BALLOON CATHETER METHOD FOR REDUCING RESTENOSIS VIA IRREVERSIBLE ELECTROPORATION
Restenosis or neointimal formation may occur following angioplasty or other trauma to an artery such as by-pass surgery. This presents a major clinical problem which narrows the artery. The invention provides a balloon catheter with a particular electrode configuration. Also provided is a method whereby vascular cells in the area of the artery subjected to the trauma are subjected to irreversible electroporation which is a non-thermal, non-pharmaceutical method of applying electrical pulses to the cells so that substantially all of the cells in the area are ablated while leaving the structure of the vessel in place and substantially unharmed due to the non-thermal nature of the procedure.
This application claims the benefit of U.S. Provisional Application Nos. 61/040,110, filed Mar. 28, 2008 and 61/156,368, filed Feb. 27, 2009, which applications are incorporated herein by reference.GOVERNMENT RIGHTS
This invention was made with government support under federal grant no. NIH R01 RR018961 awarded by the U.S. National Institutes of Health (NIH). The United States Government has certain rights in this invention.FIELD OF THE INVENTION
The present invention relates to a medical device and method for the prevention of vascular re-stenosis using electroporation. More particularly, the present invention relates to a balloon catheter device with electrodes for electroporating the inner wall of a vascular structure to prevent re-stenosis.BACKGROUND OF THE INVENTION
Catheters, and more particularly, balloon catheters have been used to treat stenosis of a vascular or other anatomical tubular structure. In one such procedure, called percutaneous transluminal angioplasty or PTA, a balloon catheter is inserted into a vessel and advanced to the site of the stenosis or lesion where the balloon is inflated against the lesion. Pressure applied to the stenosis by the surface of inflated balloon compresses the lesion, pushing it radially outward and widening or restoring the luminal diameter of the vessel. Various forms of PTA have been used to treat peripheral arterial stenosis, coronary lesions and other non-vascular tubular structures such as biliary ducts.
Notwithstanding the importance of PTA procedures in restoring normal blood flow to an anatomical region, one problem associated with PTA procedures is the undesired re-growth of the lesion, commonly known as re-stenosis. Re-stenosis, a re-narrowing of the vessel lumen, usually occurs within three to six months after the angioplasty procedure. Studies have demonstrated a re-stenosis rate after angioplasty in up to 50% of patients treated. Although the use of stents has reduced the re-stenosis rate to approximately 30% of the procedures, re-stenosis remains a significant clinical problem, particularly for those patients whose general health is not conducive to repeat interventional procedures.
The main cause of re-stenosis following angioplasty procedures is due to vessel wall trauma created during the procedure. Evidence has shown that scar tissue forms as endothelial cells that line the inner wall of the blood vessel re-generate in response to the vessel wall injury created during angioplasty. An overgrowth of endothelial cells triggered by the trauma leads to a re-narrowing of the vessel and eventual re-stenosis of the treated area. Cutting wire balloon catheters, also known in the art, have been used to “score” a stenotic lesion in a more controlled, precise manner. Although it is contemplated that scoring a lesion will lead to less procedural vessel trauma, endothelial cell re-growth and re-stenosis, to date there are no studies that effectively demonstrate this.
Recently, advances in stent technology have included drug-eluting stents which are intended to reduce the occurrence of re-stenosis even further. These types of stents are coated with a drug designed to suppress growth of scar tissue along the inner vessel wall over an extended period of time. The drug is slowly released or eluted, thus reducing the occurrence and extent of re-stenosis when compared with bare stents. Although shown to be effective in further reducing re-stenosis, there are several known problems with drug-eluting stents including an increased risk in some patient populations of localized blood clots after the drug has been completely eluted, usually after six or more months. Clot formation in the coronary system can lead to heart attack and death. Other problems include stent fracture and other known risks associated with long-term implants.
Therefore, it is desirable to provide a device and method for the prevention of re-stenosis associated with primary angioplasty and/or stenting procedures that is safe, easy and does not require placement of a stent.SUMMARY OF THE INVENTION
A catheter device for insertion into a vessel which device is used for reducing neotima or reducing the occurrence of restenosis is disclosed. The present invention can utilize basic structural configurations of a balloon catheter device modified to incorporate electrodes which can be electrically connected to a power source for the administration of electrical pulses which can provide for irreversible electroporation. Thus, a device of the invention includes a basic balloon catheter configuration having a first electrode positioned at a distal end of the catheter. A second electrode is positioned at a point relative to the first electrode so as to allow electrical current to flow between the first and second electrodes and through vascular tissue. The device includes a power source and electrical connections from the power source to the electrodes. The power source provides electrical pulses to the electrodes for durations, voltages, current amounts and combinations thereof so as to provide sufficient electrical flow to substantially all of the vascular cells in the area of an artery (which has been subjected to trauma) to irreversible electroporation (IRE) which is preferably done before neointima occurs.
In an aspect of the invention the catheter is a balloon catheter and the electrodes may encircle the catheter in a spiral configuration.
In one embodiment the first and second electrodes are designed for use following a by-pass surgery or alternatively are designed for use following angioplasty with a balloon angioplasty device which may be the same device to which the electrodes are connected.
The system of the invention may be comprised of two separate catheter devices wherein a first catheter device is a balloon catheter which is used for carrying out balloon angioplasty and a second catheter which is specific for use in the IRE.
The system of the invention is designed for use wherein the IRE is carried out using a voltage, and a current within defined ranges over a defined period of time and in the absence of drug being delivered into the vascular cells.
In another embodiment of the invention the device comprises an electrical power source which provides electrical pulses which provide voltage, current and are provided for a duration so as to avoid thermal damage to a target area and surrounding tissues while obtaining the IRE on the target area.
In another embodiment of the device the power source is designed to emit pulses wherein the pulses have a duration from 50 to 200 microseconds and the device may be designed for carrying out the IRE immediately following balloon angioplasty or alternatively the IRE may be carried out immediately prior to balloon angioplastly.
The system of the invention includes an electrical power source which is specifically designed for carrying out the IRE so as to reduce restenosis or neointimal and avoid thermal damages. The power source may be designed to deliver a range of different voltages, currents and duration of pulses as well as number of pulses. The system may be designed to provide for pulse durations from about 50 to 200 microseconds and may administer a current in a range of from about 2,000 V/cm to about 6,000 V/cm. The power source may provide between 2 and 25 pulses upon activation and may be designed to provide a specific number of pulses which are at a specific known duration and with a specific amount of current. For example, the power source may be designed upon activation to provide 10 pulses for 100 microseconds each providing a current of 3,800 V/cm±50%, ±25%, ±10%, ±5%.
A method of reducing, attenuating or eliminating the intimal formation on a patient that has undergone a surgical procedure in a target area of an artery is disclosed. The method first involves diagnosing a subject which may be a human subject suffering from coronary artery disease and specifically identifying a target area of an artery in the subject which is partially blocked by plaque. A procedure is performed whereby blockage in the target area is moved or removed from the artery so as to increase blood flow through the target area of the artery. This procedure can be balloon angioplasty whereby the plaque is forced away from the area of flow or can involve by-pass surgery whereby the blocked area of the artery is completely removed.
After the procedure is carried out vascular cells in the area subjected to trauma by the angioplasty or surgery are subjected to irreversible electroporation (IRE). The IRE may be carried out (1) before, (2) at substantially the same time, or (3) just after the procedure (e.g. angioplasty) is carried out, but is carried out before restenosis occurs to obtain the best results. The IRE may be carried out by the use of electrodes which are present on or near the balloon portion of the balloon catheter used in the angioplasty. The IRE is carried out using a voltage and current within defined ranges over a defined period of time. Further, the IRE is carried out in the absence of a drug being delivered to the vascular cells in a manner which would effect the growth of the cells.
