Abstract:
A method and apparatus for solidifying inflamed and unstable plaque on the interior of a blood vessel including inserting a catheter assembly into a human blood vessel while the assembly is in a first, collapsed configuration, advancing the catheter assembly through the blood vessel, stopping at predetermined intervals and expanding the catheter assembly to a second, expanded configuration such that a plurality of temperature detectors contact the interior wall of the blood vessel. The areas of increased temperature are indicative of inflamed and unstable plaque, which is to be stabilized using at least one multi-temperature device, such as a Peltier device, to solidify the plaque and reduce the possibility of a myocardial infarction.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates, in general, to methods and apparatuses for solidifying inflamed/unstable plaque on the interior of a blood vessel.  
         DISCUSSION OF RELATED ART  
         [0002]    Arterial plaque of varying size and location can develop in a human cardiovascular system. A build-up of plaque over a number of years can cause blood vessel occlusion and associated heart failure. Lipid pools are trapped reservoirs of potentially dangerous plaque material that, when released into the blood stream, can cause complete stoppage or major reduction or disruption of blood flow in a vessel. If this occurs in a cardiovascular vessel or other critical vessel, it can cause sudden flow stoppage and possibly death. Lipid pools containing arterial plaque that becomes inflamed and unstable incur an increased risk of ulceration and rupture. When a lipid pool rupture develops, the material flows out into the vessel, causing the blood to quickly thicken or coagulate and form a blood clot. This can cause a myocardial infarction.  
           [0003]    Importantly, lipid pools containing inflamed and unstable plaque are indicated by associated localized temperature variations of the interior blood vessel wall surface. Specialized temperature sensors such as those disclosed in U.S. Pat. No. 5,871,449 can be used to sense localized temperature variations of blood vessel wall surfaces within human arteries. These sensors can detect the presence of lipid pools containing inflamed and unstable plaque, which have up to a two and a half degree increase in artery wall temperature.  
           [0004]    Various methods of plaque removal include compression or removal of the plaque, which typically results in residual sites of injury and a predisposition toward recurrent plaque occlusion. These methods are alternatives to the more traumatic and expensive coronary bypass procedures. One example of a plaque removal method involves the use of an atherectomy device for physically cutting and removing the plaque from the affected arteries. Another commonly used method to increase blood flow involves balloon angioplasty, which reduces the arterial blockage by dilation of the lumen of the artery. Before the balloon is inserted, a laser may be used to create a channel in the artery by heating and melting the plaque. Unfortunately, these methods suffer from some serious drawbacks.  
           [0005]    Regarding atherectomy and angioplasty methods, the devices used to remove the plaque often cause damage to the interior walls of the artery due to scarring caused by cutting and misdirection of laser energy. Moreover, laser energy can burn a hole through the wall of an artery if the laser is not controlled properly. In addition, cutting or melting of liquid lipid pools can release toxic fluids into the blood stream and cause instantaneous blood clots. Accordingly, there exists a need to develop a safer method of removing unstable plaque from the interior of an artery.  
           [0006]    The present invention involves the use of multi-temperature devices or heating-cooling devices, such as Peltier devices, to apply heat and/or cold to solidify a lipid pool such that the lipid pool is stabilized and less likely to create a sudden release of plaque. The multi-temperature devices can be used alone or in combination with the aforementioned or other techniques for removing the solidified plaque.  
         SUMMARY OF THE INVENTION  
         [0007]    A separate aspect of the invention involves a method and apparatus for solidifying inflamed and unstable plaque on the interior wall of a blood vessel. The method initially entails inserting a catheter assembly into a human blood vessel while the assembly is in a first, collapsed configuration. Next, the catheter assembly is advanced through the blood vessel, stopped at predetermined intervals and expanded to a second, expanded configuration such that at least one temperature detector contacts the interior wall of the blood vessel. A noted increase in temperature of an area of the internal wall of the blood vessel is indicative of inflamed, unstable plaque, which may be stabilized by applying heat and/or cold to the areas of increased temperature to solidify the plaque and reduce the possibility of a sudden release into the bloodstream.  
           [0008]    Another separate aspect of the invention involves a method and apparatus for eliminating inflamed and unstable plaque from the interior of a blood vessel by applying heat or cold using at least one multi-temperature device having a hot side and a cold side powered by an electrical current having a polarity. The multi-temperature device can be used to heat and or cool the lipid pool. An example of a multi-temperature device is a Peltier device, which has a cold side and a hot side. Other methods of coagulating or solidifying the lipid material use electrically generated resistance heating or pipes a heated gas or liquid media to the desired site. The cold temperature can also be generated by the expansion of liquid to a gas or by the injection of a cold liquid/gas media into a multi-temperature therapy plate. By reversing the polarity of the electrical current applied to a Peltier device, one can change the hot side to the cold side and vice-versa. In addition, the catheter assembly includes a therapy plate positioned in between the at least one multi-temperature device and the interior of the blood vessel wall that includes imbedded temperature sensors for sensing variation in blood vessel temperature at a plurality of areas along the interior wall of the blood vessel.  
