Patent Publication Number: US-8123741-B2

Title: Treating internal body tissue

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application is a continuation of U.S. patent application Ser. No. 11/082,677 filed on Mar. 17, 2005 by Marrouche et al., now U.S. Pat. No. 7,674,256, the contents of which are fully incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     This document relates to treating internal body tissue, such as ablating heart tissue. 
     BACKGROUND 
     A normal heart beat initiates at the sinoatrial node, located proximal the right atrium of the heart. The sinoatrial node causes electrical impulses to spread through the right and left atria, which in turn causes the atria to contract. The impulses travel to the atrioventricular node and then through the walls of the ventricles, thereby causing the ventricles to contract. Such contractions force blood out of the heart to the lungs and body. When the heart operates under a regular pattern of electrical impulses, the heart beats at a generally constant rhythm—filling with blood and contracting in a normal fashion. 
     Atrial fibrillation is a common source of irregular heart rhythms. It affects millions of people in the United States, and thousand of new cases of atrial fibrillation are diagnosed each year. When a patient suffers from atrial fibrillation, irregular electrical impulses begin and spread through the atria. The resulting rhythm is disorganized and inconsistent. The atria do not contract in a regular rhythm because the impulses are traveling through the atria in a disorderly fashion. 
     Patients who suffer from atrial fibrillation may experience various symptoms, such as heart palpitations, a lack of energy, dizziness, chest pains, pressure or discomfort in the chest, and breathing difficulty. Some people may have atrial fibrillation without exhibiting any symptoms at all, but chronic atrial fibrillation can result in future problems including blood clotting (increased risk of suffering a stroke) and heart failure. 
     Various options may be used to treat atrial fibrillation and to restore normal heart rhythm. For example, a patient with atrial fibrillation may receive medications or a pacemaker device to prevent blood clots and control the heart rate. In some circumstances, heart surgery may be performed to treat atrial fibrillation. For example, the Cox-Maze procedure is a surgery that may require an incision in the patient&#39;s sternum, and in many instances, requires a heart-lung machine to oxygenate and circulate the blood during surgery. 
     Another treatment option is catheter ablation therapy. For example, a catheter may be used to perform pulmonary vein isolation ablation, in which a circular balloon at the tip of the catheter is inserted into the pulmonary vein. Material in the balloon at the tip of the catheter is then heated to ablate tissue inside the pulmonary vein. A circular scar is formed in the pulmonary vein as an attempt to create a conduction block to stop passage of irregular impulses firing from within the pulmonary vein. Forming the scar tissue inside the pulmonary vein is not always successful at preventing atrial fibrillation. 
     The design of the catheter ablation device has an effect on the success rate of the catheter ablation procedures. One factor that affects the design of the catheter ablation device is the efficacy of delivering the ablating energy. If, for example, the catheter device is improperly sized or unable to adjust to the contours of the target tissue, some portion of the target tissue may remain after the ablating procedure. The living tissue may not block the irregular impulses from the pulmonary vein to the atrium, thus permitting future occurrences of atrial fibrillation. 
     Another factor that affects the design of the catheter ablation device is the isolation of the ablating energy. If, for example, the catheter ablation device does not properly isolate the ablating energy to the target tissue or delivers excess energy, some live tissue in a non-targeted area may be unnecessarily destroyed. In such circumstances, the catheter ablation procedure may cause pulmonary vein stenosis (a narrowing of the passageway), which may result in more serious cardiovascular problems for the patient. 
     SUMMARY 
     Some embodiments of the invention relate to a device for treating atrial fibrillation. In certain embodiments, the device is capable of causing scar tissue to form in ostial areas of the atrium rather than inside the pulmonary vein. In such embodiments, the device may include a tissue treatment member that is operable to form an annular area of ablated tissue along the outer portion of the ostium in an area known as the antrum. 
     A number of embodiments include a system to treat tissue internal to a body. The system includes an elongate member having a proximal portion, a distal portion, and at least one lumen extending therethrough. The system further includes a tissue treatment member disposed at the distal portion of the elongate member. The tissue treatment member is in fluid communication with the lumen. Also, the system includes an anchor member adjustably engaged with the tissue treatment member. When the anchor member is disposed distally of the tissue treatment member and disposed in a position at least partially in a pulmonary vein, the tissue treatment member is annularly adjustable relative to the position of the anchor member so as to contact an ostial area. 
     Certain embodiments include a system for treating tissue internal to a body. The system includes a catheter assembly having a distal end and a proximal end, and an anchor member disposed near the distal end of the catheter assembly. The anchor member is configured to be received in a pulmonary vein. The system also includes a thermal treatment device engaged with the catheter assembly proximally of the anchor member. The system further includes a steering mechanism disposed at least in part between the anchor member and the thermal treatment device to cause the thermal treatment device to contact one or more ostial areas. 
     Some embodiments include a method of treating tissue internal to a body. The method includes directing an anchor member at least partially into a pulmonary vein and securing at least a portion of the anchor member to the pulmonary vein. The method further includes directing a tissue treatment member toward an ostium proximate an atrium and the pulmonary vein. Also, the method includes annularly adjusting the tissue treatment member relative to the position of the anchor member so as to treat tissue at an ostial area proximate the atrium and the pulmonary vein. 
     These and other embodiments may be configured to provide one or more of the following advantages. First, atrial fibrillation may be treated by forming an annular conduction block area along the outer portion of the ostium in an area known as the antrum. By causing scar tissue to form in ostial areas of the atrium rather than in the pulmonary vein, the likelihood of preventing atrial fibrillation may be increased. Second, the tissue treatment member may be used independent of the ostium size near the target site. Even if the tissue treatment member is substantially smaller than the targeted ostial area, it may be adjusted relative to the anchor member to contact the targeted ostial areas. Third, in embodiments where the anchor member can be secured at various locations inside the pulmonary vein, the tissue treatment member can be directed to the ideal ostial area locations. Fourth, in some embodiments where the tissue treatment member uses cryo ablation technology, an annular lesion may be formed in the antrum with as few as one to five cryo lesions, thereby reducing the time required to perform the medical operation. Some or all of these and other advantages may be provided by the embodiments described herein. 
