Patent Publication Number: US-2007123824-A1

Title: Systems and methods for directing valves that control a vacuum applied to a patient

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      The present application claims priority to U.S. Provisional Application 60/727,678 (filed on Oct. 17, 2005); and the following U.S. Provisional Applications, all filed on Jun. 7, 2006: 60/811,866; 60/811,993; 60/811,864; 60/811,999; and 60/812,002. All the foregoing applications are incorporated herein by reference. 
    
    
     TECHNICAL FIELD  
      The present disclosure is directed generally to systems and methods for directing valves that control a vacuum applied to a patient.  
     BACKGROUND  
      The human heart is a complex organ that requires reliable, fluid-tight seals to prevent de-oxygenated blood and other constituents received from the body&#39;s tissues from mixing with re-oxygenated blood delivered to the body&#39;s tissues.  FIG. 1A  illustrates a human heart  100  having a right atrium  101 , which receives the de-oxygenated blood from the superior vena cava  116  and the inferior vena cava  104 . The de-oxygenated blood passes to the right ventricle  103 , which pumps the de-oxygenated blood to the lungs via the pulmonary artery  114 . Re-oxygenated blood returns from the lungs to the left atrium  102  and is pumped into the left ventricle  105 . From the left ventricle  105 , the re-oxygenated blood is pumped throughout the body via the aorta  115 .  
      The right atrium  101  and the left atrium  102  are separated by an interatrial septum  106 . As shown in  FIG. 1B , the interatrial septum  106  includes a primum  107  and a secundum  108 . Prior to birth, the primum  107  and the secundum  108  are separated to form an opening (the foramen ovale  109 ) that allows blood to flow from the right atrium  101  to the left atrium  102  while the fetus receives oxygenated blood from the mother. After birth, the primum  107  normally seals against the secundum  108  and forms an oval-shaped depression, i.e., a fossa ovalis  110 .  
      In some infants, the primum  107  never completely seals with the secundum  108 , as shown in cross-sectional view in  FIG. 1C  and in a left side view in  FIG. 1D . In these instances, a patency  111  often having the shape of a tunnel  112  forms between the primum  107  and the secundum  108 . This patency is typically referred to as a patent foramen ovale or PFO  113 . In most circumstances, the PFO  113  will remain functionally closed and blood will not tend to flow through the PFO  113 , due to the higher pressures in the left atrium  102  that secure the primum  107  against the secundum  108 . Nevertheless, during physical exertion or other instances when pressures are greater in the right atrium  101  than in the left atrium  102 , blood can inappropriately pass directly from the right atrium  101  to the left atrium  102  and can carry with it clots, gas bubbles, or other vaso-active substances. Such constituents in the atrial system can pose serious health risks including hemodynamic problems, cryptogenic strokes, venous-to-atrial gas embolisms, migraines, and in some cases even death.  
      Traditionally, open chest surgery was required to suture or ligate a PFO  113 . However, these procedures carry high attendant risks, such as postoperative infection, long patient recovery, and significant patient discomfort and trauma. Accordingly, less invasive techniques have been developed. Most such techniques include using transcatheter implantation of various mechanical devices to close the PFO  113 . Such devices include the Cardia® PFO Closure Device, Amplatzer® PFO Occluder, and CardioSEAL® Septal Occlusion Device. One potential drawback with these devices is that they may not be well suited for the long, tunnel-like shape of the PFO  113 . As a result, the implanted mechanical devices may become deformed or distorted and in some cases may fail, migrate, or even dislodge. Furthermore, these devices can irritate the cardiac tissue at or near the implantation site, which in turn can potentially cause thromboembolic events, palpitations, and arrhythmias. Other reported complications include weakening, erosion, and tearing of the cardiac tissues around the implanted devices.  
      Another potential drawback with the implanted mechanical devices described above is that, in order to be completely effective, the tissue around the devices must endothelize once the devices are implanted. The endothelization process can be gradual and can accordingly take several months or more to occur. Accordingly, the foregoing techniques do not immediately solve the problems caused by the PFO  113 .  
      Still another drawback associated with the foregoing techniques is that they can be technically complicated and cumbersome. Accordingly, the techniques may require multiple attempts before the mechanical device is appropriately positioned and implanted. As a result, implanting these devices may require long procedure times during which the patient must be kept under conscious sedation, which can pose further risks to the patient. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIGS. 1A-1D  illustrate a human heart having a patent foramen ovale (PFO) in accordance with the prior art.  
       FIG. 2  illustrates a catheter configured in accordance with an embodiment of the invention and positioned proximate to a PFO.  
       FIG. 3  is an isometric illustration of a working portion of the catheter shown in  FIG. 2 .  
       FIG. 4  is a partial cross-sectional side elevation view of the working portion shown in  FIG. 3 .  
       FIGS. 5A and 5B  illustrate the operation of a catheter in accordance with an embodiment of the invention.  
       FIG. 6A  is an end view of a catheter working portion configured in accordance with further embodiments of the invention.  
       FIGS. 6B-6C  illustrate an electrode coupled to a deployable catheter in accordance with another embodiment of the invention.  
       FIG. 6D  illustrates a front isometric view of a catheter having an inflatable member tilted in accordance with another embodiment of the invention.  
       FIG. 6E  illustrates a catheter having an inflatable member shaped in accordance with another embodiment of the invention.  
       FIG. 6F  is a side view of a catheter having an electrode with a concave upper surface in accordance with another embodiment of the invention.  
       FIG. 6G  is a rear isometric illustration of a catheter working portion carrying an inflatable member having ribs in accordance with another embodiment of the invention.  
       FIG. 6H  is a cross-sectional, isometric illustration of an inflatable member having portions with different wall thicknesses in accordance with another embodiment of the invention.  
       FIG. 6I . is a cross-sectional, isometric illustration of a working portion having an inflatable member with multiple chambers in accordance with another embodiment of the invention.  
       FIG. 6J  illustrates an inflatable member configured to carry a recirculating fluid in accordance with still another embodiment of the invention.  
       FIG. 6K  illustrates a working portion having a heat sink configured in accordance with an embodiment of the invention.  
       FIGS. 7A-7C  illustrate a console and disposable collection unit configured in accordance with an embodiment of the invention.  
       FIGS. 8A-8B  illustrate further aspects of an embodiment of the disposable collection unit shown in  FIG. 7A .  
       FIGS. 9A-9B  schematically illustrate control valve operations in accordance with an embodiment of the invention.  
       FIG. 10  is an illustration of a display portion of a console configured in accordance with an embodiment of the invention.  
       FIG. 11A  is a block diagram illustrating components of a control system in accordance with an embodiment of the invention.  
       FIG. 11B  is a flow diagram illustrating operation of a catheter control system in accordance with still another embodiment of the invention.  
       FIG. 11C  is a flow diagram illustrating operation of a catheter control system in accordance with yet another embodiment of the invention.  
       FIG. 12  is a partially schematic illustration of a liquid collection vessel configured in accordance with another embodiment of the invention. 
    
    
     DETAILED DESCRIPTION  
      A. Introduction  
      Aspects of the present invention are directed generally to methods and devices for directing valves that control a vacuum applied to a patient, for example to draw portions of cardiovascular tissue together. A method in accordance with one aspect includes receiving a first input to apply vacuum to an orifice of a device positioned within a patient and in response to the first input, automatically directing a first valve coupled between the orifice and a vacuum source to move from a closed state to an open state. The method can further include receiving a second input to cease applying the vacuum to the orifice and in response to the second input, the method can include automatically directing the first valve to move from the open state to the closed state, automatically directing a second valve coupled between the orifice and atmospheric pressure to move from a closed state to an open state, and automatically directing the second valve to move back from the open state to the closed state. Accordingly, certain aspects can allow the practitioner to have the vacuum supplied by the device automatically halted and the device automatically vented and then reclosed.  
      A system in accordance with another aspect includes a first valve automatically changeable between an open state and a closed state, with the first valve being coupleable between a vacuum source and a patient device having an orifice positioned to be placed inside a patient. The system can further include a second valve automatically changeable between an open state and a closed state and coupleable between the orifice and atmospheric pressure. A controller can be operatively coupled to the first valve, the second valve, and an input device. The controller can be configured to receive a first input to apply vacuum to the orifice and in response to the first input, automatically direct the first valve to move from the closed state to the open state. The controller can further be configured to receive a second input to cease applying the vacuum to the orifice, and in response to the second input, can automatically direct the first valve to move from the open state to the closed state, automatically direct the second valve to move from the closed state to the open state, and automatically direct the second valve to move back from the open state to the closed state.  
      B. Catheters and Associated Methods for Treating Cardiac Tissue  
       FIGS. 2-5B  illustrate a catheter  220  and methods for using the catheter  220  to treat cardiovascular tissue, in accordance with several embodiments of the invention. These Figures, as well as  FIGS. 6A-6K  and the associated discussion, illustrate implementations of representative devices and methods in the context of cardiac tissues. In other embodiments, at least certain aspects of these devices and methods may be used in conjunction with other tissues, including other cardiovascular tissues (e.g., veins or arteries).  
      Beginning with  FIG. 2 , the catheter  220  can include a proximal end  222  coupled to a control unit  240 , and a distal end  221  having a working portion  228  configured to be placed in a patient&#39;s heart  100 . At least part of the catheter  220  can be flexible so as to allow the catheter  220  to absorb stresses without disturbing the working portion  228 . The distal end  221  of the catheter  220  can be inserted into the patient&#39;s heart  100  via the inferior vena cava  104  or another blood vessel, and can be threaded along a guidewire  223 . The catheter  220  can include a vacuum system  238  having vacuum ports  237  that are used to evacuate fluids (and/or solids, e.g., blood clots) in the region surrounding the distal end  221 . The vacuum ports  237  can have a slot shape as shown in  FIG. 2 , or other shapes in other embodiments. The force of the applied vacuum can draw portions of the cardiac tissue toward each other and toward the catheter  220 .  
      The catheter  220  can also include an energy transmitter  230  (e.g., an electrode  231 ) that directs energy (e.g., RF energy) to the cardiac tissue portions to bond the tissue portions together. Much of the following discussion references an energy transmitter  230  that includes the electrode  231 , but in other embodiments, the energy transmitter can include other devices and/or devices that transmit other forms of energy (e.g., ultrasonic energy or laser energy). Any of these devices may generate heat that, in addition to fusing the tissue together, may cause the tissue to adhere to the catheter  220 . Accordingly, in at least some embodiments, an optional fluid supply system can provide fluid to the working portion  228  to prevent the cardiac tissue from fusing to the electrode  231  or other portions of the energy transmitter  230 , and/or to increase the penetration of the electrical field provided by the electrode  231 . Details of the fluid supply system are not shown in  FIG. 2 , but are described in greater detail in U.S. Provisional Application 60/727,678, previously incorporated herein by reference.  