           [0009]    A further separate aspect of the invention involves a method and apparatus for removing undesired energy caused by at least one multi-temperature device by the process of heat sinking using a heat exchanger. The process of heat sinking includes circulating a liquid or gas through the heat exchanger located within the blood vessel to remove the excess energy from the procedural site. The heat exchanger may be lined with internal starburst fins or may include a large lumen to allow the passage of a probe, like a guide wire or catheter. The liquid can be condensed gas or refrigerant, water, or blood from the blood stream and the gas may be air. Air or gas must be contained within plumbing and not allowed to mix with the patient&#39;s blood.  
           [0010]    Another separate aspect of the present invention involves a method and apparatus for eliminating inflamed and unstable plaque from the interior of a blood vessel by applying heat and/or cold using at least one multi-temperature device to solidify the plaque and then removing the solidified plaque resultant from the procedure using atherectomy.  
           [0011]    An additional separate aspect of the invention involves a method and apparatus for eliminating inflamed and unstable plaque from the interior of a blood vessel using a catheter assembly including an expander, which may be a balloon, a plurality of multi-temperature devices, a therapy plate, temperature sensors, a temperature controller and a control box. The plurality of multi-temperature devices is stacked one on top of another to increase the overall thermal energy differential. The control box contains the circuitry to control temperature and to monitor the temperatures of the therapy plate and the vessel wall.  
           [0012]    The invention may include any one of these separate aspects individually, or any combination of these separate aspects.  
           [0013]    Other features and advantages of the invention will be evident from reading the following detailed description, which is intended to illustrate, but not limit, the invention. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    The drawings illustrate the design and utility of preferred embodiments of the present invention, in which similar elements are referred to by common reference numerals.  
         [0015]    [0015]FIG. 1 is a front plan view of an apparatus for treatment of lipid pools including a handle and a catheter assembly.  
         [0016]    [0016]FIG. 2 is a cross-sectional view of the catheter assembly shown in FIG. 1 in an expanded configuration within a human artery.  
         [0017]    [0017]FIG. 3A is a cross-sectional view of a first catheter assembly embodiment.  
         [0018]    [0018]FIG. 3B is a cross-sectional view of second catheter assembly embodiment.  
         [0019]    [0019]FIG. 3C is a cross-sectional view of third catheter assembly embodiment.  
         [0020]    [0020]FIG. 3D is a cross-sectional view of fourth catheter assembly embodiment.  
         [0021]    [0021]FIG. 4 is a plan view with portions fragmented of an alternative catheter assembly embodiment.  
         [0022]    [0022]FIG. 5 is a cross-sectional view of a plurality of stacked multi-temperature devices. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0023]    With respect to FIGS. 1 and 2, a plaque stabilizer device  10  includes a catheter  20  having a distal tip  30  and a guide sheath  35 , and a handle  40  which can have a steering control  50  for the distal tip  30  of catheter  20  and a temperature control  60  for a catheter assembly  70 . For example, moving the temperature control  60  toward the “hottest” position increases the temperature, while moving the temperature control  60  toward the “coldest” position decreases the temperature. FIG. 1 does not illustrate the catheter  20  or distal tip  30  because these structures are covered by the guide sheath  35 . A cable  75  extending from the rear of handle  40  connects to a control box  80 , which functions as a power supply and a temperature monitor for the catheter assembly  70 . The catheter assembly  70  is attached to handle  40  via guide sheath  35 , through which catheter  20  may freely pass.  
         [0024]    With respect to FIG. 2, the catheter assembly  70  is depicted within a human artery  100  having unstable arterial plaque  105  within inflamed and unstable lipid pools  110  The material in these pools  110  can be congealed by application of heat and/or cold. This thickening or solidification will reduce the possibility of a sudden release of the dangerous plaque  105  from the lipid pool  110 .  
         [0025]    The lipid pool  110  is typically an entrapped volume between the interior vessel wall  112  and a layer of stable plaque  115  holding a pool of unstable plaque  105 . Lipid pools  110  containing arterial plaque  105  that becomes inflamed and unstable incur an increased risk of ulceration and rupture. When lipid pools  110  rupture, a blood clot typically forms which will likely grow and cause a myocardial infarction.  
