Device for treating valvular insufficiency and method of delivery thereof - Patent Application 20070122997

Abstract

A device for treating valvular insufficiency includes an expandable anchor attached to a transvalvular spacer and a delivery system for delivering the device and deploying and positioning it prior to fixation of the transvalvular spacer.

Description

[Technical Field]

[0001] Related Applications This application claims priority to U.S. Provisional Patent Application No. 63 / 430,085, filed December 5, 2022, which is incorporated herein by reference in its entirety. [Background technology]

[0002] The present invention relates to a device for treating valvular insufficiency and a catheter system for delivering and retrieving the device. Embodiments of the invention relate to a device including a transvalvular spacer attached to an atraumatic anchor positionable within the atrium, and a delivery system capable of deploying and positioning the spacer prior to fixation of the device.

[0003] Valvular insufficiency is a heart condition characterized by the inability of the heart valves to close completely, resulting in valve regurgitation or leakage.

[0004] Anatomically, these valves are part of the heart's dense connective tissue, known as the cardiac skeleton, and are responsible for regulating blood flow through the heart and great vessels. Valvular insufficiency, caused by valve malfunction or failure, can lead to impaired cardiac function and reduced blood flow throughout the body. Treatment for damaged valves can include medical therapy alone, surgical valve repair (valvuloplasty), or valve replacement (prosthetic heart valve insertion).

[0005] Atrioventricular valve incompetence can lead to blood leaking or backflow from the ventricle into the atrium (regurgitation) instead of being ejected when the ventricle contracts.

[0006] Valvular regurgitation is a common type of valvular insufficiency that is usually treated with valve replacement or repair, either through open-heart surgery or minimally invasive (percutaneous) procedures.

[0007] Although percutaneous valve replacement / repair is less traumatic for the patient and can be used in patient populations who are not candidates for open-heart surgery (e.g., due to advanced age or comorbidities), challenges remain regarding implant delivery and positioning, as well as long-term intracardiac stability and functionality.

[0008] Therefore, it would be highly beneficial to have a device for correcting valvular insufficiency and a system for delivering and retrieving the device. Summary of the Invention

[0009] According to one aspect of the present invention, there is provided a device for treating valvular regurgitation, the device including: a transvalvular spacer for providing a coaptation surface for the leaflets of a heart valve; and an expandable anchor attached to the transvalvular spacer and for positioning the transvalvular spacer across the heart valve when expanded within a heart chamber, the expandable anchor having a proximal connector attachable to a first element of a delivery system and a distal connector attachable to a second element of a delivery system, the first and second elements being movable in opposite directions to expand the expandable anchor.

[0010] According to an embodiment of the invention, the transvalvular spacer maintains its position relative to the heart valve when the first and second elements are moved in opposite directions.

[0011] According to an embodiment of the present invention, the degree of movement of the first element and the second element determines the degree of expansion of the anchor.

[0012] According to an embodiment of the present invention, the device further includes a coupling element for engaging a retrieval catheter.

[0013] According to an embodiment of the invention, the connecting element is configured to engage via a lasso or snare.

[0014] According to another aspect of the present invention, there is provided a device for treating valvular insufficiency, the device including: a transvalvular spacer for providing a coaptation surface for the leaflets of a heart valve; and an expandable anchor attached to the transvalvular spacer and for positioning the transvalvular spacer across the heart valve when expanded within a heart chamber, the expandable anchor including a plurality of struts, some of the struts including flexible portions that allow the transvalvular spacer to tilt relative to the expandable anchor when the expandable anchor is expanded.

[0015] According to an embodiment of the present invention, the flexible portion is a corrugated portion. This flexible junction between the anchor and the spacer allows the atrial portion to maintain a static position, while the spacer can easily fill the coaptation gap between the native valve leaflets during ventricular contraction.

[0016] According to another aspect of the present invention, there is provided a method for treating valvular insufficiency, the method comprising: deploying a transvalvular spacer within a heart valve, the transvalvular spacer having a balloon for providing a coaptation surface for the leaflets of the heart valve; inflating the balloon within the heart valve to a volume that meets a coaptation target; and expanding an expandable anchor attached to the transvalvular spacer within a heart chamber to secure the transvalvular spacer across the heart valve.