      The working portion  228  can also include an inflatable member  260  (e.g., a balloon, sack, pouch, bladder, membrane, circumferentially reinforced membrane, or other suitable device) located proximate to the electrode  231 . The inflatable member  260  can be selectively deployed and inflated to aid in releaseably sealing the catheter  220  at or proximate to the target tissue to which energy is directed. When the inflatable member  260  is inflated, the electrode  231  can project from the inflatable member  260  in a distal direction so that the electrode  231  is in intimate contact with the target tissue.  
      The control unit  240  can control and/or monitor the operation of the inflatable member  260 , the energy transmitter  230 , and the vacuum system  238 . Accordingly, the control unit  240  can include an inflatable member controller  245 , an energy transmitter control/monitor  241 , and a vacuum control/monitor  242 . The control unit  240  can also include other controls  244  for controlling other systems or subsystems that form portions of, or are used in conjunction with, the catheter  220 . Such subsystems can include, but are not limited to, the fluid supply system described above, and/or temperature and/or impedance detectors that determine the temperature and/or impedance of the cardiac tissue and can be used to prevent the energy transmitter  230  from supplying excessive energy to the cardiac tissue. The subsystems can also include current sensors to detect the current level of electrical signals applied to the tissue, voltage sensors to detect the voltage of the electrical signals, and/or vision devices that aid the surgeon or other practitioner in guiding the catheter  220 . The control unit  240  can include programmable, computer-readable media, along with input devices that allow the practitioner to select control functions. The control unit  240  can also include output devices (e.g., display screens) that present information corresponding to the operation of the catheter  220 . Further details regarding several of the foregoing features are described later with reference to  FIGS. 7A-12 .  
       FIG. 3  is an enlarged, isometric illustration of the working portion  228  of the catheter  220  shown in  FIG. 2 . As shown in  FIG. 3 , the inflatable member  260  can have a roughly triangular or pear-like shape when viewed head-on that, in at least some cases, is roughly similar to the shape of the fossa ovalis. It is expected that the shape of the inflatable member  260  will facilitate sealing the inflatable member  260  against the septal tissue, while the electrode  231  projects away from the inflatable member  260  to extend at least part way into the PFO, with the vacuum ports  237  exposed. Particular aspects and combinations of aspects of the features shown in  FIGS. 2 and 3  are described in greater detail below with reference to  FIG. 4 .  
       FIG. 4  is a partial cross-sectional illustration of the working portion  228  of the catheter  220 , positioned proximate to a PFO  113 , and taken generally along line  4 - 4  of  FIG. 3 . The working portion  228  is elongated generally along a terminal axis  225 . The electrode  231  and/or the inflatable member  260  can be asymmetric relative to the terminal axis  225 . An expected benefit of this arrangement is that it can allow for an improved seal between the working portion  228  and the adjacent cardiac tissue, and/or improved energy delivery from the electrode  231  to the tissue.  
      In a particular embodiment, the inflatable member  260  can include a first inflatable portion  262  (e.g., an inferior portion) and a second inflatable portion  263  (e.g., a superior portion) that extend by different distances from the terminal axis  225 . In particular, the first inflatable portion  262  can extend away from the terminal axis  225  by a distance D 1  that is less than a distance D 2  by which the second inflatable portion  263  extends away from the terminal axis  225 . A representative value for D 1  is about 8 mm. Accordingly, a greater portion of the inflatable member  260  can contact the secundum  108  then the primum  107 . As will be described in greater detail below with reference to  FIGS. 5A-5B , this arrangement can take advantage of the more robust structure of the secundum  108 .  
      The inflatable member  260  can be constructed from a compliant urethane material (e.g., having a durometer value of from about 50 to about 80 on the Shore A scale). One such material includes Pellethane®, available from the Dow Chemical Company of Midland, Mich. This material can be readily bonded to the shaft of the catheter  220  thermally or adhesively, and can be selected to be translucent or transparent, allowing the practitioner to view a fluid contrast agent that may be used to inflate the inflatable member  260 . The material forming the inflatable member  260  can also be selected to be quite compliant so as to conform to the tissue against which it temporarily seals, without displacing or distorting the tissue by a significant amount. Such compliancy can also make the inflatable member  260  easier to stow aboard the catheter  220 , as the catheter is introduced into the patient&#39;s body (prior to inflation), and as the catheter is removed from the patient&#39;s body (after inflation and treatment). The material forming inflatable member  260  can be thin (e.g., 25-50 microns thick) to facilitate compliancy. In particular embodiments, the material forming the inflatable member  260  can be thicker at some portions than at others, to produce the desired shape after inflation. For example, the most distal face and/or perimeter sections of the inflatable member  260  may be constructed to be thinner than other portions of the inflatable member  260 . When inflated with a liquid, this thin portion may more readily take a rounded shape and will remain compliant, so as to assist in providing improved sealing under vacuum, and/or assist in placing the electrode  231  at a selected axial position inside the PFO tunnel  112 . Further details of such an arrangement are described later with reference to  FIG. 6H .  
      The inflatable member  260  can be inflated with any suitable fluid, including saline. The fluid can also include a contrast agent to aid the practitioner in locating the inflatable member  260  relative to other structures. In particular embodiments, the contrast agent can include MD-76®R or Optiray® 320 available from Mallinckrodt, Inc. of St. Louis, Mo. The contrast agent can be diluted to reduce its viscosity and therefore increase the rate with which the inflatable member  260  is inflated and deflated. For example, the inflation fluid can include 10-50% contrast agent (the remainder being saline), with 25% or 50% contrast agent in particular embodiments. With fluid compositions having these characteristics, a representative inflatable member  260  carried by a representative catheter  220  (e.g., one having an internal diameter of 0.025-0.28 inches) can be fully inflated in 10-15 seconds or less.  
      The electrode  231  can also be asymmetric relative to the terminal axis  225 . For example, the electrode  231  can include a first electrode portion  232  (e.g., an inferior portion) and a differently shaped second electrode portion  233  (e.g., a superior portion). The first electrode portion  232  can form a first electrode angle  234  relative to the inflatable member  260 , and the second electrode portion  233  can form a second, different electrode angle  235  relative to the inflatable member  260 . For example, the second electrode angle  235  can be approximately 90° (so that the superior surface is generally parallel to the terminal axis  225 ), while the first electrode angle  232  can have a value other than 90°. In a particular embodiment, the first electrode angle  234  can have a value of about 147°, corresponding to an acute angle relative to the terminal axis  225  of about 33°. In other embodiments, the first electrode angle  234  can have other values, e.g., other values greater than 90°. Such angles can include angles in the range of from about 130° to about 160°, corresponding to acute angles relative to the terminal axis  225  of from about 50° to about 20°.  
      As a result of the foregoing arrangement, the first electrode portion  232  can have a conical shape with a relatively large external surface area, which can increase the efficiency with which the adjacent cardiac tissue is heated during the tissue welding operation. The taper angle of the first electrode portion  232  may also aid in directing the RF energy emitted from the electrode  231  directly into the PFO tunnel  112  to more efficiently weld this tissue. The presence of the inflatable member  260  (which is generally, if not entirely non-conductive) can also act to direct RF energy forward into the tissue immediately adjacent to the PFO tunnel  112 . In addition, the taper angle of the first electrode portion  232  can more accurately align this portion of the electrode  231  with the natural orientation of the adjacent primum  107 . The relatively short axial length of the electrode  231  can (a) reduce the extent to which the electrode  231  displaces the primum  107 , and/or (b) allow the electrode  231  to be placed in relatively short PFO tunnels  112 , while still providing effective PFO sealing.  
      In a particular embodiment, the electrode  231  can be manufactured from 17-4 stainless steel or an equivalent electrically conductive, bio-compatible material including, but not limited to platinum or platinum iridium. These materials can be suitable for conducting RF energy, and also for machining small features (e.g., the vacuum ports  237  shown in  FIG. 3 ). These materials are also relatively easy to bond to the shaft and/or associated shaft components of the catheter  220 .  
      In operation, it is typically desirable to seal the PFO  113  as quickly as possible so as to minimize the invasiveness of the procedure. However, if electrical energy is delivered too aggressively (e.g., via too high a current level), the adjacent tissue may bond or stick to the electrode  231 . When the electrode  231  is later removed from the patient, it can disrupt or de-bond the tissue weld. High current can also create local “hot spots” that can result in potentially damaging eruptions of steam. In addition, the impedance of the tissue adjacent to the electrode  231  can increase rapidly when heated, which in turn reduces the penetration of the RF energy emitted by the electrode. This “impeding out” effect can therefore reduce the extent and strength of the resulting tissue seal. On the other hand, if the current density is reduced by reducing the applied current, the welding process can take longer to perform. If the current density is reduced by increasing the electrode size, the electrode diameter may become too large to be easily introduced into the patient, and/or may unnecessarily heat adjacent tissue.  
      To address the foregoing effects, the catheter  220  can include a heat transfer element (e.g., a heat sink)  270  that is in thermal communication with the electrode  231  and, in an embodiment shown in  FIG. 4 , extends in a proximal direction along the catheter  220  away from the electrode  231 . The heat sink  270  can be electrically insulated from its surroundings, for example, via a thin, thermally conductive, but electrically insulating film or coating  271  that can include Teflon® or another biocompatible material. The coating  271  can have a sleeve shape to fit over the heat sink  270 , with a representative thickness of 1-10 microns, and a representative thermal resistance of 2° C./watt or less. The heat sink  270  can also be formed from a material having a relatively high thermal conductivity, such as silver or a silver alloy. In other embodiments, the heat sink  270  can be formed from copper, gold, or alloys of these metals, or plated-on combinations of metals. For example, in a particular embodiment, the heat sink  270  is formed from a gold plated, silver-copper alloy. The gold plating provides a good interface with the adjacent cardiac tissue, and the silver-copper alloy (e.g., approximately 90% silver and approximately 10% copper in a representative embodiment) provides high thermal and electrical conductivity, combined with good material strength and machinability. In a particular embodiment, the gold plating can have a thickness of from about 2 microns to about 20 microns (e.g., about 5 microns) and in other embodiments, the plating thickness can have other values. The heat sink  270  can be formed integrally with the electrode  231  (e.g., the heat sink  270  and the electrode  231  can be machined or cast or otherwise formed from a single piece of metal stock), or the heat sink  270  can be an initially separate component that is placed in intimate, contiguous thermal contact with the proximal surface of the electrode  231 . In either arrangement, the heat sink  270  can have a generally cylindrical shape with internal openings to accommodate vacuum channels, inflation channels and/or electrical leads. Accordingly, the outer surface of the heat sink  270  can be positioned in thermal contact with and adjacent to the inner annular surface of the inflatable member  260  and also the fluid within the inflatable member  260 . As a result, the heat sink  270  can transfer heat from the electrode  231  to the fluid within the inflatable member  260 .  
