Loop thrombectomy device

A thrombectomy device may include an elongate torsion member having a proximal end and a distal end, and a plurality of helically arranged engagement members disposed at a distal portion of the elongate torsion member. Preferably, at least a portion of the engagement members has a rounded, atraumatic shape. The engagement members have a collapsed state where the engagement members are compressed toward the elongate torsion member, and an expanded state where the engagement members are expanded radially outward. Preferably, the engagement members are attached to and extends radially outward from the elongate torsion member at a different longitudinal point such that the engagement members are spaced longitudinally and circumferentially from each other when in the expanded state. When the thrombectomy device is deployed in a body lumen or cavity, the engagement members expands out to contact a wall of the body lumen or cavity.

BACKGROUND

This invention relates generally to medical devices and particularly to a device for removing blood clots, or thrombi, from body vessels, such as the small arteries associated with the brain.

The presence of blood clots or thrombus in the vascular system is a very dangerous condition that if left untreated can cause serious and potentially life-threatening disease. Thrombi within the vasculature can form as a result from a variety of causes, such as trauma, disease, surgery, stagnant flow of blood, and foreign devices in the vasculature. Typically, a thrombus present in an arterial blood vessel tends to migrate in the direction of flow from a large diameter artery to smaller diameter arteries. The thrombus continues to flow with the blood until it becomes lodged against the vessel wall and is unable to advance. In some instances, the thrombus partially or completely blocks blood flow through the artery thereby preventing blood from reaching the tissue disposed downstream of the thrombus. Denying blood flow for an extended period of time can result in damage or death of the tissue beyond this point. The result can be loss of toes or fingers, or even entire legs in more severe circumstances. Moreover, thrombi in the venous system can migrate to the lungs and become a pulmonary embolus, which is usually fatal. In other instances, thrombi can migrate into the cerebral circulation and cause stroke and death.

Currently, thrombus removal, or thrombectomy, may be performed in a variety of ways. For example, the clot may be dissolved through chemical lysis using drugs. While this method is adequate, clot lysis has significant disadvantages in that it is a very slow process taking hours or even days to complete. Additionally, the drugs utilized in clot lysis cause the blood to thin, thereby leaving a patient susceptible to serious hemorrhage complications.

Thrombectomy may also be performed using mechanical devices. Typically, these devices are inserted into a patient's vasculature and delivered to a treatment site over a guide wire using the Seldinger or modified Seldinger technique, which is well known in the art. Generally, these mechanical devices have the disadvantage that they are usually not strong enough or dense enough to adequately capture and remove a thrombus. This is because these devices must be small and flexible in order to negotiate the tortuous anatomy where clots are likely to be found.

One type of common thrombectomy device is a balloon that is inflated in a vessel and then withdrawn to pull a clot(s) into a conventional sheath. The sheath may then be withdrawn from the patient to remove the captured clot(s). Other devices are simple open ended catheters into which a clot is aspirated and removed from the patient.

Although adequate for some applications, these devices have disadvantages. For example, the balloon catheter devices must be first advanced through the clot before they can be inflated and retracted. The process of penetrating the clot with the balloon catheter device tends to push the clot deeper into the arterial circulation where it becomes even more difficult to remove. Further, this system is not well suited to small vessels (below about 3.5 mm) because the catheter portion begins to approach the size of the vessel being treated, making it even more difficult, if not impossible to penetrate the thrombus without pushing it further into the vessel. Additionally, these mechanical devices must be designed so that they do not damage the vessel wall during the thrombectomy process, which may result in further clotting. As a result, the structure of these devices is typically very flimsy, thus compromising the ability to actually retain the clot during the removal process.

These same issues also plague devices using wire spirals or coils that can be collapsed and expanded into the clot, or basket like devices that are expanded inside of or distal to the thrombus and then retracted in an effort to pull the thrombus out of the vessel. These devices frequently collapse during the withdrawal process or actually macerate the thrombus into finer clots which then can migrate farther downstream, making them even harder to capture.

