Low profile stent delivery system and method

A low profiled stent delivery system includes a balloon catheter with a balloon mounted at a first location, and a balloon expandable stent crimped about the balloon catheter at a second location. The stent expands from a crimped state to a less than fully expanded state responsive to movement of an auxiliary expander from a first configuration to a second configuration. An inner diameter of the stent in the less than fully expanded state is greater than an outer diameter of the balloon in a deflated state. After repositioning the balloon within the less than fully expanded state, the balloon is inflated to fully expand the stent.

TECHNICAL FIELD

The present disclosure relates generally to placement of balloon expanded stents via inflation of a balloon, and more particularly to a low profile structure in which the stent is initially crimped at a location separated from the main balloon of the balloon catheter.

BACKGROUND

Stent delivery systems that utilize a balloon expandable stent mounted about a balloon have seen considerable success for many years. However, the practical limitations prevent typical balloon expanded stent structures from being manufactured to fit through low profile sheaths (such as seven French or less) to deliver stents to small diameter passageways. These structural limitations are due to practical limitations in producing small diameter catheters, practical limitations in balloon structures, and limitations in outer diameter of balloon expandable stents in a crimped state. These problems are complicated by the fact that these limitations are stacked in a typical structure in which the stent is mounted in a crimped state on a folded deflated balloon. Thus, without resorting to untested exotic materials, there are practical limits as to the outer diameter of the stent deployment system due to the limitations on how small the diameter can be made to be where the stent is crimped about the deflated balloon.

The present disclosure is directed toward one or more of the problems set forth above.

SUMMARY

In one aspect, a low profile stent delivery system includes a balloon catheter with a balloon mounted about a catheter at a first location along a length of the catheter. A balloon expandable stent is crimped about the catheter at a second location that is separated from the first location. An auxiliary expander is movable with respect to the stent between a first configuration and a second configuration. The stent expands from a crimped state to a less than fully expanded state responsive to movement of the auxiliary expander from the first configuration to the second configuration. An inner diameter of the stent in the less than fully expanded stent is greater than an outer diameter of the balloon in a deflated state.

In another aspect, a low profile stent delivery system includes a balloon catheter that includes a catheter and a balloon mounted about the catheter at a first location along its length. The low profile stent delivery system has a first configuration characterized by a balloon expandable stent being crimped about the catheter at a second location that is separated from the first location. The system has a second configuration characterized by the balloon expandable stent being in a less than fully expanded state at the second location. The inner diameter of the stent in less than fully expanded state is greater than an outer of the balloon in a deflated state. The system has a third configuration characterized by the balloon expanded stent being in the less than fully expanded state at the first location. The delivery system as a fourth configuration characterized by the balloon expandable stent being in a fully expanded state at the first location in contact with the balloon.

In another aspect, a method for delivering a balloon expandable stent to a treatment location includes positioning a sheath that is seven French or less in a passageway. A low profile stent delivery system is slid through the sheath. A balloon expandable stent of the low profile stent delivery system is expanded from a crimped state to a less than fully expanded state. A balloon of the low profile stent delivery system is moved with respect to the stent to a position within the less than fully expanded stent. The stent is expanded from the less than fully expanded state to a fully expanded state at the treatment site by inflating the balloon.