The IRE is not carried out in order to provide for reversible electroporation of substantially all of the cells. Reversible electroporation is carried out when the pores of the cells are temporarily opened and after the procedure go back to normal size and the cells survive. Others carry out electroporation in a manner so as to prevent excessive cell lysing (see U.S. Pat. Nos. 6,865,416 and 6,342,247). With irreversible electroporation the pores of the cells are opened and are opened to a degree that they do not return to normal size and the cells die, so excessive lysing of cells is desired. Thus, irreversible electroporation requires more voltage, current or time in order to obtain the desired result as compared to reversible electroporation. The amount of current used and the time it is applied must be controlled in accordance with the invention in order to avoid thermal damage. The result sought per the present invention is to have substantially all of the vascular cells of the targeted area of the artery ablated or killed but to not raise the temperature of that area sufficiently to cause thermal damage and denature proteins. By avoiding thermal damage the structure of the artery and surrounding tissue remains in place. However, due to the irreversible electroporation the vascular cells are killed and as such do not form scar tissue (neointimal) in the area thereby reducing or avoiding restenosis.
The methodology of the invention may involve carrying out the IRE at substantially the same time the balloon angioplasty or by-pass surgery is carried out. It would be possible to carry out the IRE prior to angioplasty or by-pass surgery or other trauma event or carry out the IRE at substantially immediately after the balloon angioplasty or by-pass surgery or other trauma event is carried out. The timing of carrying out the IRE relative to the timing of the trauma event is important in order to avoid the occurrence of restenosis and avoid as much as possible the artery being blocked with respect to blood flow.
In addition to the timing of the IRE the parameters of the IRE in terms of voltage/current/pulse duration are important. These parameters are important so as to go beyond reversible electroporation and obtaining irreversible electroporation. Further, the parameters are important so as to avoid thermal damage. It is undesirable to heat the area in that too much heat can cause denaturation of the proteins. Denaturation of the proteins results in breakdown of those proteins which thereafter can result in structural breakdown of the vessel which is undesirable. Thus, the method of the invention is intended to go beyond reversible electroporation to obtain irreversible electroporation but not obtain thermal damage.
Before the present method of treating restenosis and device and system used for same are described, it is to be understood that this invention is not limited to particular devices or method steps described, as such may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting, since the scope of the present invention will be limited only by the appended claims.
Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit unless the context clearly dictates otherwise, between the upper and lower limits of that range is also specifically disclosed. Each smaller range between any stated value or intervening value in a stated range and any other stated or intervening value in that stated range is encompassed within the invention. The upper and lower limits of these smaller ranges may independently be included or excluded in the range, and each range where either, neither or both limits are included in the smaller ranges is also encompassed within the invention, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included in the invention.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, the preferred methods and materials are now described. All publications mentioned herein are incorporated herein by reference to disclose and describe the methods and/or materials in connection with which the publications are cited.
It must be noted that as used herein and in the appended claims, the singular forms “a”, “and”, and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a target area” includes a plurality of such target area and reference to “restenosis” includes reference to one or more areas of restenosis and equivalents thereof known to those skilled in the art, and so forth.
The publications discussed herein are provided solely for their disclosure prior to the filing date of the present application. Nothing herein is to be construed as an admission that the present invention is not entitled to antedate such publication by virtue of prior invention. Further, the dates of publication provided may be different from the actual publication dates which may need to be independently confirmed.Electroporation
Electroporation is defined as a phenomenon that makes cell membranes permeable by exposing them to certain electric pulses. As a function of the electrical parameters, electroporation pulses can have two different effects on the permeability of the cell membrane. The permeabilization of the cell membrane can be reversible or irreversible as a function of the electrical parameters used. Reversible electroporation is the process by which the cellular membranes are made temporarily permeable. The cell membrane will reseal a certain time after the pulses cease, and the cell will survive. Reversible electroporation is most commonly used for the introduction of therapeutic or genetic material into the cell. Irreversible electroporation, also creates pores in the cell membrane but these pores do not reseal, resulting in cell death.
Irreversible electroporation has recently been discovered as a viable alternative for the ablation of undesired tissue. See, in particular, PCT Application No. PCT/US04/43477, filed Dec. 21, 2004. An important advantage of irreversible electroporation, as described in the above reference application, is that the undesired tissue can be destroyed without creating a thermal effect. When tissue is ablated with thermal effects, not only are the cells destroyed, but the elastin, collagen and other extra-cellular matrix components (tissue scaffolding) of blood vessels are also destroyed. This thermal mode of damage detrimentally affects the tissue, that is, it destroys the vasculature structure and bile ducts, and produces collateral damage.
Irreversible and reversible electroporation without thermal effect to ablate tissue offers many advantages. One advantage is that it does not result in thermal damage to target tissue or other tissue surrounding the target tissue. Another advantage is that it only ablates cells and does not damage blood vessel structure itself. Accordingly, irreversible electroporation may be used to treat the inner wall of a blood vessel during or immediately following balloon angioplasty to prevent the re-growth of endothelial cells.
Human arteries and veins are comprised of three layers; the intima which is the thinnest and innermost layer; the media which is the thickest and middle layer; and an outer adventitia layer comprised of connective tissue. The medial layer is comprised mainly of smooth muscle cells which play a prominent role in re-stenosis of previously treated vessels. It is believed that in reaction to the vessel wall trauma associated with balloon angioplasty, the smooth muscle cells within the medial layer proliferate causing a thickening of the overall vessel wall and consequently, a reduction in the luminal diameter of the vessel. This is also known as hyperplasia of the smooth muscle cells.
In another aspect of the invention, smooth muscle cells of the vessel are selectively destroyed without damage to the non-cellular tissue of the vessel. By selectively destroying smooth muscle cells through irreversible electroporation, the proliferation response of the vessel is suppressed. As irreversible electroporation is a non-thermal treatment modality, adjacent structures are not damaged by the electrical field. As an example, the connective non-cellular tissue of the vessel (collagen, elastin and other extra-cellular components) is not impacted by the non-thermal electrical current. Instead, the treated vessel wall is gradually repopulated with endothelial cells that regenerate over a period of time but do proliferate or thicken into a stenotic lesion.
In another aspect of the invention, the electroporation catheter of the current invention may be used to treat native stenotic lesions as well as stenoses or strictures of other bodily organs. Target treatment areas may include claudication of peripheral arteries, stenotic buildup in dialysis fistulas and grafts, carotid artery stenosis and renal artery strictures as well as venous lesions. Also within the scope of this invention are non-vessel lumens including but not limited to biliary tract blockages, bowel obstructions, gastric outflow strictures as well as any other bodily lumen narrowing or occlusion.
Thus in one aspect of the invention, a method of treating stenotic lesions is presented wherein an electrical field ablates vessel wall cells to prevent re-growth of the lesion after angioplasty or other treatment. By suppressing re-proliferation of vessel wall cells, re-stenosis after angioplasty or stenting may be prevented. In addition, the method described herein may be used in lieu of drug-eluting stents which have demonstrated only limited success in preventing stent re-stenosis. In yet another aspect of the invention, the electrical parameters may be set to create an electrical field that temporarily or reversibly electroporate cellular structures. The smooth muscle cells comprising the target lesion will temporarily permiablize, allowing the transport of a drug into the intracellular structure. Drugs may include anti-stenotic agents that may further prevent smooth cell proliferation or cytotoxic drugs, such as a chemotherapy agent if the stricture is caused by a cancerous growth.Specific Embodiments
There are a range of different catheter device type configurations which can be used in connection with the present invention. Some examples of devices which could be modified to obtain the basic objects of the invention include the balloon catheter device of U.S. Pat. No. 7,150,723 teaching a medical device including guidewire and balloon catheter for curing a coronary artery. Another catheter device which might be modified to utilize the aspects of the invention is the device of U.S. Pat. No. 7,273,487 disclosing a balloon catheter having a multi-layered shaft with variable flexibility. Still another balloon catheter device is taught within U.S. Pat. No. 7,351,214 disclosing a steerable balloon catheter. Yet another device is taught within U.S. Pat. No. 7,481,800 disclosing a triple lumen stone balloon catheter and method. The present invention is not specific to any of these embodiments and other embodiments can be used to provide various catheter configurations which include first and second electrodes connected to a power source which provides to the electrodes a sufficient amount of electrical energy to carry out irreversible electroporation on substantially all of the cells in the vessel target area without subjecting the target area or surrounding area to thermal damage.
Others have endeavored to develop devices and methods for preventing restenosis. The present invention can be used by itself. However, it is also contemplated to utilize the device and methods of the present invention in combination with other methods for reducing restenosis. A possible example includes the device and method disclosed within U.S. Pat. No. 5,947,889 which discloses a balloon catheter to prevent restenosis after angioplasty and process for producing a balloon catheter.
