Patent Description:
Atrial fibrillation (AF) is the most common perpetual arrhythmia seen in clinical practice and is associated with a risk of causing ischemic stroke. Therefore, the prevention of atrial fibrillation is of great significance. Recent studies have shown that left atrial appendage (LAA) closure is an effective countermeasure to the risk of AF-caused ischemic stroke.

Existing occluders used for LAA closure can be generally divided into two categories: cage-like ones represented by Watchman devices, which are characterized by an easy-to-fabricate integral skeleton; and two-piece ones represented by LAmbre devices, which are characterized by consisting of a locator and an occluding disc connected to the locator. During use, the locator is anchored in the LAA to provide a riveting effect. LAA closure relies principally on the occluding disc that fits over the LAA orifice, although the locator also makes a certain contribution to the occlusion. Both these types of occluders suffer from the drawback that, once they are decoupled and released, their retrieval is difficult and has to rely on the use of a snare which is, however, associated with a very low success rate.

At present, there are various semi-retrievable occluder designs featuring placement of an occluder body followed by the release of an anchor. However, these designs are prone to occluder release failure.

<CIT>, <CIT>, <CIT> and <CIT> disclose medical devices comprising a stent according to the preamble of claim <NUM>.

It is an object of the present invention to provide a medical instrument according to claim <NUM> that resorts to a constraining structure to allow a stent to be less deformed within a delivery sheath and avoid tangling of a trailing section of the stent, thereby resulting in an increased success rate in release of the stent.

In pursuit of the above object, a present embodiment provides a medical instrument comprising a stent having a proximal end and an opposing distal end, wherein the distal end of the stent is configured with an expanded configuration and a collapsed configuration, wherein a trailing section of the stent at the distal end comprises a plurality of protrusions, and wherein the medical instrument further comprises a constraining structure comprising a body and a clamping mechanism, the clamping mechanism disposed at the distal end of the body, the body extending from the proximal end of the stent to the distal end thereof, the clamping mechanism limiting relative movement of the protrusions by passing through all or some of them.

Optionally, the clamping mechanism may comprise a single clamping member which passes either sequentially through all the protrusions or spaced ones of the protrusions.

Optionally, the clamping mechanism may comprise at least one clamping member each passing at opposite ends through different ones of the protrusion.

Optionally, the clamping mechanism may comprise a plurality of clamping members arranged circumferentially around the stent, each of the clamping members passing at one end thereof through one of the protrusions, the clamping members passing through different protrusions.

Optionally, the number of the clamping members may be smaller than or equal to the number of the protrusions.

Optionally, the number of the protrusions may be twice the number of the clamping members.

Optionally, each clamping member may be a wire-like member made of a elastic material.

Optionally, the material of the wire-like member may be a nickel-titanium alloy or stainless steel.

Optionally, the clamping member may be shaped like the letter "C" or "V".

Optionally, each clamping member may be curved relative to the body at an angle ranging from <NUM>° to <NUM>°.

Optionally, the medical instrument may further comprise a proximal fixation member disposed at the proximal end of the stent and configured to bring the stent into a closed configuration at the proximal end.

Optionally, the medical instrument may further comprise a distal fixation member and a pull mechanism, the pull mechanism comprising a number of pull elements each tied, at a first end, to the distal fixation member and, at a second end, to the distal end of the stent, the distal fixation member configured to be able to move toward the proximal fixation member and thus switch the distal end of the stent from the expanded configuration to the collapsed configuration.

Optionally, the medical instrument may further comprise a biocompatible membrane which covers part of a surface of the stent, with the protrusions exposed therefrom.

Optionally, the medical instrument may further comprise a delivery device comprising a hollow push tube and a drive component, the hollow push tube detachably coupled at a distal end thereof to the proximal end of the stent, the drive component inserted through the hollow push tube into the stent and detachably coupled within the stent to the distal end thereof, the drive component configured to cause the distal end to switch from the expanded configuration to the collapsed configuration, wherein the body extends from the proximal end of the stent through the hollow push tube to the distal end of the stent.

The medical instrument of the present invention according to claim <NUM> has the following advantages over the prior art:.

Objects, advantages and features of the present invention will become more apparent from the following more detailed description of various embodiments thereof, which is to be read in connection with the accompanying drawings. Note that the drawings are provided in a very simplified form not necessarily drawn to exact scale for the only purpose of facilitating easy and clear description of the disclosed embodiments.