DETAILED DESCRIPTION

Referring initially toFIGS. 1-3, a low profile stent delivery system20includes a balloon catheter21that includes a catheter22and a balloon23mounted about the catheter at a first location24along a length of the catheter. A balloon expandable stent31is crimped about the catheter at a second location26that is separated from the first location24. A balloon expandable stent according to the present disclosure means a stent that is plastically expanded, which is not a self expanding stent that is biased toward an expanded state. An auxiliary expander40is movable with respect to the stent31between a first configuration41as showingFIG. 1and a second configuration42as shown inFIG. 2. In this embodiment, balloon23can be considered a main balloon, and the auxiliary expander40includes an auxiliary balloon43mounted about the catheter22at the second location26. The auxiliary balloon43is deflated in the first configuration41and inflated in the second configuration42. Catheter22may have a reduced diameter in the region of location26relative to a diameter at location24, as shown. Auxiliary balloon43may comprise a suitable medical balloon known in the art, but may preferably comprise a non-compliant balloon, which may or may not be mounted about a reduce diameter section of catheter22as shown inFIG. 1. The stent31expands from a crimped state32, as shown inFIG. 1to a less than fully expanded state33as shown inFIG. 2responsive to movement of the auxiliary expander40from the first configuration41(auxiliary balloon43un-inflated) to the second configuration42(auxiliary balloon43inflated). An inner diameter35of the stent31in the less than fully expanded state33is greater than an outer diameter27of the main balloon23in a deflated state25. By locating the crimped stent31away from the main balloon23, the overall profile of the stent delivery system20can be reduced because the radial thicknesses of the main balloon23and the crimped stent31are no longer stacked upon one another as in typical prior art balloon expanded stent delivery systems. Those skilled in the art will appreciate that maybe the biggest driver in reducing profile is the outer diameter of the stent31in the crimped state32. Thus, in most instances of a low profile stent delivery system20according to the present disclosure, the outer diameter of the stent31in the crimped state32will be equal to or greater than an outer diameter of the main balloon23in its deflated state25as shown inFIGS. 1 and 2. Although not readily apparent inFIGS. 1 and 2, those skilled in the art will appreciate that main balloon23will likely be folded in a manner well known in the art when in its deflated state25. Although not necessary, the auxiliary balloon43will likely have the same or less compliance relative to main balloon23.

After the auxiliary balloon43has expanded stent31to its less than fully expanded state33as shown inFIG. 2, the auxiliary balloon43may be deflated and the balloon catheter21maneuvered to position the main balloon23within the stent31. Thereafter, the main balloon23may be inflated as shown inFIG. 3to change the stent31from the less than fully expanded state33to a fully expanded state34as shown inFIG. 3. Of note is the fact that the outer diameter28of the main balloon23in an inflated state29is greater than an outer diameter44of the auxiliary balloon43in an inflated state45. Although not necessary, balloon catheter21may define a wire guide lumen36that opens through a distal end37of catheter22. Although utilizing the wire guide lumen36as also an inflation lumen for one or both of the main balloon23and auxiliary balloon43is within the scope of this disclosure, the illustrated embodiment is shown as including a separate inflation lumen38that is defined by catheter22. Both main balloon23and auxiliary balloon43may share the common inflation lumen38.

In the illustrated embodiment, a rupture disk54may be positioned to block the inflation lumen38between the first location24corresponding to main balloon23and the second location26corresponding to auxiliary balloon43. The auxiliary balloon43may be configured to move from the un-inflated first configuration41to the inflated second configuration42responsive to a first inflation pressure in the inflation lumen38. The ruptured disk54may be configured to rupture at a rupture pressure that is greater than the first inflation pressure. The main balloon23is constructed to move from the deflated state28to the inflated state29responsive to a second inflation pressure that is equal to or greater than the rupture pressure associated with rupture disk54. By allowing the thickness dimensions of the stent31and main balloon23to not be stacked, the low profile stent delivery system20is constructed to be slidably received through a sheath that is seven French or less. This enables the stent delivery system20to deliver a stent31to peripheral small diameter blood vessels previously unreachable with larger diameter conventional stent delivery systems.

Referring now toFIGS. 4-6, a second embodiment of a low profile stent delivery system120differs from the previous embodiment in that the auxiliary expander40includes a wedge70, as opposed to the auxiliary balloon43of the previous embodiment. Otherwise, several of the features of this embodiment include identical numbers because they represent similar features as the first embodiment. Low profile stent delivery system120includes a balloon catheter121that includes a catheter122and a balloon23mounted about the catheter122at a first location24along the length of the catheter. Like the previous embodiment, a balloon expandable stent31is crimped about the catheter122at a second location26that is separated from the first location24. The auxiliary expander, which includes wedge70is movable with respect to the stent31between a first configuration41as shown inFIG. 4to a second configuration42as shown inFIG. 5. In particular, wedge70may be positioned within catheter122and be movable from a first position71to a second position72. In this embodiment, first position71is distal to the second location26, and second position72is proximal to the second location26. Thus, in this embodiment, wedge70is connected to a tether74that allows the user to pull the wedge70from the first position71to the second position72. Movement of wedge70occurs responsive to tension in tether74. In an alternative embodiment, not shown, the wedge could be initially positioned proximal to the second location26and be pushed to a second location distal of the second location26responsive to advancement of a compression member coupled to wedge70in a distal direction. Although not necessary, both wedge70and tether74may be positioned in inflation lumen38, which is the means by which main balloon23is inflated.