Those skilled in the art will understand that these specific examples provided here are carried out in order to demonstrate the utility of the present invention and that modification of the devices and methodology may be carried out in order to obtain specific preferred embodiments which are intended to be within the scope of the present invention. An example of a specific embodiment is provided below.
Restenosis following coronary angioplasty represents a major clinical problem. Irreversible Electroporation (IRE) is a non-thermal, non-pharmacological cell ablation method. IRE utilizes a sequence of electrical pulses that produce permanent damage to tissue within a few seconds. Examples provided here show that the left carotid arteries of 8 rats underwent in vivo intimal damage using 2 Fogarty angioplasty catheters. The procedure was immediately followed by IRE ablation in 4 rats, while the remaining 4 were used as the control group. The IRE ablation was performed using a sequence of 10 direct current pulses of 3800 V/cm, 100 μs each, at a frequency of 10 pulses per second, applied across the blood vessel between two parallel electrodes. The electrical conductance of the treated tissue was measured during the electroporation to provide real time feedback of the process. Left carotid arteries were excised and fixated after a 28-day follow-up period. Neointimal formation was evaluated histologically. The use of IRE was successful in 3 out of 4 animals in a way that is consistent with the measurements of blood vessel electrical properties. The integrity of the endothelial layer was recovered in the IRE-treated animals, compared with control. Successful IRE reduced neointima to media ratio (0.57±0.4 vs. 1.88±1.0, P=0.02). The present invention shows that the in vivo results of attenuation of neointimal formation using IRE. The invention provides a method which uses IRE to attenuate neointimal formation after angioplasty damage in a mammal such as a human and provides a method of treating coronary artery restenosis after balloon angioplasty.Balloon Catheter Embodiments
Catheter shaft 15 construction is illustrated in more detail in
The electrically conductive wire 114 is comprised of an electrically conductive material such as nitinol or copper and may be dimensioned at 0.004″ thick by 0.015″ wide. The inner and outer insulative layers which block electrical current ensure that the electrical current path of the inner electrically conductive tubing 110 remains isolated from the current path of the electrically conductive wire 114. Although not shown in
When assembled, first and second longitudinal electrodes 25 and 27 are in an overlapping arrangement relative to each other as shown in
The electrode assembly 26 of
Detail B-B of
In operation, first and second longitudinal electrodes 25 and 27 each may carry an opposite polarity electrical charge. For example, first electrode 25 may carry a negative electrical charge and second electrode 27 may carry a positive electrical charge. As a result of this arrangement, an electrical field is created between active electrode zones 115 of the first and second electrodes 25 and 27 which are of opposite polarity. For example an electrical current may be created between positively charged leg 57 of second electrode 27 and negatively charged leg 44 of first electrode 25. In the same manner, an electrical current may be created between legs 44 and 59, between legs 59 and 42, and between legs 42 and 57.
As will be explained in more detail below, the resulting electrical field created by the application of electrical energy of opposite polarities to the legs of the first and second creates a substantially 360 degree electrical field zone surrounding the balloon, which when inflated is in contact with the inner wall of the vessel. Consequentially, the entire circumference of the inner wall of the target vessel is subject to a therapeutic electrical field. The electrical field is restricted to the active electrode portions 45, 47, 77, and 79 of the longitudinal electrodes 25 and 27 because these portions are not insulated. As previously mentioned, the un-insulated portions of electrodes 25 and 27 correspond to the constant diameter body portion of the balloon. Those portions of electrodes 25 and 27 that correspond to the proximal and distal balloon cones 32, 34 and necks 37, 39 are insulated and accordingly will not generate and electrical field. Only the vessel wall is treated; any blood present within the vessel lumen is not impacted by the treatment as no electrical field is generated from the insulated portions of the device.
As shown in
The distal portion of electrode assembly 26 is illustrated in two enlarged, cross-sectional partial views of
Detail D-D of
In a constrained state, as shown in
An alternative embodiment of the electroporation balloon catheter of the present invention with a balloon and electrode assembly is shown in a plan view in
Details of the spiral electrodes are shown in
Electrode 85 and 87 may be comprised of any conductive material known in the art. For example, the electrodes may be formed of a nitinol tube which has been laser cut and memory set to the desired spiral profile. Alternatively, electrodes 85 and 87 may be comprised of a conductive ink which is applied in the desired pattern to the exterior balloon surface. As an example, the conductive ink may be comprised of an adhesive binder material loaded with silver particles. Other conductive materials such as gold or steel may also be used. In one embodiment, the conductive ink may be applied in the desired pattern to the balloon surface using a pen-like applicator and a rotating lathe type fixture. The application of conductive ink may be between 0.001″ and 0.002″ in thickness.
First spiral electrode 85 is positioned over balloon 19 with distal electrode collar 89 coaxially surrounding distal balloon neck 39. In one embodiment, first spiral electrode 85 is of a positive polarity. Extending proximally from electrode collar 89, electrode section 91a partially surrounds balloon cone 34 and comprises the beginning of the first helical turn. The spiral electrode 85 pattern continues proximally along the surface of balloon body 35, as illustrated by electrode cross-sections 91b, 91c, 91d, 91e and 91f. The proximal tail 93 of the first electrode spiral is not visible, but is positioned adjacent to proximal balloon cone 32. A second or negative spiral electrode 87 includes a proximal collar 95 that coaxially surrounds balloon proximal neck 37. Extending distally from collar 95, electrode section 97a partially surrounds proximal balloon cone 32 and comprises the beginning of the spiral pattern. The negative electrode spiral pattern continues proximally along the surface of the balloon body 35, as illustrated by electrode cross-sections 97b, 97c, 97d, 97e and 97f. The distal tail 99 of negative spiral electrode is not visible, but is positioned adjacent to the balloon cone 34.
The resulting surface pattern of the combined spiral electrodes 85 and 87 is a double helix configuration with alternating polarity electrodes positioned along the balloon surface. When electrical current of opposite polarity is applied to electrodes 85 and 87, an electrical field is generated between the positive spiral electrode 85 and the negative spiral electrode. With the electrical current flowing from positive to negative, an electrical field is created between each set of helical turns. As an example, electrical current will flow from 91a to 97f, from 91b to 97e and from 91c to 97d. The effect of this electrical field pattern is that the majority of the balloon surface is within the active electrical field. This is advantageous in that since the electrical field encompasses substantially the entire balloon surface, the resulting ablation zone will uniformly encompass the vessel wall area corresponding to the balloon surface.
Each wire has a dedicated lumen within shaft 119, as shown in
Electrically conductive wires 127 and 129 are in connection with spiral electrodes 85 and 87 at electrode collars 95 and 89 respectively. Electrode wire 133 exits electrode wire lumen 127 at side port exit 150 just proximal to electrode collar 95. Upon exit, electrically conductive wire 127 is attached to the outer surface of collar 95, whereby completing the electrical pathway between the electrical generator and the spiral electrode 123. Wire 133 is attached to the spiral electrode collar 95 using either a conductive epoxy or other attachment method known in the art. In a similar manner electrode wire 135 exits wire lumen 129 at a side port exit 152 just distal to the electrode collar 89. Upon exit, electrically conductive wire 129 is attached to the outer surface of collar 89, whereby establishing the electrical pathway to the spiral electrode 85. In an alternative embodiment, electrically conductive wire 135 may exit wire lumen 129 within the balloon interior 45. In this embodiment, the insulated wire 135 is sandwiched between the distal balloon neck 39 and the outer surface of catheter shaft 119, exiting from the distal end of balloon neck 39 to make contact with electrically conductive collar 89.
