Surgery – Diagnostic testing – Flexible catheter guide
Reexamination Certificate
1999-08-19
2001-07-03
O'Connor, Cary (Department: 3736)
Surgery
Diagnostic testing
Flexible catheter guide
Reexamination Certificate
active
06254550
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to medical devices and, in particular, to a wire guide.
BACKGROUND OF THE INVENTION
Balloon angioplasty, a medical procedure by which an occluded or narrowed blood vessel is dilated and reopened using an inflatable balloon mounted on a catheter, was pioneered by Andreas Greuntzig in the 1970's. The coronary version of this new procedure, Percutaneous Transluminal Coronary Angioplasty (PTCA), soon became recognized as a highly effective method of treating diseased coronary artery disease. More recently, angioplasty has become a standard approach for treatment of renal artery stenoses. Percutaneous Transluminal Renal Angioplasty (PTRA), with its low rate of complications, has now largely replaced surgery as treatment for renal artery stenoses, which are common contributing factors in patients diagnosed with arterial hypertension, renal insufficiency, or cardiac insufficiency.
The basic angioplasty procedure usually involves percutaneously introducing a guiding catheter through an introducer sheath to the target site and then engaging the ostium of the vessel. A wire guide is fed through the guiding catheter and ostium where it is placed across the lesion in the vessel. Finally, a balloon catheter is introduced over the wire guide and positioned at the lesion to dilate the vessel. Increasingly more often, a stent is also placed following balloon dilatation to prevent restenoses of the lesion. One procedure for placing the balloon catheter at the treatment site is known as the “Push-Pull” Technique whereby the physician advances the balloon catheter through the guiding catheter (“push”) while applying slight forward pressure to the latter. At the same time, an assistant holds the proximal end of the wire guide, providing gentle traction (“pull”). Care must be taken during the advancement of the catheter to avoid dislodging the wire guide from the treatment site. This is especially of concern during a renal procedure due to the relatively short length of the renal artery and the acute angle of the artery relative to the aorta.
The unique anatomy of the renal vessels presents difficulties when using existing wire guides for PTRA. Many physicians select wire guides developed for coronary procedures which are designed to facilitate negotiation of tortuous vessels and minimize trauma to small delicate coronary arteries. Because of their required flexibility, coronary wire guides usually lack the desired stiffness for PTRA. A stiffer wire guide permits better tracking by the catheter over the wire. However, a stiff wire guide can also subject the vasculature to forces during manipulation that are capable of perforating the vessel or injuring the ostial takeoff from the aorta into the renal vessel. The wire guide receives much of the up and down stresses during the procedure and transfers them to the vessel wall. These same stresses are often responsible for dislodging the distal end of the wire guide from the orifice, necessitating withdrawal of the catheter and reintroduction of the wire guide. If the wire guide enters the ostium of the vessel at the correct angle, the stresses are instead received by the catheter, thus protecting the fragile vessel. Furthermore, the typical stresses at that site during manipulation of a straight wire can also cause thrombus to shear from the vessel wall, often leading to an embolus and related serious complications.
SUMMARY OF THE INVENTION
The foregoing problems are solved and a technical advance is achieved in an illustrative preformed wire guide having a flexible tip portion that is atraumatic to the vessel as the wire guide is advanced, the flexible tip portion having a distal tip and a proximal portion that includes a preformed bend approximating the takeoff angle of a vessel, for example, a renal artery relative to the aorta from which it branches. By producing a wire guide with the correct anatomical preformed bend, there is much less risk of trauma to the vessel. A related benefit of the present invention is lowering the risk of displacing thrombus that often forms just inside the ostium, especially in the presence of a stenotic lesion. A straight wire would receive much of the force at the turn into the ostium created by the advancing catheter and potentially transfer much of that force to the wall of the vessel. By forming the bend in the wire guide, the forces created from the catheter tracking over the wire are exerted on the catheter itself and not to the vessel wall where injury or disruption of thrombus can occur. Nitinol can be permanently shaped by annealing with extreme heat, or by cold-working which involves overstressing the wire. To produce a more rigid bend segment for protecting the vessel, cold working the nitinol mandril is preferred over the annealed embodiment which exhibits less resistance to the tracking forces of the catheter.
The second major benefit of having an anatomically shaped preformed bend is providing a portion of the wire guide to serve as an anchor to maintain the device within the vessel during advancement of a catheter over the wire. A straight wire guide would be much more likely to become dislodged during the course of tracking the catheter to the treatment site.
In a preferred embodiment of the illustrative invention, the flexible tip portion includes a spring coil wire that is attached over a solid wire mandril. The transition between the highly-flexible atraumatic tip and the stiffer mandril is relatively abrupt, compared to typical wire guides, due to the short available length of vessel in which the anchoring portion of the mandril can reside and the need for that mandril to be of sufficient stiffness to maintain a proper anchor. A bend having a preferred range of 30° to 150° formed in the mandril wire allows the wire guide to more easily enter the ostium of the renal artery or vein, depending on the particular anatomy of the patient, and whether a superior or inferior approach is used. A more preferred range of bend angles is 45° to 135°, with the most preferred range being 60° to 120°. The improved ability to access the renal vessel can reduce the need for using a guiding catheter to place the wire guide, thereby eliminating a step of the procedure and the attendant risks.
The solid mandril wire is of sufficient stiffness to retain the anatomical preformed bend and allow the wire guide to remain anchored in the vessel while a catheter is being fed over the wire. In the preferred embodiment of the invention, the mandril wire is made of a superelastic material such as a nickel-titanium (Ni—Ti) alloy (commercially available as nitinol). The bend in the mandril is formed by mechanically stressing (cold working) and plastically deforming the wire while in its austenitic state to create at least a partial localized zone of martensite. The nitinol wire can be made relatively thin while still retaining the preformed bend and the requisite stiffness. Other possible materials for the mandril include elastic biocompatible metals such as stainless steel, titanium, or tantalum.
While the potential benefits of cold working nitinol wire to plastically deform the original shape have not been fully appreciated by manufacturers of wire guides and other medical devices, there are two primary advantages over the standard annealing method. The first involves the differences in how the device behaves as bending stresses are applied. In the absence of applied stress, the annealed wire guide is completely in an austenitic state, even in the curved regions. When sufficient stress is applied anywhere upon the length of the device, the face-centered crystals of the austenitic material shift to martensite until the stress is removed. Thus, the bend and straight portions of the annealed wire guide have very similar flexural properties. In contrast, the cold-worked wire guide is comprised of regions of both austenite and martensite along its length. Consequently, the preformed bend of a cold-worked renal wire guide remains in at least a partial martensitic state and does not
Kirts Beth A.
McNamara Thomas O.
Morris Edward J.
Cook Incorporated
Godlewski Richard J.
Ness Anton P.
O'Connor Cary
Szmal Brian
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