Wedge70may be flexible between a larger profile as shown due to the inclusion of a wedge opener73. Wedge opener73may be connected to a separate tether78that is configured to cause the wedge opener73to detach from wedge70after wedge70has been moved to the second position72. For instance, the connection between wedge70and wedge opener73maybe engineered to be weak relative to the expected tension in tether74when wedge70is withdrawn proximally away from stent31. After becoming disconnected as shown inFIG. 6, the wedge opener73and its associated tether78are no longer useful and may remain inside or near main balloon23. At the same time, wedge70may collapse and be withdrawn in a proximal direction from stent delivery system120so that it does not present an obstacle to inflation of main balloon23via inflation lumen38. Thus, the connection between the wedge70and the wedge opener73may be weak such that sufficient tension in tether74will break that connection and detach the opener73from wedge70. This detachment permits the wedge70to collapse to a low profile for travel through a catheter lumen, which may be the inflation lumen38as shown.

In one example variation, the wedge70may itself be a small balloon that is inflated via a passageway in tether74. In such as case, the wedge balloon would be deflated after being pulled through the stent31. Alternatively, the wedge70may be made from a porous material that permits inflation of main balloon23without removal of wedge70from catheter122. In still another version, the wedge70may be made to include a non-Newtonian fluid/material that changes properties based on forces applied to it. In still another version, the wedge70could be made from a dissolvable material, and a solvent may be introduced via the inflation lumen38after the wedge70has moved stent31to its less than fully expanded configuration as shown inFIG. 5. Like the earlier embodiment, movement of wedge70from the first position71to the second position72causes the stent31to expand from a crimped state32to a less fully expanded state33. Thereafter, catheter122can be maneuvered with main balloon23deflated to position the main balloon within the less than fully expanded stent31. Thereafter, the main balloon23can be inflated as shown inFIG. 6to expand the stent31to a fully expanded state34.

Referring now in addition toFIGS. 7-10, still another embodiment of a low profile stent delivery system220is illustrated. This embodiment shares some similarities with the first two embodiments, and like features include the same numbering system. However, this embodiment differs from the earlier embodiments by the reverse locations of the main balloon23and the auxiliary balloon43. This embodiment also differs by the inclusion of a stent securement mechanism60. Nevertheless, those skilled in the art will appreciate that the delivery systems20and120described previously could also include a stent securement mechanism60as described infra. Where the same numbers are used as per the previously described embodiments, the earlier description using those numbers also applies. The stent securement mechanism60is mounted to catheter222of balloon catheter221, and is movable from an inactive configuration61as shown inFIGS. 7 and 8to an active configuration63as shown inFIGS. 9 and 10. The function of the stent securement mechanism60is to help prevent stent31in its less than fully expanded state33from sliding out of place when the balloon catheter21is maneuvered betweenFIGS. 8 and 9to position the main balloon23within the less than fully expanded stent31. This strategy permits the stent31to be expanded from its crimped state32to its less than fully expanded state33at the location where the stent31will eventually be fully expanded. In the inactive configuration61, the stent securement mechanism60may have an outer diameter62that is less than an outer diameter39of the stent31in its crimped state32. In the active configuration63, the stent securement mechanism60is positioned to contact a distal end46of stent31when the stent31is in the less than fully expanded state33.