Other embodiments of the electroporation catheter of the current invention are shown in
In yet another embodiment of the invention the balloon electrode assembly 431 may be comprised of a mesh or woven layer which includes electrodes as shown in
The method of using the electroporation balloon catheter of the current invention to prevent re-stenosis of a vessel will now be described with reference to FIGS. 16 and 17A-E. To begin the procedure, access is gained to the vessel using techniques known in the art such as the Seldinger needle/guidewire access technique as shown in step 201 of
Once correctly positioned within the anatomical lumen, electrical connectors 11 of the catheter 10 are connected to an electrical generator (205). This completes an electrical circuit between the electrodes and the generator. This step may be performed at any time prior to applying the electrical pulses to the device. Treatment protocol parameters such as pulse width, number of pulses and voltage are set using the generator interface (207). Typical ranges include but are not limited to a voltage level of between 100-3000 volts, a pulse duration of between 20-100 μsec, and between 10 and −500 total pulses. By varying parameters of voltage, number of electrical pulse and pulse duration, the electrical field will either produce irreversible or reversible electroporation of the smooth muscle cells comprising the inner vessel wall or endothelium 509. In one embodiment of the invention, ten electrical pulses of 3500 V/cm at a frequency of 10 Hz may be used. In another embodiment, 90 electrical pulses of 1750 V/cm at a frequency of 1 Hz may be used. These ranges ensure that damage caused by Joule heating is avoided.
In another aspect of the invention, conductance of the electrical current may be measured during the procedure to monitoring clinical endpoints. As an example, a successful treatment may be identified by changes in conductance during the applied pulses and an overall decrease in conductance. Measuring conductance will make it possible to calibrate the current, voltage, and pulse duration parameters to avoid thermal damage and obtain IRE. The conductance changes when the cells are porated.
Once the lumen has been sufficiently enlarged by angioplasty, electrical pulses of a predetermined pulse width and voltage are applied across the electrodes. Pulses are applied while the balloon remains inflated (211). This provides not only contact between the electrodes and vessel wall, but also ensures that blood is not present in the electrical field. The conductivity of blood is known to be higher than the vessel wall. Accordingly, the treatment may be compromised if a significant amount of blood was present in the target area of the vessel since the electrical current would be directed to the bloodstream rather than the vessel wall.
Based on the electrical parameters chosen as part of the treatment protocol, an electrical field gradient is generated between opposite polarity electrodes of sufficient strength to non-thermally electroporate the smooth muscle cells in the target vessel wall 501. The generated electrical field is represented in
If the electrical generator treatment parameters are set to deliver electrical pulses within the reversible range therapeutic agents may be injected through the catheter lumen to the target lesion site. The agent will be transported to the smooth muscle cell interior through the transient cellular membrane openings. The membrane openings will then close retaining the therapeutic agent within the cell interior. Anti-restenosis drugs such as Paclitaxel and Vasculast as well as other agents known in the field may be introduced into the cell.
Once sufficient electrical energy has been delivered to the vessel wall 507, the balloon catheter 10 is deflated, causing distal collar 55 to move distally along the catheter shaft 19. The plurality of electrodes legs collapse against the deflating balloon 19 as shown in
Since the voltage pulse generation pattern from the generator does not generate damaging thermal effect, and because the voltage pulses only ablate living cells, the treatment does not damage blood, blood vessel connective tissue or other non-cellular or non-living materials such as the catheter itself. The application of energy may be delivered to the vessel wall without damaging the balloon or other components of the catheter that might be damaged by temperatures created by a thermal therapy such as radiofrequency, laser, microwave or cryoplasty.
In another aspect of the invention, by periodically administering the electrical pulses according to a predetermined schedule, native stenotic lesions maybe prevented altogether.EXAMPLES
The following examples are put forth so as to provide those of ordinary skill in the art with a complete disclosure and description of how to make and use the present invention, and are not intended to limit the scope of what the inventors regard as their invention nor are they intended to represent that the experiments below are all or the only experiments performed. Efforts have been made to ensure accuracy with respect to numbers used (e.g. amounts, temperature, etc.) but some experimental errors and deviations should be accounted for. Unless indicated otherwise, parts are parts by weight, molecular weight is weight average molecular weight, temperature is in degrees Centigrade, and pressure is at or near atmospheric.Example 1 Method
Eight Sprague-Dawley rats weighting 300-350 grams were used in this pilot study. All animals received humane care from a properly trained professional in compliance with both the Principals of Laboratory Animal Care and the Guide for the Care and Use of Laboratory Animals, published by the National Institute of Health (NIH publication No. 85-23, revised 1985).
Each animal was anaesthetized throughout the procedure. The left common carotid artery was exposed, and intimal denudation was performed as previously described. [Maor, et al. “The Effect of Irreversible Electroporation on Blood Vessels “Technol Cancer Res Treat. 6, 2007: 255-360; Touchard, et al. “Preclinical Restenosis Models Challenges and Successes,” Toxicologic Pathology, 34, pp. 2006: 11-18.] Briefly, the left external carotid artery was incised, and a 2F Fogarty arterial embolectomy catheter (Edwards Lifesciences) was advanced through the incision to the left common carotid artery. The balloon was inflated and drawn back three consecutive times. At the end of the procedure the balloon was deflated, extracted and the left external carotid artery was ligated.
Four rats were used as control, and their skin incision was sutured immediately at the end of the procedure. In the remaining four rats, a custom made electrode clamp with two parallel disk electrodes (diameter=5 mm) was applied on the left common carotid artery, very close to its bifurcation to the internal and external carotid arteries, at the exact site of intimal damage (see
Animals were euthanized with an overdose of Phenobarbital. The arterial tree was perfused with 10% buffered formalin for 40 minutes, and the left and right carotid arteries were exposed near the bifurcation of the internal and external carotid arteries. One slice of 1 cm from each artery, at the core of the treated area, was used for histological analysis. Each slice was fixed with 10% buffered formalin, embedded in paraffin, and sectioned with a microtome (5-μm-thick). One section was stained with hematoxylin and eosin. The endothelial layer was assessed by lectin immunostaining. Each slide was photographed at ×200 magnification, and the following areas were measured: tunica media area, neointimal area and lumen area. The unequal variance t-test method was used to evaluate the statistical difference between the measured areas of the two different groups.Results
All animals survived the procedures. Conductance of the arterial wall decreased during successive direct current pulses (
Conductance was measured during IRE pulses and was used to monitor the successful use of the electroporation device. Successful IRE was assigned to those cases in which significant conductance increase was observed during applied pulses, as depicted in the case shown in
After 28 days, histological analysis was used to compare the IRE-treated and the control group (
Examples of the endothelial layer in the different animals are shown in
The results demonstrate the ability of IRE to reduce restenosis. There was reduced neointimal formation following successful IRE, compared with control animals. Based on histological analysis, the extra cellular matrix component of the arterial wall was maintained; there was no evidence of necrosis, aneurysm formation, or thrombosis, and there was remarkable recovery of the endothelial layer. Thermal damage to this layer was avoided.
Atherosclerosis, arterial remodeling and restenosis following angioplasty are complex processes, in which the arterial wall in general, and the vascular smooth muscle cells in particular, play a role. [Ward, et al. “Arterial Remodeling Mechanisms and Clinical Implications,” Circulation. 102, 2000: 1186-1191; Davies, et al. “Pathobiology of intimal hyperplasia,” Br J. Surg. 81, 1994: 1254-69; Lusis, et al. “Atherosclerosis,” Nature. 407, 2000: 233-241.]
Results provided here show that compared with non-IRE treated controls, there is significant decrease in neointimal formation 28 days after intimal damage in IRE-treated arteries. In a previous study we showed that in the same model, IRE induced significant reduction in the VSMC population without apparent damage to elastic fibers. [Maor, et al. “The Effect of Irreversible Electroporation on Blood Vessels “Technol Cancer Res Treat. 6, 2007: 255-360.] Clarke et al. [“Apoptosis of vascular smooth muscle cells induces features of plaque vulnerability in atherosclerosis,” Nat Med. 12, 2006: 1075-1080] investigated the role of VSMC per se in vascular disease. Using transgenic mice expressing human diphtheria toxin receptor on all VSMCs, they showed that apoptosis of 50-70% of the VSMC population in normal arteries induced no endothelial loss, inflammation, reactive proliferation, thrombosis, remodeling or plaque formation.
The results provided here show that by selectively destroying the VSMC population without affecting the extracellular matrix, the specific non-thermal IRE ablation method described here significantly reduces the potential ability of neointimal formation, without significant damage to arterial function and overall structure.