     The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  is a cross-sectional view of a portion of a system for treatment of tissue internal to a body. 
         FIGS. 2A-B  are views of a cross-section of a heart with a portion of the system of  FIG. 1  disposed in the heart. 
         FIG. 3  is a cross-sectional view of a portion of the system of  FIG. 1  disposed in the heart. 
         FIG. 4  is a cross-sectional view of certain components of a system proximal to heart tissue. 
         FIG. 5  is a cross-sectional view of certain components of the system of  FIG. 4 . 
         FIG. 6  is a cross-sectional view of certain components of the system of  FIG. 4 . 
         FIG. 7  is a cross-sectional view of certain components of the system of  FIG. 4 . 
         FIG. 8  is a cross-sectional view of certain components of a system proximal to heart tissue. 
         FIG. 9  is a cross-sectional view of certain components of the system of  FIG. 8 . 
     
    
    
     Like reference symbols in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , a system  100  to treat tissue internal to a body includes an anchor member  210  disposed distally of a tissue treatment member  300 . A steerable portion  250  is disposed between the anchor member  210  and the tissue treatment member  300  so that the tissue treatment member  300  is adjustable relative to the anchor member  210 . The system  100  may include a number of tools at a proximal portion  110  that remain external of a patient&#39;s body when in use. Each of the tools at the proximal portion  110  may be used by a medical practitioner to perform various functions at a distal portion  120  of the system  100 . Each of the tools may be coupled to one or more associated lumens in the system  100  using one or more manifolds (not shown in  FIG. 1 ) at the proximal portion  110 . For the purpose of the following discussion, the depicted embodiments are directed to a system  100  that is particularly suitable for pulmonary vein isolation ablation or other similar treatments. However, with some modifications in construction, the system  100  may be used for other medical applications not fully discussed herein 
     In some embodiments, an anchor device  200  includes an anchor member  210  that is disposed at a distal end of an anchor catheter  220 . The anchor member  210  may include an expandable structure, such as a balloon, that is capable of expanding to press against a vein wall. For example, a saline solution may be forced into the anchor member to cause expansion of the balloon structure. Other inflation fluids may also be used, including liquids and gases. 
     The anchor catheter  220  may include a wall to define an inflation lumen  222  that extends from the proximal portion  110  to the distal portion of the system  100 . The inflation lumen  222  is in fluid communication with balloon  210  such that a pressure source, like a plunger disposed in a chamber or a pump device, may deliver pressurized fluid (e.g., saline solution) to expand the balloon  210 . In certain embodiments, the pressure source  224  may be in fluid communication with the inflation lumen  222  via a manifold (not shown in  FIG. 1 ) disposed at the proximal portion  110  of the system  100 . 
     Still referring to  FIG. 1 , in embodiments in which the anchor member  210  includes a balloon, the anchor balloon  210  may include one of a number of constructions. The material of the anchor balloon  210  may be selected from polymers including, but not limited to, polyolefin copolymer, polyester, polyethylene teraphthalate, polyethylene, polyether-block-amide, polyamide, polyimide, nylon, latex and urethane. The anchor balloon  210  may be made by blow molding a polymer extrusion into the desired shape. In some embodiments, the anchor balloon  210  may be constructed to expand to the desired shape when pressurized, but the balloon  210  will not elastically deform substantially beyond the desired shape. A number of ancillary processes may be used to affect the material properties of the anchor balloon  210 . For example, the polymer extrusion may be exposed to gamma radiation which alters the polymer infrastructure to provide uniform expansion during blow molding and additional burst strength when in use. In addition, the molded balloon  210  may be exposed to a low temperature plasma field which alters the surface properties of the balloon  210  to provide enhanced adhesion characteristics. Those skilled in the art will recognize that other materials and manufacturing processes may be used to provide a balloon  210  suitable for use with the system  100 . 
     In some embodiments, the anchor catheter  220  may include a guide wire lumen  232  that extends from the proximal portion  110  to the distal portion  120 . The guide wire lumen  232  may be adjacent to the inflation lumen  222 , as shown in  FIG. 1 . In this embodiment, the guide wire lumen  232  includes a tubular wall  234  that extends through the catheter  220  and the balloon  210  such that the anchor device  200  may slidably pass over a wire structure that is disposed in the guide wire lumen  232 . As such, the anchor member  210  (e.g., anchor balloon) may be guided to a target site internal to a body by sliding the anchor device  200  over a guide wire  252  that was previously directed to the target site. A marker band  235  may be attached to the tubular wall  234  in the balloon  210  so that the position of the balloon  210  in the patient&#39;s body may be visualized using known imaging techniques. 
     In this embodiment, an over-the-wire manifold (not shown in  FIG. 1 ) may be coupled to the guide wire lumen  232  at the proximal portion  110  of the system  100  so that a guide wire instrument  252  can be controlled and adjusted at the proximal portion  110 . For example, the guide wire instrument  252  may be coupled with a handle member  254  that may be grasped by a physician near the proximal portion  110  so that the guide wire instrument  252  may be slidably adjusted relative to the anchor device  200  at the distal portion  120 . Such a handle member  254  allows the treating physician to more easily grip and manipulate the guide wire instrument  252 . Optionally, the manifold may also incorporate a strain relief device (not shown in  FIG. 1 ) to reduce the likelihood of kinking the guide wire instrument  252 . 