As used herein, the singular forms "a", "an" and "the" include plural referents, unless the context clearly dictates otherwise. As used herein, the term "plurality" means two or more, unless the context clearly dictates otherwise. As used herein, the term "or" is generally employed in the sense of "and/or", unless the context clearly dictates otherwise. The term "proximal end" generally refers to an end closer to an operator who operates a medical instrument, and the term "distal end" generally refers to an end farther away from the operator. Like reference numerals indicate like elements throughout the accompanying drawings.

The core concept of the present invention is to provide a medical instrument including a stent and a constraining structure configured to constrain a trailing section of the stent to avoid both excessive deformation of the stent and tangling of its trailing section during its delivery. These can facilitate successful expansion of the stent after it is released from a sheath, thereby ensuring its successful release and resulting in an increased success rate of a surgical procedure using the stent. It is added that the medical instrument of the present invention can be used to close the LAA as well as other body lumens, such as blood vessels, or as a vascular filter, a heart valve stent, a stent graft, or the like.

More specifically, the stent of the present invention has a first proximal end and an opposing first distal end. The first distal end is configured with an expanded configuration and a collapsed configuration. The trailing section at the first distal end includes a number of protrusions. The constraining structure of the present invention includes a body and clamping mechanism provided at a distal end of the body. During practical use, the body extends from the first proximal end to the first distal end, and the clamping mechanism passes through all or some of the protrusions and thus limits their relative movement. In this way, not only tangling of the trailing section is prevented during collapse of the stent, but also mutual stressing of components (e.g., a hollow push tube and a pull mechanism) involved in the delivery and release processes is avoided. Moreover, the stent is allowed to be less deformed within a delivery sheath, additionally reducing the risk of tangling of the stent's trailing section.

For example, practical use of the medical instrument of the present invention for LAA closure may involve the following processes:.

The medical instrument of the present invention may further include a proximal fixation member, which is disposed at the first proximal end and configured to bring the stent into a closed configuration at the same end. The medical instrument may further include a distal fixation member and a pull mechanism. The pull mechanism may include a number of pull elements (including, but are not limited to, those capable of withstanding only tension, such as strings and wires, or those capable of withstanding both compression and tension). In the pull mechanism, each of the pull elements may be tied, at a first end, to the distal fixation member and, at a second end, to the first distal end. Additionally, the distal fixation member is configured to be able to move toward the proximal fixation member to cause the pull mechanism to switch the stent from the expanded configuration to the collapsed configuration around the first distal end, allowing semi-retrieval of the stent. The present invention is not limited to any particular shape of the protrusions on the stent's trailing section. For example, they may be serrated, wavy, trapezoidal or otherwise.

The inventors have found that, when the stent is compressed and collapses around the first distal end during delivery, tangling of the protrusions on the trailing section may occur, making the trailing section unable to expand after the stent is released. During the effort to overcome this problem, the inventors have also found that the tangling of the protrusions is basically attributable to winding and crossing of them that can be easily caused by their relative movement. Therefore, through effectively controlling relative movement of the protrusions by passing the clamping mechanism in the constraining structure through all or some of the protrusions, deformation of the stent during delivery can be effectively controlled to avoid tangling of its trailing section.

The medical instrument of the present invention may further comprise a delivery device for use with the stent. The delivery device may include a hollow push tube and a drive component. The hollow push tube may be detachably coupled at a distal end thereof to the first proximal end of the stent. The drive component may be inserted through the hollow push tube into the stent and detachably coupled within the stent to the first distal end thereof. In this way, the drive component can drive the stent to switch from the expanded configuration to the collapsed configuration around the first distal end. In preferred embodiments, the hollow push tube is detachably coupled at the distal end thereof to the aforementioned proximal fixation member, and the drive component is inserted sequentially through the hollow push tube and the proximal fixation member and detachably coupled to the distal fixation member. In this way, the drive component can drive the distal fixation member to move toward the proximal fixation member, which will in turn drive the pull mechanism to cause the stent to inwardly collapse around the first distal end thereof. Further, the body of the constraining structure may pass through the hollow push tube, the proximal fixation member and the distal fixation member and protrude out of the stent from the first distal end thereof, thereby allowing the clamping mechanism to unfold outside the first distal end to constrain the trailing section at the same end. Thus, the hollow push tube in the delivery device enables delivery, release and relocation of the stent, and the drive component in the delivery device enables loading and semi-retrieval of the stent. However, as previously described, as an alternative to the hollow pull tube, the drive component may be implemented as a flexible pull member.

