System for removing a clot from a blood vessel

Abstract

A system for removing an obstruction from a blood vessel. The system can include a catheter with a proximal section with a proximal section lumen diameter and a distal section with a distal section lumen diameter less than the proximal section lumen diameter. The system can include a clot retrieval device with a clot engaging element. The system can include a shaft advanceable through the lumen of the catheter to the obstruction in the vessel. The shaft can include a shaft proximal section, a shaft distal section attached to the clot engaging element with a diameter less than that of the shaft proximal section and configured to cross the obstruction. The shaft proximal section diameter can be larger than the diameter of the distal section lumen diameter of the catheter, thereby inhibiting the shaft proximal section from distally advancing through the catheter distal section.

Description

INTRODUCTION

Acute ischemic stroke (AIS) is a worldwide problem for which until recently there have been only limited therapy options available for patients. One option for such patients is a lytic drug called tPa, which can be administered either intravenously or intra-arterially. More recently various mechanical thrombectomy and/or revascularization devices have become available which aim to dislodge and remove the clot using mechanical means. These devices are typically advanced through a small catheter (called a microcatheter) to the site of the occlusive blood clot, whereupon they are deployed from this microcatheter and engaged with the clot. It would be advantageous for the patient and physician that this microcatheter be as flexible and small in diameter as possible, as these attributes enable the microcatheter to be advanced through tortuous vessel anatomies with ease without harming the vessel walls, and also enable the microcatheter to be advanced across the clot without pushing the clot further distally or dislodging a portion of the clot which might embolize another vessel. However it may be challenging for a mechanical thrombectomy and/or revascularization device to pass through such a small diameter microcatheter. One particular challenge involves the ability to push the device through the microcatheter, especially around tortuous bends in distal anatomies. Many mechanical thrombectomy and/or revascularization devices consist of a clot engaging element attached to the distal end of an elongate wire or shaft. This shaft extends exterior of the patient and is used by the physician to advance the device through the microcatheter to the site of the obstruction. This shaft therefore needs to be robust enough, and stiff enough, to be able to push the engaging element against significant resistance as it enters regions of tortuosity. However if the device is to be used with a very small diameter microcatheter (as is desirable) then the diameter of the shaft is limited to a size somewhat smaller than the inner diameter of this microcatheter. This trade-off between microcatheter profile and shaft profile means that conventional mechanical thrombectomy and/or revascularization devices either a) are compatible with very small diameter microcatheters but suffer from having flimsy shafts which are easily damaged and cannot effectively transmit a push force to advance the device around significant tortuosity, or b) are fitted with sufficiently large diameter shafts to have good robustness and pushability but are not compatible with very small diameter microcatheters.

It is desirable for a Thrombectomy Device (TD) to have a very low delivery profile in order to cross an occlusive clot easily and without dislodging any clot material. Most TDs are delivered through a microcatheter, and it is the microcatheter (and typically an inner guidewire) that first cross the clot. After that the guidewire is removed and the TD is advanced through the microcatheter. Thus it is desirable that the TD be compatible with microcatheters that are as small as possible in diameter. A further advantage of a small diameter microcatheter is that increased space is available between the microcatheter and the inner surface of a guide catheter or intermediate catheter through which it passes. This increased space makes it easier to aspirate blood and clot from the site of occlusion through the guide or intermediate catheter, which is a method typically used in conjunction with use of a thrombectomy device. Some physicians choose to remove the microcatheter completely before aspirating in order to increase this space and reduce the resistance to flow through an intermediate catheter, particularly if a large diameter microcatheter and/or small diameter intermediate catheter is used. It would be desirable if such a step were not required.

It is generally necessary to have some clearance between the inner diameter of a catheter and the outer diameter of the shaft of a device that is passed through it. Without any clearance the shaft would not move freely through the catheter and would be very difficult to advance. The clearance required depends on both the internal diameter of the catheter (its lumen) and the degree or tortuosity of the vasculature in which it is positioned. In relatively low levels of tortuosity a small clearance between shaft and catheter lumen may be perfectly adequate, but in higher levels of tortuosity greater clearance may be required to permit free movement. For example, in the case of a neurovascular thrombectomy system used in middle cerebral artery via femoral access: a clearance of less than 0.003″ (ie 0.0025″, 0.002″ or even less than 0.002″) may be adequate for the proximal section of the system which sits proximal of the patients aortic arch take off, while a clearance of 0.003″ or more may be required to permit free movement of the thrombectomy device shaft through the microcatheter in the section of the system distal of the common carotid artery.