     While the embodiment depicted in  FIG. 1  shows a construction in which the guide wire lumen  232  is adjacent to the inflation lumen  232 , it is also contemplated that a coaxial construction or other appropriate arrangement may be used. In the coaxial construction, the guide wire lumen  232  would extend inside the inflation lumen  222 . The inflation lumen  222  would have a larger relative diameter than the non-coaxial embodiment so as to accommodate the tubular wall around the guide wire lumen  232 . A support connection may be desired between the tubular wall around guide wire lumen  232  and the wall around the inflation lumen  222  that would prevent relative longitudinal movement therebetween while allowing an inflation fluid to pass through. 
     Still referring to  FIG. 1 , the tissue treatment member  300  is disposed near a distal end of an elongate member  310  that extends from the proximal portion  110  of the system  100  to the distal portion  120 . In some embodiments, the tissue treatment member  300  includes a cryo ablation device that is capable of contacting an ostial area near a pulmonary vein. In such embodiments, the tissue treatment member  300  may have an one or more balloons adapted to deliver cryo treatment to nearby tissue—similar to certain features of particular embodiments described in U.S. Pat. No. 5,868,735 to Lafontaine, which is incorporated herein by reference. The tissue treatment member  300  may also include a guide lumen  312  through which the anchor device  200  (and the guide wire instrument  252  therein) may pass. While the embodiment depicted in  FIG. 1  shows a construction for use in cryo ablation therapy, it is contemplated that other embodiments may include a tissue treatment member having a construction for use with RF energy ablation. For example, a tissue treatment member  300  may include a single balloon having electrodes disposed therein and being expandable with application of a chemical solution that can be heated using RF energy. 
     In the embodiment shown in  FIG. 1 , the elongate member  310  has one or more lumens extending therethrough, each of which may be coupled to an associated manifold (not shown in  FIG. 1 ) at the proximal portion  110 . For example, the elongate member  310  may include a catheter that has a plurality of coaxial lumens—a vacuum lumen  322  in fluid communication with an external balloon  320  and has a guide lumen  312  that permits the tissue treatment member  300  to be slidably engaged with the anchor catheter  220 . The vacuum lumen  322  is in fluid communication with the external balloon  320  such that a vacuum source  324 , such as a plunger disposed in a chamber or a vacuum pump device, may withdraw fluid from a safety chamber  321  in the external balloon  320 . The vacuum source  324  may be in fluid communication with the vacuum lumen  322  via a manifold (not shown in  FIG. 1 ) disposed at the proximal portion  110  of the system  100 . The safety chamber  321  may be defined by the external balloon  320  and may be sized to fit over the internal balloon  350  when coolant is cycled through the coolant chamber  351  (described in more detail below). For example, the safety chamber  321  may be evacuated by application of a vacuum from the vacuum source  324 . When the coolant material is cycled through the coolant chamber  351  to inflate the internal balloon  350 , the external balloon  320  may inflate with the internal balloon  350 . (The gap between the external balloon  320  and the internal balloon  350  is shown in  FIG. 1  for illustrative purposes only. It should be understood that at least a portion of the external balloon  320  may contact the internal balloon  320  when the safety chamber  321  is evacuated by application of a vacuum.) The external balloon  320  provides a safety feature to reduce the likelihood of coolant seeping into the patient&#39;s body in the event that the internal balloon  350  breaks or otherwise permits coolant to leak from the coolant chamber  351 . If coolant leaks from the coolant chamber  351 , the leaked coolant material would be evacuated from the safety chamber  321  by application of the vacuum force. 
     The guide lumen  312  may be configured to slidably engage the outer surface of the anchor catheter  220 . The guide lumen  312  includes a tubular wall  314  that passes through the tissue treatment member  300  such that a portion of the anchor catheter  220  and the anchor member  210  (e.g., anchor balloon) may be disposed distally from an open end of the guide lumen  312 . A marker band  315  may be attached to the tubular wall  314  in the tissue treatment member  300  so that the position of the tissue treatment member  300  in the patient&#39;s body may be visualized using known imaging techniques. While the embodiment depicted in  FIG. 1  shows a construction in which the vacuum lumen  322  is coaxial with the guide lumen  312 , it should be understood other embodiments may include an vacuum lumen  322  that is adjacent to the guide lumen  312 . 
     Still referring to  FIG. 1 , the elongated member  310  may include an input lumen  352  and an output lumen  356  that are in fluid communication with an internal balloon  350 . The input lumen  352  may be defined by an intake tube  353  that extends from the internal balloon  350  to the proximal portion  110  of the system  100 . Similarly, the output lumen  356  may be defined by an exhaust tube  357  that extends from the internal balloon  350  to the proximal portion  110  of the system  100 . In some embodiments, the distal orifice of the intake tube  353  may have a smaller diameter than the distal orifice of the exhaust tube  357 , which can facilitate proper control of the coolant material during cryo ablation procedures. The input lumen  252  is in fluid communication with a valve  354   a  near the proximate portion  110  of the system  100 . The valve  354   a  is coupled to a coolant source  354   b , which may include a refrigeration unit for controlling the temperature of the coolant. A proximal end of the output lumen  356  can be in fluid communication with the coolant source  354   b  for purposes of recycling the coolant material. Alternatively, the proximal end of the output lumen  356  can be in fluid communication with a drain for disposal of the cycled coolant. In some alternative embodiments, the input and output lumens  352  and  356  may have a coaxial construction. In such embodiments, the input and output lumens may be coaxially disposed around the guide lumen  312 . 
