| Stent for treating vulnerable plaque -> Monitor Keywords |
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Stent for treating vulnerable plaqueRelated Patent Categories: Prosthesis (i.e., Artificial Body Members), Parts Thereof, Or Aids And Accessories Therefor, Arterial Prosthesis (i.e., Blood Vessel), Stent Structure, Having Multiple Connected BodiesStent for treating vulnerable plaque description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20080051878, Stent for treating vulnerable plaque. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND OF THE INVENTION [0001] The present invention relates to vascular repair devices, and in particular to intravascular stents, which are adapted to be implanted into a patient's body lumen, such as a blood vessel or coronary artery, for the treatment of unstable or vulnerable, human atherosclerotic plaque. [0002] Currently, the treatment of unstable or vulnerable plaque presents a significant therapeutic challenge to medical investigators. Vulnerable plaque is characterized by a basic lesion which is a raised plaque beneath the innermost arterial layer, the intima. Atherosclerotic plaques are primarily composed of varying amounts of long chain extracellular matrix (ECM) proteins that are synthesized by smooth muscle cells. The other primary lesion component of atherosclerotic plaque includes lipoproteins, existing both extracellularly and within foam cells derived primarily from lipid-laden macrophages. In a more advanced lesion, a necrotic core may develop, consisting of lipids, foam cells, cell debris, and cholesterol crystals, and myxomatous configurations with crystalline lipid forms. The necrotic core is rich in tissue factor and quite thrombogenic, but in the stable plaque it is protected from the luminal blood flow by a robust fibrous cap composed primarily of long chain ECM proteins, such as elastin and collagen, which maintain the strength of the fibrous cap. The aforementioned plaque represents the most common form of vulnerable plaque, known as a fibroatheroma. Histology studies from autopsy suggest this form constitutes the majority of vulnerable plaques in humans. A second form of vulnerable plaque represents a smaller fraction of the total, and these are known as erosive plaques. Erosive plaques generally have a smaller content of lipid, a larger fibrous tissue content, and varying concentrations of proteoglycans. Various morphologic features that have been associated with vulnerable plaque, include thinned or eroded fibrous caps or luminal surfaces, lesion eccentricity, proximity of constituents having very different structural moduli, and the consistency and distribution of lipid accumulations. With the rupture of fibroatheroma forms of vulnerable plaque, the luminal blood becomes exposed to tissue factor, a highly thrombogenic core material, which can result in total thrombotic occlusion of the artery. In the erosive form of vulnerable plaque, mechanisms of thrombosis are less understood but may still yield total thrombotic occlusion. [0003] Although rupture of the fibrous cap in a fibroatheroma is a major cause of myocardial infarction (MI) related deaths, there are currently no therapeutic strategies in place to treat lesions that could lead to acute MI. The ability to detect vulnerable plaques and to treat them successfully with interventional techniques before acute MI occurs has long been an elusive goal. Numerous finite element analysis (FEA) studies have proved that, in the presence of a soft lipid core, the fibrous cap shows regions of high stresses. Representative of these studies include the following research articles, each of which are incorporated in their entirety by reference herein: Richardson et al. (1989), Influence of Plaque Configuration and Stress Distribution on Fissuring of Coronary Atherosclerotic Plaques, Lancet, 2 (8669), 941-944; Loree et al. (1992), Effects of Fibrous Cap Thickness on Circumferential Stress in Model Atherosclerotic Vessels, Circulation Research, 71, 850-858; Cheng et al. (1992), Distribution of Circumferential Stress in Ruptured and Stable Atherosclerotic Lesions: A Structural Analysis With Histopathological Correlation, Circulation, 87, 1179-1187; Veress et al. (1993), Finite Element Modeling of Atherosclerotic Plaque, Proceedings of IEEE Computers in Cardiology, 791-794; Lee et al. (1996), Circumferential Stress and Matrix Metalloproteinase 1 in Human Coronary Atherosclerosis: Implications for Plaque Rupture, Atherosclerosis Thrombosis Vascular Biology, 16, 1070-1073; Vonesh et al. (1997), Regional Vascular Mechanical Properties by 3-D Intravascular Ultrasound Finite-Element Analysis, American Journal of Physiology, 272, 425-437; Beattie et al. (1999), Mechanical Modeling: Assessing Atherosclerotic Plaque Behavior and Stability in Humans, International Journal of Cardiovascular Medical Science, 2 (2), 69-81; and Feezor et al. (2001), Integration of Animal and Human Coronary Tissue Testing with Finite Element Techniques for Assessing Differences in Arterial Behavior, BED-Vol. 50, 2001 Bioengineering Conference, ASME 2001. Further, these studies have indicated that such high stress regions correlate with the observed prevalence of locations of cap fracture. Moreover, it has been shown that subintimal structural features such as the thickness of the fibrous cap and the extent of the lipid core, rather than stenosis severity are critical in determining the vulnerability of the plaque. The rupture of a highly stressed fibrous cap can be prevented by using novel, interventional, therapeutic techniques such as specially designed stents that redistribute and lower the stresses in the fibrous cap. [0004] One of the avenues to reduce cap rupture is to reinforce the strength and increase thickness of the fibrous cap. Studies have shown that placement of the intravascular stent at a lesion site can induce neointimal thickening. Using the same reasoning, placing an intravascular stent at the vulnerable plaque site can induce