To date, different methods to ablate or stop the proliferation of cells in the different layers of the arterial wall have been suggested. These methods include cryoplasty, brachytherapy, photodynamic therapy, drug-eluting stents and genetic manipulations using gene therapy. [Tanguay, et al. “Percutaneous endoluminal arterial cryoenergy improves vascular remodelling after angioplasty,” Thromb. Haemost. 92, 2004: 1114-1121; Yiu, et al. “Vascular Smooth Muscle Cell Apoptosis Induced by ‘Supercooling’ and Rewarming” J Vasc Interv Radiol. 17, 2006: 1971-1977; Fava, et al. “Cryoplasty for Femoropopliteal Arterial Disease: Late Angiographic Results of Initial Human Experience,” J Vasc Interv Radiol. 15, 2004: 1239-1243; Laird, et al. “Cryoplasty for the Treatment of Femoropopliteal Arterial Disease Results of a Prospective, Multicenter Registry,” J Vasc Interv Radiol. 16, 2005: 1067-1073; Samson, et al. “CryoPlasty Therapy of the Superficial Femoral and Popliteal Arteries: A Single Center Experience,” Vasc. Endovascular Surg. 40, 2007: 446-450; Lagerqvist, et al. “Long-Term Outcomes with Drug-Eluting Stents versus Bare-Metal Stents in Sweden,” N Engl J. Med. 356, 2007: 1009-1019; Leon, et al. “Localized Intracoronary Gamma-Radiation Therapy to Inhibit the Recurrence of Restenosis after Stenting,” N Engl J. Med. 344, 2001: 250-256; Waksman, et al. “Two-year follow-up after beta and gamma intracoronary radiation therapy for patients with diffuse in-stent restenosis,” Am. J. Cardiol. 88, 2001: 425-428; Teirstein, et al. “New Frontiers in Interventional Cardiology: Intravascular Radiation to Prevent Restenosis,” Circulation. 104, 2001: 2620-2626; Salame, et al. “The Effect of Endovascular Irradiation on Platelet Recruitment at Sites of Balloon Angioplasty in Pig Coronary Arteries,” Circulation. 101, 2000: 1087-1090; Cheneau, et al. “Time Course of Stent Endothelialization After Intravascular Radiation Therapy in Rabbit Iliac Arteries,” Circulation. 107, 2003: 2153-2158; Waksman, et al. “Intracoronary photodynamic therapy reduces neointimal growth without suppressing re-endothelialisation in a porcine model,” Heart. 92, 2006: 1138-1144; Mansfield, et al. “Photodynamic therapy: shedding light on restenosis.” Heart. 86, 2001: 612-618; Stone, et al. “A Polymer-Based, Paclitaxel-Eluting Stent in Patients with Coronary Artery Disease,” N Engl J. Med. 350, 2004: 221-231; Moses, et al. “Sirolimus-Eluting Stents versus Standard Stents in Patients with Stenosis in a Native Coronary Artery,” N Engl J. Med. 349, 2003: 1315-1323; Makinen, et al. “Increased Vascularity Detected by Digital Subtraction Angiography after VEGF Gene Transfer to Human Lower Limb Artery: A Randomized, Placebo-Controlled, Double-Blinded Phase II Study,” Mol Ther. 6, 2002: pp. 127-133; Hedman, et al. “Safety and Feasibility of Catheter-Based Local Intracoronary Vascular Endothelial Growth Factor Gene Transfer in the Prevention of Postangioplasty and In-Stent Restenosis and in the Treatment of Chronic Myocardial Ischemia. Phase II Results of the Kuopio Angiogenesis Trial (KAT),” Circulation. 2003: 01.1
The IRE methodology disclosed and described here is different from and has advantages over these other methods for reducing restenosis. The nature of the IRE mechanism alone is to produce only nanoscale defects in the cell membrane. [Chen, et al. “Membrane electroporation theories: a review.” Med Biol Eng Comput. 44, 2006: 5-14.] In the absence of thermal damage, IRE does not affect connective tissue, the extracellular matrix, nor does it denaturizes proteins. [Maor, et al. “The Effect of Irreversible Electroporation on Blood Vessels.” Technol Cancer Res Treat. 6, 2007: 255-360; Lee, et al. “Distinguishing Electroporation from Thermal Injuries in Electrical Shock By MR Imaging.” Conf Proc IEEE Eng Med Biol Soc. 6, 2005: 6544-6546.] Therefore, the integrity of the extracellular matrix is retained during the process. The extra-cellular matrix plays an important role in arterial remodeling and in the elastic properties of the arterial wall. [Li, et al. “Elastin is an essential determinant of arterial morphogenesis,” Nature. 393, 1998: 276-280.] One explanation for the absence of aneurysm formation in accordance with the present invention may be that IRE does not damage elastin or collagen within the arterial wall. One of the problems with an intra-arterial stent is the intense extra cellular formation in the later stages of restenosis, probably due to the mechanical damage caused by the stent. [Chung, et al. “Enhanced extracellular matrix accumulation in restenosis of coronary arteries after stent deployment,” J Am Coll Cardiol. 40, 2002: 2072-2081.1 Because electrical fields can either produce IRE or not, without any gradual modalities of damage, the margins of the treated region are well delineated and do not extent beyond the area of application of the IRE field. Therefore, with IRE the effect can be achieved only in the area of interest, without collateral damage. The use of the IRE method of the present invention is a non-pharmacological method, and therefore there is less concern regarding allergic reaction or drug safety.
IRE, and electroporation in general, produces nano-scale defects in the cell membrane and thereby facilitates unimpeded ion transport across the membrane. [Chen, et al. “Membrane electroporation theories: a review.” Med Biol Eng Comput. 44, 2006: 5-14.] Therefore, successful IRE results in immediate changes in the passive electrical properties of the tissue that can be measured and employed as a feedback mechanism for real time control of the technique. In fact, within the context of reversible electroporation, such strategy has been described previously for individual cells [Huang et al. “Micro-electroporation: improving the efficiency and understanding of electrical permeabilization of cells,” Biomed. Microdevices. 3, 1999: 145-150], cell cultures [Pavlin, et al. “Effect of Cell Electroporation on the Conductivity of a Cell Suspension,” Biophys. J. 88, 2005: 4378-4390] and tissues. [Davalos, et al. “A Feasibility Study for Electrical Impedance Tomography as a Means to Monitor Tissue Electroporation for Molecular Medicine,” IEEE Trans. Biomed. Eng. 49, 2002: 400-403; Cukjati, et al. “Real time electroporation control for accurate and safe in vivo non-viral gene therapy,” Bioelectrochemistry. 70, 2007: 501-507.]
A common, and expected, observation in previous studies in which in vivo conductance has been measured during the application of a sequence of high voltage pulses, either for reversible or for irreversible electroporation [Ivorra, et al. “In vivo electrical impedance measurements during and after electroporation of rat liver,” Bioelectrochemistry. 70, 2007: 287-295; Pavselj, et al. “The course of tissue permeabilization studied on a mathematical model of a subcutaneous tumor in small animals,” IEEE Trans. Biomed. Eng. 52, 2005: 1373], is that electrical conductance increases during the sequence and not only within the pulses. The only exception seems to be the skeletal muscle under IRE. In that particular case, conductance measured at the pulses is quite constant during the whole sequence. In accordance with the methodology of the present invention, conductance decreases during the sequence of pulses. With the understanding that we are not bound to a particular theory or explanation, we believe that a plausible hypothesis is that IRE pulses cause contraction of the arteries [Jackson, et al. “Regional variation in electrically-evoked contractions of rabbit isolated pulmonary artery,” Br J. Pharmacol. 137, 2002: 488-496] and that such contraction results in an increase of the impedance of the arteries, particularly of the smooth muscle tissue. [Liao, et al. “The Variation of Action Potential and Impedance in Human Skeletal Muscle during Voluntary Contraction,” Tohoku J. Exp. Med. 173, 1994: 303-309; Shiffman, et al. “Electrical impedance of muscle during isometric contraction,” Physiol. Meas. 24, 2006: 213-234.]