     In some embodiments using cryo ablation technology, the internal balloon  350  defines a coolant chamber  351  where a coolant material may be cycled. The chamber  351  may be sized such that coolant material input from the intake tube  353  evaporates in whole or in part in the chamber  351  before exiting through the exhaust tube  357 . The internal balloon  350  may expand to a desired shape when pressurized, but will not elastically deform substantially beyond the desired shape. The material of the internal balloon  350  and the external balloon  320  may vary depending on the coolant type and the conditions within the cooling chamber. In some embodiments, the internal and external balloons  350  and  320  may comprise a polymer material, such as polyolefin copolymer, polyester, polyethylene teraphthalate, polyethylene, polyether-block-amide, polyamide, polyimide, nylon, latex, or urethane. For example, certain embodiments of the tissue treatment member  300  may include an internal balloon  350  comprising PEBAX® 7033 material (70D poly ether amide block). In such examples, the external balloon  320  may also comprise the PEBAX® 7033 material or another appropriate material. 
     The coolant material that is cycled into the coolant chamber  351  is one that will provide the appropriate heat transfer characteristics consistent with the goals of treatment. In some embodiments, liquid N 2 O can be used as a cryogenic fluid. When liquid N 2 O is used in the tissue treatment member  300 , it can be transported to the coolant chamber  351  in the liquid phase where it evaporates at the orifice of intake tube  353  and exits through the exhaust tube  357  in the gaseous state. Other embodiments of the tissue treatment member  300  may use Freon, Argon gas, and CO 2  gas as coolants. Further yet, some embodiments of the tissue treatment member  300  may use coolants (which would enter and exit the coolant chamber  351  as a liquid), such as Fluisol, or a mixture of saline solution and ethanol. 
     Optionally, the temperature of the tissue treatment member  300  can be monitored by thermo-resistive sensors (not shown in  FIG. 1 ) proximate to the external balloon  320 , the internal balloon  350 , or both. As described in the previously referenced U.S. Pat. No. 5,868,735 to Lafontaine, the temperature can be monitored either absolutely with pre-calibrated sensors and/or relatively between two or more sensors. Depending on the treatment goals and monitored temperature, the flow rate of the coolant into the catheter can be adjusted to raise or lower the temperature of the tissue treatment member  300 . 
     Still referring to  FIG. 1 , the system  100  includes a steerable portion  250  disposed between the tissue treatment member  300  and anchor member  210 . The steerable portion  250  permits the tissue treatment member  300  to be adjusted relative to the distally positioned anchor member  210 . The steerable portion  250  may include various mechanisms to adjust the position of the tissue treatment member  300  relative to the anchor member  210 . For example, the steerable portion  250  may include a shape memory element  255  that is movably or fixedly engaged with the anchor device  200 , the tissue treatment member  300 , or both. The shape memory element  255  may be pre-formed to have a curved portion  256  such that when the shape memory element  255  is rotated, the tissue treatment member  300  is adjusted annularly relative to the anchor member  210 . The pre-formed shape memory element may comprise a superelastic Nitnol material that was exposed to austenitic/martensite processing. In an alternative example, the steerable portion  250  may include one or more pull wires that are operated at the proximal portion  110  of the system  100  to control the position of the tissue treatment member  300  relative to the anchor member  210 . 
     In addition, multiple elongate shape memory members may be attached to the walls of the steerable portion  250  at locations in which it is desired to shorten the walls. For example, such element may be placed at the same longitudinal location, and spaced around the periphery guide wire instrument  252  or the anchor catheter  220 . In some embodiments, three shape memory wires may be spaced around the periphery of the guide wire instrument  252  at 120-degree separations, which would permit any one or two of those three wires to be shortened (e.g., by applying an electrical charge to the shape memory material) so as to adjust the tissue treatment member  300  relative to the anchor member  210 . In another example, the shape memory elements may be positioned at multiple longitudinal locations along the guide wire instrument  252  so as to bend the instrument in multiple directions. In such embodiments, the shape memory elements may be wires that shorten when subjected to an electric current, and which elongated when the current is removed so that controlled application of electrical current may provide steering control. 
     Referring now to  FIGS. 2A-B , some embodiments of the system  100  may be configured to ablate tissue in a heart  400 . In such embodiments, the tissue treatment member  300  may be directed to ostial areas proximate the left atrium  402  outside a pulmonary vein  405 . In the depicted embodiment, the anchor member  210  may include an expandable balloon. As described in more detail below in connection with  FIG. 3 , the anchor balloon  210  of the anchor device  200  may be sized to press against a wall  410  of a pulmonary vein  405 . The anchor balloon  210  is sized to fit in a pulmonary vein  405  and to expand to a desired shape to press against a wall  410  of the pulmonary vein  405 . As such, the tissue treatment member  300  may be disposed outside of the pulmonary vein  405  and may be biased against an ostial area in the left atrium  402 . For example, the tissue treatment member  300  may be in contact with an outer ostial area in the left atrium  402  known as the antrum. When the coolant is cycled into the chamber  351  ( FIG. 1 ), heat transfer may occur between the contacted ostial area and the tissue treatment member  300 . Such heat transfer may cause ablation of tissue cells proximate the ostial area, as described in more detail below. 
     As shown in  FIGS. 2A-B , when a particular ostial area has been ablated by the tissue treatment member  300 , the steerable portion  250  may provide the proper guidance to adjust the tissue treatment member  300  to another ostial area so as to form an annular area of ablated tissue along the ostium. The tissue treatment member  300  may be adjusted relative to the anchor balloon  210  as described below in connection with  FIG. 3 . Because the tissue treatment member  300  can be adjusted relative to the anchor member  210  in the pulmonary vein  405 , the system  100  may perform catheter ablation therapy independent of the ostium size in the left atrium  402 . For example, if an outer diameter of the tissue treatment member  300  is 22-mm, the system  100  may be used during PV isolation treatment to form an annular area of ablated tissue along an ostium having a diameter of 20-mm, 30-mm, 40-mm, or greater. A physician is not required to use a larger size of tissue treatment member  300  in order to treat tissue in a relatively larger-sized ostium. Furthermore, because the anchor balloon  210  can be secured at various depths in the pulmonary vein  405 , the tissue treatment member  300  can be directed to the desired ostium location even if the ostium is of a relatively small or relatively large size. 