Many TDs today are compatible with microcatheters with an inner lumen of approximately 0.021″ and an outer diameter of 0.025″ to 0.034″ or more. These TDs can therefore be mounted on shafts that have an outer diameter of up to approximately 0.018″ (to comfortably fit in the 0.021″ lumen). Some TDs are compatible with smaller microcatheters which have a lumen of approximately 0.016″ to 0.17″ and an outer diameter as low as approximately 0.020″. These lower profile catheters may be more easily advanced into tortuous distal vessels and may cross clots more easily due to their lower profile. However a TD that is designed to fit through one of these catheters must have a shaft diameter of approximately 0.014″ or less. The bending stiffness of a 0.014″ shaft is 63% lower than that of a 0.018″ shaft of the same material, because the bending stiffness is proportional to the fourth power of the shaft diameter. Therefore the pushability of the 0.014″ shaft is also much less than that of the 0.018″ shaft. Thus a 0.014″ shaft would need to have a much higher modulus of elasticity than an 0.018″ shaft in order to deliver a similar level of “pushability”. However it is desirable that these shafts are made from a superelastic or shape memory material such as nitinol so that they retain their shape and do not become kinked or deformed after use, as they may need to be reused for additional clot retrieval passes if the first is not successful. One way to attain a higher modulus and hence recover some pushability would be to change shaft material to stainless steel or other relatively high modulus material. However this means compromising on the kink resistance and durability of the nitinol shaft. Thus there is a need for a solution to this undesirable trade-off problem.

The solutions provided herein are applicable not just to AIS, but also to the removal of obstructions from vessels throughout the body, such as peripheral arteries and veins, coronary vessels and pulmonary vessels where embolism can be a serious problem.

STATEMENTS OF INVENTION

According to the invention there is provided a system for removing obstructions from a blood vessel, the system comprising a clot retrieval device and a catheter. The clot retrieval device comprises a clot engaging element and an elongate shaft; the clot engaging element having a first collapsed delivery configuration and a second expanded deployed configuration. The elongate shaft has a shaft proximal section, a shaft distal section and a shaft intermediate section between the shaft distal and proximal sections. The clot engaging element being attached to the shaft distal section of the elongate shaft. The catheter has a catheter proximal section, a catheter distal section, and a catheter intermediate section between the proximal and distal sections. The catheter proximal section has an inner proximal lumen and an outer proximal diameter, the catheter distal section having an inner distal lumen and an outer distal diameter.

In one embodiment the maximum diameter of the shaft proximal section is greater than the inner distal lumen of the catheter distal section.

In one embodiment the maximum diameter of the shaft proximal section is less than 0.003″ smaller than the inner distal lumen of the catheter distal section.

In one embodiment the maximum diameter of the shaft proximal section is less than 0.002″ smaller than the inner distal lumen of the catheter distal section.

In one embodiment the maximum diameter of the shaft proximal section is greater than the maximum diameter of the shaft distal section.

In one case the inner proximal lumen of the catheter is larger than the inner distal lumen of the catheter.

In some cases the outer proximal diameter of the catheter is larger than the outer distal diameter of the catheter.

In one embodiment the outer proximal diameter of the catheter is equal to the outer distal diameter of the catheter (see, e.g., FIG. 6).

The clot engaging element may be self-expandable. The clot engaging element may comprise a self-expanding nitinol body.

The invention also provides a method for removing obstructions from a blood vessel comprising:—

• • providing a clot retrieval device and a catheter system according to the invention;
  • positioning a guide catheter or sheath proximal of an obstruction in a blood vessel;
  • advancing a guidewire towards the obstruction;
  • advancing the catheter over the guidewire;
  • removing the guidewire;
  • advancing the elongate clot retrieval shaft through the catheter with the clot retrieval element in the collapsed delivery configuration;
  • advancing the catheter and the shaft through the obstruction;
  • deploying the clot engaging element in the obstruction;
  • retracting the catheter to a position proximal of the clot retrieval element; and
  • retrieving the clot retrieval element and the clot captured by the retrieval element.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more clearly understood from the following description of an embodiment thereof, given by way of example only, with reference to the accompanying drawings, in which:

FIG. 1A is a cross sectional side view of a clot retrieval system according to the invention;

FIG. 1B is a cross sectional side view of a clot retrieval system according to the invention;

FIGS. 2A to 2E are views illustrating the clot retrieval system in use;

FIG. 3 is a cross sectional side view of a portion of a clot retrieval system according to the invention;

FIG. 4 is a cross sectional side view of a portion of a conventional clot retrieval system;

FIG. 5 is a cross sectional view through FIGS. 3 and 4; and

FIG. 6 is a cross sectional side view of a clot retrieval system according to the invention.

