Stent inductive heating catheter

Details Stent inductive heating catheter Stent inductive heating catheter

2000-06-15

2002-09-10

Kearney, Rosiland S. (Department: 3739)

Surgery

Instruments

Electrical application

C607S098000, C607S101000, C607S105000

Reexamination Certificate

active

06447508

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to apparatus for removing obstructive material from an occluded lumen of a patient, and more specifically to a catheter mounted electrode device disposable within an occluded stent implanted within a lumen and operative to cause an electrified current to flow through the stent and cause ablation of obstructive material formed in and around the stent.
2. Description of the Prior Art
Obstructive material may be formed in virtually all of the lumens in a body, and may be composed of many different substances. These obstructions may interfere with material transport and fluid flow within the lumen. One example of obstructive material formed within a lumen is atherosclerotic plaque formed within a coronary artery. Other obstructions may occur in any vein or artery such as a coronary, carotid, neurological, peripheral, or renal vein or artery. Additional types of lumens which may be obstructed include bile ducts, all lumens of the genital-urinary tract such as fallopian tubes, and lumens of the gastrointestinal tract such as the intestines or colon. Examples of obstructive material include: all forms of plaque such as fatty plaque, fibrous plaque, and calcific plaque; fibrotic material; mucous; thrombus; and blood clots. The above mentioned lumens and obstructive materials are given as examples only.
A variety of methods and devices have been developed to remove obstructive material from occluded lumens, or to at least alleviate the obstruction. Catheters equipped with cutting blades may be used to slice the obstruction from the lumen. Other methods use heat to resolve obstructive material. It is known that localized heating of a blood vessel wall may prevent the proliferation of smooth muscle cells which are believed to cause restenosis. Laser angioplasty devices generally supply energy to the tip of a catheter to cauterize or bum away obstructions.
Radio frequency (RF) ablation is also known in the prior art for ablating obstructive material formed within a lumen. RF current is directed from an RF power source to an ablating electrode, from which the RF current is provided to the obstructive material. In a monopolar RF ablation device, current return is typically provided via a conductive plate attached to the body of the patient and coupled to the power supply. In a multipolar RF ablation device, more than one electrode is provided at the distal end of the catheter, and the current flows through the obstructive material between at least two of these electrodes. An example of an RF catheter is described in Jannsen (U.S. Pat. No. 5,454,809).
Balloon angioplasty is another common method of removing obstructive material from an occluded lumen. In accordance with balloon angioplasty techniques, a catheter having a deflated balloon is introduced into an occluded lumen and the balloon is inflated. The inflated balloon applies pressure to the obstruction, and to the wall of the lumen. The balloon stretches the lumen, so that fluid flow through the lumen may be improved. However, balloon angioplasty tends to stretch the elastic artery beyond its ability to recoil causing the lumen to contract after the balloon is deflated and withdrawn from the lumen. A well known solution to the problem of lumen contraction is to insert a stent into the lumen.
A stent typically comprises an expandable coil spring or wire-mesh tube. In accordance with a common method for implanting a stent within an occluded lumen, the stent is mounted upon an inflatable balloon catheter. The catheter assembly is then delivered to the occluded area, and the balloon is inflated to radially force the stent into contact with the occlusion. As the stent expands, the lumen of the blood vessel is opened and blood flow is restored. After complete expansion of the stent, the balloon catheter is deflated and removed, leaving the stent behind to buttress and prevent elastic recoil of the blood vessel wall.
While stents have proven effective in preventing lumen restriction, complications often may arise in their use. In particular, obstructions may build up in or through the stent in much the same manner as they would if the stent was not in place, such as by, for example, tissue growth. The stent may irritate the tissue and may allow for thrombin, plaque, or other substances to accumulate on the interior surface of the stent, and on the outer surface of the stent between the stent and the lumen. Such accumulation, referred to as restenosis, may again restrict fluid flow through the lumen, so that efficacy of the stent is reduced or, in severe cases, eliminated. Stent restenosis affects approximately 20% of all stents placed in the coronary vasculature. The problem of restenosis is commonly addressed by attempting to dilate the lumen of the vessel with conventional balloon angioplasty, or by the use of various atherectomy devices. Stent manufacturers have tried to address the problem of restenosis using antifibrogenic coatings, and in some instances with the use of radioactive materials contained within the stent.
Another method for removing obstructive material from within a stent is RF ablation. However, the presence of a stent in an occluded lumen causes some complications for RF ablation because stents are typically formed of conductive material. If an ablating electrode comes into contact with the stent, a short circuit could occur, which may damage the ablation catheter, the stent, or the lumen.
Jannsen (U.S. Pat. No. 5,749,914, filed May 28, 1996, and issued May 12, 1998) discloses an electrosurgical device for ablation of obstructive material within a stent. The device includes a catheter, or elongate flexible tube, having a distal end and a proximal end. One or more ablation electrodes are positioned at the distal end of the catheter, and a power supply is provided in electrical communication with the electrodes. The electrodes are shielded from direct contact with the stent in order to prevent a possible short circuit that may occur if the electrode contacts the stent. The catheter is inserted into the stent, and a first ablation electrode disposed proximate the distal end of the catheter is shielded from physical contact with the stent by a lip of the catheter wall.
Jannsen describes a plurality of circumferentially divided electrodes seated in an annular ridge formed in the exterior wall of the catheter, the electrodes being sized so that they are recessed within the annular ridge. Jannsen also discloses a plurality of ring electrodes disposed along the longitudinal axis of the catheter. A plurality of spacers, projecting radially away from the catheter axis, are disposed between adjacent ones of the ring electrodes. The spacers have a diameter greater than the diameter of the ring electrodes so that the electrodes are prevented from contacting the stent.
According to Jannsen, the stent may conduct current and act as a virtual ground shielding all tissue located exterior to the stent. Jannsen further discloses directly grounding a stent via conducting stylets or probes extending radially from the catheter in order to improve the shielding effect of the stent. A return electrode is provided in electrical communication with the current supply, the return electrode being attachable to a patient. Jannsen discloses a return electrode sized so that it will contact the stent, thereby grounding the stent. This lowers the impedance between the return electrode and the ablating electrodes, and allows for precise ablating of obstructive material between the electrodes and the stent.
As described in Jannsen, it may be inconvenient to have the electrode sized to contact the stent, because the electrode may then interfere with the longitudinal motion of the catheter through the stent. One solution to this problem, as described by Jannsen, is to use an, inflatable balloon located beneath the electrode to selectively increase the diameter of the catheter at the position of the electrode to bring the electrode into contact with the stent. The b

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