      Heat can readily transfer from the heat sink  270  into the fluid within the inflatable member  260 . Furthermore, because the material forming the inflatable member  260  is quite thin, heat can readily transfer from the fluid inside the inflatable member  260  to the surrounding blood and/or tissue. The fluid within the inflatable member  260  is expected to circulate throughout the inflatable member  260  due to convection resulting from the heat supplied by the heat sink  270  and/or the electrode  231 , and/or due to mechanical agitation produced by the beating heart in which the inflatable member  260  is positioned.  
      In particular embodiments, the heat sink  270  can extend in a proximal direction beyond the inflatable member  260 , as shown in  FIG. 4 . Accordingly, the heat sink  270  can be cooled directly by the circulating blood, as well as indirectly by the fluid in the inflatable member  260 . In other embodiments, the heat sink  270  can be cooled solely by either direct or indirect heat transfer. The arrangement of the heat sink  270 , the inflatable member  260 , and the electrode  231  provides a low thermal resistance pathway for heat to be conveyed away from the electrode  231  and the immediately adjacent tissue. In still further embodiments, heat can be transferred away from the electrode  231  in accordance with related techniques, including those disclosed in U.S. Pat. No. 4,492,231, incorporated herein by reference.  
      In still further embodiments, other techniques can be used to reduce or eliminate sticking between the tissue and the electrode  231 , in addition to or in lieu of transferring heat with the heat sink  270 . For example, the voltage applied to the electrode  231  can be limited to a particular range. In some cases, when tissue desiccation occurs at the interface between the electrode  231  and the adjacent tissue, the electric field strength tends to increase. This can result in voltages high enough to achieve ionization or arcing in the liquid (or in some cases, gas) between the tissue and the electrode surface. Accordingly, in at least some embodiments, the maximum voltage provided by the system may be clamped or capped, for example, at 50 volts rms.  
      In operation, it is expected that the heat sink  270  can transfer heat from the electrode  231  at a rate sufficient to prevent or at least reduce sticking between the electrode  231  and the adjacent cardiac tissue. For example, the heat sink  270  is expected to transfer heat from the electrode  231  rapidly enough to keep the electrode  231  within 6° C. of the patient&#39;s body temperature, in at least one embodiment, and within 4° C. of the patient&#39;s body temperature in a further particular embodiment. The interface between the electrode  231  and the adjacent cardiac tissue is expected to experience a limited temperature increase of 10° C. or less, per watt of energy removed by the heat sink  270  (e.g., in an aft or proximal direction away from the electrode  231  and/or away from the adjacent cardiac tissue). For example, the temperature increase may be about 2° C. per watt of removed heat energy, with the amount of removed heat energy at a level of about one watt. At the same time, the amount of thermal energy applied to the adjacent tissue can be about 10 watts. It is expected that this arrangement will allow tissue sealing to within a very close distance of the electrode  231 , without causing the tissue to adhere to the electrode  231  itself. For example, the secundum  108  and the primum  107  can seal to each other beyond a distance of about 0.3 mm. from the electrode  231 . It is also expected that transferring heat from the electrode  231  will reduce the rate at which the adjacent cardiac tissue experiences a significant impedance increase as it is heated and welded. An expected benefit of this arrangement is that the RF energy can penetrate deeper into the PFO tunnel  112  (lengthwise and/or widthwise) before the increase in impedance inhibits the transmission of RF energy. As a result, the seal between the primum  107  and the secundum  108  is expected to be more extensive, more complete and/or more robust than it otherwise would be. In particular, for larger PFOs, deeper penetration with more energy delivered in both a lengthwise and a widthwise direction can provide for a broader tissue seal with an increased seal surface area.  
      The working portion  228  of the catheter  220  can also include a guidewire conduit or lumen  224  that extends through the electrode  231 . The guidewire conduit  224  slideably receives the guidewire  223  over which the catheter  220  is introduced into the heart. The guidewire conduit  224  can also control the path of the guidewire  223  relative to the catheter  220 . As is shown in  FIG. 4 , the distal portion of guidewire conduit  224  can be oriented at a non-zero path angle  226  relative to the terminal axis  225 . In a particular aspect of this embodiment, the guidewire conduit  224  can be oriented so that the path angle  226  is approximately 9°. In other embodiments, the path angle  226  can have other values (e.g., in the range of from about 3° to about 20°). As a result of this construction, the guidewire  223  will be oriented obliquely relative to the terminal axis  225 . This arrangement can more accurately align the axis of the guidewire  223  with the axis of the PFO tunnel  112  into which the guidewire  223  is inserted. As a result, the guidewire  223  is expected to be less likely to push, “tent” or otherwise displace the primum  107  away from the secundum  108 , which augments the RF treatment/welding process.  
      The remainder of the generally hollow interior portion of the catheter  220  can operate as a vacuum lumen  239 . Accordingly, the vacuum lumen  239  can have a relatively large cross-sectional area transverse to the terminal axis  225  to efficiently draw a vacuum through the catheter  220 . When coupled to a vacuum source, the vacuum lumen  239  can provide a vacuum to the vacuum ports  237  ( FIG. 3 ) to draw the septal tissue into contact with the electrode  231 . In a particular embodiment, the catheter  220  can be constructed from a reinforced, braided material to resist collapsing under vacuum.  
      The catheter  220  can include a catheter bend  219  positioned so that the terminal axis  225  is offset relative to a longitudinal axis L of the immediately adjacent portion of the catheter  220 . The bend  219  can be pre-formed into the catheter  220 , but the catheter  220  can be flexible enough so that as it is inserted through an introducer sheath and threaded along the guidewire  223  (e.g., through the femoral vein), it will tend to straighten out. Once it enters the less constrained volume within the heart, the catheter  220  can assume its bent configuration. In a particular embodiment, a bend angle  227  between the terminal axis  225  and the longitudinal axis L can have a value of about 45°, and in other embodiments, the bend angle  227  can have other values. For example, the bend angle  227  can have a value in the range of from about 20° to about 90° in one embodiment, and from about 30° to about 80° in another embodiment. The catheter  220  can also be bent relatively uniformly (e.g., at a generally constant and relatively small radius) relative to a center of curvature  229  located in the plane of  FIG. 4 . In particular embodiments, the bend angle  227  can be adjustable by the practitioner. For example, the catheter  220  can include one or more cables or other control features (not shown in  FIG. 4 ) that the practitioner can manipulate to adjust the value of the bend angle  227  and improve the practitioner&#39;s ability to accurately position the electrode  231  and the inflatable member  260 . In a particular embodiment, the practitioner can use a steerable introducer sheath or a steerable outer catheter to aid in positioning the electrode  231  and the inflatable member  260 .  
      The bend angle  227 , the guidewire exit angle  226 , and the first electrode angle  234  can have deliberately selected orientations relative to each other. For example, the bend angle  227 , the guidewire exit angle  226 , and the first electrode angle  234  can all be located in the same plane (e.g., the plane of  FIG. 4 ). The maximum amount by which the first inflatable portion  262  extends from the terminal axis  225  (e.g., D 1 ) and the maximum amount by which the second inflatable portion  263  extends from the terminal axis  225  (e.g., D 2 ) can also be located in the plane of  FIG. 4 . Accordingly, the generally flat superior surface of the electrode  231  and the apex of the inflatable member  260  can face in one direction, while the tapered surface of the electrode  231  and the base of the inflatable member  260  can face in the opposite direction. As a result of this orientation, the working portion  228  (including the electrode  231 , the inflatable member  260 , and the guidewire conduit  224 ) can all be symmetric relative to the plane of  FIG. 4 , although these components are asymmetric relative to the terminal axis  225 . As will be described below with reference to  FIGS. 5A-5B , providing a known relationship between the foregoing angles and orientations can improve the accuracy with which the practitioner aligns the working portion  228  prior to a PFO sealing procedure, particularly when a significant axial pressure may be applied to the catheter  220  to aid in sealing the working portion  228  to the adjacent tissue.  
       FIGS. 5A-5B  illustrate the operation of the catheter  220  in accordance with an embodiment of the invention. Beginning with  FIG. 5A , the catheter  220  is inserted into the right atrium  101  to seal a PFO  113  between the right atrium  101  and the left atrium  102 . Accordingly, the practitioner can first pass the guidewire  223  into the right atrium  101  and through the tunnel portion  112  of the PFO  113  using one or more suitable guide techniques. For example, the guidewire  223  can be moved inferiorally along the interatrial secundum  108  until it “pops” into the depression formed by the fossa ovalis  110 . This motion can be detected by the practitioner at the proximal end of the guidewire  223 . The tunnel  112  is typically at least partially collapsed on itself prior to the insertion of the catheter  220 , so the practitioner will likely probe the fossa ovalis  110  to locate the tunnel entrance, and then pry the tunnel  112  open. Suitable imaging/optical techniques (e.g., fluoroscopic techniques, intracardiac echo or ICE techniques, and/or transesophageal electrocardiography or TEE can be used in addition to or in lieu of the foregoing technique to thread the guidewire  223  through the tunnel  112 . Corresponding imaging/optical devices can be carried by the catheter  220 .  
      Once the guidewire  223  has been inserted through the PFO  113  and into the left atrium, the catheter  220  is passed along the guidewire  223 . The inflatable member  260  is initially in its collapsed state, as shown in  FIG. 5A . The inflatable member  260  may include pleats and/or other features that allow it to fold neatly and compactly along the catheter  220  so as to fit through existing introducer sheaths as the catheter  220  is inserted into the body.  
      The practitioner may in some instances wish to use the inflatable member  260  to help determine the size and/or geometry of the PFO tunnel  112 . Representative features of interest to the practitioner include the diameter, length, entrance shape and/or angle of the PFO tunnel  112 . In one process, the practitioner inserts the working portion  228  into the PFO tunnel  112  until the inflatable member  260  is within the tunnel  112 . Using a suitable visualization technique (e.g., ICE or fluoroscopy), the practitioner can then slowly and/or incrementally inflate the inflatable member  260  until the inflation is constrained by the primum  107  and/or the secundum  108 . Even though the primum  107  and the secundum  108  may not be readily visible (as they may not be during fluoroscopy visualization), the inflated inflatable member  260  will be visible. By measuring the size of the inflatable member  260  (at one or more locations) on a display monitor, and scaling this dimension relative to the known diameter of the working portion  228 , the practitioner can estimate the size of the tunnel  112 . This information can help the practitioner determine treatment parameters, including how far to insert the electrode  231 , how to position the inflatable member  260 , how much forward pressure to apply to the inflatable member  260 , how much to inflate the inflatable member  260 , and/or how much energy to deliver with the electrode  231 .  
      If the inflatable member  260  is used to size the tunnel  112 , it can then be deflated and withdrawn from the tunnel  112  into the right atrium  101 . Once the catheter  220  is in the right atrium  101 , the inflatable member  260  is inflated, as is shown in broken lines in  FIG. 5B , and the inflatable member  260  may now be used to provide the additional function of sealing the interface between the catheter  220  and the adjacent cardiac tissue. The practitioner can rotate the catheter  220  about its longitudinal axis L until the catheter  220  is at the desired orientation. In an embodiment such as that described above with reference to  FIG. 4 , in which the asymmetric features of the working portion  228  are all aligned, the practitioner can adjust the position of one such feature, and know that the remaining features will also be aligned. For example, in some cases, the bend angle  227  of the catheter  220  may be the feature most visible to the practitioner. In other cases, the inflatable member  260  may be the most visible. In either case, the practitioner can align one feature (e.g., the most readily visible feature) with an individual patient&#39;s cardiac landmarks, and know that other features (e.g., the electrode  231 ) will have a known, proper orientation.  
