Patent Application
20070043420
This invention relates generally to medical devices and procedures, and more particularly to a method and system of deploying a stent-graft in a vascular system.
Prostheses for implantation in blood vessels or other similar organs of the living body are, in general, well known in the medical art. For example, prosthetic vascular grafts formed of biocompatible materials (e.g., Dacron or expanded, porous polytetrafluoroethylene (PTFE) tubing) have been employed to replace or bypass damaged or occluded natural blood vessels. A graft material supported by framework is known as a stent-graft or endoluminal graft. In general, the use of stent-grafts for treatment or isolation of vascular aneurysms and vessel walls which have been thinned or thickened by disease (endoluminal repair or exclusion) are well known. Many stent-grafts, are “self-expanding”, i.e., inserted into the vascular system in a compressed or contracted state, and permitted to expand upon removal of a restraint. Self-expanding stent-grafts typically employ a wire or tube configured (e.g. bent or cut) to provide an outward radial force and employ a suitable elastic material such as stainless steel or Nitinol (nickel-titanium). Nitinol may additionally employ shape memory properties. The self-expanding stent-graft is typically configured in a tubular shape of a slightly greater diameter than the diameter of the blood vessel in which the stent-graft is intended to be used. In general, rather than inserting in a traumatic and invasive manner, stents and stent-grafts are preferably deployed through a less invasive intraluminal delivery, i.e., cutting through the skin to access a lumen or vasculature or percutaneously via successive dilatation, at a convenient (and less traumatic) entry point, and routing the stent-graft through the lumen to the site where the prosthesis is to be deployed.
Intraluminal deployment is typically effected using a delivery catheter with coaxial inner (plunger) and outer (sheath) tubes arranged for relative axial movement. The stent is compressed and disposed within the distal end of an outer catheter tube in front of an inner tube. The catheter is then maneuvered, typically routed though a lumen (e.g., vessel), until the end of the catheter (and the stent-graft) is positioned in the vicinity of the intended treatment site. The innertube is then held stationary while the outertube of the delivery catheter is withdrawn. The inner tube prevents the stent-graft from being withdrawn with the outer tube. As the outer tube is withdrawn, the stent-graft radially expands so that at least a portion of it is in substantially conforming surface contact with a portion of the interior of the lumen e.g., blood vessel wall.
Some stent-graft deployment systems use a disc shaped or shallow cup plunger configuration to act as a barrier at a distal end (position relative to its deployed location in the vasculature from the heart) of a stent-graft to prevent movement of the stent graft relative to the catheter center member as and until an outer tube or sheath is withdrawn, causing the springs on the distal end of the stent-graft to deploy or release upon sheath retraction without much control by the physician. A shallow cup plunger provides no extra control of the radial deployment of the distal end of the stent graft.
In instances where the springs at the proximal end of the stent graft are held captured to the catheter to permit repositioning, the unconstrained release of the distal end of the stent graft limits how far the outer tube or sheath can be retracted before repositioning cannot be done. So once the distal end of the stent-graft is deployed, the physician loses the ability to manipulate the stent-graft axially, radially, or tortially or in a twisting manner. Thus, existing cup plunger assemblies fail to encapsulate (hold) the distal end of stent-grafts before, during, and after deployment of a sheath and further fail to contribute to the controlled deployment of the stent-graft after an outer sheath is withdrawn in a delivery configuration where the proximal end is also held constrained, or had been held by another mechanism prior to deployment of the distal end.
In a first embodiment according to the present invention, a stent-graft release mechanism can include a catheter, a coaxial inner tube having a cup at a distal end where the coaxial inner tube is placed about the catheter, a release plate affixed to the catheter, and a mechanism for axially moving the release plate relative to the cup.
In a second embodiment, a stent-graft deployment system can include a stent-graft, a catheter having a flexible catheter tip attached to a catheter shaft of the catheter, a retractable primary sheath containing the stent-graft in a first constrained small diameter configuration around said catheter shaft near said flexible tip, and a cup plunger having a cup operatively coupled at the end thereof for retaining a distal end of the stent graft in a constrained position, where the cup plunger moves coaxially in relation to the catheter and the retractable primary sheath. The stent-graft deployment system can further include a release plate coupled to the catheter, wherein the release plate moves coaxially relative to the cup for pushing the distal end of the stent graft beyond an outer edge of the cup in order to release the stent-graft from the constrained position to enable stent-graft deployment.
In a third embodiment, a method of deploying a stent-graft using a stent-graft deployment system having a stent-graft release mechanism and a retractable primary sheath, includes the steps of loading the stent-graft deployment system with a stent-graft, where the distal end of the stent-graft is retained within a cup of the stent-graft release mechanism and tracking the stent-graft deployment system over a guide wire to a location before a target area. The method can further include the step of retracting the primary sheath to expose at least a proximal portion of the stent-graft and moving a release plate from within a lower portion of the cup to beyond a distal edge of the cup to at least partially deploy the stent-graft in the target area.
In the third embodiment, the method can further include the step of retaining apexes of Nitinol springs of the distal end of the stent-graft within the cup before deployment. The catheter can be coupled to the release plate and the step of moving the release plate can include the step of rotating a luer that coaxially moves the catheter relative to the cup. A secondary sheath can move axially within the primary sheath wherein the method can further include the step of moving the stent-graft to a location within a target area while the primary sheath is retracted as the secondary sheath is exposed. The step of moving the release plate can include the step of axially moving the release plate relative to the cup. Additionally, the method can further include the step of releasing the stent-graft from the delivery system after moving the release plate beyond an edge of the cup.