The medical instrument of the present invention will be described in greater detail below with reference to the accompanying drawings. In the following description, its use for left atrial appendage (LAA) closure is described as an example, but this should not be construed as limiting the present invention in any sense.

<FIG> is a schematic elevation view of the structure of a medical instrument according to an embodiment of the present invention. <FIG> is a schematic stereoscopic view of the structure of the medical instrument according to an embodiment of the present invention. <FIG> shows the medical instrument in a configuration where it has been released with a stent trailing section being unanchored according to an embodiment of the present invention. As shown in <FIG>, the medical instrument <NUM> includes a stent <NUM>, a delivery device <NUM> and a constraining structure <NUM>.

Referring to <FIG>, the stent <NUM> has a first proximal end and an opposing first distal end. The stent <NUM> is configured to be closed at the first proximal end and open at the first distal end. A trailing section at the first distal end includes a number of protrusions <NUM>. The present invention is not limited to any particular shape of the protrusions <NUM>, and non-limiting examples thereof include a serrated shape. The stent <NUM> further includes a proximal fixation member <NUM> disposed at the first proximal end to close the stent at this end. The stent <NUM> further includes a distal fixation member <NUM> and a pull mechanism <NUM>. The pull mechanism <NUM> includes a number of pull elements <NUM>. The present invention is not limited to any particular number of the pull elements <NUM>, as long as the stent can be pulled at the first distal end and thus collapsed around this end. Specifically, the number of the pull elements <NUM> may be less than, equal to or greater than that of the protrusions <NUM>. Preferably, the number of the pull elements <NUM> is equal to the number of the protrusions <NUM>. Moreover, each of the pull elements <NUM> is connected, at a first end thereof, to the distal fixation member <NUM> and, at a second end thereof, to the first distal end.

Referring to <FIG>, the delivery device <NUM> includes a hollow push tube <NUM> and a hollow pull tube <NUM>. In practical use, a distal end of the hollow push tube <NUM> is detachably coupled to the first proximal end of the stent <NUM>, more preferably to the proximal fixation member <NUM>. The present invention is not particularly limited to how the coupling is established. Optionally, the distal end of the hollow push tube <NUM> may be threadedly coupled to the proximal fixation member <NUM>. According to the present invention, the hollow pull tube <NUM> acts as drive component. It is inserted through the hollow push tube <NUM> and is detachably coupled within the stent <NUM> to the first distal end thereof. Preferably, the hollow pull tube <NUM> is inserted sequentially through the hollow push tube <NUM> and the proximal fixation member <NUM> and then detachably coupled to the distal fixation member <NUM>. The present invention is not particularly limited to how the detachable coupling is established. Optionally, the hollow pull tube <NUM> may be threadedly coupled at a distal end thereof to the distal fixation member <NUM>. Preferably, the stent <NUM> further includes a hollow guide member <NUM> proximally fixed to the first proximal end of the stent <NUM>. Optionally, the hollow guide member <NUM> may be proximally fixed to the proximal fixation member <NUM> and arranged in coaxiality with the proximal fixation member <NUM> in order to allow the distal fixation member <NUM> and at least part of the pull mechanism <NUM> be inserted into the hollow guide member <NUM> from a distal end thereof. This facilitates control of the orientation and direction of the stent <NUM> when it is deformed for easier retrieval. Additionally, the hollow pull tube <NUM> is inserted through the proximal fixation member <NUM> into the hollow guide member <NUM> and detachably coupled to the distal fixation member <NUM>. In this way, by pulling a proximal end of the hollow pull tube <NUM>, the distal fixation member <NUM> will be driven to move toward the proximal fixation member <NUM> and then cause inward collapse of the stent <NUM> around the first distal end by acting on the pull mechanism <NUM>. As a result of the collapse, all the protrusions <NUM> may come closer to, or even into abutment against, one another.

A body <NUM> of the constraining structure <NUM> is passed through the hollow push tube <NUM> and the stent <NUM> and then out of the stent <NUM> from the first distal end thereof. More specifically, the body <NUM> is sequentially passed through the hollow push tube <NUM>, the proximal fixation member <NUM>, the hollow guide member <NUM> and the distal fixation member <NUM> and then out of the stent <NUM> from the first distal end thereof so that a clamping mechanism <NUM> at a distal end of the body <NUM> is disposed outside the first distal end. The clamping mechanism <NUM> is configured for insertion into all or some of the protrusions <NUM> on the trailing section of the stent <NUM>, which can limit relative movement of the protrusions <NUM> and constrain the stent's trailing section.