         [0026]    In one embodiment of the present invention, the catheter assembly  70  is to be used as a heating/cooling apparatus for transforming inflamed and unstable liquid lipid pools  110  into stable or solidified, non-flowing lipid pools  110 , which are less likely to suffer a rupture. The catheter assembly  70  includes multi-temperature devices  120 , heat exchanger  130 , expander  140  and therapy plate  150  having temperature sensors  155 . In all of the embodiments and figures, multi-temperature device  120  may be, for example, a device which has both a heating and a cooling surface (e.g., a heating-cooling device) or a Peltier device. Likewise, any reference to a Peltier device in the description of the embodiments can be changed to a different kind of multi-temperature device. Preferably, the multi-temperature device  120  is a Peltier device. As depicted in FIGS.  3 A- 3 C, therapy plate  150  has a rounded tissue-contacting surface  160  to provide maximum surface area contact with internal artery wall  112 . Alternatively, the tissue-contacting surface  160  can be flat as depicted in FIG. 3D, or other shapes as required or desired.  
         [0027]    Importantly, lipid pools  110  containing inflamed and unstable plaque  105  have associated localized temperature variations of the interior blood vessel wall  112 . Temperature sensors  155  are used to sense localized temperature variations of the blood vessel wall  112  within human artery  100 . By detecting the presence of increased temperatures, the sensors  155  can anticipate the presence of lipid pools  110  containing inflamed and unstable plaque  105 , which have up to a two and a half degree increase in temperature.  
         [0028]    Preferably, the temperature sensors  155  comprises a plurality of thermistors  155  or thermocouples  155  located on the tissue-contacting surface  160  of the therapy plate  150  so that they can directly monitor tissue temperature. Additional temperature sensors  155  can be imbedded within the therapy plate  150  in order to more accurately monitor its temperature. The thermocouples  155  are electrically connected to the control box  80  by sensor leads (not shown), which extend through respective therapy plate through holes (not shown). Therapy plate  150  is preferably made of metal such as copper or silver, but can alternatively be made of any thermally conductive material.  
         [0029]    Multi-temperature devices  120  are small solid-state devices that typically operate as heat pumps and in this example embodiment, are Peltier devices. When a DC current of one polarity is supplied by control box  80  in one direction, heat is moved from the bottom side  200  of the Peltier devices  120  to top side  210 , where it must be removed with a heat sink. A “cold” bottom side  200  can be used to solidify or “freeze” inflamed and unstable lipid pools  110  located within artery  100 . If the current from control box  80  is reversed, the polarity of the Peltier devices  120  switches and bottom side  200  becomes the “hot” side. A “hot” bottom side  200  can be used to solidify inflamed and unstable lipid pools  110  by “cooking” the affected areas. The current can then be reversed to cool the affected area to reduce any thermal damage to the vessel walls  
         [0030]    With respect to FIG. 2, a layer of multi-temperature devices  120 , such as Peltier devices, is in thermal contact with therapy plate  150 , which is in direct contact with the interior surface of the vessel, which in this view is plaque  115 . Using temperature control  60 , a physician can adjust the electrical current supplied by control box  60  to power multi-temperature devices  120  and apply heat or cold to inflamed and unstable lipid pools through therapy plate  150 . Additionally, control box  60  has a read out of arterial wall temperature and therapy plate  150  temperature to aid the physician in regulating the current supplied to the multi-temperature devices  120  and thereby the regulating the provision of heat/cold to the vessel.  
         [0031]    In order to achieve a greater temperature differential, a plurality of multi-temperature devices  120  may be stacked on top of each other. The maximum difference in temperature of an individual device  120  is dependent on the magnitude of the electrical current and the temperature of the other side of the device  120 . By stacking additional devices  120  on top of each other, the maximum difference in temperature can be increased until the electrical dissipation overloads the thermal capabilities of the multi-temperature device  120 .  
         [0032]    With respect to FIG. 5, in the operation of a three-layer stacked multi-temperature device  500 , such as a Peltier device, for obtaining a cold surface, a first layer  510  has a number of devices  520  with “cold” side  530 . The “hot” side  540  of these devices  520  abuts a “cold” side  550  of a second layer  560  having more devices  570  than the first layer  510  in order to account for the additional energy caused by the inefficiency of the first layer  510  of devices  520 . The “hot” side  580  of the second layer  560  abuts “cold” side  590  of a third layer  600 . The third layer  600  consequently needs to have even more devices  610  in order to remove the thermal energy from “hot” side  620 . In other words, the devices  520  are stacked so the total temperature effect is cumulative.  
         [0033]    If the multi-temperature device  500  is used as a cooling device, the “hot” thermal energy from “hot” side  620  must be removed or dissipated. Conversely, if the multi-temperature device  500  is used as a heating device, the polarity of the device  500  is switched such that one side  530  produces “hot” thermal energy and other side  620  produces “cold” thermal energy, which must be removed or dissipated. Additional thermal energy due to the inefficiency of the multi-temperature device  500  will also have to be removed. Both the thermal and additional energy due to the inefficiency of the multi-temperature device  500  are preferably dissipated by heatsinking using the heat exchanger  130 .  
