Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Thermal applicators
Reexamination Certificate
1997-05-06
2001-04-24
Nasser, Robert L. (Department: 3736)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Thermal applicators
C606S029000, C607S105000, C607S156000
Reexamination Certificate
active
06223085
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to treating blood vessels, and in particular, to preventing restenosis after an angioplasty dilatation treatment, or other controlled injury, of a stenotic region of a blood vessel.
Percutaneous transluminal coronary angioplasty (PTCA) is commonly used to treat an artery obstructed by a stenosis. In PTCA, a catheter having a balloon at its distal end is advanced through the cardiovascular system until the balloon lies across the stenosis. The balloon is then inflated under a pressure and for a time sufficient to cause the blood vessel to be permanently dilated in region of the stenosis. This permanent dilation results from the force of the balloon breaking an internal elastic laminate boundary between an intima and a medial cell layer of the blood vessel. This permanent dilation caused by PTCA is a controlled injury having beneficial therapeutic effects. Other therapeutic injuries can be caused by interventional procedures other than PTCA.
The blood vessel frequently reacts to the disruption of these tissue layers (caused by PTCA or other intervention) by restenosing, sometimes resulting in reocclusion of the blood vessel. A significant factor in restenosis is the proliferation of smooth muscle cells in the medial cell layer of the blood vessel. Another factor in restenosis includes an acute thrombotic reaction which is associated with exposure of the medial cell layer to blood circulating in the vessel. Finally, elastic recoil in the blood vessel wall, which reduces or eliminates the permanency of the dilation, and remodeling of plaque in the stenosed region are also associated with restenosis.
Various attempts at solving the problem of restenosis after PTCA, or other vessel injuries, have been offered but none provide an overall acceptable solution. These prior attempts include using drugs to inhibit medial smooth cell proliferation or the delivery of ionizing radiation (e.g., Beta emitters, x-rays, gamma-rays) to neutralize the medial smooth cell layer and thereby prevent smooth cell proliferation. However, delivery of ionizing radiation is difficult to handle and poses a risk of exposure to health care providers. Various methods of applying heat to the vessel wall (e.g., conductive transfer via hot balloon, laser, infrared) have been presented to minimize restenosis. Examples of several of these approaches are disclosed in Weinberger U.S. Pat. No. 5,503,613, Abele et al. U.S. Pat. No. 5,496,311, Sterzer U.S. Pat. Nos. 4,924,863 and 5,098,429, Lennox U.S. Pat. No. 4,955,377, and Spears U.S. Pat. No. 5,092,841. However, none of these methods satisfactorily prevent restenosis after a PTCA treatment or other blood vessel injury. Although stents have also been used to open and maintain a blood vessel in a patent state, stents require permanent placement in the vessel.
SUMMARY OF THE INVENTION
A method of the present invention reduces restenosis of a stenotic region of a blood vessel by radiating microwave energy from a microwave antenna to kill a medial tissue layer of the blood vessel in the stenotic region. The radiation is applied during or after inflation of a dilatation balloon of a PTCA catheter to permanently dilate the stenotic region. Alternatively, the radiation is applied after another interventional procedure that therapeutically injuries a stenotic region of a blood vessel. Killing the medial cell layer with microwave radiation prevents smooth muscle cell proliferation in the stenotic region, which is believed to be a primary factor in restenosis. In addition, in instances when the radiation is applied during dilatation of the stenotic region, the dilatation balloon forms a seal against the inner wall surface of the blood vessel. This seal prevents blood in the vessel from contacting the stenotic region, thereby preventing the potentially triggering of medial layer smooth cell proliferation and/or an acute thrombotic reaction in the blood vessel, which is also associated with restenosis. In addition, preservation of the intima by thermal protection (i.e., cooling) via dilatation balloon further insulates the medial cell layer from exposure to agents which could trigger smooth muscle cell proliferation.
In one embodiment, the method of the present invention further includes circulating cooling fluid within cooling lumens of the catheter to cool the blood circulating in the blood vessel about a shaft of the catheter. This cooling action prevents the circulating blood from coagulating during the application of microwave radiation to the stenotic region of the blood vessel. The cooling fluid within the cooling lumens also conductively cools an inflation fluid within the dilatation balloon thereby permitting the balloon inflation fluid to cool an inner wall surface of the blood vessel in the stenotic region during the application of microwave radiation to the medial cell layer in the stenotic region. This cooling action further aids in preventing the thrombotic action from the coagulation of blood in the vessel and along the vessel wall, which is associated with restenosis.
Finally, in one embodiment, the catheter includes a perfusion means for directing the passage of blood from the vessel into and through the catheter and back into the blood vessel to maintain circulation of blood through the blood vessel during dilatation of the stenotic region.
The method and device of the present invention acts in at least three ways to prevent restenosis after a balloon dilatation angioplasty procedure (or other interventional procedure causing a therapeutic injury to the blood vessel) by neutralizing several factors associated with restenosis. First, application of microwave radiation kills the medial cell layer, which is associated with smooth muscle cell proliferation. Second, the method preferably excludes blood from the stenotic region until after the medial cell layer is destroyed since exposure of circulating blood to the medial cell layer is also associated with restenosis. Third, cooling action prevents coagulation of blood circulating in the blood vessel and prevents thrombotic action along the vessel wall in the stenotic region, both of which are associated with restenosis and other health risks. Fourth, cooling action protects the intima and also may prevent restenosis.
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Dann Mitchell
Flachman Jonathan L.
Hirose Teruo T.
McGrath Jonathan R.
Rudie Eric N.
Kinney & Lange
Nasser Robert L.
Urologix Inc.
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