Specifically, the constraining structure <NUM> includes the body <NUM> and the clamping mechanism <NUM> disposed at the distal end of the body <NUM>. In one embodiment, the clamping mechanism <NUM> includes plurality of, e.g., two, three, four, five or even more, clamping members <NUM>. Referring to <FIG> and <FIG>, the clamping mechanism <NUM> includes a plurality of clamping members <NUM> inserted into some or all of the protrusions <NUM> to retain the trailing section of the stent that has been collapsed at the first distal end, preventing relative movement of all the protrusions <NUM> at the first distal end and thereby making them impossible to undesirably tangle with one another. In this way, the constraining structure and the hollow push tube when both loaded within the delivery sheath will not move relative to each other, facilitating shape control of the stent by an operator for easier delivery and retrieval. More specifically, in order to load the stent <NUM>, the hollow pull tube <NUM> may be manipulated to slightly collapse the stent <NUM> around the first distal end thereof so that the stent <NUM> collapsed at the first distal end can be placed into the delivery sheath. Subsequently, the constraining structure <NUM> is passed into the stent <NUM> until the clamping mechanism <NUM> comes out of the stent <NUM> from the first distal end thereof, and the clamping mechanism <NUM> is then manipulated to engage and thereby firmly constrain the trailing section by virtue of its own structure, thus maintaining it in the collapsed configuration. At this point, the operator does not need to manipulate the hollow pull tube <NUM> anymore, allowing it to move relative to the hollow push tube <NUM> to mitigate deformation of the stent in the delivery sheath. In this way, for example, as shown in <FIG>, the deformed stent's orientation and direction are well controlled. After the hollow push tube <NUM> is manipulated to push the stent <NUM> out of the delivery sheath, the constraining structure <NUM> may still constrain the stent's trailing section until the stent <NUM> is tuned to a desired target site. Following that, the body <NUM> of the constraining structure <NUM> may be pulled proximally so that the clamping mechanism <NUM> is expanded or deformed to no longer constrain the trailing section of the stent. Since this trailing section is elastic, it will self-expand by virtue of the resilience. As a result, anchoring features <NUM> on the stent are directed toward and then penetrate the LAA wall.

A more detailed description is given below with reference to <FIG>. At first, as shown in <FIG>, after the stent <NUM> is pushed out of the delivery sheath, it is introduced into the left atrial appendage (LAA) S while being constrained by the constraining structure <NUM>. At this point, the hollow push tube <NUM> can be manipulated to adjust the position of the stent <NUM>, for example, by moving it forth and back along the direction indicated by the arrow A, or by rotating it along the direction indicated by the arrow B, until it is positioned as desired. Next, as shown in <FIG>, after the stent <NUM> has been positioned as desired, the clamping mechanism <NUM> can be removed simply by pulling the constraining structure <NUM> gently by the operator. As a result, the trailing section of the stent <NUM> is freed, and the anchoring features <NUM> are enabled to penetrate the LAA wall. After that, the constraining structure <NUM> may be withdrawn along the direction indicated by the arrow C. Finally, as shown in <FIG>, after successful release of the stent <NUM>, the operator may successively withdraw the constraining structure <NUM>, the hollow push tube <NUM> and the hollow pull tube <NUM> from the human body, accomplishing the closure of the LAA.

Further, the clamping members <NUM> are preferably wire-like members with sufficient strength and desirable deformability, which enable firm clamping while allowing successful release by virtue of elastic deformation. Furthermore, the clamping members <NUM> may be made of an elastic material or a shape memory material, which imparts excellent deformability and sufficient mechanical properties to the clamping mechanism <NUM>. For examples, the material of the clamping members <NUM> may be selected from a nickel-titanium alloy or stainless steel. More preferably, the clamping members <NUM> are nickel-titanium wires, optionally round nickel-titanium wires with a diameter optionally of <NUM>. Such nickel-titanium wires have sufficient stiffness and good deformability and allow a reduced size during delivery.

The present invention is not limited to any particular number of such clamping members <NUM>, and the number may be determined depending on the size of the stent's trailing section. How the clamping members <NUM> retain the stent's trailing section will be described in greater detail below in the context of <NUM> protrusions <NUM> being provided on the trailing section of the stent <NUM>, as an example.