The results provided here show a failure to induce IRE in one of the animals. This may have been caused by not applying the electrodes properly to the artery so that the resulting electrical contact was not good enough over the artery. Direct short-circuiting of the electrodes or through plasma or saline solution does not seem plausible because it would have caused larger conductivity than the measured conductivity during the pulses (
Successful IRE depends on parameters such as electric field magnitude, pulses length and frequency. The reason for choosing the particular electrical parameters used in this study are consistent with the mode of application of IRE of the present invention. These are electrical parameters that were assessed to be high enough to ensure irreversible electroporation [Davalos, et al. “Tissue Ablation with Irreversible Electroporation,” Ann. Biomed. Eng. 33, 2005: 223-231; Edd, et al. “In vivo results of a new focal tissue ablation technique: irreversible electroporation.” IEEE Trans Biomed Eng. 53, 2006: 1409-15; Miller, et al. “Cancer Cells Ablation with Irreversible Electroporation,” Technol Cancer Res Treat. 4, 2005: 699-705; Rubinsky, “Irreversible electroporation in medicine.” Technol. Cancer Res Treat. 6. 2007: 255-60; Rubinsky, et al. “Irreversible electroporation: a new ablation modality—clinical implications.” Technol Cancer Res Treat. 6, 2007: 37-48; Ivorra, et al. “In vivo electrical impedance measurements during and after electroporation of rat liver,” Bioelectrochemistry. 70, 2007: 287-295; Maor, et al. “The Effect of Irreversible Electroporation on Blood Vessels” Technol Cancer Res Treat. 6, 2007: 255-360; Touchard, et al. “Preclinical Restenosis Models Challenges and Successes,” Toxicologic Pathology, 34, pp. 2006: 11-18; Dev, et al. “Intravascular Electroporation Markedly Attenuates Neointima Formation After Balloon Injury of the Carotid Artery in the Rat.” J Interven Cardiol. 13, 2000: 331-338] but which do not cause damaging levels of Joule heating. We used a sequence of 10 direct current pulses of 115 Volts (i.e. electrical field of approximately 3800 V/cm), 100 μs each, at a frequency of 10 pulses per second. These parameters where partially based on previous reports that showed successful tumor cell ablation with IRE. [Miller, et al. “Cancer Cells Ablation with Irreversible Electroporation,” Technol Cancer Res Treat. 4, 2005: 699-705; Rubinsky, et al. “Irreversible electroporation: a new ablation modality—clinical implications.” Technol Cancer Res Treat. 6, 2007: 37-48; Al-Sakere, et al. “Tumor Ablation with Irreversible Electroporation.” PLoS ONE. 2, 2007: e1135.] Since the arterial wall has different morphology, and since we did not have data regarding the specific susceptibility of vascular smooth muscle cells to IRE, we used an electrical field that was higher than any previous report but low enough not to produce thermal damage within the constraints of the treated tissue dimensions. Those skilled in the art will be able to follow the results provided here to show the relation between conductance measurements during the procedure and IRE efficiency.
The examples described here used rodent carotid artery model. This model is an acceptable animal model of restenosis [Touchard, et al. “Preclinical Restenosis Models: Challenges and Successes,” Toxicologic Pathology, 34, pp. 2006: 11-18; Narayanaswamy, et al. “Animal Models for Atherosclerosis, Restenosis, and Endovascular Graft Research,” J Vasc Interv Radiol. 11, 2000: 5-17], but it is important to clarify that our experiments were performed on arteries that were not atherosclerotically changed. However, we believe these results can be readily applied to humans to show the efficacy of IRE in atherosclerotically changed arteries.
Our electrodes were clamping the artery on its outer surface, but this does not imply that this method will be used as an invasive procedure. Previous reports have already demonstrated the ability to design and use intra-vascular devices in order to induce reversible electroporation of the arterial wall. [Dev, et al. “Intravascular Electroporation Markedly Attenuates Neointima Formation After Balloon Injury of the Carotid Artery in the Rat.” J Interven Cardiol. 13, 2000: 331-338.] Those skilled in the art will understand that similar designs can be used to achieve IRE on humans using intra-vascular devices.
The invention provides in vivo, long-term results of a new non-thermal, non-pharmacological strategy to attenuate neointimal formation following intimal damage. Importantly, the invention provides for the treatment of restenosis following coronary angioplasty and the delivery of that treatment with real time control.
The method of the invention can be used in preventing and/or ablating coronary and peripheral restenosis process, while also playing a role in attenuating atherosclerotic processes in clinically important locations, such as coronary, carotid and renal arteries.Example 2 Summary of Method and Results
33 Sprague-Dawley rats were used to compare NTIRE protocols. Each animal had NTIRE applied to its left common carotid using custom-made electrodes. The right carotid artery was used as control. Electric pulses of 100 microseconds were used. Eight IRE protocols were compared: 1-4) 10 pulses at a frequency of 10 Hz with electric fields of 3500, 1750, 875 and 437.5 V/cm and 5-8) 45 and 90 pulses at a frequency of 1 Hz with electric fields of 1750 and 875 V/cm. Animals were euthanized after one week. Histological analysis included VSMC counting and morphometry of 152 sections. Selective slides were stained with elastic Van Gieson and Masson trichrome to evaluate extra-cellular structures. Most efficient protocols were 10 pulses of 3500 V/cm at a frequency of 10 Hz and 90 pulses of 1750 V/cm at a frequency of 1 Hz, with ablation efficiency of 89±16% and 94±9% respectively. Extra-cellular structures were not damaged and the endothelial layer recovered completely.SUMMARY CONCLUSION
NTIRE is a promising, efficient and simple novel technology for VMSC ablation. It enables ablation within seconds without causing damage to extra-cellular structures, thus preserving the arterial scaffold and enabling endothelial regeneration. This study provides scientific information for future anti-restenosis experiments utilizing NTIRE.Method
Thirty three Sprague-Dawley rats weighting 160-280 grams were used in this study. All animals received humane care from a properly trained professional in compliance with both the Principals of Laboratory Animal Care and the Guide for the Care and Use of Laboratory Animals, published by the National Institute of Health (NIH publication No. 85-23, revised 1985).
Animals were anaesthetized with an intramuscular injection of Ketamin and Xylazine (90 mg/Kg and 10 mg/Kg, respectively). The left common carotid artery of each animal was exposed and a custom made electrode clamp with two parallel disk electrodes was applied on the left common carotid artery as previously described. (Maor E, Ivorra A, Leor J, Rubinsky B. Irreversible Electroporation Attenuates Neointimal Formation After Angioplasty. Biomedical Engineering, IEEE Transactions on. 2008; 55(9):2268-2274) The custom made electrode clamp consists of two printed circuit boards (1.5 mm thickness) with disk electrodes (diameter=5 mm) made of copper (70 μm thickness) plated with gold (manufacturing process by Sierra Proto Express, Sunnyvale, Calif.).
Animals were divided to eight different groups (
All pulses were 100 μs in length. The number of pulses, the applied electric field, and the frequency of the pulses differed between the groups as summarized in
Animals were euthanized with an overdose of Phenobarbital followed by bilateral chest dissection. Gross inspection of carotid arteries was used to identify arterial wall integrity or intraluminal massive thrombus formation. The arterial tree was perfused with 10% buffered formalin, and the left and right carotid arteries were harvested near the bifurcation of the internal and external carotid arteries. The treated area was cut to two or three consecutive slices. One section from each slice was used for histological analysis. Each slice was fixed with 10% buffered formalin, embedded in paraffin, and sectioned with a microtome (5-μm-thick). Sections were stained with hematoxylin and eosin. Each section was photographed at ×200 magnification, and the following parameters were quantitatively evaluated: number of VSMC nuclei in each of the three layers of the Tunica Media, total area of the Tunica Media, and the average thickness of the Tunica Media based on 5 different measurements in each section. VSMC concentration was calculated by dividing the total number of nuclei by the measured area of the Tunica Media. The paired t-test method was used to evaluate the statistical difference between the measured areas of the control versus IRE-treated groups.