      When the catheter  220  is properly oriented, it is advanced along the guidewire  223  until the electrode  231  extends just inside the PFO tunnel  112 , and the inflatable member  260  (generally having the shape indicated by broken lines in  FIG. 5B ), contacts the secundum  108  and the primum  107 . At this point, the practitioner can apply an axial force to the catheter  220 , causing the inflatable member  260  to bear against the secundum  108  and the primum  107 . Because the secundum  108  is relatively robust, it tends to cause the second inflatable portion  263  of the inflatable member  260  to deform, as indicated in solid lines in  FIG. 5B . Because the primum  107  is more compliant, it tends to react to the axial and circumferential pressure by conforming around the first inflatable portion  262 , as is also shown in solid lines in  FIG. 5B . The guidewire  223  can remain in position in the PFO tunnel  112  during this phase of the process. At this point, the vacuum system can be activated to draw a vacuum through the vacuum ports  237  ( FIG. 3 ) of the electrode  231 , drawing the secundum  108  and the primum  107  against the electrode  231  and the inflatable member  260 , and removing blood and/or other fluids from the treatment site.  
      The practitioner can use any of several techniques to determine when the proper seal between the working portion  228  and the adjacent tissue is achieved, and/or to determine how to make adjustments, if necessary. For example, the practitioner can receive at least a gross indication of a proper seal by observing the shape of the inflatable member  260 . When the inflatable member  260  assumes a shape generally similar to that shown in solid lines in  FIG. 5B  (visible via fluoroscopy, ICE, or another suitable visualization technique), the practitioner can receive an indication that the inflatable member  260  is in at least approximately the correct location, and/or that the proper axial pressure is being applied. The practitioner can also observe the rate at which blood or other fluid is withdrawn through the catheter  260 , and can determine that the proper seal is achieved when the blood flow ceases or reaches a de minimis level. If the blood flow does not cease within the expected time frame, the practitioner can use the oxygenation level of the blood to determine the location of the leak. For example, if the withdrawn blood is deoxygenated, this may indicate that the leak is at the right atrium. If the blood is oxygenated, this may indicate that the leak is at the left atrium. For example, the presence of oxygenated blood may indicate that the PFO tunnel  112  is not fully collapsed, which may in turn indicate that the catheter  220  is propping the tunnel  112  open (e.g., if the catheter  220  is inserted too far into the tunnel  112 ). The practitioner can determine the oxygenation level of the blood by direct observation of the blood color, and/or by observing measurements from suitable devices, such as a pulse oximeter. Once the expected location of the leak is determined, the practitioner can adjust (e.g., reduce) the level of applied vacuum, re-position the catheter  220  and/or adjust the pressure of the inflatable member  260 , and re-apply the vacuum until the proper seal is achieved.  
      Once the catheter  220  is securely held in position under the force of vacuum, the guidewire  223  can be pulled back into the catheter  220  so as not to extend into the PFO tunnel  112 . At this time, the vacuum drawn on the cardiac tissue keeps the working portion  228  in a fixed position with the inflatable member  260  sealably positioned against the cardiac tissue. In at least some cases, the temporary vacuum seal between the catheter  220  and the adjacent cardiac tissue is strong enough to allow the practitioner to release his or her handhold on the catheter  220 , allowing the practitioner the freedom to use his or her hands for other tasks. The energy transmitter  230  (e.g., the electrode  231 ) is then activated to heat the adjacent cardiac tissue and bond or at least partially bond the primum  107  and the secundum  108 , thereby closing the PFO tunnel  112 .  
      As shown in  FIG. 5B , the asymmetry of the inflatable member  260  can allow for a greater portion of the inflatable member  260  to temporarily bear and seal against the secundum  108  than against the primum  107 . An advantage of this feature is that the secundum  108  is generally more robust than the primum  107 , and is expected to be better able to support the inflatable member  260  without undergoing a significant displacement, even if the practitioner applies an axial pressure to the catheter  220 . As a result, the primum  107  can be less likely to be displaced away from the secundum  108  and/or the electrode  231  in a manner that may detract from the treatment process. Put another way, an alternate inflatable member that (a) is symmetric relative to the terminal axis  225 , and (b) has the same surface area facing toward the PFO tunnel  112  as the inflatable member  260 , may tend to extend inferiorly by a distance sufficient to push and/or stretch the primum  107  away from the secundum  108  and/or the electrode  231 . An advantage of an embodiment of the inflatable member  260  shown in  FIG. 5B  is that it can reduce the extent to which the primum  107  is displaced or stretched, and can therefore increase the extent to which the primum  107  is tightly drawn against the electrode  231  and the secundum  108  during the tissue welding process. At the same time, the inflatable member  260  is configured to collapse down to a diameter that is small enough to allow use with readily available introducer sheaths (as shown in  FIG. 5A ).  
      The foregoing feature can be particularly appropriate for short PFO tunnels  112 . It may be difficult to obtain a good seal between the inflatable member  260  and such tunnels because if the primum  107  is displaced, stretched, or distorted, the exit of the PFO tunnel  112  (in the left atrium  102 ) may open, causing the influx of fluid (blood) and inhibiting close contact between the secundum  108  and the primum  107 . As described above, the asymmetrical shape of the inflatable member  260  can at least reduce the extent to which the primum  107  is displaced, stretched, or distorted in the region immediately adjacent to the PFO tunnel  112 . Other shape features can also contribute to this effect. For example the relatively flat base of the inflatable member  260  allows the primum tissue to form a good seal with the inflatable member  260 . In particular, the flat base may tend not to bulge away from the terminal axis, and accordingly may be less likely to displace the primum  107  away from the electrode  231 . The asymmetrical shape of the inflatable member  260  can also increase accuracy of the alignment between the electrode  231  and the entrance of the PFO tunnel  112 . This can in turn allow the RF energy to be directed more evenly into the PFO tunnel  112 , rather than into the primum  107 .  
      The pressure to which the inflatable member  260  is inflated can be relatively low in comparison to pressures typically used for angioplasty and other catheter balloons. For example, the inflatable member  260  can be inflated to a value of from 0.2 to 10 psi in one embodiment, and from 0.5 to 3 psi in a more particular embodiment. Pressure can be applied to the inflatable member  260  manually via a syringe filled with a liquid (e.g., a contrast agent), or automatically. The low pressures can be monitored with a suitable pressure gauge. These low pressures can further enhance the ability of the inflatable member  260  to conform to the local tissue topology and form a tight seal under vacuum. In operation, the practitioner can also apply axial pressure, and/or rotate the catheter  220  slightly clockwise or counterclockwise until a good seal is achieved. As discussed above, the fixed relative orientation of the various asymmetric features of the catheter  220  can reduce the extent to which the practitioner must make such adjustments.  
      In particular embodiments, the extent to which the inflatable member  260  is inflated can change the shape (as well as the size) of the inflatable member  260 . For example, increasing the inflation pressure can increase axial length of the inflatable member  260 , and therefore decrease the distance by which the electrode  231  projects forward of the inflatable member  260 . This technique can be used to control the extent to which the electrode  231  penetrates into the PFO tunnel  112 . The greater the inflation pressure, the more the inflatable member  260  tends to expand forwardly toward the electrode  231 , and the shorter the distance by which the electrode  231  will penetrate into the PFO tunnel  112 . In other embodiments, the inflation pressure applied to the inflatable member  260  can be used to control the orientation of the electrode  231 . For example, at higher inflation pressures, the second portion  263  may tend to bulge forward more than does the first portion  262 . As a result, when the inflatable member  260  is placed against the primum  107  and the secundum  108 , it may tilt slightly counterclockwise (in the plane of  FIG. 5B ), inclining the electrode  231  toward the secundum side of the PFO tunnel  112 . This motion can in turn align the guidewire  223  more with the secundum side of the PFO tunnel  112  than with the primum side, thereby reducing the tendency for the guidewire  223  to push or “tent” the primum  107  away from the electrode  231  and the secundum  108 . As mentioned above, the primum  107  tends to be thinner than the secundum  108 , and may therefore be more susceptible to “tenting,” in the absence of aligning the guidewire  223  along the secundum side of the PFO tunnel  112 .  
      The orientation of the guidewire conduit  224  can supplement or in some cases replace the tilted orientation of the inflatable member  260  as a feature by which to orient the guidewire  223  along the secundum side of the PFO tunnel  112 . For example, when the guidewire conduit  224  is inclined relative to the terminal axis  225  (as shown in  FIG. 5B ), the guidewire  223  will tend to exit the electrode  231  at an angle that is more accurately aligned with the naturally occurring angle of the PFO tunnel  112 . As described above, an advantage of this feature is that the guidewire  223  will have a reduced tendency to push the relatively thin primum  107  away from the electrode  231  as the guidewire  223  is deployed into the PFO tunnel  112 . Accordingly, the likelihood for tightly sealing the primum  107  against the electrode  231  and the secundum  108 , and therefore providing a secure seal between the primum  107  and the secundum  108 , can be significantly increased. In some embodiments, the guidewire  223  can be withdrawn from the PFO tunnel  112  during tissue sealing (as described above), and in other embodiments, the guidewire  223  can remain in the tunnel  112  during this process. In another embodiment, the guidewire  223  may remain in the tunnel for the initial portion of the treatment, and may be withdrawn during the delivery of RF energy.  
       FIG. 5B  also illustrates the second electrode portion  233  bearing against the limbus  217  of the secundum  108 . Because the second electrode angle  235  is approximately 90° rather than a significantly larger value, the electrode  231  will tend to “hook” upwardly against the limbus  217  rather than slide way from the limbus  217 . Accordingly, once the electrode  231  is located at the entrance of the PFO tunnel  112 , it will be less likely to be displaced (e.g., upwardly and to the left in  FIG. 5B ) during the application of forward pressure and the tissue welding operation. This arrangement can also allow the practitioner to more readily feel when the electrode  231  is properly seated at the entrance of the PFO tunnel  112 . In other embodiments, this function can be achieved with an electrode  231  having a second electrode angle  235  with a value other than 90°. For example the second electrode angle can be in the range of about 80°-100° in one embodiment, and about 70°-110° in another embodiment. In still further embodiments, the superior surface of the electrode  231  can be concave (as described later with reference to  FIG. 6E ) to further enhance engagement with the limbus  217 .  