Still other devices utilize corkscrew shaped members that are collapsed into an outer delivery sheath and passed through the clot before they can be deployed and retracted. The action of pushing a device through the center of the clot forces the clot deeper into the artery and may fragment the clot, making it an even more dangerous embolus. Typically, such corkscrew devices have a smooth rounded tip to prevent the corkscrew from penetrating the vessel wall or otherwise damaging the vessel wall as it is screwed into the clot. With these devices, however, the smooth, rounded central tip itself does not screw into the clot; rather the central tip is pushed into the clot and then the remainder of the corkscrew is screwed into the clot. As with basket, coil, and balloon devices, this pushing force may also force the thrombus deeper into the vessel. Further, the corkscrew also exerts a pulling force on the periphery of the clot in addition to the pushing force focused on the center of the clot. These counter forces tend to macerate or fragment the clot and result in only a small part of the clot being captured. Some corkscrew devices may substitute a sharp tip that can screw directly into the clot. However, sharp tips can penetrate the vessel wall just as easily as they can penetrate and capture the clot. Accordingly, such devices are seldom used since they carry the very high risk of penetrating the vessel wall. Further, when a bead or ball is applied to the tip of the device that is large enough to protect the vessel wall, it is usually so large that it will tend to push the clot distally rather than penetrate the clot such that the clot can be captured and removed.

Another disadvantage common to conventional balloon, coil, basket, and corkscrew thrombectomy devices is that they tend to have relatively large cross-sectional profiles and, in turn, are overly stiff for use in small tortuous vessels of the brain. Therefore, it has become apparent to the inventor that a need exists for an improved mechanical thrombectomy device.

SUMMARY

Thrombectomy devices are described which may allow for a lower profile configuration that adaptably expands to contact a vessel wall and minimizes or eliminates maceration of a thrombus. The invention may include any of the following aspects in various combinations and may also include any other aspect described below in the written description or in the attached drawings.

In one embodiment a thrombectomy device may include an elongate torsion member having a proximal end and a distal end, and a plurality of helically arranged engagement members disposed at a distal portion of the elongate torsion member. Preferably, at least a portion of the engagement members has a rounded, atraumatic shape. The engagement members have a collapsed state where the engagement members are compressed toward the elongate torsion member, and an expanded state where the engagement members are expanded radially outward. Preferably, the engagement members are attached to and extend radially outward from the elongate torsion member at different longitudinal points such that the engagement members are spaced longitudinally and circumferentially from each other when in the expanded state.

In one aspect, when the thrombectomy device is deployed in a body lumen or cavity, the engagement members expands out such that the rounded atraumatic shaped portion of the engagement members are in contact with a wall of the body lumen or cavity. In one embodiment, an entirety of the engagement members consists of a loop of wire having a rounded atraumatic shape that extends from the longitudinal point on the torsion member in a continuous manner. Preferably, the wire is made of a material having super-elastic characteristics.

In some embodiments, the elongate torsion member may be a metallic shaft made from a flexible metallic material and the wire of each of the engagement members is permanently attached to the different longitudinal points. In other embodiments, the elongate torsion member is a torque cable that is woven from a plurality of metallic wire strands. In this embodiment, the wire forming the engagement members may be a single continuous wire woven into the torque cable, or each engagement member may be made of a separate wire. Preferably, both the strands forming the torque cable and the wire forming the engagement members are made of nitinol.

In one aspect, a torque shaft may be fixedly attached to the proximal end of the elongate torsion member. In another aspect, a handle may engage the torque shaft such that when the handle is rotated, the engagement members are also rotated.

In one embodiment, the thrombectomy device may also include an inner sheath disposed around the elongate torsion member. Preferably, the inner sheath has a diameter that is less than an outer diameter of the helical arrangement of engagement members in the expanded state, and includes a spring member disposed at a distal end thereof. The spring member preferably has a compressed configuration in which a diameter of the spring member is substantially equal to a diameter of the inner sheath, and an expanded configuration in which at least a portion of the spring member has a diameter that is larger than the diameter of the inner sheath. In one aspect, the spring member may have a proximal end that is restrained and a distal end that is unrestrained in the expanded state, such that the spring member has a cone like shape when expanded.

In another aspect, a substantially inelastic outer sheath may be disposed on an outer surface of the inner sheath and slidably movable thereupon, the outer sheath thereby restraining the spring member in the compressed configuration.

A method of using a thrombectomy device may include introducing the thrombectomy device percutaneously into a body lumen or cavity proximal of a thrombosis and expanding the device such that the plurality of engagement members are in the expanded state and at least a portion thereof contacts a wall of said body lumen or cavity.