neointimal thickening, which in turn will increase the cap thickness. However, a special stent pattern, rather than the traditional workhorse stent, should be used to stent these lesions. A pattern which induces less shear stress upon expansion, less point stress upon the vessel wall and delayed neointimal thickening should be used for stent vulnerable plaques. [0005] Stents are generally tubular-shaped devices which function to hold open a segment of a blood vessel, coronary artery, or other body lumen. They are particularly suitable for use to support and hold back a dissected arterial lining which can occlude the fluid passageway therethrough. [0006] Various means have been described to deliver and implant stents. One method frequently described for delivering a stent to a desired intraluminal location includes mounting the expandable stent on an expandable member, such as a balloon, provided on the distal end of an intravascular catheter, advancing the catheter to the desired location within the patient's body lumen, inflating the balloon on the catheter to expand the stent into a permanent expanded condition and then deflating the balloon and removing the catheter. One of the difficulties encountered using prior art stents involved maintaining the radial rigidity needed to hold open a body lumen while at the same time maintaining the longitudinal flexibility of the stent to facilitate its delivery. Once the stent is mounted on the balloon portion of the catheter, it is often delivered through tortuous vessels, including tortuous coronary arteries. The stent must have numerous properties and characteristics, including a high degree of flexibility, in order to appropriately navigate the tortuous coronary arteries. This flexibility must be balanced against other features including radial strength once the stent has been expanded and implanted in the artery. While other numerous prior art stents have had sufficient radial strength to hold open and maintain the patency of a coronary artery, they have lacked the flexibility required to easily navigate tortuous vessels without damaging the vessels during delivery. [0007] Generally speaking, most prior art intravascular stents are formed from a metal such as stainless steel, which is balloon expandable and plastically deforms upon expansion to hold open a vessel. The component parts of these types of stents typically are all formed of the same type of metal, i.e., stainless steel. Other types of prior art stents may be formed from a polymer, again all of the component parts being formed from the same polymer material. These types of stents, the ones formed from a metal and the ones formed from a polymer, each have advantages and disadvantages. One of the advantages of the metallic stents is their high radial strength once expanded and implanted in the vessel. A disadvantage may be that the metallic stent lacks flexibility which is important during the delivery of the stent to the target site. With respect to polymer stents, they may have a tendency to be quite flexible and are advantageous for use during delivery through tortuous vessels, however, such polymer stents may lack the radial strength necessary to adequately support the lumen once implanted into an occlusive fibromuscular lesion of 70% stenosis or greater. [0008] What has been needed and heretofore unavailable is a stent that can be used to treat a vulnerable plaque by reducing the cap stresses. The present invention satisfies this need and others. SUMMARY OF THE INVENTION [0009] The present invention is directed to an intravascular stent assembly that can be used to treat a lesion with vulnerable plaque by reducing the cap stresses. The invention also includes methods of using the stent assembly for the treatment of the same. [0010] The stent assembly embodying features of the invention can be readily delivered to the desired body lumen, such as a coronary artery (peripheral vessels, bile ducts, etc.), by mounting the stent assembly on an expandable member of a delivery catheter, for example a balloon, and advancing the catheter and stent assembly through the body lumen to the target site. Generally, the stent is compressed or crimped onto the balloon portion of the catheter so that the stent assembly does not move longitudinally relative to the balloon portion of the catheter during delivery through the arteries, and during expansion of the stent at the target site. The stent is relatively flexible along its longitudinal axis to facilitate delivery through tortuous body lumens yet is stiff and stable enough radially in an expanded condition to maintain the patency of a body lumen such as an artery when implanted therein. [0011] In one embodiment, the stent assembly of the invention includes a series of cylindrical rings formed with undulations and located within distal, center, and proximal sections of the stent. The undulations of the rings located in the center section may have either smaller or larger cross-sectional widths than the undulations of the rings in the distal and proximal sections in order to accommodate the vulnerable plaque section of the artery. Links are incorporated to connect all the cylindrical rings together into the stent assembly. The center section may be coated with a polymer to increase surface area. [0012] In another embodiment, the stent assembly of the present invention includes a series of cylindrical rings with undulations and also located within distal, center, and proximal sections of the stent. Similarly, the undulations of the rings located in the center section may have either smaller or larger cross-sections than the undulations of the rings in the distal and proximal sections in order to accommodate the vulnerable plaque section of the artery. The rings are directly connected to each other, generally without the need for separate links. The center section may also be coated with a polymer to increase surface area. [0013] The resulting stent structures are a series of radially