     Referring now to  FIG. 3 , the anchor balloon  210  of the anchor device  200  may be configured to fit inside a vessel, such as a pulmonary vein  405 , and expand to a desired shape to press against a wall  410  of the vessel. In this embodiment, the steerable portion  250  is disposed between the tissue treatment member  300  and the anchor balloon  210 . As such, the tissue treatment member  300  may be disposed outside of the pulmonary vein  405  and biased against an area  455  of the ostium  450 . When the coolant is cycled into the chamber  351 , heat transfer may occur between the contacted ostial area  455  and the tissue treatment member  300 . Such heat transfer may cause ablation of tissue cells proximate the ostial area  455  in the left atrium  402 . In cases in which the tissue treatment member  300  is not large enough to contact the entire ostium  450 , the system&#39;s steerable portion  250  may provide the proper guidance to adjust the tissue treatment member  300  to a second ostial area  456  of the ostium  450  so as to form an annular area of ablated tissue along the ostium  450 . 
     As previously described, the steerable portion  250  may include a shape memory element  255  that includes a pre-formed curved portion  256 . The shape memory element  255  may be integral with the guide wire instrument  252 , and in some embodiments, the entire length of the guide wire instrument  252  may comprise a shape memory material. Because pre-formed curved portion  256  comprises only a relatively small portion of the guide wire instrument  252 , some embodiments may include a guide wire instrument that is not comprised of a shape memory material along its entire length. For example, in the embodiment shown in  FIGS. 1 and 3 , the guide wire instrument  252  includes a shape memory element  255  that is joined at a distal end of a flexible wire  253  comprising a metal or polymer material. 
     Still referring to  FIG. 3 , when the targeted tissue in the first ostial area  455  is sufficiently ablated by the tissue treatment member  300 , the physician may apply a torque to the guide wire instrument  252  at the proximal portion  110  ( FIG. 1 ). The torque may be applied, for example, by grasping and rotating the handle member  254  ( FIG. 1 ) at the proximal portion  110 . Such action causes the guide wire instrument  252  (including the shape memory element  255  at the distal portion of the instrument  252 ) to rotate in the guide wire lumen  232  of the anchor device  200 . In this embodiment, rotation of the shape memory element  255  causes the tissue treatment member  300  to shift with a substantially annular motion  301  relative to the anchor member  210  (e.g., anchor balloon). As such, the steerable portion  250  can provide the proper guidance to adjust the tissue treatment member  300  relative to the anchor member  210  to form an annular area of ablated tissue along the ostium  450 . In many cases, the annular area may be formed using one to five cryo lesion ablations, and sometimes only one to three cryo lesion ablations, from the tissue treatment member  300 . Such cryo lesion ablations, for example, can be formed by contacting the tissue treatment member  300  for approximately 30 to 120 seconds, depending on coolant material in the chamber  351 , the conditions in the patient&#39;s body, and other factors. 
     By forming an annular area of ablated tissue along the ostium  450  (rather than inside the pulmonary vein  405 ), the catheter ablation therapy may be more effective in treating atrial fibrillation. The annular area of ablated tissue may form an annular scar along the ostium  450 , thereby creating a conduction block to stop passage of irregular impulses from within the pulmonary veins to the heart wall. Furthermore, because the steerable portion  250  can be used to adjust the tissue treatment member  300  relative to the anchor member  210 , the tissue treatment member  300  may form an annular area of ablated tissue along an outer portion of the ostium  450  known as the antrum. It is believed that, in some cases, forming an annular scar along the antrum is more effective in preventing future occurrences of atrial fibrillation. Some embodiments of the system  100  permit adjustment of the tissue treatment member  300  to form such an annular area of ablated tissue along the antrum even if the antrum is substantially larger than the tissue treatment member  300 . 
     In operation, the system  100  may be directed to the targeted internal body tissue in stages. For example, the anchor device  200  may be directed to a location proximate the targeted tissue, such as through the left atrium and inside the pulmonary vein, before the tissue treatment member  300  is guided over the anchor catheter  220 . Alternatively, the tissue treatment member  300  may be directed to a location proximate the targeted tissue, such as inside the left atrium, before the anchor device  200  is guided through the guide lumen  312  of the tissue treatment member  300  toward the pulmonary vein. 
     Referring to  FIG. 4 , some embodiments of the system  100  may include a guide wire instrument  252  that is directed from a proximal portion  110  outside of the patient&#39;s body to a location proximate the targeted tissue, such as through the left atrium  402  and into the pulmonary vein  405 . In these embodiments, the guide wire instrument  252  may provide guidance for other instruments that are subsequently directed toward the targeted tissue. In certain embodiments, the guide wire instrument  252  may include an atraumatic tip or a soft, flexible portion at its distal end. Such a tip may facilitate steering and guiding of the guide wire instrument  252  through the various vessels inside the patient&#39;s body. For example, the guide wire instrument  252  may be directed from a vein in the patient&#39;s leg toward the heart  400 , where the guide wire instrument  252  passes from the right atrium, through the atrial septum, and into the left atrium  404 . 