         [0034]    With respect to FIGS. 2, 3B and  3 D, heat exchanger  130  preferably is an elongated, thermally conductive cylinder having a circular aperture  210  for the circulation of blood and for the passage of catheter  20 , but may be formed in other configurations. The aperture  210  could be, for example, an elliptical, oval, rectangular, or other shaped aperture. Also preferably, heat exchanger  130  is made of metal such as copper or silver, but can alternatively be made of any thermally conductive material. Heatsinking is best accomplished by using the blood circulating through aperture  210  of heat exchanger  130  to carry the undesired energy away. Alternatively, heatsinking or removing unwanted thermal energy may be achieved by circulating a cold media such as water or gas through the heat exchanger  130 .  
         [0035]    With respect to FIGS. 3A and 3C, the heat exchanger  130  can consist of several alternative configurations. Referring to FIG. 3A, a plurality of starburst fins  220  surround the internal perimeter of circular aperture  210 . These fins  220  are integral with heat exchanger  130  and made with the same or different thermally conductive material such that the surface area for conducting the undesired thermal energy is significantly increased. FIG. 3C depicts an alternative embodiment for a heat exchanger  130 , which has a serrated blood-contacting surface  230  having a plurality of recesses for increased surface area contact and enhanced heat conducted to the blood stream. Increased surface area allows more unwanted thermal energy to be transferred away from the therapy plate.  
         [0036]    With respect to FIGS. 2 and 3A- 3 D, the catheter assembly  70  may include expander  140 , if desired, for correctly positioning the therapy plate  150  against the plaque on the artery wall  112 . The expander is preferably a balloon  140  that is capable of expansion from a first collapsed configuration as shown in FIGS. 3A and 3C to a second, expanded configuration as shown in FIGS. 2, 3B and  3 D. Balloon  140  is elastic and inflatable with fluid such as saline, air, CO 2 , or another fluid through inflation lumen (not shown) extending through guide sheath  35 . In use, the catheter assembly  70  is inserted and advanced in the blood vessel  100  while in the collapsed configuration. At predetermined locations, the catheter assembly  70  is stopped and balloon  140  is inflated to the expanded configuration pressing therapy plate  150  against artery wall  112 . Temperature sensors  155  detect areas of inflamed and unstable plaque  105  by detecting increased temperatures. Once these areas are identified, the catheter assembly  70  is used to stabilize the plaque by heating and/or cooling the affected areas.  
         [0037]    The congealed or solidified plaque resultant from the procedure can either be left in place if stable or removed by procedures such as atherectomy. Atherectomy type catheters are used to remove material from the blood vessel walls and therefor remove the congealed or non-fluid material before it causes a blockage. These catheters have a rotating blade that cuts the material to be removed from the vessel wall and captures it inside a cylinder ahead of the rotating blade. Performing atherectomy on solidified plaque is far less dangerous than when the plaque is in liquid form because the possibility of toxic fluid leaking out, mixing with the blood stream and forming a blood clot has been significantly reduced.  
         [0038]    In the alternative embodiment shown in FIG. 4, a catheter assembly  300  includes a conventional Peltier diode  310  associated with an electrode  320  on the distal tip  30  of catheter  20 , which is also electrically coupled by wire  330  to the control box  80 . The materials of the diode  310  are preferably complex alloys, one doped “p” and the other doped “n”, creating a diode junction. An applied voltage potential passes current from a control box  80  through the junction. The polarity of the voltage creates a “cold” side  340  of the diode  310 , which is coupled in thermal conductive contact to the electrode  320 , and, a “hot” side  350  of the diode  310 , which is coupled in thermal conductive contact to a heat exchanger  360 . The heat exchanger  360  can be carried on the catheter  20  away from the electrode  320  and in contact with the blood pool.  
         [0039]    The passage of current through the diode  310  creates a heat pump action from cold side  340  to hot side  350 , conducting heat energy from the thermal mass of the electrode  320  to the heat exchanger  360 . Heat energy can thus be transferred from the thermal mass of the electrode to cool it. Conversely, the polarity of the diode  310  can be reversed so that heat energy is transferred to the thermal mass of the therapy plate to heat it.  
         [0040]    Any one or more of the features depicted in FIGS.  1 - 4 , or described in the accompanying text, may be interchanged with that of another figure to form still other embodiments.  
         [0041]    While preferred embodiments and methods have been shown and described, it will be apparent to one of ordinary skill in the art that numerous alterations may be made without departing from the spirit or scope of the invention. Therefore, the invention is not limited except in accordance with the following claims.