The system 10 includes a primary sheath 20 (preferably made of a semi-rigid material such as PTFE) initially covering an optional secondary sheath 14 (preferably made of woven polyethylene terephthalate (PET)). The secondary sheath 14 can be more flexible than the retractable primary sheath 20. The deployment system 10 is able to separately retract the primary and secondary sheaths.
The primary sheath should have enough stiffness and column strength to provide adequate pushability as the system 10 tracks through small diameter vessels that tend to conform to the shape of the delivery system. The secondary sheath utilizes its greater flexibility (at the expense of column strength) to improve trackability and advancement, in vessels with larger diameters that do not tend to conform to the shape of the delivery system, particularly through areas having tight radiuses. So, where prior deployment systems utilizing just a semi-rigid primary sheath were prone to kinking while tracking through an area with a tight radius, the secondary sheath of the present invention avoids kinking and easily adapts to the shape of the vessel which reduces advancement force while tracking through the vessels with tight curves. The greater flexibility and potential for larger sheath diameter in the secondary sheath can greatly reduce resistance to deploy the stent graft in areas with tight curves.
The deployment system 10 also includes a stent-graft 15 initially retained within the secondary sheath 14. As described herein, the stent-graft 15 is a self-expanding, Nitinol/Dacron stent-graft system designed for endovascular exclusion of Thoracic Aortic Aneurisms (TAA). The deployment system 10 includes a cup 16 and release plate 17 as shown in
As shown in
Referring to
Operationally, once the secondary sheath 14 is exposed as shown in
In summary, the stent-graft release mechanism uses a cup that encapsulates the distal end of the stent-graft before, during and after deployment of the sheath and/or a proximal end of the stent-graft. The cup also serves as a positive engagement mechanism when the stent-graft is partially deployed in a flexible sheath such as the secondary sheath.
When using a proximal lock that retains the proximal end of the stent-graft during deployment, the stent-graft release mechanism provides additional maneuverability to a partially deployed stent-graft (See FIGS. 6A-D). The cup and release plate further enable a controlled deployment of the distal end of the stent-graft after withdrawal of a sheath. More specifically, to release the distal end of the stent-graft, the cup (16), which holds the spring apexes, can be retraced with respect to the catheter inner member (21) while the release plate (17) remains stationary which prevents the stent-graft from being dragged back with the cup. In this way, the cup and release plate enable the deployment of a stent-graft by acting as an engagement mechanism for the stent-graft so the sheath can be retraced over the stent-graft while in a partially expanded flexible sheath.
The embodiment of
In an alternative embodiment where no secondary sheath is necessarily used as shown in
Close up schematic plan views of another stent-graft deployment delivery system using an alternative arrangement stent-graft release mechanism 50 are shown in
The cap 27 can be formed from a shroud portion of the tapered tip 25 which is coupled at the distal end of the inner tube 61. Within the shroud portion (formed by the tubular body portion of the cap 27) preferably resides a back plate (disc) 57 coupled to a distal end of the outer tube 60 that serves as a proximal stop for the stent-graft 63 preventing movement in a proximal direction. The tubular body portion of the shroud portion may also include a support ring 56 near the proximal end of the tapered tip 25 to provide additional rigidity to the cap 27. Additionally, a proximal lock 62 is also coupled to a distal area of the outer tube 60. The proximal lock 62 preferably includes at least one or a plurality of ribs 64 that serves as an axial constraint for the stent-graft 63. The proximal end (or the proximal springs 65, 67, 68 and 69) of the stent-graft 63 cannot deploy until the ends of the proximal lock 62 clear the bottom end of the shroud portion of the tip.
A stent-graft can include a polyester or Dacron material (forming the graft material) sewn to a Nitinol support structure using polyester sutures. The Nitinol wire is used to form a skeletal structure that provides support, strength and stability to the stent-graft. The stent-graft can also have a support member on the proximal end of the stent-graft that is left mainly uncovered by the graft material. The uncovered portion will typically have a sinusoidal pattern with a predetermined number of apexes protruding up. The apexes form what is known as the proximal spring or springs of the stent-graft. As shown, the gap between the back plate 57 and the proximal lock 62 is preferably designed to hold the protruding apexes of the proximal spring. The apexes straddle the ribs 64 of the proximal lock 62 and remain trapped between the back plate 57 and the proximal lock until the relative movement between the outer tube 60 and the inner tube 61 exposes the gap and the proximal springs 65, 67, 68, and 69. In other words, the apexes cannot release from the ribs 64 on the proximal lock 62 while the apexes remain within the shroud portion of the cap 54. When the inner tube 61 and coupled tapered tip 25 are advanced forward exposing the proximal lock 62, the apexes of the proximal springs 65, 67, 68, 69 release from the respective ribs 64 of the proximal lock 62. The release results in the deployment of the proximal end of the stent-graft 15. Note that while the proximal springs 65, 67, 68, 69 remain in the gap and within the cap or shroud portion of the tapered tip 25, the proximal springs remain axially constrained as well as radially constrained. The support ring 56, usually made of metal, helps prevent the radial force of the proximal springs from distorting the shape of the tapered tip and particularly the shroud portion of the tapered tip.
Note that
Referring to
Embodiments shown are ideally suited for introducing the stent-graft deployment system into a femoral artery and advancing the stent-graft deployment system through an iliac artery into the aorta for repair of an aortic aneurysm and more specifically in tracking the stent-graft deployment system through a portion of an thoracic arch when the secondary sheath has been exposed after the retraction of the primary sheath and without any kinking of the primary sheath. The embodiments shown also provide greater control in the final placement and deployments
Additionally, the description above is intended by way of example only and is not intended to limit the spirit and scope of the invention and it equivalent as understood by persons skilled in the art.