DETAILED DESCRIPTION

Referring to FIGS. 1A and 1B of the drawings there is illustrated a system 24 for removing obstructions such as clot from a blood vessel, the system comprising a clot retrieval device 8 having a clot retrieval element 7 mounted at the distal end of an elongate shaft 9 and a catheter 2 which in this case is a microcatheter which is used to deliver the clot retrieval element 7 in a collapsed delivery configuration across a clot. The clot retrieval element 7 is deployed from the catheter 2 into an expanded deployed configuration for clot retrieval. FIG. 1a shows the system with the clot retrieval element 7 in the deployed expanded condition. FIG. 1b shows the system with the clot retrieval element 7 collapsed within the distal portion 16 of the microcatheter 2, just prior to deployment.

The catheter 2 comprises a catheter proximal section 15, a catheter distal section 16, and a catheter intermediate section 6 between the proximal and distal section. The catheter distal section 16 has an inner distal lumen and an outer distal diameter. The catheter proximal section 15 has an inner proximal lumen and an outer proximal diameter. The catheter comprises a hub 19 at its proximal end to which is typically attached a rotating haemostasishemostasis valve (RHV) 20, through which fluids may be injected or aspirated and which incorporates a seal to prevent the ingress of air and loss of blood or other fluids.

The shaft 9 of the clot retrieval device comprises a shaft proximal section 17, a shaft distal section 18 and a shaft intermediate section 10 between the shaft distal and proximal sections. The clot engaging element 7 is attached to the shaft distal section 18 of the shaft 9 at connection point 23 and may be self-expandable. For example, the clot engaging element may be formed from or comprise a self-expanding Nitinol body. Indicator bands 21 and 22 may be provided on the proximal shaft 17, to inform the user of the proximity of the clot retrieval element 7 to the distal end of the microcatheter 2.

The catheter 2 has a stepped diameter. The distal section 16 of the catheter 2 has a low profile (for example 0.16″ inner diameter (ID)/0.020″ outer diameter (OD)) for excellent flexibility and clot crossing capability. The proximal section 15 of the catheter 2 has a larger inner (and outer) diameter to accommodate a robust and pushable proximal shaft 17 of the clot retrieval device.

In one embodiment of the invention the maximum diameter of the shaft proximal section 17 is larger than the inner distal lumen of the catheter distal section 16. In another similar embodiment the shaft proximal section 17 is very slightly smaller than the inner distal lumen of the catheter distal section 16, so that the catheter can be completely withdrawn over the shaft when in a relatively straight configuration, while still benefiting from a robust large diameter shaft.

As the catheter 2 is not typically withdrawn more than a short distance during use, the shaft proximal section 17 may be even larger than the internal diameter (ID) of the distal section 16 of the catheter 2. In some cases the shaft proximal section 17 is only slightly smaller (i.e. 0.003″ or less smaller or 0.002″ or less smaller) than the ID of the distal section 16 of the catheter 2—for example the distal section of the catheter may have a lumen of 0.0175″, and the shaft proximal section may have an OD of 0.016″. This diameter difference allows the microcatheter 2 to be completely withdrawn over the device shaft 9 if desired, provided that the larger diameter proximal portion of the device shaft 17 is not positioned in a region of significant tortuosity.

FIGS. 2a to 2e show a method of use of the clot retrieval system 24 of this invention. FIG. 2a shows a clot 1 lodged in vasculature 25 causing an obstruction to the flow of blood. A large diameter guide catheter or sheath 5 is positioned in a vessel proximal of the obstructive clot. A microcatheter 2 is advanced through the guide or sheath 5 towards the clot 1 with the aid of guidewire 3. A region of tortuosity exists between the distal end of guide or sheath 5 and the clot 1, comprising at least one tight bend 4. Such tortuosity may comprise bends if radii less than 1 Omm and in some cases less than 5 mm, and may also comprise “figure of 8” loops and compound curves are very difficult to navigate through without a highly flexible microcatheter. In addition the clot itself may be difficult to cross. Hence it is advantageous to provide a flexible and low profile distal segment 16 in a microcatheter such as that of this invention, which also comprises a supportive and robust proximal section 15 with which to advance the catheter through the challenging region of tortuosity and across the clot. The length of the distal low profile, flexible section 16 is at least long enough such that only this low profile section reaches the clot 1, and most preferably such that only this low profile section reaches the region of tortuosity distal of the guide or sheath 5. For treatment of AIS this catheter section is therefore ideally at least 5 cm in length and is most preferably between 10 cm and 30 cm in length. In other embodiments the distal section 16 may extend to as much as 100 cm or more, which will provide the benefit of increased luminal space for aspiration within an intermediate catheter (if used), but at the cost of some pushability performance of the microcatheter.