      In an embodiment discussed above, the catheter bend angle  227  is located in a single plane, and is aligned with features of the inflatable member  260  and the electrode  231 . As discussed above, this arrangement can allow the practitioner to position the inflatable member  260  and the electrode  231  based on the (perhaps more visible) bend in the catheter  220 . In other embodiments, the catheter bend angle  227  need not be contained to a single plane, e.g., in cases where a multi-plane bend angle improves the practitioner&#39;s ability to position the inflatable member  260  and/or the electrode  231 , and/or in cases where the inflatable member  260  and/or the electrode  231  are more visible to the practitioner than is the bend angle  227 .  
       FIGS. 6A-6K  illustrate catheter working portions having electrodes and/or inflatable members configured in accordance with still further embodiments of the invention. For example,  FIG. 6A  illustrates two representative working portions  628   a ,  628   b , each with an offset curve shown in dashed lines in  FIG. 6A , along with corresponding centers of curvature  629   a ,  629   b . In each of these embodiments, the working portions  628   a ,  628   b  are curved about a corresponding center of curvature  629   a ,  629   b  that is offset laterally from the center of curvature  229  initially shown in  FIG. 4  and superimposed for purposes of illustration in  FIG. 6A . In at least some cases (depending upon cardiac geometry), the offset center of curvature of the working portions  628   a ,  628   b  can improve the alignment of the inflatable member  260  and the electrode  231  relative to the PFO treatment site.  
       FIGS. 6B-6C  illustrate a catheter  620   b  configured to house a deployable inner catheter, in accordance with another embodiment of the invention. Referring first to  FIG. 6B , the catheter  620   b  can carry an electrode  631   b  in a stowed (e.g., more proximal) position. In this position, the electrode  631   b  has a spatial relationship relative to a corresponding inflatable member  660   b  that is generally similar to that shown in  FIG. 4 .  FIG. 6C  illustrates the electrode  631   b  after it has been deployed from the catheter  620   b  to a more distal position. The electrode  631   b  can be attached to an inner catheter  620   c  that is received within the outer catheter  620   b  for axial movement relative to the inflatable member  660   b . In operation, the practitioner can deploy the electrode  631   b  by a selected distance relative to the inflatable member  660   b , for example, to control the extent to which the electrode  631   b  penetrates the PFO tunnel. This technique can be used in addition to, or in lieu of, controlling the extent to which the inflatable member  660   b  is inflated, as described above with reference to  FIG. 5B . An advantage of this particular embodiment is that the electrode  631   b  can keep the relatively thin primum  107  ( FIG. 5B ) from being pushed or “tented” away from the secundum  108  ( FIG. 5B ) in short PFO tunnels. In other embodiments, the catheter can include other arrangements that allow for relative motion between the electrode  631   b  and the inflatable member  660   b . For example, the inflatable member  660   b  can be carried by a catheter that is axially movable relative to a catheter carrying the electrode  631   b.    
      The shape of the inflatable member  660   b  can be selected to correspond to the shape of the fossa ovalis or other relevant physiological feature. For example, if a particular patient or group of patients (human or non-human) has a fossa ovalis with a shape that is significantly different than the average shape, the practitioner can select an inflatable member with a corresponding mating shape. In a particular example shown in  FIGS. 6B-6C , the inflatable member  660   b  can have a generally round shape, rather than the generally triangular shape shown in  FIG. 6A . In another embodiment, shown in  FIG. 6D , an inflatable member  660   d  can have a generally oval shape that is also expected to seal around the perimeter and interior of the fossa ovalis, in at least some embodiments, depending upon patient physiology. In other embodiments, the inflatable members can have other shapes that may depend upon the geometry of the particular fossa ovalis against which the inflatable members are intended to seal. In still further embodiments, the inflatable member can have a “generic” shape (e.g., round, oval, generally triangular) and can be so flexible that it readily conforms to different fossa ovale having a variety of different shapes. Accordingly, the practitioner can select a device having an inflatable member with a shape (e.g., perimeter shape, or distal portion shape) that generally reflects and/or conforms to the perimeter shape of the patient&#39;s fossa ovalis.  
      In certain embodiments, the inflatable member  660   d  need not be asymmetric relative to the terminal axis  225 . For example, the inflatable member  660   d  can have an oval shape, as shown in  FIG. 6D , but can be positioned symmetric relative to the terminal axis  225 , so that the terminal axis  225  passes through the center of the inflatable member  660   d . In other embodiments, the inflatable member can have another shape (e.g., a round shape) that may also be symmetric relative to the terminal axis  225 . The shape, as well as the symmetry or lack of symmetry, can be selected by the practitioner based on the characteristics of the particular patient being treated, or other parameters.  
       FIG. 6E  is a side elevation view of the catheter  620   b  carrying an inflatable member  660   e  configured in accordance with another embodiment of the invention. In one aspect of this embodiment, the inflatable member  660   e  is tilted relative to the terminal axis  225 . Accordingly, an inflatable member tilt angle  659  between the inflatable member  660   e  and the terminal axis  225  has a value other than 90° (e.g., less than 90°). One result of this arrangement is that when the inflatable member  660   e  is positioned up against the primum  107  and secundum  108 , the electrode  631   b  will be oriented more toward the secundum side of the PFO than the primum side of the PFO. As described above, this can reduce the tendency for the corresponding guidewire  623  to displace the primum  107 , and can instead cause the guidewire  623  to track along the secundum side of the PFO tunnel. Another potential result of this arrangement is that the acute second electrode angle  635  between the electrode  631   b  and the inflatable member  660   e  can increase the tendency for the electrode  631   b  to hook the limbus  217 , and provide intimate contact with the secundum  108 . Additionally, this arrangement may allow for the more intimate contact between the electrode  631   b  and the adjacent tissue, resulting in a more efficient energy transfer to the tissue.  
       FIG. 6F  is a side elevation view of an electrode  631   f  shaped in accordance with still another embodiment of the invention. In one aspect of this embodiment, the electrode  631   f  can include a second or superior portion  633  having a dished, concave and/or saddle-shaped superior surface  636 . This shape can further increase the tendency for the electrode  631   f  to “hook” the limbus  217 , and thereby improve the ability of the electrode  631   f  to remain in position during a tissue sealing procedure. This feature can also better resist axial pressure applied to the catheter by the practitioner. In particular, as the practitioner moves the catheter into the patient&#39;s body, the electrode  631   f  can tend to move upwardly against the limbus  217 . The saddle shape of the superior surface  636  can prevent this force from dislodging the electrode  631   f.    
       FIG. 6G  illustrates the catheter  620   b  carrying an inflatable member  660   g  configured in accordance with another embodiment of the invention. The inflatable member  660   g  can include a forwardly facing first portion  662   g  and a rearwardly facing second portion  663   g . The second portion  663   g  can include multiple ribs or other reinforcing members  664  that increase the stiffness of the second portion  663   g  relative to the first portion  662   g . The ribs  664  can be formed integrally with the surface of the inflatable member  660   g , or the ribs can be formed using other techniques, including adhesively attaching the ribs  664  after the inflatable member  660   g  has been formed. The ribs  664  can be located at the exterior surface of the inflatable member  660   g , as shown in  FIG. 6G , or at the interior surface. In at least some embodiments, the increased stiffness provided by the ribs  664  is expected to improve the ability of the inflatable member  660   g  to seal against the adjacent cardiac tissue by (a) providing enhanced support to the second portion  663   g  while (b) allowing the first portion  662   g  to flex in a conformal manner at the site of contact with the cardiac tissue and (c) resisting axial movement resulting from pressure imparted by the practitioner (discussed previously with reference to  FIG. 6F ).  
       FIG. 6H  illustrates an inflatable member  660   h  having a first or forwardly facing inflatable portion  662   h  and a second or rearwardly facing inflatable portion  663   h , each of which has a different stiffness in accordance with another embodiment of the invention. For example, the first inflatable portion  662   h  can be formed from a material having a lower durometer value than that of the second inflatable portion  663   h . In another aspect of this embodiment, the thickness of the material forming the first inflatable portion  662   h  can be less than that of the material forming the second inflatable portion  663   h . In still further embodiments, these features can be combined with each other and/or with other characteristics to produce different stiffnesses in each portion. Each inflatable portion  662   h ,  663   h  can include an attachment section  667  that is bonded to the corresponding catheter (not shown in  FIG. 6H ) using an adhesive or other bonding technique. The inflatable portions  662   h ,  663   h  can be connected to each other at a seam  666 , for example, with an appropriate adhesive or weld (e.g., an RF weld). Each of the inflatable portions  662   h ,  663   h  can be blow-molded or formed in another suitable fashion. Such techniques are available from Interface Associates of Laguna Nigel, California and are also appropriate for forming inflatable members from a single element (e.g., without the seam  666 ).  
      One feature of the foregoing arrangement is that the first inflatable portion  662   h  can readily conform to the topology of the cardiac tissue, which can in turn provide for a good vacuum seal with the tissue. At the same time, the second inflatable portion  663   h  can have enough rigidity to maintain the overall shape of the inflatable member  660   h  even as the practitioner pushes the catheter and the inflatable member  660   h  in an axial direction to seal the inflatable member  660   h  against the cardiac tissue.  
       FIG. 6I  illustrates a catheter  620   i  carrying an inflatable member  660   i  having two independently controllable inflatable chambers, including a first chamber  662   i  and a second chamber  663   i . A chamber wall  665  separates the two chambers from each other. The catheter  620   i  can include separate first and second inflator lumens  661   a ,  661   b , each with independent fluid communication with a respective one of the chambers  662   i ,  663   i . Accordingly, the practitioner can control the shape, rigidity, and/or other characteristic of the inflatable member  660   i  by controlling the amount of pressure applied to each of the chambers  662   i ,  663   i . For example, the practitioner can apply a relatively low pressure to the first chamber  662   i , allowing the first chamber  662   i  to conform more readily to the adjacent cardiac tissue. At the same time, the practitioner can apply higher pressure to the second chamber  663   i  to provide for a more rigid support.  
       FIG. 6J  illustrates another embodiment in which a recirculating fluid is used to inflate an inflatable member  660   j . The first inflator lumen  661   a  can have a supply port  668   a  positioned in one region of the inflatable member  660   j  (e.g., toward the electrode  631   b ), and the second inflator lumen  661   b  can have a return port  668   b  located in another region of the inflatable member  660   j  (e.g., in a proximal direction from the electrode  631   b ). Fluid is pumped into the inflatable member  660   j  via the supply port  668   a , and returned via the return port  668   b , as indicated by arrows J. The pressure and flow rate of the fluid can be controlled to control the extent to which the inflatable member  660   j  is inflated. Accordingly, in at least some embodiments, the inflatable member  660   j  can include an internal pressure transducer  669  that provides a feedback signal to allow the practitioner to monitor and control the inflation pressure. In another embodiment, the inflation pressure can be controlled automatically, based on the feedback signal. A temperature signal (e.g., provided by a thermocouple) can also provide an appropriate feedback mechanism. In any of these embodiments, the recirculating fluid in the inflatable member  660   j  can increase the rate at which heat is removed from the heat sink  270 , and therefore the rate at which the electrode  631   b  is cooled. The recirculating fluid can also be directed into other system components, in addition to or in lieu of the inflatable member  660   j . For example, the recirculating fluid can be cycled through the electrode  631   b , provided the electrode  631   b  is outfitted with appropriate internal channels.  