[0017] According to an embodiment of the invention, the transvalvular spacer maintains its position relative to the heart valve when the expandable anchor is expanded.

[0018] According to an embodiment of the present invention, the method further comprises the step of deflating the balloon and re-inflating it if necessary.

[0019] According to an embodiment of the present invention, the expandable anchor further includes a coupling element for engaging a retrieval catheter.

[0020] According to an embodiment of the present invention, the method further comprises the steps of deflating the transvalvular spacer and engaging the coupling element using the retrieval catheter.

[0021] Unless otherwise defined, scientific and technical terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods and materials are described below. In case of conflict, the present specification, including definitions, will control. Furthermore, these materials, methods, and examples are illustrative only and not intended to be limiting. [Brief explanation of the drawings]

[0022] The present invention will now be described, by way of example only, with reference to the accompanying drawings. With particular reference to the drawings in detail, it will be emphasized that the details shown are merely exemplary and are presented for the purpose of illustratively discussing preferred embodiments of the invention, and that the details shown are presented to provide the most informative and easily understandable explanation of the principles and conceptual aspects of the invention. In this regard, it is not intended to go into more detail about the structure of the invention than is necessary for a fundamental understanding of the invention, and by reference to this description in conjunction with the drawings, those skilled in the art will understand how various forms of the invention may be embodied in practice. The drawings are as follows: [Figure 1] 1A-B show the anchor portion of the device in a collapsed state (FIG. 1A) and an expanded state (FIG. 1B). [Figure 2] 2A-C show a side view (FIG. 2A), an isometric top view (FIG. 2B), and a top view (FIG. 2C) of the device with the anchor portion expanded. [Figure 3] FIG. 3 shows the device with the anchor portion engaged with a tubular member of a delivery system used to deploy the anchor. [Figure 4]4A-E show delivery of the device 10 and expansion of the anchors followed by expansion of the spacer. [Figure 5] FIG. 5 shows the retrieval of the device using a lasso-like capture method. [Figure 6] 6A-C show a prototype of the device at various stages of anchor deployment. [Figure 7] FIG. 7 shows the heart model used to test the prototype device of FIGS. 6A-C. [Figure 8] Figures 8A-B show the results of in silico testing of the prototype lobe (Figure 8A) and flexible strut (Figure 8B). [Figure 9] Figure 9 shows fluoroscopic images (short-axis and long-axis projections) taken during clinical testing of the design prototype. DETAILED DESCRIPTION OF THE INVENTION

[0023] The present invention relates to devices that can be used to correct valvular insufficiency. Specifically, the present invention can be used to percutaneously treat valvular insufficiency by delivering, positioning, and securing a device that includes a transvalvular spacer attached to an atraumatic atrial anchor.

[0024] The features and operation of the present invention may be more clearly understood with reference to the following drawings and accompanying description.

[0025] Before proceeding with a detailed description of at least one embodiment of the invention, it is to be understood that the invention is not limited to the applications set forth in the following description or illustrated by way of example. The invention is capable of other embodiments and of being practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting.

[0026] Implants and techniques for correcting valvular insufficiency due to incomplete leaflet coaptation have been described in the prior art. These devices include an atrial or ventricular anchor attached to a spacer that is positioned within the valve orifice to seal against the native valve leaflets when they are closed. While these implants are generally effective at sealing against the closed leaflets, delivery or fixation methods are often less than optimal.

[0027] In the course of practicing the present invention, the inventors have devised an implant and delivery system that addresses the limitations of prior art devices while providing many additional advantages in function and long-term stability. Specifically, the delivery system and device allows the user to position and deploy the leaflet coaptation portion (spacer) of the device prior to deploying and securing the anchor portion, thereby optimizing coaptation before full device deployment.

[0028] Thus, according to one aspect of the present invention, there is provided a device (implant) and a catheter system for introduction and retrieval for treating valvular regurgitation. As used herein, the term "valvular regurgitation" refers to malfunction of the valve leaflets leading to valve leakage or regurgitation. Valvular regurgitation can be caused by, for example, congenital heart disease, infection, stenosis of the valve leaflets, dilated or stretched valve annulus, ruptured chordae, dilated cardiomyopathy, or valve prolapse.