Once the microcatheter has been successfully advanced across the clot 1, the guidewire 3 is removed as shown in FIG. 2b, so that clot retrieval device 8 can be advanced through the lumen of the microcatheter 2 towards the target clot as shown in FIG. 2c. The microcatheter 2 is then retracted to allow the clot retrieval element 7 to expand within and grip the clot 1 as shown in FIG. 2d. The distal shaft section 18 ideally has a longer length than the distal microcatheter section 16, so that the microcatheter can be retracted to a position proximal of the clot retrieval element as shown in FIG. 2d. As with the microcatheter, the larger diameter and stiffer proximal section 17 of the clot retrieval device shaft provides the shaft with greater pushability than would be the case with a lower profile shaft, enabling the user to advance the device more easily through the challenging region of tortuosity distal of the guide or sheath 5, and around tight bend 4.

Once the clot retrieval element 7 has been deployed within the clot it may be left for a few minutes to expand and embed within the clot or it may be withdrawn immediately according to the physicians preference. In either case the clot and retrieval element may be withdrawn directly back into guide or sheath 5, or an intermediate catheter 11 may be used in a “tri-axial” set-up as shown in FIG. 2e. Aspiration though the guide/sheath and/or intermediate catheter is typically used to assist in creating a reversal of blood flow and safely retrieving back the clot and any clot fragments that may be liberated. This aspiration can be applied by means of a syringe or vacuum pump connected to the proximal end of the intermediate catheter. If this aspiration is applied through an intermediate catheter the space within the lumen of this catheter has a significant impact on the flow rate that can be created for a given aspiration force. As a maximum of 1 atmosphere vacuum can be created by a syringe or vacuum pump the luminal space is a critical factor in optimizing the effect of this vacuum on flow rate.

FIG. 3 shows a simplified view of a cross section through a system incorporating an intermediate catheter 11 as shown in use in FIG. 2e. The intermediate catheter 11 may have a stepped profile as shown with a large lumen in proximal section 13 than in distal section 12, or in other embodiments may have a constant inner diameter. The distal luminal space 30 and proximal luminal space 31 are the areas between the outer surface of the microcatheter 2 and the inner surface of the intermediate catheter 11 through the aspiration force is applied. The effective flow rate through such a system is a function of the cross-sectional areas and lengths of spaces 30 and 31, and the viscosity of the fluid in question (which is blood). Thus it is advantageous to maximize the cross-sectional areas and minimize the lengths of spaces 30 and 31.

FIG. 4 shows a simplified view of a cross section through a conventional thrombectomy system incorporating an intermediate catheter 52, a microcatheter 53 with a continuous non-stepped inner lumen, and a clot retrieval device shaft 51. Comparing FIGS. 3 and 4 it can be seen that the system of this invention depicted in FIG. 3 has a much larger distal luminal space 30 than the distal luminal space 60 provided by the conventional system of FIG. 4. This provides a major advantage in that with the system of this invention aspiration can be very effectively applied without the need to remove the microcatheter from the patient. Removal of the microcatheter can be both time consuming and difficult as thrombectomy device shafts are not typically long enough to permit this to be done without the addition of an extension piece to the shaft.

FIG. 5 shows a cross-sectional view representative of that through the systems of both FIG. 3 and FIG. 4, where clot retrieval shaft 82 lies within microcatheter 81, which in turn sits within the lumen of intermediate catheter 80, leaving luminal space 83 between the two for aspiration.

The invention enables clot retrieval devices with robust and pushable shafts to be used in conjunction with flexible, small diameter microcatheters, and enables aspiration forces to be effectively transmitted through an intermediate or guide catheter without the need for removing the microcatheter.

The clot retrieval device may, for example, be of the type described in our US2013/0345739A or US2014/0371779A the entire contents of which are incorporated herein by reference.

The invention is not limited to the embodiment hereinbefore described, with reference to the accompanying drawings, which may be varied in construction and detail.

Claims

1. A system for removing an obstruction from a blood vessel, the system comprising: a catheter comprising: a proximal section with a proximal section lumen diameter, anda distal section with a distal section lumen diameter less than the proximal section lumen diameter; anda clot retrieval device comprising: a clot engaging element having a first collapsed delivery configuration and a second expanded deployed configuration; anda shaft comprising: a shaft proximal section, anda shaft distal section attached to the clot engaging element and configured to cross the obstruction;wherein intermediate and distal sections of the catheter and shaft are advanceable through the blood vessel towards the obstruction; andwherein the shaft proximal section is stiffer than the shaft distal section.