       FIG. 6K  is a partially exploded, partially cutaway illustration of an embodiment of the catheter working portion  228  initially described above with reference to  FIG. 2 . The working portion  228  can include the electrode  231  attached to the heat sink  270 , which is in turn attached to a braided catheter shaft  603 . The heat sink  270  can include one or more glue grooves  601  that retain a suitable adhesive for bonding the metallic heat sink  270  to the shaft  603 . The heat sink  270  includes a vacuum lumen  639  (e.g., an integral, hollow center section) that aligns concentrically with the braided shaft  603 , and couples to the vacuum ports  237  in the electrode  231 . An inflator lumen  661  provides fluid to the inflatable member  260 . The thin electrically insulating coating  271  (a portion of which is shown in  FIG. 6K ) allows for a high degree of thermal communication between the heat sink  270  and (a) fluid in the inflatable member  260  (directly, and through one of the inflatable member attachment sections  667   a ) and ( b ) to blood outside the inflatable member (directly, and through another of the inflatable member attachment sections  667   b ). As discussed above, heat transferred to fluid within the inflatable member  260  is then transmitted to the surrounding blood and tissue via the walls of the inflatable member  260 .  
      The electrode  231  is attached to the heat sink  270  via any of several techniques, including welding, laser welding, brazing, laser brazing, soldering, spin/friction welding, bonding, or other techniques that provide a good thermal connection between these components. One such technique includes providing an interference fit between features on the heat sink  270  and corresponding features on the electrode  231 . One component may be heated and the other cooled prior to assembly, so that as the components reach equilibrium, they join tightly together. In some cases, the electrode  231  can be attached to the heat sink  231  with a thermally, conductive adhesive, in which case, the electrode  231  can include glue grooves  601 . The electrode  231  can also include a tab  602  to which an electrical lead (not shown) is attached. In another embodiment, the electrode  231  and the heat sink  270  can be formed as a single unit, e.g., via a casting and/or machining process.  
      In other embodiments, the working portion  228  can have other arrangements. For example, the heat sink  270  can be shorter, so that the joint between the heat sink  270  and the braided shaft  603  is located within the inflatable member  260 . In still another embodiment, the heat sink  270  may not be necessary, and can instead be replaced with an adapter (e.g., formed from a plastic), having a geometry generally similar to that of the heat sink  270 . Accordingly, the electrode  231  can be adhesively attached to the adapter using a suitable adhesive that is carried in the glue grooves  601 . In yet another embodiment, the inflatable member can be eliminated from the working portion  228 . For example, in some instances (e.g., when the patient has a relatively long PFO tunnel), the electrode  231  can be inserted well within the tunnel and the vacuum drawn through the electrode  231  itself can be sufficient to form a temporary seal between the electrode  231  and the adjacent cardiac tissue during the tissue bonding or welding operation, without the need for the additional sealing action provided by the inflatable member.  
      C. Systems and Methods for Controlling the Application of Energy to Cardiac Tissue  
       FIGS. 7A-11C  illustrate systems and methods for controlling the manner in which procedures are carried out on cardiac tissue, for example, the manner in which RF energy and vacuum are applied to septal tissue during a PFO closure procedure.  FIG. 7A  illustrates an embodiment of the control unit  240  (shown schematically in  FIG. 2 ), which includes a console  780  and a foot unit  785 . Both the console  780  and the foot unit  785  can include input devices  781  for controlling the overall system. The console  780 , the foot unit  785  and the operation of the input devices  781  are described in greater detail below.  
      The console  780  can include a housing  782  that is clamped to a pole (not shown in  FIG. 7A ) to reduce the footprint occupied by the console  780 , and to facilitate placement and storage of the console  780 . The housing  782  carries some of the input devices  781 , along with associated electronics and ports for providing services to the catheter  220 , the proximal portion of which is shown in  FIG. 7A . For example, the housing  782  can carry a main power switch  784  located at a rearwardly facing surface of the console  780 . Positioning the main power switch  784  at the rear of the console  780  can reduce the likelihood for a practitioner to inadvertently deliver multiple doses of energy to the patient because the practitioner must take the step of reaching behind the console  780  to reset the main power switch  874  before administering a subsequent dose of energy. In other embodiments, other techniques may be employed to achieve this purpose, and in at least some of those embodiments, an alternate main power switch  784   a  can be positioned at the forwardly facing surface of the console  780 . In yet another arrangement, the practitioner can use a separate reset switch  784   b  instead of the main power switch  784 ,  784   a . In any of these embodiments, the status of the various functions provided by the console  780  can be presented at a display  783 , which is described in further detail with reference to  FIG. 10 .  
      The console  780  can include a catheter power port  788  which is coupled to the catheter  220  with an electrical lead to provide power to the electrode  231  ( FIG. 2 ). A ground pad port  788   a  can be coupled to a patient ground pad to complete the monopolar electrical circuit. The console  780  can also include a vacuum source port  793 , which is coupled to either an external source of vacuum (e.g., a hospital-wide vacuum network, or a dedicated vacuum pump) or an internal source. For example, the console  780  can have an internal vacuum source (e.g., a vacuum pump) accessible via an internal source port  772 . When the console  780  includes the internal vacuum source, the vacuum source port  793  can be connected to the internal source port  772  by simply bending the associated conduit (which terminates at the vacuum source port  793 ) around to attach to the internal source port  772 . In any of these arrangements, the vacuum source can be configured to provide evacuation to an absolute pressure of from about 50 mm. Hg to about 300 mm. Hg, and, in a particular embodiment, about 50 mm. Hg.  
      The console  780  also includes a catheter vacuum port  795 , which is coupled to the catheter  220  to provide the vacuum to the working portion of the catheter. A disposable collection unit  790  can be releasably attached to the console  780  to collect fluids drawn from the patient&#39;s body, thereby preventing the fluids from contaminating the vacuum source. Accordingly, the disposable collection unit  790  can include a clear-walled liquid collection vessel  791  having graduation markings  794  that indicate the volume of liquid removed from the patient during a procedure. The total volume of the liquid collection vessel  791  can be selected to be below a level of fluid that can be safely withdrawn from the patient. Accordingly, the collection vessel  791  can provide valuable information to the practitioner about the total volume of liquids withdrawn during each procedure. Such information can also include the rate at which liquids are withdrawn from the patient, which the practitioner can gauge by observing the rate at which liquids accumulate in the collection vessel  791 , and/or by observing liquids passing through clear conduits of the system. In certain embodiments, the disposable collection unit  790  can also include a paddle wheel or other device that indicates the liquid flow rate to the practitioner. In any of these embodiments, the liquid collection vessel  791  can be coupled to an interface unit  792  that releasably couples the collection unit  790  to the housing  782 .  
      In a particular embodiment, the entire collection unit  790  (e.g., both the collection vessel  791  and the interface unit  792 ) can be securely attached to each other to form a unitary structure so as to prevent either unit from being separated from the other, without irreparably damaging the entire collection unit  790 . In another embodiment, the collection vessel  791  and the interface unit  792  can be separable from each other. An advantage of having the collection vessel  791  and the interface unit  792  inseparable from each other is that bodily fluids are less likely to leak from the collection unit, thereby reducing the likelihood for practitioners or others to come into contact with the fluids. The unitary structure is also easy for the practitioner to install and remove. Because the entire collection unit  790  is disposable (in at least one embodiment), it can also be simple and efficient for the practitioner to dispose of.  
      In operation, the catheter  220  is connected to the appropriate ports of the console  780 , and introduced into the patient&#39;s body. The console  780  is activated by turning on the main power switch  784 . Vacuum is applied to the patient by activating a vacuum switch  786  located at the foot unit  785 . After an appropriate seal is achieved between the working portion of the catheter  220  and the adjacent tissue, RF energy is provided to the patient by activating an RF switch  787 . The vacuum switch  786  and the RF switch  787  can be located on opposite sides of the foot unit  785  to provide the practitioner with a clear indication of which switch is which. In addition, these switches can be configured to provide other sensory cues that distinguish the switches from each other. For example, the RF switch  787  can require a higher input force for activation than does the vacuum switch  786 . In a particular embodiment, the RF switch  787  may take up to ten pounds of force to activate, while the vacuum switch  786  may take less than one pound to activate.  
      The system can optionally include still further features to prevent the RF energy from being applied inadvertently. For example, the system can include an RF arming switch  787   a  that must be activated prior to activating the RF switch  787 . In another arrangement, the RF switch  787  must be activated twice (once to arm and once to deliver power) before electrical energy is actually provided to the patient. In other embodiments, the vacuum switch  786 , the RF switch  787 , and/or other input devices of the control unit  240  can have other configurations.  
      The system can include other safety features in addition to or in lieu of those described above. For example, the practitioner may wish to use a different catheter and/or electrode (e.g., a smaller electrode) when performing a procedure on children than when performing the procedure on adults. A pediatric catheter can have a preselected impedance or other characteristic value that is deliberately chosen to be different than the corresponding characteristic value of an adult catheter. When the practitioner attaches the catheter to the catheter power port  788 , the control unit  240  can automatically detect the nature of the catheter, and can automatically adjust certain parameters. For example, as will be described in greater detail below with reference to  FIG. 10 , the system can automatically set energy and/or vacuum levels. If these levels should be adjusted (e.g., made lower) for pediatric or other special applications, the system can automatically make the adjustments.  
      In any of the foregoing embodiments, after the procedure has been completed, the disposable collection unit  790  can be removed from the console  780  and replaced with a new disposable collection unit  790  prior to initiating a similar procedure on another patient.  FIG. 7B  illustrates the disposable collection unit  790  in the process of being removed from the console  780 . In a particular aspect of this embodiment, the disposable collection unit  790  can be removed by simply pressing a release latch  759 , rotating the collection unit, and lifting it forwardly and upwardly away from the console  780 , without the use of tools.  
       FIG. 7C  illustrates the console  780  after the disposable collection unit  790  has been removed. The console  780  can include a valve unit  750  having at least one actuator  751  that acts on the disposable collection unit  790 . For example, the actuator  751  can include one or more linear actuators, rotary actuators or other suitable devices. In an embodiment shown in  FIG. 7C , the valve unit  751  can include a first piston  752   a  and a second piston  752   b , each of which operates on the disposable collection unit  790  to control the pressure in the vacuum lumen of the catheter  220  ( FIG. 7A ). The console  780  generally (e.g., the valve unit  750  in particular) can also include a first receiving portion  789  (e.g., a recess) that removably receives a corresponding portion of the disposable collection unit  790 . The first receiving portion  789  can also include first registration features  779  that locate the disposable collection unit  790  and, in at least one embodiment, provide a simple hinge line about which the disposable collection unit  790  can be rotated. Further details of this arrangement are described below with reference to  FIGS. 8A-9B .  