The structure of a portion encircled by the dashed box in <FIG> will be described with reference to its enlarged views. As shown in <FIG>, the clamping mechanism <NUM> may include two wires each having a shape resembling the letter "C" and crossing each other. The wires may provide two C-shaped clamping members <NUM> each defining two hooked fingers. The four hooked fingers may pass through and engage some of the protrusions <NUM>. Moreover, because of interaction among the <NUM> protrusions on the stent, all these protrusions would be retained and prevented from relative movement. Alternatively, as shown in <FIG>, the clamping mechanism <NUM> may include five wires, each of which may be curved at one end to provide one clamping member <NUM>. The five clamping members <NUM> formed by the wires may be spaced apart circumferentially and function like similar hooked fingers which may pass through and engage some of the protrusions <NUM>. In this way, all the protrusions can also be effectively retained and prevented from relative movement. Yet alternatively, as shown in <FIG>, the clamping mechanism <NUM> may include ten wires. With similarity to the variant shown in <FIG>, each of the wires may be curved at one end to provide one clamping member <NUM>, and the ten clamping members <NUM> may be spaced apart circumferentially and function like similar hooked fingers. However, in this case, all the protrusions <NUM> are populated and retained by the respective hooked fingers.

In other embodiments, each clamping member <NUM> may be shaped like the letter "V" and define two hooked fingers. In such embodiments, the clamping mechanism <NUM> may include only one clamping member <NUM> which is C-shaped or V-shaped, for example. Some of the protrusions <NUM> can be retained by passing the two hooked fingers of the clamping members <NUM> respectively into them. In alternative embodiments, the clamping mechanism <NUM> may include a plurality of clamping members <NUM>. In these cases, the clamping members <NUM> may each define either one or two hooked fingers and may be used in combination. In the case of only one hooked finger, each clamping member <NUM> may be situated outside the stent <NUM> at one end and pass through one of the protrusions <NUM> at the other end. Moreover, the individual clamping members <NUM> may pass through different protrusions.

According to the present invention, limiting relative movement of all or some of the protrusions <NUM> by passing the clamping members <NUM> in the constraining structure <NUM> through the protrusions <NUM> can advantageously constrain the protrusions in a loose and orderly manner, which allows even easier expansion of the stent's trailing section. In the present embodiment, each protrusion <NUM> is a hollow structure defining an opening, through which one end of a clamping member <NUM> can pass to engage the stent <NUM>.

It is added that in the case of the clamping mechanism <NUM> including a single clamping member, the clamping member may define two hooked fingers, and the number of the hooked fingers is smaller than the number of the protrusions. When the clamping mechanism <NUM> includes a plurality of clamping members <NUM>, each clamping member <NUM> may define one hooked finger, and the number of the hooked fingers is smaller than or equal to that of the protrusions. That is, the number of the clamping members is smaller than or equal to the number of the protrusions.

A description is set forth below in the context of a plurality of clamping members <NUM>. For example, the number of the clamping members <NUM> is equal to that of the protrusions <NUM> so that the protrusions <NUM> can be populated with the respective clamping members <NUM>, as shown in <FIG>. As another example, the number of the clamping members <NUM> is less than the number of the protrusions <NUM>. Preferably, the number of the protrusions <NUM> is twice that of the clamping members <NUM>. For example, the former may be <NUM>, and the latter may be accordingly <NUM>. This can reduce the size of the clamping mechanism <NUM>, allowing a smaller size during delivery. More preferably, the protrusions may be populated by the clamping members <NUM> so that there are one or more unpopulated protrusions between every two adjacent populated protrusions. Alternatively, in the case of <NUM> protrusions <NUM> and <NUM> clamping members <NUM>, there may be one unpopulated clamping member <NUM> between every two adjacent populated protrusions. This can take into account both compactness during delivery and clamping performance. Further, more clamping members <NUM> with a smaller diameter may be provided. For example, when the number of the clamping members <NUM> is four or five, they may be made of round nickel-titanium wires with a diameter of <NUM>. As another example, when ten clamping members <NUM> are provided, they may be nickel-titanium wires with a diameter of <NUM>.