     As previously described, the guide wire instrument may include a shape memory element  255 . The shape memory element  255  may extend along the entire length of the guide wire instrument or, as shown in  FIG. 4 , may extend from a distal end of a flexible wire  253  comprising a metal or polymer material. The shape memory element  255  includes a pre-formed curved portion  256  that may be constrained to a substantially straightened shape during guidance of the guide wire instrument  252  through the body. For example, the curved portion  256  may be disposed in a thin-walled sheath  257 , such as a hypotube, to constrain the shape memory element  255  into a substantially straightened shape. The sheath  257  may be slidably engaged with at least a portion of shape memory element  255  such that the sheath may retract in a proximal direction away from the curved portion  256  when the guide wire instrument  252  reaches the desired location in the patient&#39;s body. The retraction of the sheath  257  may be control by a physician at the proximal portion  110  ( FIG. 1 ) of the system  100 . 
     Referring now to  FIG. 5 , the anchor device  200  may be directed over the guide wire instrument  252  toward the desired location, such as the pulmonary vein  405 . As previously described, the anchor device  200  includes a guide wire lumen  232  through which the guide wire instrument  252  may pass. At the proximal portion  110  ( FIG. 1 ), the tubular wall  234  of the guide wire lumen  232  may be directed over the guide wire instrument  252 . From there, the anchor device  200  may be forced to slide over the guide wire instrument  252  through the left atrium  402  and into the pulmonary vein  405 . In some embodiments, the sheath  257  ( FIG. 4 ) may remain over the curved portion  256  until after the anchor member  210  is guided into the pulmonary vein  405 . The marker band  235  may be used to visualized the location of the anchor member  210  in the pulmonary vein  405 . When the anchor member  210  is properly positioned in the pulmonary vein  405 , the pressure source  224  ( FIG. 1 ) may deliver pressurized fluid (e.g., saline solution) through the inflation lumen  222  to expand the anchor balloon  210 . In this embodiment, the anchor member  210  includes an expandable balloon. When expanded to its pressurized shape, the anchor balloon  210  presses against the wall  410  of the pulmonary vein  405  to secure its position in the pulmonary vein  405 . 
     Referring to  FIG. 6 , when the anchor device  200  is properly secured in the pulmonary vein  405 , the sheath  257  may be retracted from the curved portion  256  of the shape memory element  255 . The shape memory element  255  may then return to its pre-formed curved shape when no longer constrained by the sheath  257 . The sheath  257  need only be retracted to a position that permits the curved portion  256  to return to its biased shape. In this embodiment, the sheath  257  is retracted to a position over the flexible wire  253  and just proximal of the shape memory element  255 . At least a portion of the sheath  257  that extends over the curved portion  256  may be rigid enough to constrain the shape memory element  255 . The portions of the tubular wall  234  and the anchor catheter  220  that are disposed over the curved portion  256  may be substantially less rigid than the rigid portion of the sheath  257 . As such, those portions of the tubular wall  234  and the catheter  220  deform to one or more curves that are somewhat similar to the curved portion  256 . 
     In some embodiments, the shape memory element  255  may also include a second curved portion  259  that is generally distal of the anchor balloon  210 . The second curved portion  259  may curved away from the distal opening of the tubular wall  234  when the sheath  257  no longer constrains the second curved portion  259 . In these embodiments, the second curved portion  259  may serve to hinder the guide wire instrument  252  (including the shape memory element  255 ) from shifting in a proximal direction relative to the anchoring balloon  210 . In other embodiments, the distal end of the guide wire instrument  252  may include a distal tip that is larger than the distal opening of the tubular wall  234  so that the distal tip is prevented from shifting proximally relative to the anchoring balloon  210 . Alternatively, the guide wire instrument  252  may remain in slidable engagement with the tubular wall  234  such that the distal end of the guide wire instrument  252  is permitted to shift in a proximal or distal direction relative to the anchoring balloon  210 . 
     Referring to  FIG. 7 , the tissue treatment member  300  may be directed over the outer surface of the anchor catheter  220  toward the desired location, such as the left atrium  402 . The curved portion  256  of the shape memory element  255  may bias the anchor catheter  220  toward an ostial area  455  in the left atrium  402 . When the tissue treatment member  300  approaches the steerable portion  250  of the system  100 , the tissue treatment member  300  may be guided proximate to the ostial area  455 . The position of the tissue treatment member  300  may be visualized by a physician using the marker band  315  and known imaging techniques. After the tissue treatment member  300  is guided to the proper position, the coolant material may be cycled through the coolant chamber  351  (e.g., through intake and exhaust tubes  353  and  357 ) while a vacuum is applied to the safety chamber  321 . The tissue treatment member  300  may be directed over the anchor catheter  210  (and the guide wire instrument  252  therein) so as to contact the ostial area  455 . For example, a physician may grasp an outer surface  305  of the elongate member  310  (or a handle member attached thereto) at the proximal portion  110  ( FIG. 1 ) of the system  100  and then force the tissue treatment member  300  to press against the ostial area  455 . The heat transfer that occurs between the ostial area  455  and the tissue treatment member  300  may cause ablation of the tissue proximate the ostial area  455 . 
     As previously described in connection with  FIG. 3 , when the targeted tissue in the first ostial area  455  is sufficiently ablated by the tissue treatment member  300 , the physician may apply a torque to the guide wire instrument  252  at the proximal portion  110  ( FIG. 1 ). Such action causes the guide wire instrument  252  (including the shape memory element  255  at the distal portion of the instrument  252 ) to rotate in the guide wire lumen  232  of the anchor device  200 , which may cause the tissue treatment member  300  to shift with a substantially annular motion relative to the anchor member  210 . As such, the steerable portion  250  can provide the proper guidance to adjust the tissue treatment member  300  relative to the anchor member  210  to form an annular area of ablated tissue along the ostium  450 . Forming an annular area of ablated tissue along the ostium  450  (rather than inside the pulmonary vein  405 ) may be more effective at treating atrial fibrillation. Furthermore, because the steerable portion  250  can be used to adjust the tissue treatment member  300  relative to the anchor member  210 , the tissue treatment member  300  may form an annular area of ablated tissue along an outer portion of the ostium  450  known as the antrum. It is believed that, in some cases, forming an annular scar along this outer ostial area known as the antrum is more effective in preventing future occurrences of atrial fibrillation. 