       FIG. 8A  is a rear view of the disposable collection unit  790  shown in  FIG. 7A , after it has been removed from the console  780  ( FIG. 7C ). The interface unit  792  can include a second receiving portion  896  having second registration features  897  that cooperate with the first registration features  779  shown in  FIG. 7C . For example, the second registration features  897  can include closed-end channels that slip over the peg-shaped first registration features  779 . Accordingly, the first and second registration features,  779 ,  897  may have only one engaged configuration, a configuration that is easily and readily implemented by the practitioner. The interface unit  792  can also include an interface housing  898  having multiple piston access openings  899  through which the pistons  752   a ,  752   b  ( FIG. 7C ) move to access corresponding fluid conduits.  
       FIG. 8B  illustrates the valve unit  750  from the console  780  ( FIG. 7C ), along with the disposable collection unit  790 , from which the interface housing  898  ( FIG. 8A ) has been removed. The interface unit  792  includes a first conduit  855   a  that extends between the catheter vacuum port  795  and the liquid collection vessel  791 . The first conduit  855   a  can include a flexible material that passes adjacent to a first valve pinch point  754   a . When the first piston  752   a  presses against the first conduit  855   a  at the first valve pinch point  754   a , the first conduit  855   a  closes. Accordingly, the first piston  752   a  can form part of a first valve  853   a . The interface unit  792  can also include a second conduit  855   b  connected between the first conduit  855   a  and an air intake or vent port  856 . The second conduit  855   b  can pass adjacent to a second valve pinch point  754   b , and can accordingly be closed when the second piston  752   b  is activated (the second piston  752   b  forming part of a second valve  853   b ). The interface unit  792  can still further include a third conduit  855   c  that extends between the liquid collection vessel  791  and the vacuum source port  793 . A filter (e.g., a Gortex® filter) and/or desiccant housing  857  can be coupled between the third conduit  855   c  and the liquid collection vessel  791  to remove impurities and/or vapor upstream of the vacuum source, which is not shown in  FIG. 8B . A filter and/or desiccant can also be provided at the air intake or vent part  856  to restrict/prevent liquid from passing into or out of the vent port  856 . This arrangement can accordingly protect the vacuum source. Because the housing  857  and the vent port  856  are parts of the disposable collection unit  790 , the components contained in them (e.g., the filter and/or desiccant) can be configured for a single use, and need not be maintained by the practitioner or other personnel. As a result, the apparatus can be simpler and less expensive to own and maintain than are existing devices.  
      In operation, both the first valve  853   a  and the second valve  853   b  are normally closed when unpowered, with the first piston  752   a  pinching the first conduit  855   a  closed at the first valve pinch point  754   a , and the second piston  752   b  pinching the second conduit  855   b  closed at the second valve pinch point  754   b . When the practitioner directs vacuum to be applied to the patient, the first valve  853   a  opens, coupling the catheter vacuum port  795  to the vacuum source port  793 . At this point, vacuum is drawn through the catheter vacuum port  795 , the first conduit  855   a , the liquid collection vessel  791 , the third conduit  855   c  and the vacuum source port  793 , as indicated by arrows in  FIG. 8B , to clamp the patient&#39;s cardiac tissue against the electrode  231  ( FIG. 5B ). After the PFO sealing procedure has been completed, the first valve  853   a  closes, cutting off communication between the vacuum source and the catheter  220  ( FIG. 5B ). However, the pressure at the catheter vacuum port  795  and in the catheter  220  itself will typically remain below atmospheric pressure. Accordingly, the second valve  853   b  can open to vent the catheter vacuum port  785  and the catheter  220  to atmospheric pressure, via the second conduit  855   b  and the air intake port  856 . When the catheter is open to atmospheric pressure, the vacuum seal between the cardiac tissue and the electrode  231  is released, allowing the practitioner to remove or reposition the electrode  231 . After a suitable venting period, the second valve  853   b  can automatically return to its closed state. This arrangement can save power (e.g., when the second valve  853   b  is a normally closed valve that is unpowered when closed) and can prevent fluids from escaping from the patient&#39;s body through the catheter  220 .  
      One feature of an embodiment of the disposable collection unit  790  is that it includes the conduits  855   a ,  855   b . Another feature is that the conduits  855   a ,  855   b  have fixed positions that are consistent from one unit  790  to the next. The corresponding valves  853   a ,  853   b  (in the console  780 ) also have fixed positions. Another feature is that the conduits  855   a ,  855   b  are configured for a single use. The foregoing features differ from existing pinch valve arrangements, in which a practitioner typically stretches and installs a length of flexible tubing into the pinch valve, and may use the tubing over and over. A drawback with the existing pinch valve arrangement is that if the practitioner fails to install the flexible tubing properly or consistently (an event which is made more likely because the tubing must be stretched), the valves will not operate properly. An advantage of an embodiment of the invention described above is that the conduits  855   a ,  855   b  are installed at the time of manufacture, are disposable, and need not be manipulated by the practitioner during use.  
      Another feature of the disposable collection unit  790  and the console  780  is that the patient&#39;s bodily fluids are contained by and come in contact with only the disposable single-use collection unit  790  and not the rest of the multi-use console  780 . An advantage of this arrangement is that it is easy for the practitioner to use, and it reduces if not eliminates the likelihood for contacting the practitioner (or a subsequent patient) with the bodily fluids of the patient currently undergoing the procedure.  
       FIGS. 9A and 9B  schematically illustrate the first and second valves  853   a ,  853   b , along with an activation diagram that depicts operation of the valves in accordance with an embodiment of the invention. When a “VAC ON” input signal is received (e.g., when the practitioner activates the vacuum switch  786  shown in  FIG. 7A ), the first valve  853   a  opens to allow communication between the vacuum source port  793  and the catheter vacuum port  795 . When a “VAC OFF” input signal is received (e.g., when the practitioner re-activates the vacuum switch  786 ), the first valve  853   a  closes, and the second valve  853   b  opens to vent the catheter  220 . In a particular embodiment, the second valve  853   b  can remain open for a period of from about two to about five seconds to allow full venting of the catheter, after which the second valve  853   b  automatically closes. Both the first valve  853   a  and the second valve  853   b  can then remain closed until a new “VAC ON” input is received.  
      One feature of an embodiment of the arrangement described above is that the system can automatically vent the catheter to atmospheric pressure upon receiving a signal to deactivate the application of vacuum to the patient. For example, the system can include one or more computer-readable media containing instructions that direct the automatic operation of the valves. This automated feature can have several advantages. For example, this feature can allow the practitioner to quickly and automatically vent the catheter to (or at least toward) atmospheric pressure, which in turn allows the practitioner to quickly move the electrode within the body (if necessary), or remove the catheter from the patient&#39;s body after completing a procedure. Because the operation is automatic, it can reduce or eliminate the likelihood that the practitioner will attempt to move the electrode while vacuum is still applied. This feature can therefore reduce the likelihood for damage to the patient&#39;s cardiac tissue.  
      Another feature of an embodiment of the foregoing arrangement is that the automatic operation of the valves can be quicker than conventional manual techniques. An advantage of this feature is that it can reduce patient blood loss during a procedure. Another advantage is that it can reduce the amount of time required to reposition the catheter (if necessary), and therefore reduce the time required to complete the procedure.  
      Another feature of an embodiment described above is that the second valve  853   b  can automatically open at the same time the first  853   a  valve is closing. An advantage of this feature is that it can reduce the likelihood for the catheter and/or cable/tubing assembly to “buck” or move suddenly when the vacuum is suddenly removed. As a result, the practitioner can maintain control of the catheter without having to manually open one valve while simultaneously and manually closing the other.  
      Certain aspects of the embodiments described above with reference to  FIGS. 7A-9B  include a vacuum source that provides a generally continuous, generally constant level of vacuum to the catheter. In other embodiments, the vacuum can be applied in other manners. For example, instead of a vacuum pump, the collection vessel  791  shown in  FIG. 7A  can be pre-evacuated prior to use, and can have a volume sufficient to provide vacuum over the course of an entire procedure (e.g., from 1-9 minutes, 1-5 minutes, or up to about 2 minutes for a single procedure). In a particular application, the collection vessel  791  has a volume of from about one-half pint to about three pints (e.g., about one pint or less). The volume of the collection vessel  791  may not need to be larger because once a firm seal is established between the catheter and the patient&#39;s tissue, the pressure in the vessel  791  should remain approximately constant. The absolute pressure in the vessel  791  can be from about 50 mm. Hg to about 300 mm. Hg, and in a particular embodiment, about 50 mm. Hg. The other portions of the disposable collection unit  790  and the console  780  can be generally similar to those described above, except that the third conduit  855   c  ( FIG. 8B ) and the vacuum source port  793  ( FIG. 8B ) can be eliminated. In use, the pressure within the collection vessel  791  will only increase or remain constant over at least some time intervals. In fact, an advantage of the pre-evacuated, single use collection vessel  791  is that it can eliminate the need for an on-site vacuum pump or other high-volume vacuum source.  
       FIG. 10  is a partially schematic illustration of the information presented to the practitioner at the display  783  of the console  780  during a representative procedure, independent of the manner in which vacuum is provided to the catheter. The display  783  can present a remaining treatment time indicator  1078  (indicating the amount of time remaining during which the electrode or other energy transmitter is active). A representative treatment time for a PFO sealing procedure is 2 minutes, though treatment times can be less, or (as described above) can range up to or beyond 9 minutes in some cases. Different treatment times may be appropriate for procedures other than PFO sealing procedures. In any of these cases, if the treatment is halted prior to normal completion, the remaining treatment time indicator  1078  can remain visible for a predetermined time to allow the practitioner to record the indicated value. Alternatively, the indicated value can remain visible until the practitioner resets the system via the main power switch  784  or the reset switch  784   b . An “RF On” indicator  1074  indicates when the electrode is active, and a “Vac On” indicator  1077  indicates when vacuum is active. A “Treatment End” indicator  1075  identifies when the treatment is over, and a “Low Vacuum” indicator  1076  indicates when the vacuum is outside a target range (e.g., if there is a leak in the system that prevents sufficient vacuum from being drawn on the patient). For example, if the absolute pressure exceeds a target value in the range of from about 250 mm Hg to about 300 mm Hg, as measured by an appropriately positioned pressure transducer, the “Low Vacuum” indicator  107   b  can illuminate or otherwise activate. The system can automatically prevent the corresponding valve (e.g., the first valve  853   a , shown in  FIG. 9 ) from opening until a sufficient vacuum level is restored. Optionally, the console  780  can also include an “RF armed” indicator  1073  for example, if the operator must first arm the RF delivery function before activating it. In such a case, the foot unit  785  ( FIG. 7A ) can include the RF arming switch  787   a . The RF armed indicator  1073  can be visible (as shown in  FIG. 10 ) and/or audible. As shown in  FIG. 10 , the information displayed to the practitioner and the available options for the practitioner can be relatively simple and straightforward. Further details of embodiments that include these features are described below with reference to  FIGS. 11A-11C .  