[0029] The device of the present invention comprises an expandable anchor designed to transition from a linear configuration (collapsed state) to a torus-like configuration (expanded state) and a transvalvular spacer that can be sized to achieve optimal coaptation of the leaflets in valves with regurgitation.

[0030] Positioning and deployment of the spacer (e.g., expansion to the correct diameter) occurs prior to fixation (i.e., without prior or simultaneous placement of anchor portions), allowing the user to accurately position and expand the spacer and confirm optimal adhesion prior to sheathing and fixation of the anchor portions of the device.

[0031] The anchor can be fully or partially deployed by a dedicated mechanism located within the delivery catheter, allowing it to be released from the catheter outer tube without fully deploying and securing the device. The anchor is deployed by holding the proximal end of the anchor in place while pushing the distal end with the two tubular members (push / pull rods) of the delivery system.

[0032] The device further includes a transvalvular spacer attached to the distal end (opposite the delivery side) of the anchor. The spacer can be a solid spacer, a foam spacer, a fluid-filled spacer, or any form of spacer capable of providing a coaptation surface for the valve leaflets (e.g., to seal against the leaflets when the valve is closed). One embodiment of a spacer comprising flexible struts housed within an inflatable balloon is described in detail below.

[0033] The device of the present invention is delivered using a specialized catheter system (delivery system) that has several unique features. The delivery catheter contains two tubular elements that engage two connectors on the anchor portion of the device. These connectors are located at opposite ends of the anchor (hubs 17 and 19, described in more detail below).

[0034] The present invention also includes a retrieval catheter and mechanism that allows for retrieval of the device following its deployment by capturing the proximal end of the anchor with a lasso or snare using a specialized catheter.

[0035] Referring now to the drawings, FIGS. 1-5 show one embodiment of the present device, referred to herein as device 10.

[0036] 1A-B show the anchor 12 portion of device 10 in a collapsed (FIG. 1A) and deployed (FIG. 1B) state. Figures 2A-C show three views of anchor 12.

[0037] Device 10 includes an anchor 12 attached to a spacer 20. Anchor 12 is comprised of struts 14 that are transitionable from a straight configuration to a volume-filling configuration. Struts 14 are fabricated from Nitinol or other alloys, for example, by laser cutting from a tube or sheet. Struts 14 are 0.3-0.6 mm wide and 0.3-0.6 mm thick. Anchor 12 has an expanded outer diameter (OD) of 50-90 mm and a height of 13-45 mm, and collapses to an OD of 3-5 mm and a length of 80-140 mm.

[0038] As shown in Figures 2A-C, struts 14 include six proximal struts 16 and six distal struts 18. Struts 16 branch from a proximal central hub 17, and struts 18 branch from a distal central hub 19. Struts 16 and 18 are divided into lobes 21 that are interconnected at joints 27. Although six struts are shown in Figures 2A-C, any number of struts 16 and 18 (e.g., four, five, seven, eight, or more of each) can be provided.

[0039] The anchor 12 can include five to seven proximal and distal struts (six shown), which, when expanded, form a toroidal, space-filling anchor. The function of the expanded configuration is to secure the device 10 by applying atraumatic radial pressure to the interior wall of the chamber (e.g., the atrium). The anchor struts have a "closed-cell" design, allowing them to transition from a collapsed state to an expanded state without entangling or snagging on tissue. That is, each lobe terminates at a junction with no open ends, allowing the anchor to safely expand in diameter within the heart chamber volume. Additionally, the lobes are oversized to provide large openings to avoid hemodynamic disruption and allow for future device access through the anchor struts.

[0040] To allow the spacer 20 to bend (tilt) relative to the anchor 12, the struts 18 of the anchor 12 include flexible (e.g., wavy) portions 25 that are elastically bendable, allowing the spacer 20 to bend (bend left and right) relative to the anchor 12.

[0041] The spacer 20 shown in FIGS. 1A-B and 3 is comprised of struts 22 surrounded by an inflatable balloon 24 .

[0042] The balloon 24 can be adhered to the struts 22 with the ends folded outward or everted inward, the latter configuration ensuring that potentially traumatic implant edges do not face against tissue.