The device is rotatably advanced toward the thrombus such that the rounded atraumatic shape of the engagement members translate longitudinally along the wall of the lumen or cavity in a corkscrew shaped path. As the thrombectomy device is rotatably advanced, the thrombus is twistingly engaged by the plurality of helically arranged engagement members such that the thrombus is captured within the helical arrangement of engagement members.

In one aspect, if the thrombectomy device includes an inner sheath disposed around the elongate torsion member, the inner sheath comprising a compressed spring member disposed at a distal end thereof, the spring member may be expanded, thereby causing the distal end of the inner sheath to expand radially. The thrombectomy device including the captured thrombus is then retracted into the inner sheath through the expanded distal end. In another aspect, the thrombectomy device is linearly withdrawn into the inner sheath. In yet another aspect the thrombectomy device is rotatably withdrawn into the inner sheath.

The foregoing paragraphs have been provided by way of general introduction, and are not intended to limit the scope of the following claims. The presently preferred embodiments, together with further advantages, will be best understood by reference to the following detailed description taken in conjunction with the accompanying drawings.

DETAILED DESCRIPTION

Referring now to the Figures,FIGS. 1 and 2illustrate a distal portion of a thrombectomy device100according to an embodiment of the present invention. The thrombectomy device preferably includes an elongate torsion member110and a plurality of engagement members120. The plurality of helically arranged engagement members120are disposed at a distal portion of the elongate torsion member110, each engagement member having a collapsed state, in which the engagement members120are compressed radially inward toward the elongate torsion member110, and an expanded state, in which the engagement members120are expanded radially outward away from the elongate torsion member110. Preferably, the engagement members120extend perpendicularly away from the surface of the elongate torsion member110. Other angles of extension are contemplated, including angles toward and away from a distal end of the elongate torsion member110.

In one embodiment the torsion member110is formed from a flexible shaft or cable. In one embodiment, the elongate torsion member110is a hollow shaft that is configured to receive and be passed over a guide wire. In another embodiment, the elongate torsion member110may be a solid metallic, polymer, or composite shaft. Regardless of the construction, the elongate torsion member110preferably includes a blunt atraumatic tip112disposed at its distal-most end to prevent the thrombectomy device100from accidentally damaging tissue or puncturing a vessel or cavity wall during use.

Preferably the elongate torsion member110is torsion cable that consists of a plurality of braided wire strands. The braided configuration of the torsion cable provides flexibility in the radial direction, but minimizes spring-like energy storage from twisting and torque when rotated about its central axis. The elongate torsion member110is substantially incompressible in the longitudinal direction. Preferably, the elongate torsion member is formed of metallic wire strands, for example and without limitation, Nitinol or stainless steel. Other materials are contemplated as known in the art. Preferably, the elongate torsion member110is not a coiled (non-braided) cable as such cables tend to coil more tightly or uncoil, depending on the direction of rotation of the cable, and are not efficient at transmitting rotational force.

Each of the plurality of engagement members120may be fixedly attached to the elongate torsion member110and extend outward in a radial direction. As shown inFIGS. 1 and 3, each of the engagement members120are disposed at longitudinal and circumferential positions and are longitudinally spaced from one another such that they form a helical arrangement around and along the elongate torsion member110. Preferably, each engagement member120has the same narrow loop structure that is narrowest at the connection point on the elongate torsion member110and that progressively widens as the engagement member120moves radially outward. The radially outward most portion of each engagement member120preferably has a smooth, radial transition surface that arcs between the two sides of the loop, thereby providing an atraumatic surface for contacting a wall of a body lumen (e.g. blood vessel, etc.) or cavity. However, it should be understood that the engagement members are not limited thereto, and other atraumatic loop shapes are contemplated, for example and without limitation, teardrop, oval, and circular shapes.

In a preferred embodiment, the engagement members120are formed from a continuous length of Nitinol wire, formed as a series of “S-shaped” curved loops. The Nitinol wire may range in size from about 0.002 inches up to 0.015 inches, depending on the desired size and strength of the device. The Nitinol wire is preferably in the pseudoelastic state at body temperature to allow it to be springy and move between the compressed state, where the engagement members are folded or bent down along the elongate torsion member110for insertion into a delivery system or the like, and the expanded state. The wire size may be specified such that the thrombectomy device100is flexible and small enough for use in vessels as small as about 1 mm (e.g. cerebral vessels) or large and stiff enough for use in vessels up to about 40 mm (e.g. aorta, vena cava).