2. The system as claimed in claim 1, wherein a distal luminal space is maximized between the shaft distal section and the distal section of the catheter.

3. The system as claimed in claim 1, wherein a shaft proximal section diameter is 0.003″ or less than an inner diameter of the catheter distal section.

4. The system as claimed in claim 1, wherein an outer diameter of the proximal section of the catheter is larger than an outer diameter of the distal section of the catheter.

5. The system as claimed in claim 1, wherein an outer diameter of the shaft proximal section is greater than an inner diameter of the distal section of the catheter thereby inhibiting the shaft proximal section from distally advancing through the distal section of the catheter.

6. The system as claimed in claim 1, wherein the proximal section of the catheter is substantially robust and the catheter distal section is substantially flexible.

7. The system as claimed in claim 1, the shaft further comprising the shaft intermediate section distal of the shaft proximal section and extended between the shaft distal section and the shaft proximal section.

8. A system, comprising: a shaft comprising a proximal section with a proximal section diameter and a distal section with a distal section diameter smaller than the proximal section diameter;an expandable clot engaging element attached to the distal section of the shaft;a first catheter comprising a first catheter proximal section, a first catheter distal section, and a lumen extending therethrough, the first catheter proximal section comprising a proximal section lumen diameter larger than a distal section lumen diameter; anda second catheter comprising a second catheter proximal section and a second catheter distal section, an outer diameter of the second catheter proximal section being larger than an outer diameter of the second catheter distal section; andwherein the proximal section diameter of the shaft is greater than the distal section lumen diameter of the first catheter distal section.

9. The system as claimed in claim 8, wherein an outer diameter of the first catheter proximal section is larger than an outer diameter of the first catheter distal section.

10. The system as claimed in claim 8, wherein the second catheter has a lumen extending therethrough having a diameter larger than an outer diameter of the first catheter proximal section, the first catheter being advanceable within the lumen of the second catheter.

11. The system as claimed in claim 8, the first catheter distal section comprising an axial length between approximately 10 cm and approximately 30 cm.

12. The system as claimed in claim 8, the proximal section diameter of the shaft inhibiting the proximal section of the shaft from distally advancing through the catheter distal section.

13. A method, comprising: advancing a clot engagement element, by distally advancing a shaft through a first catheter, wherein the shaft comprises: a shaft proximal section,a shaft distal section with a diameter less than the shaft proximal section, the shaft distal section being attached to the clot engagement element, anda shaft intermediate section between the shaft proximal and distal sections,extending the first catheter across an obstruction in a blood vessel, wherein the first catheter comprises: a first catheter proximal section,a first catheter distal section with a diameter less than a diameter of the first catheter proximal section,a first catheter intermediate section between the first catheter proximal section and the first catheter distal section;advancing a second catheter to a first location proximal of the obstruction;advancing a guide catheter to a second location proximal of the obstruction;retracting the first catheter so as to expand and deploy the clot engagement element distal of the first catheter within the obstruction; andwithdrawing the clot engaging element into a lumen of at least one of the second catheter or the guide catheter to retrieve the clot engagement element and the obstruction from the blood vessel.

14. The method as claimed in claim 13, wherein the shaft intermediate section is advanceable through the first catheter proximal section, the first catheter intermediate section, and the blood vessel towards the obstruction.

15. The method as claimed in claim 13, further comprising: inhibiting the shaft proximal section from distally advancing through the first catheter distal section by preventing the proximal section diameter of the shaft from passing through the distal section lumen of the first catheter distal section.

16. The method as claimed in claim 13, further comprising: visualizing the shaft through a radiopaque indicator of the shaft.

17. The method as claimed in claim 13, further comprising the shaft proximal section being stiffer than the shaft distal section.

18. The method as claimed in claim 13, further comprising: maximizing a distal luminal space defined between the shaft distal section and the first catheter distal section.

19. The method as claimed in claim 13, further comprising: advancing a guidewire across the obstruction and through the first catheter, and removing the guidewire from the first catheter after advancing the first catheter.

20. The method as claimed in claim 13, wherein the second catheter comprises a second catheter proximal section that extends to a second catheter distal section, wherein an outer diameter of the second catheter proximal section is larger than an outer diameter of the second catheter distal section so that the second catheter distal section is advanceable at least up to and through the first catheter proximal section.