In addition, selected sections were stained with elastic Van Gieson (EVG) and Masson trichrome in order to evaluate the extra-cellular elastic and collagen fibers, respectively. Immunostaining with CD31 and CD34 antibodies (Pathology Services Inc., Berkeley, Calif.) was used to evaluate the endothelial layer.Results
All 33 animals survived the procedure. During follow-up period, there were no cases of infection, bleeding at IRE-treated arteries, thrombosis or animal mortality.NTIRE VSMC Ablation Efficiency
Results of all eight groups are summarized in
While ten pulses of 3,500 V/cm were efficient, ten pulses of lower electric fields had a minor ablation effect (1,750 V/cm, group 2: 167±66 vs. 214±38, P=0.05) or no effect at reducing VSMC population (Groups 3 & 4, 875 and 437.5 V/cm respectively). Increasing the number of pulses with electric field of 1,750 V/cm improved the ablation efficiency (VSMC population reduction of 22±30%, 86±16% and 94±9% with 10, 45 and 90 pulses respectively). Similar trend of increasing efficiency was also apparent with an electric field of 875 V/cm (63±29% and 79±17% with 45 and 90 pulses, respectively), but efficiency values were not high enough even with 90 pulses (49±40 vs. 236±31, P<0.001).
Sub-analysis of ablation efficiency at the three separate layers of the Tunica Media showed that the best results were achieved in the outer layers of the Tunica Media, and most VSMC that survived NTIRE were located in the inner most layer (
Electric conductance changed during the application of NTIRE (
Successful NITRE ablation of VSMC induced a reduction in media thickness: 25±17% reduction in group 1 (45±10 vs. 59±8 μm) and 27±7% reduction in Group 7 (37±4 vs. 51±6 em). No change in media thickness was induced in the two non-successful NTIRE groups (61±9 vs. 58±7 μm in Group 3, 61±9 vs. 60±6 μm in Group 4).
Endothelial cells of treated arteries were similar in number and morphology to those of non treated control arteries, but were negative to both CD31 and CD34 antibodies (data shown only for CD34 staining, see bottom row in
This is the first large scale, in-vivo survival experiment to evaluate and compare the effect of different NTIRE protocols on VSMC population. The results show that NTIRE can achieve efficient ablation of VSMC within seconds, without damaging extra-cellular components.
Current study results are supported by previous studies by our group. In a preliminary study evaluating NTIRE effect on blood vessels, a 87% reduction in VSMC concentration after 28 days was observed following NTIRE with similar parameters to those of Group 1 (10 pulses, 100 μsec, 10 Hz, 3800 V/cm). (Maor E, Ivorra A, Leor J, Rubinsky B. The Effect of Irreversible Electroporation on Blood Vessels. Technology in Cancer Research and Treatment. 2007; 6(4):255-360) Parameters similar to Group 1 have also been shown to significantly reduce neointimal formation following angioplasty in rodent carotid injury model. (Maor E, Ivorra A, Leor J, Rubinsky B. Irreversible Electroporation Attenuates Neointimal Formation After Angioplasty. Biomedical Engineering, IEEE Transactions on. 2008; 55(9):2268-2274).
Our results are also supported by the work of Al-Sakere et al. (Al-Sakere B, André F, Bemat C, et al. Tumor Ablation with Irreversible Electroporation. PLoS ONE. 2007; 2(11):e1135) In their in-vivo study with sarcoma tumor, best tumor ablation using irreversible electroporation was achieved with the use of 80 electroporation pulses of 100 μs at 0.3 Hz with an electrical field magnitude of 2,500 V/cm. Their most efficient protocol was the one with the largest number of pulses and the highest electric field evaluated, similar to the results presented here. Based on these results, it seems that irreversible electroporation is limited only by the joule heating effect. As long as there is no thermal damage to extra-cellular structures, increase in electric field magnitude and pulse number will be translated to larger ablation volume and better ablation efficiency.
For Groups 1 and 7, where best ablation efficiency was observed, around 10% of the VSMC population survived the ablation. Further analysis of the results demonstrated 100% efficiency in the outer layers of the Tunica Media, with all surviving cells located in the inner most layers of the arterial wall (
Our results show that reduction of the electric field magnitude can be compensated by increasing the number of NTIRE pulses. Ten pulses of 3500 V/cm achieved similar effect to 90 pulses of 1750 V/cm. However, decreasing the electric field even more to 875 V/cm caused a decrease in NTIRE efficiency even with the use of 90 pulses. This observation may be important in future NTIRE device designs, where intervention time could be reduced by increasing trans-electrode electric potential.
A common observation in previous electroporation studies, either reversible or irreversible, is that electrical conductance measured at the pulses increases during the sequence of pulses. (Ivorra A, Miller L, Rubinsky B. Electrical impedance measurements during electroporation of rat liver and muscle. In: 13th International Conference on Electrical Bioimpedance and the 8th Conference on Electrical Impedance Tomography; 2007:130-133. Available at: http://dx.doi.org/10.1007/978-3-540-73841-1—36 [Accessed Oct. 21, 2008]) The only exception to this seems to be for skeletal muscle under NTIRE. (Ivorra A, Miller L, Rubinsky B. Electrical impedance measurements during electroporation of rat liver and muscle. In: 13th International Conference on Electrical Bioimpedance and the 8th Conference on Electrical Impedance Tomography; 2007:130-133. Available at: http://dx.doi.org/10.1007/978-3-540-73841-1—36) In that particular case, conductance measured at the pulses remains quite constant during the whole sequence and it can be explained as a saturation effect of the electroporation phenomenon. However, the fact that conductance decreases during the sequence is quite surprising as it contradicts what would be expected in a simple electroporation model: electroporation increases cell membrane permeability to ions and therefore its conductance should also increase. We do not have a definitive explanation for the conductance decrease observed here. We consider that a plausible hypothesis is that NTIRE pulses cause a contraction of the arteries by stimulating the vascular smooth muscle cells and that such a contraction results in an increase in the electrical impedance of the arteries. (Liao T J, Nishikawa H. The variation of action potential and impedance in human skeletal muscle during voluntary contraction. Tohoku J Exp Med. 1994; 173(3):303-9; Shiffman C A, Aaron R, Rutkove S B. Electrical impedance of muscle during isometric contraction. Physiol Meas. 2003; 24(1):213-34; Jackson V M, Trout S J, Cunnane T C. Regional variation in electrically-evoked contractions of rabbit isolated pulmonary artery. Br J. Pharmacol. 2002; 137(4):488-496) Another explanation could be based on the fact that electroporation disturbs the osmotic balance of the cells and causes cell swelling which in turn can result in a decrease of the conductance. (Ivorra A, Miller L, Rubinsky B. Electrical impedance measurements during electroporation of rat liver and muscle. In: 13th International Conference on Electrical Bioimpedance and the 8th Conference on Electrical Impedance Tomography; 2007:130-133. Available at: http://dx.doi.org/10.1007/978-3-540-73841-1—36 [Accessed Oct. 21, 2008]) Nevertheless, we believe that such swelling cannot be manifested as fast as would be required here in order to explain the conductance decrease during the sequence, particularly in Groups 1 and 2 (sequence duration=1 second).
NTIRE is not the first method to address the challenge of VSMC ablation. Several alternative technologies have been studied, and some have become a common clinical practice for the treatment of post-angioplasty and in-stent restenosis. These technologies include: cryoplasty (Fava M, Loyola S, Polydorou A, et al. Cryoplasty for Femoropopliteal Arterial Disease: Late Angiographic Results of Initial Human Experience. J Vasc Interv Radiol. 2004; 15(11):1239-1243), brachytherapy (Leon M, Teirstein P, Moses J, et al. Localized Intracoronary Gamma-Radiation Therapy to Inhibit the Recurrence of Restenosis after Stenting. N Engl J Med. 2001; 344(4):250-256), photodynamic therapy (Waksman R, Leitch I, Roessler J, et al. Intracoronary photodynamic therapy reduces neointimal growth without suppressing re-endothelialisation in a porcine model. Heart. 2006; 92(8):1138-1144), radiofrequency ablation (Taylor G W, Kay G N, Zheng X, Bishop S, Ideker R E. Pathological Effects of Extensive Radiofrequency Energy Applications in the Pulmonary Veins in Dogs. Circulation. 2000; 101(14):1736-1742), drug-eluting stents (Stone G, Ellis S, Cox D, et al. A Polymer-Based, Paclitaxel-Eluting Stent in Patients with Coronary Artery Disease. N Engl J. Med. 2004; 350(3):221-231) and molecular-based therapies (Aubart F C, Sassi Y, Coulombe A, et al. RNA Interference Targeting STIM1 Suppresses Vascular Smooth Muscle Cell Proliferation and Neointima Formation in the Rat. Mol Ther. 2008. Available at: http://dx.doi.org/10.1038/mt.2008.291 [Accessed January 6, 2009]).