The Nitinol wire is preferably wound or otherwise incorporated into the braid structure of the elongate torsion member110, such that the engagement members120are sandwiched between two windings of wire strands of the braid structure. Because the loops of the engagement members120extend radially outward from between the wire strands, the engagement members120are arranged in an angled, spiral, helical pattern, as shown inFIG. 1. Preferably, each engagement member120does not contact the helically adjacent engagement member(s), such that the engagement members120are wholly supported by the elongate torsion member120and are circumferentially and longitudinally spaced apart from one another to create a spiral staircase-like pathway that captures and guides a thrombus around the elongate torsion member110. However, it should be understood that the embodiment is not limited thereto, and that helically adjacent engagement members120may contact or overlap with each other. Moreover, it should be understood that while Nitinol wire is utilized in the preferred embodiment, it is not limited thereto, and the wire may be made of any suitable material having elastic properties as is known in the art. Additionally, the wire may be made of a shape memory material and have a predetermined shape, e.g. curved or looped, when in an expanded state, as is known in the art. However, it should be understood that the embodiment is not limited thereto, and the wire may be made from any material that will result in a self-expanding device and may have any shape that results in a rounded, atraumatic surface for engaging a vessel wall. For example, the device may be comprised of pre-configured polymeric material, stainless steel wire, cobalt-chromium-nickel-molybdenum-iron alloy, or cobalt-chrome alloy.

In an alternative embodiment, the wire may be doped with platinum, or other radiopaque elements to increase the radiopacity of the engagement members120and facilitate visualization and placement using fluoroscopy.

Preferably, a torque shaft140is attached at a proximal end of the elongate torsion member110through a joint142, by welding, soldering, adhesive bonding, or the like. An inner catheter130may then be formed about the torque shaft140.

The thrombectomy device100described above may be used independently without any other delivery system or mechanism. Alternatively, the thrombectomy device100may be implemented using a delivery system, for example, as illustrated inFIGS. 4-5c. As shown inFIG. 4, the delivery system200includes an inner sheath150disposed about the thrombectomy device100. Preferably, the inner diameter of the inner sheath150approximates, or is slightly larger than an outer diameter of the inner catheter130such that when the thrombectomy device100is inserted into the inner sheath150, the engagement members120are flexed, or folded down along the elongate torsion member110in the compressed state. The inner sheath150may be made of Nylon, Teflon, or other suitable material as known in the art, and may include wire coils or braids to increase stiffness and prevent the compressed engagement members120from expanding or stretching the inner sheath150and to improve pushability and torquability of the delivery system200during insertion.

The inner sheath150includes an expandable distal portion152that is attached through a joint156. A spring member170is housed within the expandable distal portion152, and is held in a compressed state by an outer retention sheath160. The outer retention sheath160may be made of Nylon, Teflon, Polyethylene (PTFE), or other suitable materials as known in the art. Like the inner sheath150, the outer retention sheath160may also include wire braids or coils embedded in a wall thereof to facilitate control of the device. Additionally, the outer retention sheath160may have a tapered atraumatic distal end162to facilitate advancement through a patient's vasculature and prevent damage thereto. The spring member170may be made of super elastic or shape memory material, for example and without limitation, Nitinol.