     Referring now to  FIGS. 8-9 , some embodiments of the system may include a tissue treatment member  300  that is delivered to the desired location inside the patient&#39;s body before the anchor device. In such embodiments, the anchor device may pass through the guide lumen  312  of the tissue treatment member  300 . Also in such embodiments, the steerable portion may be coupled to the anchor device, which may eliminate the need for the guide wire instrument that passes through the anchor device. The steerable portion that is coupled to the anchor device can provide guidance to annularly adjust the tissue treatment member  300  relative to the anchor member (e.g., an expandable balloon structure). 
     Referring to  FIG. 8 , a steerable guide wire  152  may be directed to the left atrium  402  using known techniques. The guide wire  152  may include an atraumatic tip  159  to facilitate the steering and guidance of the wire  152  through the patient&#39;s body. The guide wire  152  may be sized to slidably engage the guide lumen  312  of the tissue treatment member  300 . The tissue treatment member  300  may be directed to the left atrium  402  by sliding the tubular wall  314  of the guide lumen over the outer surface of the guide wire  152 . (The coolant chamber  351  and the safety chamber  321  are shown in expanded states for illustrative purposes, and it should be understood that the chambers  321  and  351  are not expanded while being guided through the patient&#39;s body.) After the tissue treatment member is guided to the desired location in the left atrium, the guide wire  152  may be removed by sliding the wire  152  out through guide lumen  312  to a proximal portion (located outside the patient&#39;s body like the proximal portion  110  shown in  FIG. 1 ) of the system. 
     Referring to  FIG. 9 , some embodiments of the anchor device  500  include an anchor member  210  disposed at a distal end of an anchor catheter  520 . The anchor member  510  may include an expandable balloon structure. In such embodiments, the anchor catheter  520  may extend from the anchor balloon  510  proximally back to the proximal portion of the system  105  located outside the patient&#39;s body—similar to embodiments of catheter devices described in U.S. Pat. No. 5,545,133 to Burns et al, which is incorporated herein by reference. The anchor member  500  may be sized to slidably engage the guide lumen  312  of the tissue treatment member  300 . Also, a steerable portion  550  may be coupled to the anchor device  500  proximate to the balloon  510 . The steerable portion  550  that is coupled to the anchor device  500  can provide guidance to annularly adjust the tissue treatment member  300  relative to the anchor balloon  510 . 
     In the embodiment shown in  FIG. 9 , the steerable portion  550  includes a shape memory element  555  that may be pre-formed to have a curved portion  556  such that when the catheter  520  (coupled to the shape memory element  555 ) is rotated, the tissue treatment member  300  is adjusted annularly relative to the anchor balloon  510 . As previously described, the pre-formed shape memory element  555  may comprise a superelastic Nitinol material that was exposed to austenitic/martensite processing. The shape memory element  555  may also comprise multiple wires that can be made to shorten under application of electrical current. In such embodiments, the multiple wires may be positioned along the periphery of the anchor catheter  520  with each wire being spaced apart from the neighboring wire. In other embodiments, the steerable portion  550  may include various mechanisms to adjust the position of the tissue treatment member  300  relative to the anchor balloon  510 . For example, the steerable portion  550  may include one or more pull wires that are operated at the proximal portion of the system  105  to control the position of the tissue treatment member  300  relative to the anchor balloon  510 . 
     Still referring to  FIG. 9 , while the tubular wall  314  in the elongate member  310  and the tissue treatment member  300  may be sufficiently rigid to constrain the shape memory element  555 , the portion of the anchor catheter  520  that contains the curved portion  556  may be less rigid. As such, when the anchor device  500  is directed through the guide lumen  312  toward the left atrium  402 , the curved portion  556  of the shape memory element  555  may be constrained by the tubular wall  314  of the guide lumen  312 . However, when a portion of the anchor device  500  extends distally from the tissue treatment member  300  such that the curved portion  556  is no longer inside the tubular wall  314 , the shape memory element  555  returns to its biased, curved shape. 
     In some embodiments, the nonexpanded tissue treatment member  300  may be guided adjacent to the pulmonary vein  405  so that the anchor balloon  510  may be guided directly into the vein  405  and expanded to press against the vein wall  410 . Then, the tissue treatment member  300  may be slightly retracted in the proximal direction while the anchor balloon  510  remains in the pulmonary vein  405  such that the curved portion  556  of the shape memory element  555  extends distally of the tissue treatment member  300 . The anchor device  500  may include an atraumatic tip  559  that is relatively flexible to facilitate the guidance of the anchor balloon  510  into the pulmonary vein  405 . 
     In the embodiment shown in  FIG. 9 , the anchor member  500  includes a piston  524  that is disposed inside a chamber  523 . The piston  524  may act as a pressure source that forces fluid to inflate or deflate the anchor balloon  510 . A physician may apply a longitudinal force  527  to the piston  524 , which causes the inflation fluid (e.g., saline solution) to enter or withdraw from the anchor balloon  510 . The piston  524  may be located near the distal portion of the system  105  and may be actuated at the proximate portion of the system  105 —similar to embodiments described in the previously referenced U.S. Pat. No. 5,545,133 to Burns et al. In such circumstances where the pressure source is located closer to the anchor balloon  510  (rather than at the proximate portion outside the patient&#39;s body), the length of the inflation lumen  522  is reduced. The shortened inflation lumen  522  reduces both the resistance to fluid flow and may reduce the time required to inflate and deflate the anchor balloon  510 . 