[0043] The balloon 24 can be fabricated from a semi-compliant polymer using methods well known in the art. The balloon 24 can be 30-55 mm long and 10-20 mm in diameter (fully inflated). The pressure range of the balloon 24 can be from 0 atmospheres (atm) to 1 atm during normal operation.

[0044] The wall of the balloon 24 can be impermeable or semi-permeable (e.g., permeable to liquids such as water, but not to cells). A permeable balloon wall can be used for osmotic filling, as described below.

[0045] The balloon 24 can be filled with a fluid (e.g., saline or osmotic solution) through a single fluid port on the delivery catheter. Filling through the port can be accomplished using a syringe attached to the catheter's proximal fluid port. The balloon is filled with a 10-40% saline-contrast mixture, which maintains the balloon in hydrostatic and osmotic equilibrium with the surrounding blood. The balloon 24 is filled through a valve 23 (FIG. 1A) covering the fluid port on the central column 22. Fluid is injected from the proximal syringe (located outside the body) through tubing 108 of the delivery system 100 into the central column 22 and introduced into the balloon 20 through the valve 23.

[0046] Balloon 24 can be filled to a final volume and pressure at the time of delivery of device 10 (eg, prior to expansion of anchor 12).

[0047] The effectiveness of balloon 24 in coapting the valve leaflets can be tested prior to expansion of anchor 12. This can be accomplished by deploying and expanding balloon 24 and testing whether leaflet coaptation occurs while anchor 12 is in a partially deployed or deflated state with device 10 attached to a delivery system. Such a procedure is described below with reference to Figures 4A-E.

[0048] As mentioned above, the balloon 24 can be semi-permeable to allow for osmotic filling. The balloon 24 can be partially inflated with an osmotic solution (e.g., saline contrast mixture) that has a higher osmotic potential than blood (e.g., an osmolarity of 300-500 milliosmoles per liter).

[0049] The osmotic potential of blood is generally constant. Therefore, the osmotic potential of the solution used to fill the balloon 24 precisely determines the balloon's final hydrostatic pressure and volume. The osmotic mechanism prevents the fluid medium from permeating out of the balloon during use, ensuring a constant volume over time. Furthermore, the pressure to which the balloon is filled during surgery does not need to be precise, because the osmotic mechanism allows water to permeate into the balloon, naturally adjusting the volume until equilibrium between the hydrostatic and osmotic pressures is achieved.

[0050] Balloon 20 connects to anchor 12 at hub 19. Struts 22 are made from Nitinol tubing with a laser-cut pattern that allows for flexing of the implant during transcatheter delivery while providing sufficient axial stiffness to support the compressive loads applied to balloon 20 during the cardiac cycle.

[0051] As shown in FIG. 3, anchor 12 of device 10 is connected at hubs 17 and 19 to elements 106 and 108 (push / pull rods) of a delivery catheter system (this configuration is described below with reference to FIGS. 4A-E).

[0052] As described above, the device 10 of the present invention is configured to correct imperfect leaflet coaptation (valvular insufficiency) in a heart valve. The device 10 can be used to correct atrioventricular valve coaptation (bicuspid or tricuspid) by delivering the device 10 using a catheter system.

[0053] The device 10 can be delivered via a percutaneous approach, either via the jugular vein through the superior vena cava or the femoral vein through the inferior vena cava. For the mitral and tricuspid valves, the preferred approach is via the femoral vein and through the atrial septum.

[0054] 4A-E illustrate the delivery and deployment of the device 10 using a catheter system 100.

[0055] The catheter system 100 is used to deliver the device 10 as follows: Prior to delivery, the system 100 is prepared by arranging the components and accessories of the system 100 in a sterile area on a work bench and inspecting each as well as the entire system. The device 10 is removed from its packaging and loaded into the catheter system 100 by attaching the device 10 to the inner catheter 102 (including elements 106 and 108) and sheathing the device 10 and inner catheter 102 with the sheath 104.

[0056] The catheter system 100 includes a mechanism for deploying the anchor 12, which includes two movable elements 106 and 108 (push / pull rods). The mechanism is actuatable via one or more levers / triggers located on the handle of the catheter system 100. This mechanism allows the anchor 12 to be fully deployed, fully collapsed as needed, or any expanded state in between (partial deployment).