In a preferred embodiment, the spring member170is a self-expanding stent made of a super elastic material, such as Nitinol, stainless steel or the like and may be formed from a single nitinol wire that is bent in a “Z-shaped” manner. Alternatively, the spring member170may be formed by soldering individual wires together or cut from cannula to achieve the undulating structure. The diameter of the wire or thickness of the cannula of the spring member170may range from about 0.002 inches to about 0.020 inches, depending on the intended use (larger diameter vessels require thicker wire to achieve the necessary expansion force). The spring member is preferably formed from undulating or “Z-shaped” stent struts that are configured to flex between a compressed configuration, in which circumferentially adjacent stent struts abut or are disposed adjacent to one another, and an expanded configuration, in which circumferentially adjacent stent struts are angled away from each other, as known in the art. More preferably, a proximal end of the spring member170is restrained, such that when the spring member170is released from the compressed configuration, the proximal ends of the stent struts are held in place, thereby leaving only the distal ends able to expand. The resulting expanded form is essentially a funnel or cone like shape that provides a smooth transition from the expanded large diameter at the distal end of the expandable distal portion152to the smaller original diameter approximating the inner diameter of the inner sheath150at the joint156. The proximal end of the spring member170may be restrained by integrally forming a non-expanding continuous ring having a diameter substantially equal to the compressed configuration, or by mechanically connecting the proximal ends of the stent struts directly together or to a ring by welding, soldering, adhesive, sutures, etc., as known in the art. Preferably, the distal end of the expandable distal portion152is expanded such that it contacts at least a portion of the vessel/cavity wall when the spring member170is released from the compressed configuration.

As shown inFIGS. 4aand4b, the expandable distal portion152of the inner sheath150extends from the distal end of the inner sheath150proximally by an amount that substantially corresponds to the length of the spring member170. The inner sheath150and the expandable distal portion152may be attached at the joint156by adhesive or thermal bonding, as known in the art. In the embodiment shown inFIG. 4a, the expandable distal portion152is formed from a flexible and elastic material that is radially expandable when subjected to the expansive force of the spring member170and collapses freely when retracted into the outer retention sheath160. Preferably, the expandable distal portion152is an elastomeric material, such as ePTFE (elastic polytetrafluoroethylene), Thoralon, polyurethane, silicone rubber, or a membrane of thin polymers. Preferably, the expandable distal portion152has a thickness of less than one thousandth of an inch to about three thousandths of an inch. In an alternative embodiment the entire inner sheath150is formed of the same flexible, elastic material, thereby obviating the need for the joint156.

FIG. 4billustrates yet another alternative embodiment, in which the expandable distal portion152is made from a substantially inelastic material that is sized and shaped to conform to the desired expanded shape of the spring member170. When the spring member170is in its compressed configuration under the outer retention sheath160, portions154of the inelastic material are folded radially around the spring member170in a pleat like manner. When the outer retention sheath160is withdrawn in the proximal direction, it releases the spring member170, and the inner folded portions154unfold, thereby allowing the spring member170to assume its fully expanded shape.

As shown inFIGS. 5a-c, the proximal end of the delivery system includes a control handle190having a handle191, a locking pin192to prevent accidental or premature deployment, luer lock ports197for delivering radiopaque dye or clot dissolving drugs to a thrombus through the delivery system to, or removing fluid from a treatment site in a patient, a shaft194, and a knob196. Note that while the delivery and use of clot dissolving drugs are contemplated, the present invention may not require such drugs to eliminate thrombi. A proximal end of the outer retention sheath160is fixedly attached to the handle191. In operation a physician holds the knob196stationary in one hand, and pulls the handle191in a rearward direction to retract the outer sheath160. However, it should be understood that the embodiment is not limited thereto, and the proximal end of the delivery system200may utilize any sheath retracting means known in the art.

The torque shaft140preferably passes through a lumen in the handle191, the shaft194and the knob196. The torque shaft140also extends out of the proximal end of the knob156a sufficient amount to be engaged by a torque handle in the form of a pin vise180. The pin vise180includes a handle188, a threaded portion186, a locking collar184disposed around and threadably engaging the threaded portion186, and jaws182. Preferably, both the lock collar184and the handle188are knurled, or otherwise textured to facilitate rotation.

In operation, the proximal end of the torque shaft140is inserted into a central space between the jaws182. The lock collar is then rotated in a distally advancing direction, which forces the jaws182together in a radially inward direction, thereby frictionally locking the torque shaft140in place (seeFIG. 5c). Preferably, the proximal ends of the inner and outer sheaths150,160terminate in luer lock type fittings197.

FIGS. 6-8illustrate the operation of the delivery system200. Initially, the delivery system200is inserted percutaneously and advanced into a patient's vasculature to a desired treatment site using the Seldinger technique, which is well known in the art. Initially, a guide wire may be used to insert a guide sheath to the treatment site. The guide wire may then be removed, and the delivery system200may be advanced to the treatment site through the guide sheath. As described above, radiopaque material doped engagement members120, or alternatively, radiopaque markers placed on the sheaths150,160, may allow the thrombectomy device100to be visually placed at the treatment site by the physician using fluoroscopy. Preferably, the delivery system200is placed proximal of the thrombus20in the vessel or cavity.