     Still referring to  FIG. 9 , the tissue treatment member  300  forced into a position proximate an ostial area  455  due to the bias from the shape memory element  555  (and any pushing force applied to the elongated member  310  from a physician at the proximal portion of the system  105 ). The position of the tissue treatment member  300  may be visualized by a physician using the marker band  315  and known imaging techniques. After the tissue treatment member  300  is guided to the proper position, the coolant material may be cycled through the coolant chamber  351  (e.g., through intake and exhaust tubes  353  and  357 ) while a vacuum is applied to the safety chamber  321 . The tissue treatment member  300  may be directed over the outer surface of the anchor catheter  520  so as to contact the ostial area  455 . For example, a physician may grasp an outer surface  305  of the elongate member  310  (or a handle attached thereto) at the proximal portion of the system  105  so as to force the tissue treatment member  300  to press against the ostial area  455 . The heat transfer that occurs between the ostial area  455  and the tissue treatment member  300  may cause ablation of the tissue proximate the ostial area  455 . 
     When the targeted tissue in the first ostial area  455  is sufficiently ablated by the tissue treatment member  300 , the physician may apply a torque  507  to anchor catheter  520  at the proximal portion of the system. Such action causes the anchor catheter  520  (including the shape memory element  255  at the steerable portion  250 ) to rotate relative to the pulmonary vein  405 . Optionally, if the anchor balloon  510  presses against the vein wall  410  to a force that is sufficient to prevent rotation of the catheter  520 , the balloon  510  may be partially deflated while the catheter  520  is rotated and then reinflated. Rotation of the catheter  520  relative to the pulmonary vein  405  may cause the tissue treatment member  300  to shift with a substantially annular motion  502  relative to the position of the anchor balloon  510  in the pulmonary vein  405 . From there, the tissue treatment member  300  may be used to ablate tissue proximate a second ostial area  456 . As such, the steerable portion  250  can provide the proper guidance to adjust the tissue treatment member  300  relative to relative to the position of the anchor balloon  510  in the pulmonary vein  405  so at to form an annular area of ablated tissue along the ostium  450 . 
     As previously described, forming an annular area of ablated tissue along the ostium  450  (rather than inside the pulmonary vein  405 ) may be more effective at treating atrial fibrillation. Furthermore, because the steerable portion  250  can be used to annularly adjust the tissue treatment member  300  relative to the position of the anchor balloon  510  in the pulmonary vein  405 , the tissue treatment member  300  may form an annular area of ablated tissue along an outer portion of the ostium  450  known as the antrum. It is believed that, in some cases, forming an annular scar along this outer ostial area known as the antrum is more effective in preventing future occurrences of atrial fibrillation. 
     While the embodiments depicted in  FIGS. 1-9  include an anchor member having an expandable balloon, other devices may be used to stabilize the steerable portion relative to the vein. For example, a guide wire instrument may include an ostial curved portion (similar to the curved portion  256  described above) and a distal curved portion that is sized to press against the pulmonary vein wall. When the distal curved portion is in the pulmonary vein, the tissue treatment member  300  may be directed over the guide wire instrument toward the ostium, where the ostial curved portion biases the tissue treatment member  300  against an ostial area. The distal curved portion may replace the need for an anchor balloon, as it would press against a vein wall and help to stabilize the position of the ostial curved portion relative to the ostium. The anchor member may also take other appropriate forms, including an expandable stent structure or an expandable ring. The expandable stent structure or the expandable ring may be used to stabilize the steerable portion relative to the vein, and may be controlled by one or more pull wires that extend to the proximal portion of the system. In another example, the anchor member may comprise an expandable wire structure, such as medically safe filter wire. The filter wire structure may be a FilterWire EX™ system provided by Boston Scientific Corporation. The filter wire may include a shape memory element that causes the filter wire structure to selectively expand when in the pulmonary vein so that the anchor member is secured to a targeted portion of the pulmonary vein. 
     Additionally, in embodiments where the steerable portion uses a shape memory element, the shape memory element is not necessarily a pre-formed wire. For example, the shape memory element may be a tube that slides over an anchor catheter. The shape memory tube may have a curved portion that is similar to the curved portion  256  described above. In such embodiments, the shape memory tube may extend distally from the tissue treatment member  300 . When the shape memory tube is advanced over a flexible portion of the anchor catheter (after the anchor balloon is secured in the pulmonary vein), the anchor catheter is flexed and the shape memory tube biases the tissue treatment member  300  against an ostial surface. In these embodiments, the use of the pre-formed tube having the curved portion may be used as a treatment option in cases where the physician desires to annularly adjust the tissue treatment member relative to the anchor balloon in the pulmonary vein. 
     Other embodiments of the system may include a tissue treatment member having a different shape. The external and internal balloons of the tissue treatment member are not necessarily spherical, but instead may be cylindrically shaped, tear-drop shaped, prism shaped, or other shapes depending on the tissue surface, geometry that is to be treated, and other factors. 
     In some embodiments, the tissue treatment member  300  may include a single balloon construction, in which the external balloon  320  and the vacuum lumen  322  are not necessarily included. In these embodiments, the non-expanded size of the tissue treatment member  300  may be reduced. 
     Furthermore, some embodiments of the tissue treatment member do not necessarily require expandable balloons. The coolant chamber may be disposed in a substantially nonexpandable container that is adjustable relative to the anchor balloon so as to contact ostial areas. For example, the tissue treatment member may include a nonexpandable container having an outer cylindrical surface and a central guide lumen passing therethrough. When coolant cycles through the coolant chamber in the nonexpendable container, the outer cylindrical surface may be pressed against ostial areas to form an annular area of ablated tissue. 
     A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.