Surgery – Diagnostic testing – Flexible catheter guide
Reexamination Certificate
1999-05-03
2001-01-30
O'Connor, Cary (Department: 3736)
Surgery
Diagnostic testing
Flexible catheter guide
C600S002000, C600S003000
Reexamination Certificate
active
06179789
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention generally relates to improved medical apparatus and methods for treating vascular tissues. More particularly, the invention relates to enhanced radioactive stents and methods for use in maintaining a lumen of a blood vessel in which the stent is implanted to expand and maintain the enlarged vessel in a patient by delivering therapeutic RF energy through a metallic stent containing radioactive element for enhanced reduction of restenosis.
BACKGROUND OF THE INVENTION
Balloon angioplasty is a nonsurgical method of clearing coronary and other arteries, blocked by atherosclerotic plaque, fibrous and fatty deposits on the walls of arteries. A catheter with a balloon-like tip is threaded up from the arm or groin through the artery until it reaches the blocked area. The balloon is then inflated, flattening the plaque and increasing the diameter of the blood vessel opening. The arterial passage is thus widened. The benefits of angioplasty of arteries have been amply demonstrated.
There are limitations, however, to this technique's application, depending on the extent of the disease, the blood flow through the artery, and the part of the anatomy and the particular vessels involved. Plaque build-up and/or severe re-stenosis recur at about 40-50 percent of those treated. A huge number of patients experiencing a successful primary angioplasty procedure are destined to require a repeat procedure. Balloon angioplasty can only be characterized as a moderate-success procedure.
Recently, a newer technique of inserting a metallic stent is used to permanently maintain the walls of the vessel treated at its extended opening state. Vascular stents are typically composed of a biocompatible material such as a biocompatible metal wire of tubular shape, a metallic perforated tube, or a tiny mesh tube used by heart surgeons to prop open the weak inner walls of diseased arteries. The stent should be of sufficient strength and rigidity to maintain its shape after deployment, and to resist the elastic recoil of the artery that occurs after the vessel wall has been stretched. The stents are often used in conjunction with balloon angioplasty to prevent restenosis after the clogged arteries are treated. Despite of its considerable benefits, coronary stenting alone is not a panacea, as studies have shown that about 30% of the patient population subjected to that procedure will still experience restenosis. Risks of inflammation of the vessel walls are exacerbated by the presence of the stent.
When a clogged artery is widened, the plaque is broken up and the underlying collagen or damaged endothelium is exposed to the blood flow. Collagen has a prothrombotic property which is part of a body healing process. Unless collagen or the damaged endothelium is passivated, treated, or modulated, the chance for blood vessel clotting as well as restenosis still exists. Several U.S. patents disclose incorporation of drugs or radioactive elements onto the stent for slow release into the blood stream. One example is U.S. Pat. No. 5,843,163 to Wall who discloses an expandable stent having radioactive treatment means. Another example is U.S. Pat. No. 5,882,291 to Bradshaw et al. who discloses a device and methods for controlling dose rate during intravascular radiotherapy. U.S. Pat. No. 5,871,436 to Eury discloses radiation therapy method by immersing the device in a solution of the radioisotope just prior to device implantation. However, none of the above-mentioned patents disclose releasing therapeutic agents into the tissue, instead to the blood stream, at the stent contact site.
A metallic stent is generally coated with a biodegradable or non-degradable coating which incorporates a radioactive source. One particular example is U.S. Pat. No. 5,871,437 to Alt who discloses a radioactive stent for treating blood vessels to prevent restenosis. Said patent discloses that not only the restenosis triggered by the proliferation of smooth muscle cells is inhibited by a radioactive material, but the restenosis triggered by thrombus formation is also inhibited, by incorporating into the coating carrier hirudin, iloprost or other anti-coagulant. However, due to continuous blood flow to wash away the active ingredient inside the coating layer from the coated stent, the anti-restenosis effect diminishes quickly or compromised greatly. There is a clinical need to diffuse or embed the active ingredient, such as radioactive elements, anti-coagulant and the like, into the lesion site where the stent contacts the tissue of the arterial wall. An appropriate thermal energy plays a critical role in enhancing the diffusion process of an active ingredient into the tissue wall.
Radiofrequency therapeutic protocol has been proven to be highly effective when used by electrophysiologists for the treatment of tachycardia; by neurosurgeons for the treatment of Parkinson's disease; and by neurosurgeons and anesthetists for other RF procedures such as Gasserian ganglionectomy for trigeminal neuralgia and percutaneous cervical cordotomy for intractable pains. A stent deployed within a vessel, such as a coronary stent, has excellent metal-to-tissue contact surface. It becomes an ideal medium for applying thermal energy to the tissue needed for impregnation or embedding of active ingredients, such as radioactive substances or anti-coagulants. Radiofrequency protocol, which exposes a patient to minimal side effects and risks, is generally applied precisely to the stent-to-tissue contact site to obtain the desired thermal effect to accelerate the diffusion and embedding of an active ingredient into the local stent-contact tissue for prolonged therapeutic effects.
SUMMARY OF THE INVENTION
In general, it is an object of the present invention to provide a method and an improved medical apparatus for generating heat, to treat the atherosclerosis, vascular vessels, or other tissues, such as intestine, colon, ureter, uterine tube, and the like. It is another object of the present invention to provide a vascular stent having radioactive substances on the exposed surface of the stent. It is a further object of the present invention to provide a metallic implant having radioactive substances on its surface for enhanced irradiation. It is still another object to provide a medical apparatus system having radiofrequency energy to accelerate diffusing or embedding the radioactive substance into the tissue. It is another object of the present invention to provide a method and an apparatus for monitoring the temperature of the ablated tissue, and to control the temperature by utilizing a temperature control mechanism and/or algorithm for radiofrequency energy delivery. The location of the temperature sensor means is preferably at close proximity of the exposed surface of the stent apparatus or at a distal end of detachable conducting wire means. It is still another object of this invention to provide a method and an apparatus for treating atherosclerosis, vascular walls, or tubular cellular tissues in a patient by applying RF current to a stent having radioactive substance and consequently to the underlying tissues for enhanced irradiation.
Briefly, heat is generated by supplying a suitable energy source to an apparatus, which comprises electrical conductor means, in contact with the body tissues through a stent. A stent is defined in this invention as any metallic stenting element, in mesh form, coil form, perforated form, or other appropriate form, used to enlarge and maintain the enlarged tissues or vessels. Examples include coronary stent, peripheral stent, uterine stent and the like. A suitable energy source may consist of radiofrequency energy, microwave energy, ultrasonic energy, alternating current energy, or laser energy. The energy can be applied to the stent and consequently to the atherosclerosis, vascular walls, or cellular tissues through the electrode means. A DIP (dispersive indifferent pad) type returning pad or electrode, that contacts the patient, is connected to the Indifferent Electrode Co
Tu Hosheng
Tu Lily Chen
O'Connor Cary
Wingood Pamela L.
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