[0057] Such mechanical and controlled deployment is independent of the positioning and deployment of the spacer 20 and provides a number of advantages, including: (i) The positional relationship of the anchor 12 to the atrium can be assessed without causing trauma to the tissue. (ii) The positional relationship of the balloon 20 to the anchor 12 and its effectiveness can be evaluated. (iii) The anchor can be manipulated within the atrium, repositioned, and even completely collapsed to abort the procedure, all before permanent implantation.

[0058] 3, first element 106 is attachable to proximal connector 13 of anchor 12, and second element 108 is attachable to distal connector 15 of anchor 12. Moving elements 106 and 108 (disposed within inner catheter 102) in opposite directions expands anchor 12.

[0059] Connectors 13 and 15 may be made of nitinol, biocompatible stainless steel, or a polymer. The connection between anchor 12 and delivery catheter components 106 and 108 can be via flexible female gripping elements that are radially compressed to a locked position in hub 17, allowing some radial movement while still providing an axial connection. Another embodiment may include "male" finger elements that are normally expanded. These are radially compressed to a locked position by the delivery system and threadably connect to "female" slots, forming an axially rigid connection to anchor 12. In another embodiment, a suture is shown threaded through delivery system 100 and hub 17. These sutures are tensioned to keep device 10 connected to delivery system 100 until deployment, at which point the sutures are withdrawn, releasing device 10 from delivery system 100. In yet another embodiment, the end of tube 106 can include male threads and hub 19 of anchor 12 can include female threads, allowing connection and disconnection by rotating element 106.

[0060] 4A-E show the delivery of device 10 and the sequential deployment of spacer 20 and anchor 12. FIG.

[0061] The procedure begins with the insertion of a standard guidewire through a vascular access site into the target anatomical region, e.g., the right ventricle. An introducer sheath with a dilator is inserted over the wire into the vessel to create an access port. The dilator is removed, and the delivery system and implant are loaded onto the wire and delivered through the introducer sheath to the treatment site. In the case of a tricuspid valve, the implant is delivered to the right atrium, and in the case of a mitral valve, the implant is delivered to the left atrium. As shown in FIG. 4A, once the delivery system 100 reaches the target site, the sheath 104 is used to position the implant above and perpendicular to the valve annulus. Elements 106 and 108 (also referred to herein as tubes 106 and 108) are pushed out, exposing the balloon, which then traverses the valve leaflets (FIG. 4B). The balloon 20 is inflated under fluoroscopic guidance, and the sheath 104 is further used to manipulate the balloon to the desired position (FIG. 4C). Valve regurgitation is measured using echocardiography before and after balloon inflation to assess efficacy. The anchor 12 can then be deployed at the surgeon's discretion. Tubes 106 and 108 are pushed out simultaneously until anchor 12 is sufficiently exposed above the heart valve (approximately 10-30 mm) (Figure 4D). Tube 108 is held in place (in tension) at its distal end, while tube 106 is pushed in compressively at its proximal end 17. This applies an overall compressive load to the crown, pushing against proximal connector 17 and increasing its diameter without displacing the distal end of anchor 19. Up until this stage, the surgeon can deflate the balloon and resheath the entire implant, non-traumatic to the patient. Alternatively, the surgeon can choose to disconnect connectors 15 and 13, permanently deploying the device, at which point the delivery system is removed and efficacy assessed using an echocardiogram.

[0062] As shown in FIG. 5 , device 10 includes a linking element 110 for engaging a retrieval catheter 200. Retrieval catheter 200 includes a lasso / snare 202. If the surgeon desires rapid removal of the implant immediately after placement for safety or efficacy reasons, a retrieval catheter can be used as an alternative to open-heart surgery, allowing the implant to be removed after being permanently disconnected from the delivery system. The retrieval catheter is inserted through any steerable catheter and captures linking element 110 under echo and fluoroscopic guidance. Once device 10 is grasped by the lasso and retracted into the catheter, a piercing element deployed from catheter 200 can be used to puncture and deflate balloon 20.

[0063] As used herein, the term "about" refers to +- 10%.

[0064] Additional objects, advantages, and novel features will become apparent to those of ordinary skill in the art upon examination of the following examples, which are not intended to be limiting of the invention.

