Patent Application
20060047299
The art and science of interventional therapy and surgery has continually progressed towards treatment of internal defects and diseases by use of ever smaller incisions or access through the vasculature or body openings in order to reduce the trauma to tissue surrounding the treatment site. One important aspect of such treatments involves the use of catheters to place therapeutic devices at a treatment site by access through the vasculature. Examples of such procedures include transluminal angioplasty, placement of stents to reinforce the walls of a blood vessel or the like and the use of vasoocclusive devices to treat defects in the vasculature. There is a constant drive by those practicing in the art to develop new and more capable systems for such applications. When coupled with developments in biological treatment capabilities, there is an expanding need for technologies that enhance the performance of interventional therapeutic devices and systems.
One specific field of interventional therapy that has been able to advantageously use recent developments in technology is the treatment of neurovascular defects. More specifically, as smaller and more capable structures and materials have been developed, treatment of vascular defects in the human brain which were previously untreatable or represented unacceptable risks via conventional surgery have become amenable to treatment. One type of non-surgical therapy that has become advantageous for the treatment of defects in the neurovasculature has been the placement by way of a catheter of vasoocclusive devices in a damaged portion of a vein or artery.
Vasoocclusion devices are therapeutic devices that are placed within the vasculature of the human body, typically via a catheter, either to block the flow of blood through a vessel making up that portion of the vasculature through the formation of an embolus or to form such an embolus within an aneurysm stemming from the vessel. The vasoocclusive devices can take a variety of configurations, and are generally formed of one or more elements that are larger in the deployed configuration than when they are within the delivery catheter prior to placement. One widely used vasoocclusive device is a helical wire coil having a deployed configuration which may be dimensioned to engage the walls of the vessels. One anatomically shaped vasoocclusive device that forms itself into a shape of an anatomical cavity such as an aneurysm and is made of a pre-formed strand of flexible material that can be a nickel-titanium alloy is known from U.S. Pat. No. 5,645,558, which is specifically incorporated by reference herein. That vasoocclusive device comprises one or more vasoocclusive members wound to form a generally spherical or ovoid shape in a relaxed state. The vasoocclusive members can be a helically wound coil or a co-woven braid formed of a biocompatible material, and the device is sized and shaped to fit within a vascular cavity or vesicle, such as for treatment of an aneurysm or fistula. The vasoocclusive member can be first helically wound or braided in a generally linear fashion, and is then wound around an appropriately shaped mandrel or form, and heat treated to retain the shape after removal from the heating form.
The delivery of such vasoocclusive devices can be accomplished by a variety of means, including via a catheter in which the device is pushed through the catheter by a pusher to deploy the device. The vasoocclusive devices, which can have a primary shape of a coil of wire that is then formed into a more complex secondary shape, can be produced in such a way that they will pass through the lumen of a catheter in a linear shape and take on a complex shape as originally formed after being deployed into the area of interest, such as an aneurysm. A variety of detachment mechanisms to release the device from the pusher are known in the art.
Once in place in the aneurysm, the vasoocclusive coil triggers a response in the body by which tissue is deposited over and around the coil. Disruption and stagnation of the blood flow by the vasoocclusive coil triggers intra-aneurysmal thrombus formation. Endothelial cells originating from the parent artery migrate over the thrombus, covering the aneurysm neck. Leukocytes trapped within the thrombus begin to ingest platelets, red blood cells and fibrin through the process of phagocytosis. Leukocytes continue to infiltrate aneurismal thrumbus and the thrombus is transformed into myofibroblasts, or smooth muscle cells. The smooth muscle cells in the aneurysm begin to secrete collagen. Smooth muscle cells within a collagen network comprise fibro-cellular tissue. Through thrombus organization, the aneurysm sac is filled with fibro-cellular tissue promoting stability of the aneurysm sac. The tissue formation eventually occludes the aneurysm, forming a “patch” on the vascular wall and isolating the aneurysm.
In one method of promoting the biological response to the coil, a bioabsorbable suture material is tightly wound around the portion of the coil that is to be inserted into the aneurysm. The suture is tightly wound onto the coil, and the assembly is then heat cured at a relatively low temperature to fuse the suture windings together. The bioabsorbable material promotes the body's tissue building response, and results in a predictable and desirable rate of occlusion of the aneurysm. While this method of encasing the coil in bioabsorbable achieves the goal of promoting the body's tissue response, the process of tightly winding and curing the suture is relatively complicated and expensive.
A need therefore remains for a simpler and less expensive method of coating the distal portion of the vasoocclusive wire assembly so that it still provides the advantages of a bioabsorbable covering but which can be accomplished more efficiently.
Turning now to
Referring now to
Either before or after being treated as described, distal portion 34 is attached to base portion 32 by a severable portion 36 according to well-known techniques. In one such technique, severable portion 36 is formed of a low-melting, conductive metal material that can be remotely severed by passing a small electrical current through the device. The low-melting conductive metal has a sufficient electrical resistance to heat the severable portion to its melting temperature, thereby severing and releasing distal portion 34 from base portion 32. In another embodiment a single wire is used, and the distal portion is rendered severable by swaging or deforming the wire at the severing point to form a high resistance portion that rapidly heats to its melting point when a current is passed through the wire.
Referring to
Those of skill in the art will appreciate that other suture materials could be substituted, and that the invention is not limited to any specific sheathing material. The use of an extruded bioabsorbable sheath represents a significant improvement over the prior art in that it can be produced more simply and more economically than a spiral wound sheath, while at the same time providing equivalent or even better absorption properties compared to spiral-wound sheaths.