In this illustrated embodiment, the stent securement mechanism60includes a plurality of stent securement arms67that are parallel to a longitudinal axis68in the inactive configuration61. When changed to the active configuration, the stent securement arms67may deform, change shape or pivot about a mid-point (as shown) in order to inhibit migration of stent31prior to stent31being fully expanded as shown inFIG. 10. In this embodiment, balloon catheter221may include one or more radiopaque markers that could be used to help the user to confirm when the system220has been moved from the configuration ofFIG. 8into the configuration ofFIG. 9. One could expect the outer diameter62of the stent securement mechanism to increase responsive to the change from the inactive configuration61to the active configuration63. When this is done, the deflated auxiliary balloon43may be maneuvered into a hollow distal nose segment223of catheter222. Like the embodiment ofFIGS. 1-3, both main balloon23and auxiliary balloon43may share a common inflation lumen38, that is separate from a wire guide lumen36, if included. The other embodiments could also include appropriate markers to assist the user in confirming proper placement of the stent31and other features of the balloon catheter during delivery.

Referring now in addition toFIGS. 11-13, movement of the stent securement arms67of stent securement mechanism60from the inactive configuration61to the active configuration63may be achieved by the inclusion of a deployment actuator64that is in contact with the stent securement mechanism60. In the version shown inFIG. 11, the deployment actuator64may comprise a wire that is connected to the stent securement arms67, and causes the stent securement arms to move from the inactive configuration61to the active configuration63responsive to the deployment actuator wire64being pulled by the user from first position65to a second position66. Thus, the stent securement mechanism60moves from the inactive configuration61to the active configuration63responsive to movement of the deployment actuator64from the first position65to the second position66. In the version ofFIG. 12, the deployment actuator164may comprise an electrically responsive wire that changes in length responsive to a current supplied to the deployment actuator wire164. In this embodiment, application of current causes the deployment actuator wire164to shorten in response to the electric current to move the stent securement arms67to the active configuration63.FIG. 13shows still another alternative strategy in which the stent securement arms67are biased toward the active configuration63but are held in the inactive configuration61by a deployment actuator264in the form of a rupture band. Preferably, in each of the embodiments that include a stent securement mechanism60that includes a plurality of stent securement arms67, the stent securement arms67are preferably parallel to the longitudinal axis68of the catheter222when in the inactive configuration61as shown.

Referring now toFIGS. 14 and 15, a couple of alternative strategies are shown for a stent securement mechanism that does not includes the stent securement arms67of the previous embodiments. In particular, inFIG. 14, stent securement mechanism360includes a deployment actuator364that is maneuvered by rotation about its longitudinal axis from first position365to second position366to deploy the stent securement mechanism360from an inactive configuration61that is generally parallel to the longitudinal axis to a larger diameter in the active configuration63. In the embodiment ofFIG. 15, a stent securement mechanism460includes a deployment actuator wire464that is moved from a first position465corresponding to an inactive configuration61in a proximal direction to a second position466in which the stent securement mechanism460presents a larger diameter in its active configuration63. For example, the stent securement mechanism460may comprise a wire mesh that is relaxed and at a low profile when the inner mandrel is extended, but bunches up to a larger profile in the active configuration when retracted against the less than fully expanded stent31. In other versions, not shown, the stent securement mechanism maybe smaller than the inner diameter of stent31in the less than fully expanded state33, but the surface of the stent securement mechanism may be rough to prevent stent migration. In still another alternative, which is not shown, the stent securement mechanism60may comprise a small balloon positioned just distal of stent31, which is deflated in the inactive configuration61but inflated in the active configuration63.