[0065] Examples Reference to the following examples, which, together with the foregoing description, illustrate the invention in a non-limiting fashion.

[0066] Prototype testing A prototype of the device (Figures 6A-C) was fabricated using common techniques known in the art and demonstrated in a laboratory setting under physiological conditions, including implantation via a transcatheter approach in an anatomically accurate flexible cardiac model (major vessels, atria, ventricles, pulmonary arteries, etc.).

[0067] A silicone / latex heart model (Figure 7) was fabricated based on CT scan data from a patient with heart failure typical of MR or TR. The model was placed in a container filled with body temperature water, and the delivery system was primed for 15 minutes. Testing showed that the system performed as expected in this setting, successfully delivering and deploying to the simulated target anatomy. Furthermore, in-silico testing (finite element analysis using ABACUS software) was performed to demonstrate the design's resistance to high-cycle loading in the target anatomy (Figure 8A-B). The boundary conditions for this in-silico testing were measured from fluoroscopic images (short-axis and long-axis projections) acquired during clinical trials of an earlier generation of this design (Figure 9). Furthermore, preclinical studies have demonstrated the feasibility of the implant procedure in this setting.

[0068] It will be appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable subcombination.

[0069] While the present invention has been described in conjunction with specific embodiments, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art. Accordingly, the present invention is intended to embrace all such alternatives, modifications, and variations that fall within the spirit and broad scope of the appended claims.

[0070] Furthermore, all publications, patents, and patent applications mentioned herein are hereby incorporated by reference in their entirety as if each such publication, patent, and patent application was specifically and individually set forth. Furthermore, the citation or identification of any reference in this application should not be construed as an admission that such reference is available as prior art to the present invention. Section headings, if used, should not be construed as necessarily limiting. Priority documents to this application are also incorporated by reference in their entirety.

Claims

1. 1. A device for treating valvular insufficiency, comprising: (a) a transvalvular spacer for providing a coaptation surface for the leaflets of a heart valve; (b) an expandable anchor attached to the transvalvular spacer and configured to position the transvalvular spacer across the heart valve when expanded within a heart chamber, the expandable anchor having a proximal connector attachable to a first element of a delivery system and a distal connector attachable to a second element of a delivery system, the first and second elements being movable in opposite directions to expand the expandable anchor.

2. 10. The device of claim 1, wherein the transvalvular spacer maintains its position relative to the heart valve when the first and second elements are moved in opposite directions.

3. The device of claim 1 , wherein the degree of movement of the first element and the second element determines the degree of expansion of the anchor.

4. The device of claim 1 , further comprising a coupling element for engaging a retrieval catheter.

5. The device of claim 4 , wherein the coupling elements are configured to engage via a lasso.

6. 1. A device for treating valvular insufficiency, comprising: (a) a transvalvular spacer for providing a coaptation surface for the leaflets of a heart valve; (b) an expandable anchor attached to the transvalvular spacer and configured to position the transvalvular spacer across the heart valve when expanded within a heart chamber, the expandable anchor including a plurality of struts, some of the struts including flexible portions that allow the transvalvular spacer to tilt relative to the expandable anchor when the expandable anchor is expanded.

7. The device of claim 6 , wherein the flexible portion is a corrugated portion.

8. 1. A method of treating valvular insufficiency comprising: (a) deploying a transvalvular spacer within a heart valve, the transvalvular spacer having a balloon for providing a coaptation surface for the leaflets of the heart valve; (b) inflating the balloon within the heart valve to a volume that meets the coaptation target; (b) expanding an expandable anchor attached to the transvalvular spacer within the heart chamber to secure the transvalvular spacer across the heart valve.

9. 9. The method of claim 8, wherein the transvalvular spacer maintains its position relative to the heart valve when the expandable anchor is expanded.

10. 9. The method of claim 8, further comprising, following step (b), deflating the balloon and, if necessary, re-inflating it.

11. The method of claim 8 , wherein the expandable anchor further comprises a coupling element for engaging a retrieval catheter.

12. 12. The method of claim 11, further comprising the steps of: subsequent to step (b), deflating the transvalvular spacer and engaging the coupling element using the retrieval catheter.

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