       FIG. 11A  is a schematic block diagram of a system  1100  for applying treatment to a patient in accordance with an embodiment of the invention. The system  1100  can include a power delivery component  1101  (e.g., an RF generator and associated circuitry) that directs energy to the patient. The power delivery component  1101  can be activated by an activation device  1102 , which in turn responds to a user input  1105 . For example, the activation device  1102  can include the RF switch  787  described above with reference to  FIG. 7A . In a particular aspect of an embodiment shown in  FIG. 11A , the amount of energy supplied to the patient once the user activates the activation device  1102  can be fixed (e.g., at the time of manufacture) so as not to be changed by the practitioner, patient, or any other user. The amount of energy (the product of current, voltage and delivery time) can correspond to the amount typically required to seal a PFO or conduct another pre-defined cardiac tissue procedure. For a system that delivers energy at a constant current and voltage, the energy dose is determined solely by the length of time the energy is being delivered. In other systems, for which voltage and/or current vary, the treatment time may also vary, so the system may be configured to calculate a running total of energy delivered, and halt the delivery when the pre-defined energy dose is reached. A typical range of energies for a single dose is from about 10 joules to about 6500 joules. For example, in one embodiment 12 watts of power is provided for a period of two minutes, for a total energy dose of 1440 joules. In any of these arrangements, by automatically terminating the delivery of energy to the patient after the fixed amount has been delivered, the system  1100  can predictably and repeatedly deliver fixed doses of energy to a series of patients, thereby improving the reliability of the results achieved by the procedure. This can also be simpler for the practitioner to operate, because the practitioner need not calculate and input parameters such as signal voltage and/or treatment time, as is common with existing devices.  
      Parameters in addition to or in lieu of the total applied energy can also be automatically established and set, further reducing the workload on the practitioner. For example, the system  1100  can automatically set the level of vacuum applied to the catheter. In a particular embodiment, the absolute pressure can be from about 50 mm Hg to about 300 mm Hg at the patient&#39;s tissue, independent of the local atmospheric pressure. This level is expected to provide suitable clamping between the catheter and the adjacent tissue, without causing undue foaming in the liquids removed from the patient&#39;s body. In other embodiments, the vacuum level can be different and/or the system  1100  can automatically set other parameters.  
      Of course, the system  1100  can include facilities for overriding the automatic delivery of energy to the patient. For example, the system  1100  can include a manual interrupt device  1103  that responds to a user interruption input  1106 . In a particular embodiment, the user (e.g., the practitioner) can interrupt the energy provided to the patient by resetting the power switch  784  ( FIG. 7A ), the reset switch  784   b  ( FIG. 7A ), or the RF switch  787  ( FIG. 7A ). Accordingly, the practitioner can quickly halt the delivery of energy in response to some indication that such an action is warranted. In another embodiment, the system  1100  can include an automatic interrupt device  1104  that responds to a sensor input  1107 . For example, the sensor input  1107  can provide an indication of an open circuit, a short circuit, an impedance rise, a high temperature, a loss of vacuum, or another occurrence in light of which it is advisable to cease delivering energy to the patient.  
      The operation of the vacuum can be automatically tied to the application of energy to the patient, in particular embodiments. For example, in one arrangement, the system can include an electronic (or other) lockout that automatically prevents the vacuum from being turned off for a predetermined time interval following the end of energy delivery to the patient. In a particular aspect of this arrangement, the time interval is about 5 seconds, but the time interval can have other (shorter or longer) intervals as well. An advantage of this arrangement is that it precludes the practitioner from removing the energy delivery device from the patient until the energy delivery device has had an opportunity to cool down by a selected amount.  
       FIG. 11B  is a flow diagram illustrating an embodiment of a process  1120  for treating a patient, and includes reference to particular elements and functions of the systems and devices described above. Process portion  1121  can include receiving a request to initiate vacuum, e.g., via the vacuum switch  786  ( FIG. 7A ). In response to the request, process portion  1122  includes directing the initiation of vacuum. In process portion  1123 , the vacuum is monitored and the results are displayed. For example, the results can be displayed by illuminating the “Vacuum On” indicator  1077  shown in  FIG. 10 , and/or the “Low Vacuum” indicator  1076 . In process portion  1124 , a request is received to initiate the delivery of energy, in response to which energy delivery is initiated. In process portion  1125 , the system can check to determine whether an interrupt request has been received. The interrupt request can either be automatically generated or manually generated. In either instance, if an interrupt request is received, the treatment procedure is automatically terminated (process portion  1129 ). If not, process portion  1126  includes determining the delivered dose and displaying some representation of the delivered dose to the practitioner. This display can include an amount of time elapsed, an amount of energy applied, or, as shown in  FIG. 10 , an amount of time remaining until a complete dose has been delivered. In process portion  1127 , the delivered dose is compared to a pre-set dose. If the delivered dose meets or exceeds the pre-set dose (process portion  1128 ), the procedure is automatically terminated (process portion  1129 ). Otherwise, the process returns to process portion  1126 .  
      Once the process has been automatically terminated (process portion  1129 ), the system can check to see if a reset request has been received (process portion  1130 ). A reset request can include shutting the system off by tripping the main power supply switch  784  ( FIG. 7A ), or by activating another reset device. If such a request is received, the dose is reset (process portion  1131 ) and the procedure returns to process portion  1121 .  
      In several embodiments described above, the effect of the cardiac tissue undergoing an increase in impedance (e.g., “impeding out”) is an effect to be avoided because it may prevent RF energy from subsequently penetrating into the adjacent tissue. In other embodiments, for example, when heat is transferred efficiently and effectively away from the electrode, an impedance increase may be used to indicate the completion of a suitable energy dose.  FIG. 11C  illustrates a process in accordance with one such embodiment. The process can include receiving a request to initiate the delivery of energy (process portion  1124 ) and in response, delivering an initial energy dose (process portion  1140 ). The impedance of the electrical circuit that includes the treated tissue can be monitored on a continuous or intermittent basis, or detected after the initial energy dose has been delivered (process portion  1141 ). The impedance can be measured by any suitable technique, including determining a change in the voltage drop across the treated tissue. In process portion  1141 , it is determined whether the impedance has achieved a target value and/or has changed by a target amount. For example, process portion  1142  can include determining whether the impedance has increased to a predetermined threshold level, and/or determining whether the impedance has changed by a threshold amount. If the impedance has changed by or to the target value, the treatment is effectively complete and the process can further include resetting the dose in preparation for treating a subsequent patient (process portion  1144 ). If not, process portion  1143  can include delivering a follow-on energy dose. Process portions  1141 - 1143  can be repeated until the impedance value corresponds to a value indicating a completed treatment. Although not shown in  FIG. 11C , other features described above with reference to  11 B (e.g., determining whether an interrupt request has been received and displaying results) can be included in embodiments of the method shown in  FIG. 11C .  
       FIG. 12  is a side elevation view of a liquid collection vessel  1291  that includes features in accordance with further embodiments of the invention. The liquid collection vessel  1291  can be compatible with other features of the disposable collection unit  790  described above. Accordingly, the vessel  1291  can include a first conduit  1255   a  that can be coupled to the vacuum channel of the catheter, and a third conduit  1255   c  that can be coupled to the vacuum source. The first conduit  1255   a  can extend through the vessel  1291  toward the bottom of the vessel  1291 . A core  1249  (e.g., a porous core formed from a polymer) can be positioned between the open end of the first conduit  1255   a  and the open end of the third conduit  1255   c . The core  1412  can be supported in position by one or more retention rings  1247  (two are shown in  FIG. 12 ). When blood is withdrawn from the patient through the catheter, it is directed by the first conduit  1255   a  to the bottom of the vessel  1291 . As the result of the vacuum drawn on the third conduit  1255   c , the blood may tend to foam or bubble up. By positioning the core  1249  between the bottom of the vessel  1291  and the opening of the third conduit  1255   c , the likelihood for the foam to enter the third conduit  1255   c  and contaminate the vacuum source can be reduced or eliminated.  
      In a further aspect of an embodiment shown in  FIG. 12 , the core  1249  can be impregnated with an antifoaming agent or a surfactant, for example, an agent that includes silicone oil. In a further aspect of this embodiment, the antifoaming agent can be initially contained in a rupturable capsule  1248  placed in the vessel  1291  between the bottom of the vessel and the core  1249  at the time of manufacture. Accordingly, the antifoaming agent can be contained in the capsule  1248  until just prior to use. The capsule  1248  can burst under the influence of the vacuum drawn through the third conduit  1255   c , releasing the antifoaming agent into the vessel  1291 , where it can coat the core  1249  and further reduce the likelihood for foam to contaminate the vacuum source. In other embodiments, the antifoaming agent can be housed in other portions of the overall system. For example, the antifoaming agent can be housed in the interface unit  792  ( FIG. 7A ), or injected through the interface unit  792  through the vacuum port  795  ( FIG. 7A ), prior to applying vacuum to the disposable collection unit  790  ( FIG. 7A ).  
      In any of the foregoing embodiments, including that shown in  FIG. 12 , the level of vacuum applied to the catheter can also be selected to produce suitable performance while controlling the amount of liquid foaming. In a particular embodiment, the absolute pressure can be selected to be within the range of about 50 mm Hg to about 150 mm Hg (absolute). In a further particular embodiment, the absolute pressure can have a value of no less than about 50 mm Hg to avoid foaming and/or boiling. These levels can be adjusted as needed, for example, to account for different altitudes.  
      From the foregoing, it will be appreciated that specific embodiments of the invention have been described herein for purposes of illustration, but that various modifications may be made without deviating from the invention. For example, the electrodes, inflatable members, disposable collection units, and/or other components of the overall systems described above can have other shapes, sizes, and/or configurations in other embodiments. In particular embodiments, the inflatable members, energy transmitters and/or guidewire conduits described above are arranged asymmetrically with respect to the terminal axis, while in other embodiments, some or all of these components can be symmetric with respect to the terminal axis (e.g., the inflatable member can have a round shape that is concentric with the terminal axis). The energy transmitter can be configured to deliver bipolar rather than monopolar signals, for example, via multiple electrodes positioned at or near the PFO. Furthermore, while the devices described above were described principally in the context of a PFO repair procedure, devices and techniques generally similar to those described above may be used in other treatment contexts. For example, some or all aspects of the console and the valve arrangements described in the context of a PFO repair procedure with respect to  FIGS. 7A-11  may be applied in other contexts (cardiovascular or otherwise) in other embodiments. Aspects of the invention described in the context of particular embodiments may be combined or eliminated in other embodiments. Further, while advantages associated with certain embodiments of the invention have been described in the context of those embodiments, other embodiments may also exhibit such advantages, and not all embodiments need necessarily exhibit such advantages to fall within the scope of the invention. Accordingly, the invention is not limited except as by the appended claims.