Referring now to all of the low profile stent delivery systems20,120,220illustrated previously. In all cases, the delivery system includes a balloon catheter21,121,221that includes a catheter22,122,222and a balloon23mounted about the catheter at a first location24along the length of the catheter. All embodiments also include a balloon expandable stent31that is changed from a crimped configuration32to a less than fully expanded configuration33and finally to a fully expanded configuration34. All versions of the system20,120,220have a first configuration81(FIGS. 1, 4 and 7) characterized by the balloon expandable stent31being crimped about the catheter22,122,222at the second location26that is separated from the first location24. The low profile stent system20,120,220has a second configuration82(FIGS. 2, 5, and 8) characterized by the balloon expandable stent31being in a less than fully expanded state33at the second location26. The inner diameter35of the stent31of the less than fully expanded state33is greater than an outer diameter27of the main balloon23in its deflated state28. The low profile stent delivery system20,120,220may be changed to a third configuration83(FIG. 9) that is characterized by the balloon expandable stent31being in the less than fully expanded state33at the first location24corresponding to the main balloon23. This configuration is omitted from the embodiments ofFIGS. 1-6but is shown inFIG. 9with regard to that embodiment. The low profile stent delivery system20,120,220can also be changed to a fourth configuration84(FIGS. 3, 6 and 10) that is characterized by the balloon expandable stent31being in a fully expanded state34at the first location24in contact with the main balloon23.

The change from the first configuration81to the second configuration82may be done responsive to movement of the auxiliary expander40with respect to the stent31. The change from the second configuration82to the third configuration83may be done responsive to movement of the balloon23with respect to the stent31along the axis68of catheter22,122,222. Finally, the change from the third configuration83to the fourth configuration84may be accomplished responsive to inflation of the main balloon23.

INDUSTRIAL APPLICABILITY

The present disclosure finds generally applicability in any balloon expanded stent delivery application. The present disclosure finds particular application in low profile balloon expandable stent delivery systems. Finally, the present disclosure finds specific applicability to low profile stent delivery systems that can be slidably received through a sheath that is seven French or less for reaching and placing stents in hard to reach small diameter blood vessels previously unreachable with conventional stent delivery system technology.

Referring now in addition toFIGS. 16-24, a method of delivering a balloon expandable stent31to a treatment location12is illustrated. Treatment location12may be an occlusion13needing to be stented in a small diameter blood vessel of a live body10. Alternatively, body10and the associated passageway11may be artificial such as for teaching or demonstration purposes. In any event, a sheath50that is seven French or less is positioned in a passageway11as shown inFIG. 16. Next, a wire guide19may be maneuvered through sheath50through the passageway11to an occlusion13at treatment location12. As shown inFIG. 17, thereafter, the low profile stent delivery system according to any of the embodiment may be passed over wire guide19to the treatment location12. In these illustrations, the first embodiment of the low profile stent delivery system20is illustrated. The low profile stent delivery system20is slid through sheath50to position the stent31in its crimped state32in the occlusion13with the system20in its first configuration81as described earlier. Next, the stent delivery system20is changed to the second configuration82by changing the auxiliary expander40from its first configuration41to its second configuration42by inflating auxiliary balloon43. In changing fromFIG. 19toFIG. 20, the stent delivery system20is changed from its second configuration82to its third configuration83by positioning the main balloon23within the less than fully expanded stent31. Next, the system20is changed from the third configuration83to the fourth configuration84as shown inFIG. 21by inflating main balloon23to expand stent31to its fully expanded state34to open the occlusion13. Thereafter, the stent delivery system20may be maneuvered away from the treatment site12as shown inFIG. 22and eventually withdrawn completely from the body10as shown inFIG. 23. Thereafter, the wire guide19and the small diameter sheath50may be withdrawn from the body10as shown inFIG. 24, leaving the stent31in its fully expanded state34at the treatment location12.

Returning toFIG. 18, the balloon expandable stent31is expanded from the crimped state32to the less than fully expanded state33. Next, when changing from the second configuration82to the third configuration83ofFIG. 20, the balloon23is moved with respect to stent31to a position within the less than fully expanded stent31. Thereafter, the stent31is changed from its less than fully expanded state33to its fully expanded state34at the treatment site12by inflating the main balloon23as shown inFIG. 21.

In all of the embodiments, the step of expanding the balloon expandable stent31to the less than fully expanded state33is accomplished by moving the auxiliary expander40from its first configuration41to its second configuration42. In the embodiment shown, the balloon23is moved in a proximal to distal direction14when changing from the second configuration82as shown inFIG. 19to the third configuration83as shown inFIG. 20.