Once the delivery system200has been advanced to the treatment site, the outer retention sheath160is withdrawn proximally by pulling the handle191toward the knob196. As the outer retention sheath160is removed from the expandable distal portion152, the spring member170is released and automatically and immediately expands out to the diameter of the vessel/cavity such that it contacts the vessel/cavity wall10, this causes the expandable distal portion152to expand a corresponding amount, as shown inFIG. 6. Preferably, the thrombectomy device100includes a sufficient number of engagement members120to maintain good traction on the thrombus120without fragmenting the thrombus120or displacing it further downstream.

Next, the thrombectomy device100is advanced out of the inner sheath150using the pin vise180. The initial advancement through the inner sheath150may be accomplished through linear or rotational translation by pushing or rotating the pin vise180, respectively. As the pin vise is rotated, it turns the torque shaft140, which turns the elongate torsion member110and the engagement members120.

As the thrombectomy device100is advanced, the engagement members180automatically begin to flex in a radially outward direction as they pass through the expandable distal portion152, and assume the fully expanded configuration such that the engagement members150contact the vessel/cavity wall10. Once the engagement members150have contacted the vessel/cavity wall10, the thrombectomy device100is preferably rotatably advanced along the vessel/cavity wall10. Because the portions of the engagement members120that come in contact with the vessel/cavity wall10are atraumatic and present a smooth curve, the engagement members120can be safely expanded against the vessel/cavity wall10and rotatably or slidably advanced therealong without causing damage to the vessel/cavity wall10. Moreover, by expanding the engagement members120against the vessel/cavity wall10, gaps between the thrombectomy device and the vessel/cavity wall10are eliminated and any portions of the thrombus20that may break off during thrombectomy are more likely to be captured in the helical arrangement of engagement members120.

When the distal end of the thrombectomy device100contacts the thrombus20, initially, the blunt end112of the elongate torsion member110engages and forces at least a portion of the thrombus20to contact the distal most engagement members120, as shown inFIG. 7.

As the thrombectomy device continues to be rotatably advanced, the thrombectomy device100is “screwed” into the thrombus20, thereby causing the thrombus120to engage the engagement members120. In turn, the engagement members120guide the thrombus20through the helical path defined by the engagement members120along the elongate torsion member110toward the inner sheath150. Once the thrombus20is completely captured by the engagement members120, the thrombectomy device100can be either rotatably or linearly withdrawn back into the inner sheath150. As the thrombectomy device110is withdrawn into the inner sheath150, the funnel shape of the expandable distal portion152helps collect any portions of the thrombus20that may have been dislodged by the engagement and retraction process, thereby preventing such particles from being released into the bloodstream. Further, the sloped inner surface of the expandable distal portion152helps the engagement members120to gradually and securely flex back to their compressed form within the inner sheath150. After the thrombectomy device100and the thrombus20have been completely withdrawn into the inner sheath150, the outer retention sheath160may be advanced forward, thereby collapsing the spring member170. The physician may then attach a syringe or other such device to one or both of the luer locks197to inject or withdraw fluid as needed. The entire delivery system, including the thrombus20, may then be withdrawn and removed from the patient.

Alternatively, the delivery system200may be partially inserted into the thrombus20with the thrombectomy device100still restrained in the compressed state. Once the distal end of the retention sheath162has been implanted into the thrombus20, the thrombectomy device100is deployed and then rotatably advanced in the distal direction in a non-piercing manner to capture the thrombus20. In this case, the rotation of the thrombectomy device100can be used to urge the thrombus20toward the collecting sheath.

While preferred embodiments of the invention have been described, it should be understood that the invention is not so limited, and modifications may be made without departing from the invention. The scope of the invention is defined by the appended claims, and all devices that come within the meaning of the claims, either literally or by equivalence, are intended to be embraced therein. Furthermore, the advantages described above are not necessarily the only advantages of the invention, and it is not necessarily expected that all of the described advantages will be achieved with every embodiment of the invention.