However, delayed re-endothelialization (Cheneau E, John M, Fournadjiev J, et al. Time Course of Stent Endothelialization After Intravascular Radiation Therapy in Rabbit Iliac Arteries. Circulation. 2003; 107(16):2153-2158), economic impact (Weintraub W S. The Pathophysiology and Burden of Restenosis. The American Journal of Cardiology. 2007; 100(5, Supplement 1):S3-S9) and late in-stent thrombosis (Lagerqvist B, James S, Stenestrand U, et al. Long-Term Outcomes with Drug-Eluting Stents versus Bare-Metal Stents in Sweden. N Engl J. Med. 2007; 356(10): 1009-1019; Costa Mass., Sabate M, van der Giessen W J, et al. Late Coronary Occlusion After Intracoronary Brachytherapy. Circulation. 1999; 100(8):789-792) are some of the major concerns with all of the current VSMC ablation modalities. We believe NTIRE should be further investigated as an alternative to current modalities, since it has two major advantages.
First, its non-pharmacological nature can overcome biological phenomena such as cellular adaptation or acquired drug-resistance, thus achieving higher local efficiency. The non pharmacologic nature also guarantees an accurate local effect that depends entirely on electric field distribution and does not induce collateral damage to adjacent structures.
Second, its ultra short duration can decrease intervention time in the clinical setting of primary percutaneous intervention (PCI). It enables one to minimize obstruction of blood flow to viable myocardial tissue during the ablation procedure. Moreover, short intervention duration will enable prompt and full endothelium recovery by immediate recruitment of circulating progenitor endothelial cells. Incomplete neointimal coverage has been demonstrated as a probable cause for late stent thrombosis in patients with drug-eluting stents6, as well as a reason for brachytherapy failure. (Waksman R, Bhargava B, Mintz G S, et al. Late total occlusion after intracoronary brachytherapy for patients with in-stent restenosis. Journal of the American College of Cardiology. 2000; 36(1):65-68)
The complete endothelial regeneration observed in this report can be attributed to two properties of NTIRE. First, the ultra short duration of the modality enabled immediate repopulation of the endothelium by either endothelial cells from adjacent non treated areas, or by adherence of progenitor endothelial cells from the circulation. Second, the non-thermal nature of this modality minimized the insult to extra cellular components of the endothelial layer, probably creating a more comfortable environment for cellular regeneration.
Endovascular NTIRE has clinical potential for both the prevention and the treatment of restenosis following angioplasty. Due to its short duration and high efficiency NTIRE can become a preventive treatment immediately before stent deployment. It might also prove to be a valuable tool for the effective treatment of in-stent restenosis several weeks following the angioplasty.
All animals were evaluated after a follow-up period of one week. This was based on our previous study, where ablation efficiency was evident by the complete loss of VSMC population as early as one week following NTIRE. (Maor E, Ivorra A, Leor J, Rubinsky B. The Effect of Irreversible Electroporation on Blood Vessels. Technology in Cancer Research and Treatment. 2007; 6(4):255-360).CONCLUSION
This study provides scientific proof and justification irreversible electroporation as a promising non-thermal, non pharmacological, ultra short modality for the treatment of VSMC proliferation and the clinical problem of in-stent restenosis.
While the present invention has been described with reference to the specific embodiments thereof, it should be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the true spirit and scope of the invention. In addition, many modifications may be made to adapt a particular situation, material, composition of matter, process, process step or steps, to the objective, spirit and scope of the present invention. All such modifications are intended to be within the scope of the claims appended hereto.
1. A method of reducing restenosis, comprising:
- inserting into a vessel of a human patient a balloon catheter comprised of a flexible elongated shaft comprising a distal end portion for insertion into a vessel, wherein the balloon catheter is comprised of:
- a balloon positioned at the distal end portion;
- a first electrode positioned at the distal end portion of the shaft, the first electrode being comprised of a conductive material which is flexible and generally conforms to an outer surface of the balloon during expansion of the balloon;
- a second electrode positioned at a point relative to the first electrode so as to allow electrical current to flow between the electrodes and through vascular tissue to the first electrode, the second electrode being comprised of a conductive material which is flexible and conforms to an outer surface of the balloon during expansion of the balloon; and
- providing electrical pulses to the electrodes for durations and in amounts sufficient to subject substantially all vascular cells in a target area of an artery to irreversible electroporation (IRE).
2. The method of claim 1, wherein the first and second electrodes each encircle the balloon and are positioned on either side of the target area.
3. The method of claim 2, wherein the first and second electrodes each have a helical configuration around the balloon and the electrodes are positioned so that electrical current flows between the electrodes and through the target area.
4. The device of claim 1, wherein the first and second electrodes each have an elongated configuration along a proximal end of the balloon to a distal end of the balloon and the electrodes are positioned so that electrical current flows between the electrodes and through the target area.
5. The method of claim 1, further comprising:
- administering an anti-restenosis drug; and
- wherein the IRE is carried out using a voltage and a current with defined ranges over a defined period of time and in absence of drug being delivered into the vascular cells.
6. The method of claim 5, wherein the anti-restenosis drug is selected from the group consisting of paclitaxel and vasculant and is administered locally to the target area; and
- wherein electrical power source provides electrical pulses having a voltage, current, and duration so as to avoid thermal damage to a target area and surrounding tissue while obtaining IRE on the target area.
7. The method of claim 6, wherein the pulses have a duration of from 50 to 200 microseconds with a current in a range of from 2,000 V/cm to 6,000 V/cm and wherein the electrical power source is configured to apply between two and twenty-five pulses.
8. A balloon catheter device for insertion into a vessel and reducing neointima, comprising:
- a flexible elongated shaft comprising a distal end portion for insertion into a vessel;
- a balloon positioned at the distal end portion;
- a first electrode positioned at the distal end portion of the shaft, the first electrode being comprised of a conductive material which is flexible and generally conforms to an outer surface of the balloon during expansion of the balloon;
- a second electrode positioned at a point relative to the first electrode so as to allow electrical current to flow between the electrodes and through vascular tissue to the first electrode, the second electrode being comprised of a conductive material which is flexible and conforms to an outer surface of the balloon during expansion of the balloon;
- an electrical power source which provides electrical pulses to the electrodes for durations and in amounts sufficient to subject substantially all vascular cells in an area of an artery to irreversible electroporation (IRE) before neointima occurs.
9. The device of claim 8, wherein the first and second electrodes each encircle the balloon.
10. The device of claim 9, wherein the first and second electrodes each have a helical configuration around the balloon.
11. The device of claim 8, wherein the first and second electrodes each have an elongated configuration along a proximal end of the balloon to a distal end of the balloon.
12. The device of claim 8, wherein the first and second electrodes are formed from electrically conductive ink drawn on the balloon.
13. The device of claim 8, for use wherein the IRE is carried out using a voltage and a current with defined ranges over a defined period of time and in absence of drug being delivered into the vascular cells.
14. The device of claim 13, wherein the electrical power source provides electrical pulses having a voltage, current, and duration so as to avoid thermal damage to a target area and surrounding tissue while obtaining IRE on the target area.
15. The device of claim 14, wherein the electrical power source is designed to emit pulses wherein the pulses have a duration of from 50 to 200 microseconds.
16. The device of claim 8, wherein electrical power source applies current in pulses.
17. The device of claim 16, wherein the electrical power source is configured to apply pulses having a duration of from 50 to 200 microseconds.
18. The device of claim 17, wherein the electrical power source is configured to apply pulses of a current in a range of from 2,000 V/cm to 6,000 V/cm.
19. The device of claim 18, wherein the electrical power source is configured to apply between two and twenty-five pulses.
20. The device of claim 19, wherein electrical power source is configured to apply 10 pulses for 100 microseconds each at a current of 3,800 V/cm.
Filed: Mar 27, 2009
Publication Date: Oct 1, 2009
Inventors: ELAD MAOR (Berkeley, CA), JAMES J. MITCHELL (Ballston Spa, NY), ANTONI IVORRA (Berkeley, CA), WILLIAM C. HAMILTON (Queensbury, NY), BORIS RUBINSKY (Givataaim)
Application Number: 12/413,357
International Classification: A61N 1/30 (20060101);