expandable cylindrical rings which are configured so that vulnerable plaque and small dissections in the wall of a body lumen may be pressed back into position against the luminal wall, while maintaining the longitudinal flexibility of the stent both when being negotiated through the body lumens in their unexpanded state and when expanded into position. The rings within the center section are arranged to provide the section with a high surface area density to reduce the likelihood of plaque rupture by creating less stress on the plaque. The high surface area also helps to reduce the scissoring affect the center section rings may have upon expansion. Undulations within the cylindrical rings allow for an even expansion around the circumference by accounting for the relative differences in stress created by the radial expansion of the cylindrical rings. Each of the individual cylindrical rings may rotate slightly relative to their adjacent cylindrical rings without significant deformation, cumulatively providing stents which are flexible along their length and about their longitudinal axis, but which are still very stable in the radial direction in order to resist collapse after expansion. [0014] Each of the embodiments of the invention can be readily delivered to the desired luminal location by mounting them on an expandable member of a delivery catheter, for example a balloon, and passing the catheter-stent assembly through the body lumen to the implantation site. A variety of means for securing the stents to the expandable member on the catheter for delivery to the desired location is available. It is presently preferred to compress the stent onto the unexpanded balloon. Other means to secure the stent to the balloon include providing ridges or collars on the inflatable member to restrain lateral movement, using bioabsorbable temporary adhesives, or a retractable sheath to cover the stent during delivery through a body lumen. [0015] The presently preferred structures for the expandable cylindrical rings which form the stents of the present invention generally have a plurality of circumferential undulations containing a plurality of alternating peaks and valleys. The peaks and valleys are formed in generally U- and V-shaped patterns and aligned along the longitudinal axis. [0016] While the cylindrical rings and links generally are not separate structures, they have been conveniently referred to as rings and links for ease of identification. Further, the cylindrical rings can be thought of as comprising a series of U- and V-shaped structures in a repeating pattern. While the cylindrical rings are not divided up or segmented into U's and V's, the pattern of cylindrical rings resemble such configuration. The U's and V's promote flexibility in the stent primarily by flexing and may tip radially outwardly as the stent is delivered through a tortuous vessel. [0017] The undulations of the cylindrical rings can have different degrees of curvature and angles of adjacent peaks and valleys to compensate for the expansive properties of the peaks and valleys. The cylindrical rings of the stents are plastically deformed when expanded (except with NiTi alloys) so that the stents will remain in the expanded condition and therefore they must be sufficiently rigid when expanded to prevent the collapse thereof in use. [0018] With stents formed from super-elastic nickel-titanium (NiTi) alloys, the expansion occurs when the stress of compression is removed. This allows the phase transformation from martensite back to austenite to occur, and as a result the stent expands. [0019] After the stents are expanded some of the peaks and/or valleys may, but not necessarily, tip outwardly and embed in the vessel wall. Thus, after expansion, the stents may not have a smooth outer wall surface, rather they have small projections which embed in the vessel wall and aid in retaining the stents in place in the vessel. [0020] The links which interconnect adjacent cylindrical rings can have a cross-section similar to the cross-sections of the undulating components of the expandable cylindrical rings. The links may be formed in a unitary structure with the expandable cylindrical rings formed from the same intermediate product, such as a tubular element, or they may be formed independently and mechanically secured between the expandable cylindrical rings. The links may be formed substantially straight or with a plurality of undulations. They may also be used primarily to support the vulnerable plaque region or primarily to connect adjacent rings. [0021] Preferably, the number, shape and location of the links can be varied in order to develop the desired vulnerable plaque coverage and longitudinal flexibility. These properties are important to minimize alteration of the natural physiology of the body lumen into which the stent is implanted and to maintain the compliance of the body lumen which is internally supported by the stent. Generally, the greater the longitudinal flexibility of the stents, the easier and the more safely they can be delivered to the implantation site, especially where the implantation site is on a curved section of a body lumen, such as a coronary artery or a peripheral blood vessel, and especially saphenous veins and larger vessels. [0022] The stent may be formed from a tube by laser cutting the pattern of cylindrical rings and undulating links in the tube, by individually forming wire rings and laser welding them together, and by laser cutting a flat metal sheet in the pattern of the cylindrical rings and links, and then rolling the pattern into the shape of the tubular stent and providing a longitudinal weld to form the stent. Continue reading about Stent for treating vulnerable plaque... Full patent description for Stent for treating vulnerable plaque Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Stent for treating vulnerable plaque patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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