<FIG> shows another embodiment of the constraining structure <NUM>, in which a single clamping member <NUM>' is included. The clamping member <NUM>' may pass through either all or spaced ones of the protrusions. With <NUM> protrusions being provided as an example, the clamping members <NUM>' may pass through the first, second, third, fifth, sixth and seventh protrusions clockwise, with the fourth and eight protrusions being unpopulated. Additionally, the clamping member <NUM>' may be generally C-like or helical in shape. The C-like shape may have an opening. The present invention is not limited to any particular size of the opening, as long as all the protrusions can be effectively gathered and retained. The clamping members <NUM>' is preferably an elastic wire such as a nickel-titanium wire or another nickel-based alloy wire. In operation, the clamping member <NUM>' can be removed to release the stent's trailing section simply by gently pulling or turning the body <NUM>. Therefore, it is convenient to operate. The present invention is not limited to any particular method of fabricating the constraining structure <NUM>, and the fabrication can be accomplished in various ways. For example, the body <NUM> may be made as a straight rod, and the clamping mechanism <NUM> can be obtained by welding or otherwise attaching a number of wires (e.g., those as shown in <FIG>) to a distal end of the straight rod. Alternatively, a number of wires may be each curved at one end and retained in a sleeve. For example, the sleeve may be configured as the body <NUM>. Yet alternatively, the body <NUM> may be provided as a thick tube or wire, and a number of wires may be formed at its one end by cutting or otherwise. These wires may be then curved to form the clamping mechanism <NUM>.

In the case of the clamping members <NUM> being curved relative to the body <NUM>, each clamping member <NUM> may be curved relative to the body <NUM> at an angle preferably of <NUM>°-<NUM>°, with <NUM>°-<NUM>° being more preferred. The inventors have found from experiments that an angle of curvature of each clamping member <NUM> in that range can allow both effective retention and easy release. Here, if the direction from a proximal end of the body <NUM> to a distal end thereof is defined as a positive direction of an axis of the body <NUM>, then the angle of curvature is defined as an angle of curvature of each clamping member <NUM> relative to the positive direction of the axis of the body <NUM>.

Further, the stent <NUM> may further includes a biocompatible membrane covering part of an outer surface of the stent <NUM>, with the protrusions being exposed therefrom.

It is to be noted that the present application also contemplates other structural variants of the clamping members. In addition, the stent may be either a braided stent or a cut stent, without limiting the present invention.

In summary, according to the techniques according to embodiments of the present invention, in practical use, the constraining structure of the present invention can desirably constrain the stent's trailing section so that the stent is deformed in a controlled manner and can be easily delivered within the delivery sheath while being able to easily expand upon it being pushed out thereof. Additionally, tangling of the stent's trailing section is prevented, ensuring a good success rate in release of the stent that has been pushed out of the sheath. Further, according to the present invention, after the stent is pushed out of the sheath, the anchoring features on the stent will not immediately anchor to the LAA wall. This can avoid damage to the patient's LAA wall caused by an operational error of the operator and reduce the risk of an accumulated pericardial effusion during surgery.

Claim 1:
A medical instrument (<NUM>), comprising a stent (<NUM>) having a proximal end and an opposing distal end, wherein the distal end of the stent (<NUM>) is configured with an expanded configuration and a collapsed configuration, wherein a trailing section of the stent (<NUM>) at the distal end comprises a plurality of protrusions (<NUM>), and wherein the medical instrument (<NUM>) further comprises a constraining structure (<NUM>) comprising a body (<NUM>) and a clamping mechanism (<NUM>), the clamping mechanism (<NUM>) disposed at a distal end of the body (<NUM>), the body (<NUM>) extending from the proximal end of the stent (<NUM>) to the distal end of the stent (<NUM>), the clamping mechanism (<NUM>) limiting relative movement of the protrusions (<NUM>) by passing through all or some of the protrusions (<NUM>);
characterised in that
the medical instrument (<NUM>) further comprises a proximal fixation member (<NUM>) disposed at the proximal end of the stent (<NUM>) and configured to bring the stent (<NUM>) into a closed configuration at the proximal end;
and in that the medical instrument (<NUM>) further comprises a distal fixation member (<NUM>) and a pull mechanism (<NUM>), the pull mechanism (<NUM>) comprising a number of pull elements (<NUM>) each connected, at a first end, to the distal fixation member (<NUM>) and, at a second end, to the distal end of the stent (<NUM>), the distal fixation member (<NUM>) configured to be movable toward the proximal fixation member (<NUM>) so that the distal end of the stent (<NUM>) is allowed to switch from the expanded configuration to the collapsed configuration.