter of claim 6, wherein the hooking elements (2a) are defined by a bending of the end tracts (4) into a hooked shape.

8). The filter of any one of the preceding claims, wherein, in the working configuration, the wire element (2) exhibits, viewing on a plane which is peφendicular to the longitudinal axis (x), a coiled configuration in which close to a centre of the wire element (2) the coils are close to one another, while at ends of the wire element the coils are distanced one from another. 9). The filter of any one of the preceding claims, wherein, in the working configuration, the operative tract (3) is arranged in such a way that the coils of each conical spiral decrease in diameter in a direction of blood flow in the blood vessel.